I love Electrical information , I enjoy it so much I'm watching this at 4.22am In Australia , before going to work in the electrical industry , purely for enjoyment . This is me coming out , as a geek .
Thank you John, as always I learn so much from your presentations. I teach physics to Electrical apprentices among others in various career paths, but I find many apprentices have no real desire to grasp the science behind Electricity. I recommend your site to many. I always hope they learn as much from from us, to improve their own safety as much as the end user. Keep up the good work.
+John Ward 2 related Areas worthy of Further video in my view:- (1) When is a circuit a distribution-circuit that may only require 1sec (TT) or 5 sec (TN) disconnection time [>32A ?]. [presumably the TT case is where you also use a 100mA S-Type RCD as well...]. (2) Selectivity between MCBs It seems, in some circles to be accepted to use a C50 to feed a downstream B32 (e.g. submain to garage with electric-car fast-charging-point), and similarly to use a C32 to feed downstream B16 (e.g. feed to outbuilding with multiple socket-circuits). HOWEVER this is seemingly not 'guaranteed' and depends on the particular combination of devices and the exact fault-impedance and so-on and so-forth. When is a switchfuse with BS1361/DNO style fuse instead of a circuit-breaker better to feed a submain, anyway...? Discuss: What MCB-selectivity is actually 'good enough in practice', what 'passes inspection', etc...?
Thank you, that video is great! In addition: In Germany there are two other types available. You've already mentioned the type K, this was a common type here for workshops with large machines. K stands for Kraft (power), and is one of the old german types still available. The other ones were: H for Haushalt (household), manufactured until 1976. Magnetic: 2 to 3 times. Thermal: 2.1 times (up to 4A) 1.9 times (6 to 10A) 1.75 times (12 to 25A) 1.6 times (more than 25A) So it's for high impedant grids. It was replaced by type L, which was used here until 1990 before it was replaced by type B. But L is still available as circuit breakers for the replacement of Diazed fuses. In this case the housing is round and it's having an Edison thread. L for Licht (light), or later Leitungsschutz (cable protection): Magnetic is the same as B, thermal is the same as H. Picture of a screw-in MCB with Edison thread: i.ebayimg.com/00/s/NzQyWDEwMjQ=/z/-koAAOSwwBha1XbF/$_72.JPG
Only ever retro fitted type C twice, may years ago.Once when I added 4 more magnetic powered halogen lights to an existing circuit of 8 lights. The breaker would occasionally trip when the 12 lights were turned on. Changed to type C for this circuit and all was fine. Should really swap back to type B as over the years many of the in ceiling transformers have been replaced with modern electronic units.2nd place fitted was house entry lighting circuit. When using ye old tungsten bulbs the cold air rushing in from front door would mean very short life for the entrance hall way bulbs, generally bulbs blowing and taking out the breaker. This circuit was also the garage light circuit where the breakers were located, as well as any easily accessible light switches from front door. Thus one had to fumble around in the dark, in the garage to reset the breaker. Changing this to type C meat when bulb blew the breaker no longer tripped and other lights on the circuit worked fine. All not necessary now using first CFL bulbs and now LED.
Very informative. I'm studying Electrical Engineering in college and we went over cable sizes for circuits but didn't discuss the impedance of the circuit. So my understanding is you would need to have the correct size cable for the rated current but you might also need to increase the CSA to bring the impedance down to the levels specified in the guide to ensure magnetic tripping in the time allowed. Of course that doesn't really help if the circuit is already installed.
Oblivion You understand correctly! It's beneficial to have actual supply parameters and detailed specs for the load and circuit breaker. Generalisations such as Ze= 0.8 ohms for TN-S and Type C magnetic being 5-10x might imply your circuit is non compliant. But with detailed specs and measured values you would have a definite answer.
Dear John. Thank you for making all those great videos. You have great electrical knowledge and I do very appreciate it. I need to mention one comment. BS7671 doesn't provide final Zs values for Circuit Brakes. All values have to be multiply by 0.8 correction value. On Site Guide have already corrected those values compared to BS7671. Kind Regards Richard
MCB's are to protect the cable. They prevent the cable from being too hot or overheating, which may cause a fire, so indirectly protecting people. A cable constantly being too hot will deteriorate its own insulation. Current travelling excessively through a cable it was not designed to cope with, will heat the cable. When the current travelling through the cable is over a safe limit the MCB senses the current, then if the maximum current is reached for the cable, it automatically isolates the cable it is protecting. The type B, C and D MCB's are to prevent _nuisance tripping_ caused by momentarily current surges.
It is said. the trip sequence is base on IN Ampere multiplier of currents, denoted as I1 IN *1.3 (test current, no trip), I2 IN * 1.45 (garantees opening of circuit witin 1 hour) Both of these are Thermal and Bimetallic . I4 IN * 5 (electromangetic holding current, no trip), I5 IN * 10 ( el.mag garanteed to open in 0.1 millisecond) . The different characteristics A (sensitive electronic AC), B (household appliances), C (motors, large heaters) . The A, B, C, D- Char have different factors to multiply into IN (nominal Ampere), and match the power leth thru, during smallest (I2) and largest (I5) short or failcurrent, considering the cables crossection and lenght, how they are laid. the amount of load . You have to obtain A^2 sek, that is the mass of the let thru energy once it trips. thats done in the Z-line (Z-loop) calculation or measure. You select a match the short circuitbreaker max can handle, 10kA. The maximal let thru Ampere (I5) is calculated . t = k^2 * ^2 / I^2 finding the splitsecond its required to open. Then I / IN , (I5 maybe IN * 10 = 320A) . k= table specific konstant for conductor type AL or CU and insulation PVC or PEX. PVC has halogenes and chlorine deadly gases when it fumes and is hot, PEX and EPR is Halogene free. S = crossection, remember each crossection has to be calculated, if there is a reduction of crossection along the circuit), I is the Ampere of the Load. Then Match the current multiplyer fits the curve characteristis on the fuse diagram, PLSM, PKPM, dRBM (xdigital), Acti9 C120N, IC60 RCBO. And added safety is the SPD (surge protector) protecting from lightning strikes and atmospheric inductions, SPCT4, IPRD. The SPD is demanded infront of of any new sub distribution cabinet. Type 1 coarse, Type2 middle, and Type3 for finer undulations of stray currents and suggested for data and sensitive electronics on AC .
we used to have H16A circuit breakers in the house. The problem was that the microwave regularly triggered the circuit breaker. The electrician said these were already obsolete and all converted to B16A. Then there were no more problems.
Hi John Watching all your videos! There are brilliant! Would like to see more on earth rod measurements & calculating current flow in the event of a fault with neutral/earth! Thanks!
Types B,C etc are the same, however MCBs for DC are not - if using on DC you need to get ones which are designed for DC, as using AC breakers on DC will quickly destroy them.
Bjorn Roesbeke I understand the reasons behind that where socket outlet circuits are 16A radials due to the rating of the outlets. Some equipment with high inrush current will cause nuisance tripping of a B16, but not a C16. Where the norm in the UK has been ring finals with B32 MCB, the instantaneous trip values C16x10 and B32x5 are both 160A. In the UK we tend to use 20A rather than 16A breakers on socket outlet radials due to having the additional protection of fused plugs with a maximum of 13A. Then it's up to you as the designer to decide if you need B or C breakers, respecting the maximum loop impedances for proper protection.
Cheers JW. Great video. Is there any chance of touching upon mccbs, in the future with some information on maximum zs values when the device has an adjustable magnetic and thermal setting
Are you sure about the RCD not helping? I believe there is some rule here that says if you provide RCD protection you don't need to meet the impedance for magnetic tripping. The reasoning is the RCD protects against a dangerous touch voltage and it is not necessary to switch off instantly, the slow thermal protection is good enough for fire protection. I'm not 100% positive this rule is still active but I can investigate. It would apply also to plain old thermal fuses, which have no magnetic trip, when combined with an RCD.
I'm aware of that, but my thinking was that the thermal cutout will eventually get it. The requirement for breakers to switch off instantly comes (also) from preventing dangerous touch voltages in case of a L-E fault, which the GFI would prevent. There seems to be some discussion over here if the requirement to switch off within 0.4s is only applicable to L-PE or also L-N. One way to get around this problem might be to use fusible element type fuses instead of breakers in combination with a GFI to achieve higher inrush current tolerance in high impedance circuits.
VDE100-600 says if there is a GFI you generally don't even have to measure the loop impedance, make of that what you will, I'm not much further towards understanding it. The differnt standards in each country don't exactly make things easier.
Since 2017 in Germany Z_I has to be measured and Riso has to be tested between L&L and L&N. The Others important fact is, If the RCD ist used for "Basisschutz" (earth fault L-PE) or "Zusatzschutz" (earth fault L-Person) ...... In some cases the required tripping time (L-N) can be 5s instead of 0,4s. Because of is wird Situation i allways choose the Type according to 0,4s -> Z_I
The majority of breakers found in domestic installations tend to be B type, whether or not this is by design or by the fact that that’s what comes with the fuse board I don’t know
If it did not trip on a fault current due to high impedance it would still trip eventually on overload i assume ? But the cables might be over heated before this. Is that correct ?
Yes - the overload part relies on a metal strip heating up so cables could overheat if that was the only thing which disconnected a short circuit fault.
we have 110v phases in my country, I want to buy a 40A MCB, but I noticed that everybody sells these 230/400 volts MCB's no 110v breakers, so it would work properly?
Yes they will work, they are current operated, the voltage isn't particularly relevant as long as the maximum voltage isn't exceeded. Check with the MCB manufacturer to confirm the voltage range.
Very informative, thanks. One odd thing is the vertical (magnetic) part of the MCB graphs in Appendix 3, for example graph (and associated table) 3A4 and similar to your example in 21:04. 18th ed. Appendix 3A4 shows that for a 6A type B, trip time at 30A will be anywhere between 10ms and 12s (or 10ms to 5s in the associated table). If that is in fact the case, how are we to design to achieve 0.4s disconnections from Appendix data? Of course the table 41.3 defines a Zs value for 0.4s, and these data correspond to 0.95x the calculated impedance to achieve the breaking current shown in appendix 3A4, but how can we state 0.4s or better when appendix data suggests 5s (or 12s in the graph) or better, not 0.4s or better? This isn't the case for type D, which are specified separately for 0.4s and 5s. Seems there is a disparity between table 41.3 and the way data is presented in Appendix 3A4.
At 13:35 Table 41.4 there are 2 rows of Zs values for MCB type D for 10In and 20In. The 10In row of Type D has the same impedance values as a Type C MCB. Please explain. Also i am confused by 0.4 and 5 seconds. I thought all the MCB's trip almost instantaneously ? This is really confusing.
We get some violent thunderstorms here on our farm in western southern Thailand. Couple nights ago there was a local strike and fired the house RCD with a bang but not the one serving our well pumps about 10 meters away in a box on the service pole? Can you offer any explanation.
Use bigger conductors for the circuit. The majority of Zs is provided by the supply though.. in a decent installation, so you are always limited to the installation loop as a maximum current. Most domestic circuits in the UK can't meet the psc or pfc for type D devices.
Bit confused at 14:06. On one hand you are choosing a circuit breaker which should trip at a different time, but on other hand you are choosing the earth the fault loop impedance such that they all trip at the same time. What am I missing here? Are we talking about different scenarios?
The difference is between moderate overloads and a short circuit fault. All of them need to trip near instantaneously if a short circuit fault occurs (which is where the loop impedance is important), but for some applications overcurrent of a short duration may occur in normal operation, such as when starting a motor. For a motor as an example, the circuit breaker needs to be selected so that it will not trip for the high starting current of the motor, but the loop impedance needs to be low enough so that it will trip if a short circuit fault occurs.
Dear Mr. John. Would you like to help me tell some details information about Z type. As we know the Z type instantaneous tripping range is from 2In to 3In. But normally MCB make the short-time delay test is 2In or 2.55In. So now we meet the problem is the short-time delay test almost equal to the instantaneous tripping test. Would you like to tell me some details information how to use the coils and core springs to solve the prblem? thank you very much.
John Can I use a breaker that is only thermal? Let`s say a 40A breaker and a current of 420A. Would the bimetallic strip bend very fast and trip in less than .5 sec., or would the strip be melted?
Thank you. Are RCD`s and MCB`s coordinated? If there is a heavy L-E fault on a circuit, do I lose only this circuit, or the whole busbar because of a faster RCD?
Not usually. A high current L-E fault could result in either device disconnecting, but usually it's the MCB as they are much faster on high current than an RCD. One RCD for multiple MCBs is a poor design anyway, if it's undesirable for the RCD to disconnect multiple circuits then individual RCBOs is a much better option.
Hi John. I am having a TT type system. With reference to minute 13:00 of this video, the table is suggesting a system impedance which is not achievable by a TT system. How do we then go about this? Is the table not applicable for a TT system. Or will therefore all TT system require a RCD for the MCB to work? But then the selection of the MCB type could be of any kind if the impedance value is irrelevant for a TT type system. Appreciate your help..
That table and the rest of 411.4 only applies to TN systems. TT are covered further on starting at 411.5 RCDs are almost always needed to ensure disconnection on L-E faults for TT systems. MCBs are still required to cover faults between L&N and overloads, as RCDs do not detect those.
In a way. Each type has a certain trip current to ensure disconnection, and therefore the impedance of the circuit must be below a certain value to ensure the fault current is high enough. Circuits that are too long will have an impedance that is too high, so the length must be kept short enough to ensure the impedance is low enough.
Impedance between L&N will be the same or lower than the earth loop impedance, so if Zs is low enough, the other one will be as well. However it's important to confirm R1+Rn and to also measure impedance L-N where possible, as problems such as high resistance or open neutrals can occur.
hello John Ward Yours video is highly helpful however i encountered a MCB from Brown, Boveri & Cie (BBC) which is a very old defunct company which is of Type L and that type of classification is very old and i cant find any discription of it anywhere do you have any information about the same???
electrical-shop.theiet.org/books/guidance-notes/on-site-17th-ed-amd3.cfm. That said, I'd hang on for the 18th Edition which is due out next month. That way you'll only be buy once.
Hi l have just seen a consumer unit where 6 combined instant shower heaters each having a rating of about 15 amps are connected to only one type c 32amp mcb. Is this correct or safe!!!???
The breaker is thee to protect the wiring. Essentially, if the wiring is all rated for 32amps (i.e. about 4mm or more in most cases) and the impedance (Zs) at the far-end is low-enough for C32 breaker, then thats' fine. This arrangement does mean you should expect the MCB to trip if you use more than 2 of the showers at once, which is probably fine. The shower-units themselves may mandate a maximum rating of breaker. See video on "diversity". th-cam.com/video/Wq0uODypaGI/w-d-xo.html
I doubt that there is any upper value to the tripping range. It would mean that if you got beyond this colossally big value, there is no result (except to melt something).
The upper limit is the breaking capacity, which is normally printed on the device in a box, such as 6000 or 10000. Fault current exceeding that may damage the circuit breaker or weld the contacts closed.
So.. I have a B16 in my consumer unit feeding my Garage through a 2.5mm cable. On occasion, my compressor will trip the house fuse, even though I have a 16 amp fuse in the garage? If I fit a C type breaker will this cure the issue safely? I was advised by a "mate" to fit a 20A fuse but I feel that may be not the done thing?
A type C circuit breaker may resolve the tripping problem, but the circuit and supply must be tested first to ensure the impedance is low enough. The maximum impedance for a type B is double that of a type C, so it's entirely possible that a type C may not be permitted on that circuit.
I love Electrical information , I enjoy it so much I'm watching this at 4.22am In Australia , before going to work in the electrical industry , purely for enjoyment . This is me coming out , as a geek .
Its 4.32 am here in nz😂
Thank you John, as always I learn so much from your presentations. I teach physics to Electrical apprentices among others in various career paths, but I find many apprentices have no real desire to grasp the science behind Electricity. I recommend your site to many. I always hope they learn as much from from us, to improve their own safety as much as the end user. Keep up the good work.
+John Ward 2 related Areas worthy of Further video in my view:-
(1) When is a circuit a distribution-circuit that may only require 1sec (TT) or 5 sec (TN) disconnection time [>32A ?]. [presumably the TT case is where you also use a 100mA S-Type RCD as well...].
(2) Selectivity between MCBs
It seems, in some circles to be accepted to use a C50 to feed a downstream B32 (e.g. submain to garage with electric-car fast-charging-point), and similarly to use a C32 to feed downstream B16 (e.g. feed to outbuilding with multiple socket-circuits).
HOWEVER this is seemingly not 'guaranteed' and depends on the particular combination of devices and the exact fault-impedance and so-on and so-forth.
When is a switchfuse with BS1361/DNO style fuse instead of a circuit-breaker better to feed a submain, anyway...?
Discuss: What MCB-selectivity is actually 'good enough in practice', what 'passes inspection', etc...?
Thank you, that video is great!
In addition:
In Germany there are two other types available. You've already mentioned the type K, this was a common type here for workshops with large machines. K stands for Kraft (power), and is one of the old german types still available. The other ones were:
H for Haushalt (household), manufactured until 1976. Magnetic: 2 to 3 times. Thermal:
2.1 times (up to 4A)
1.9 times (6 to 10A)
1.75 times (12 to 25A)
1.6 times (more than 25A)
So it's for high impedant grids. It was replaced by type L, which was used here until 1990 before it was replaced by type B. But L is still available as circuit breakers for the replacement of Diazed fuses. In this case the housing is round and it's having an Edison thread.
L for Licht (light), or later Leitungsschutz (cable protection): Magnetic is the same as B, thermal is the same as H.
Picture of a screw-in MCB with Edison thread:
i.ebayimg.com/00/s/NzQyWDEwMjQ=/z/-koAAOSwwBha1XbF/$_72.JPG
What a fantastic video. Thank you so much for this John. very informative and very well broken down and explained. Great work :D
Another great video JW, I was a bit hazy on MCB types, but you just nailed it
Only ever retro fitted type C twice, may years ago.Once when I added 4 more magnetic powered halogen lights to an existing circuit of 8 lights. The breaker would occasionally trip when the 12 lights were turned on. Changed to type C for this circuit and all was fine. Should really swap back to type B as over the years many of the in ceiling transformers have been replaced with modern electronic units.2nd place fitted was house entry lighting circuit. When using ye old tungsten bulbs the cold air rushing in from front door would mean very short life for the entrance hall way bulbs, generally bulbs blowing and taking out the breaker. This circuit was also the garage light circuit where the breakers were located, as well as any easily accessible light switches from front door. Thus one had to fumble around in the dark, in the garage to reset the breaker. Changing this to type C meat when bulb blew the breaker no longer tripped and other lights on the circuit worked fine. All not necessary now using first CFL bulbs and now LED.
Excellent video Cheers JW
Very informative. I'm studying Electrical Engineering in college and we went over cable sizes for circuits but didn't discuss the impedance of the circuit.
So my understanding is you would need to have the correct size cable for the rated current but you might also need to increase the CSA to bring the impedance down to the levels specified in the guide to ensure magnetic tripping in the time allowed. Of course that doesn't really help if the circuit is already installed.
Oblivion You understand correctly!
It's beneficial to have actual supply parameters and detailed specs for the load and circuit breaker.
Generalisations such as Ze= 0.8 ohms for TN-S and Type C magnetic being 5-10x might imply your circuit is non compliant.
But with detailed specs and measured values you would have a definite answer.
Simon Parkinson Makes sense. Thanks for the reply :)
Every little bit of knowledge from people that know first hand is very helpful.
Nice video. A brief mention of DC circuit breakers and why AC breakers should not be used in DC circuits would be helpful.
Thank you John
Excellent information thank you ! 😊
Great video, your knowledge and ability to teach this is very appreciated thanks
It is years I am studying and now is starting to sink in
Understanding and following him 95
If you could do one on RCD types as well (if you haven't already?) that'd be great, thanks JW
Excellent video. This was on my to research list so I saved that time watching the video.
Dear John. Thank you for making all those great videos. You have great electrical knowledge and I do very appreciate it. I need to mention one comment. BS7671 doesn't provide final Zs values for Circuit Brakes. All values have to be multiply by 0.8 correction value. On Site Guide have already corrected those values compared to BS7671. Kind Regards Richard
Great explanation again John. Please could you do a video on mccb’s. Thanks
Great content your a beam of electrical light for the curious mind. An enthusiastic thumbs up 👍
thanks John
Your videos are soooo good. Thanks.
helpful and informative. Great lecture JW
Simple,and precise
Thanks Mr ward for all of your informative videos, without watching your video, I couldn't progress in my electrical installation course. Thanks again
Just checked mine and they are all type 2 on a t t system from over head wires as the house is over 200 years old which i had rewired in 1989
Can you do some vids about surge protectors?
Great video ❤
Can you please tell me what are the criteria of MCB selections from type point of view
Many thanks to you
I wish I had a brain like you, very good information 😁
Very nice & Crystal clear VDO. Can you please explain why MPCB used in Industry and disadvantages / Advantages over MCCB's.
Very informative... Any chance you could explain with Ib and In etc... rated current and breaking capacity mean while you are on the topic. Thanks.
MCB's are to protect the cable. They prevent the cable from being too hot or overheating, which may cause a fire, so indirectly protecting people. A cable constantly being too hot will deteriorate its own insulation. Current travelling excessively through a cable it was not designed to cope with, will heat the cable. When the current travelling through the cable is over a safe limit the MCB senses the current, then if the maximum current is reached for the cable, it automatically isolates the cable it is protecting.
The type B, C and D MCB's are to prevent _nuisance tripping_ caused by momentarily current surges.
It is said. the trip sequence is base on IN Ampere multiplier of currents, denoted as I1 IN *1.3 (test current, no trip), I2 IN * 1.45 (garantees opening of circuit witin 1 hour) Both of these are Thermal and Bimetallic . I4 IN * 5 (electromangetic holding current, no trip), I5 IN * 10 ( el.mag garanteed to open in 0.1 millisecond) . The different characteristics A (sensitive electronic AC), B (household appliances), C (motors, large heaters) . The A, B, C, D- Char have different factors to multiply into IN (nominal Ampere), and match the power leth thru, during smallest (I2) and largest (I5) short or failcurrent, considering the cables crossection and lenght, how they are laid. the amount of load . You have to obtain A^2 sek, that is the mass of the let thru energy once it trips. thats done in the Z-line (Z-loop) calculation or measure. You select a match the short circuitbreaker max can handle, 10kA. The maximal let thru Ampere (I5) is calculated . t = k^2 * ^2 / I^2 finding the splitsecond its required to open. Then I / IN , (I5 maybe IN * 10 = 320A) . k= table specific konstant for conductor type AL or CU and insulation PVC or PEX. PVC has halogenes and chlorine deadly gases when it fumes and is hot, PEX and EPR is Halogene free. S = crossection, remember each crossection has to be calculated, if there is a reduction of crossection along the circuit), I is the Ampere of the Load. Then Match the current multiplyer fits the curve characteristis on the fuse diagram, PLSM, PKPM, dRBM (xdigital), Acti9 C120N, IC60 RCBO. And added safety is the SPD (surge protector) protecting from lightning strikes and atmospheric inductions, SPCT4, IPRD. The SPD is demanded infront of of any new sub distribution cabinet. Type 1 coarse, Type2 middle, and Type3 for finer undulations of stray currents and suggested for data and sensitive electronics on AC .
we used to have H16A circuit breakers in the house. The problem was that the microwave regularly triggered the circuit breaker.
The electrician said these were already obsolete and all converted to B16A. Then there were no more problems.
Hi John
Watching all your videos!
There are brilliant!
Would like to see more on earth rod measurements & calculating current flow in the event of a fault with neutral/earth!
Thanks!
Actually in Italy we use mostly type C pretty much for everything, I don’t know why
Same in Romania.
it's Good understanding 😜 for bad Electrical Engineer's 🤘
Can you please do the same type of video for dc power for solar and battery installs or is it the same as A/C
Types B,C etc are the same, however MCBs for DC are not - if using on DC you need to get ones which are designed for DC, as using AC breakers on DC will quickly destroy them.
Hi , Ilike your lecture.Thanks
In Belgian residential installations, circuits are protected by C-curve breakers. B-curve breakers are rare.
Would you argue this is less safe?
No problem with safety as long as the impedance is low enough.
Here in Austria and Switzerland the C Type is also the commen Type for "normal" circuits.
Bjorn Roesbeke I understand the reasons behind that where socket outlet circuits are 16A radials due to the rating of the outlets.
Some equipment with high inrush current will cause nuisance tripping of a B16, but not a C16.
Where the norm in the UK has been ring finals with B32 MCB, the instantaneous trip values C16x10 and B32x5 are both 160A.
In the UK we tend to use 20A rather than 16A breakers on socket outlet radials due to having the additional protection of fused plugs with a maximum of 13A.
Then it's up to you as the designer to decide if you need B or C breakers, respecting the maximum loop impedances for proper protection.
If the installation was say 6 type C MCBs protected by an RCD, would the RCD help with the failed Z's readings if there were any ☺️
Why type K and Z and not just type E and F? Also what do the letters stand for in TNS and other system types?
Cheers JW. Great video. Is there any chance of touching upon mccbs, in the future with some information on maximum zs values when the device has an adjustable magnetic and thermal setting
Mr Jhon
At what current Btype 32 Amp and C Type 32 Amp MCB start triping.
Nice👍
Are you sure about the RCD not helping?
I believe there is some rule here that says if you provide RCD protection you don't need to meet the impedance for magnetic tripping. The reasoning is the RCD protects against a dangerous touch voltage and it is not necessary to switch off instantly, the slow thermal protection is good enough for fire protection. I'm not 100% positive this rule is still active but I can investigate.
It would apply also to plain old thermal fuses, which have no magnetic trip, when combined with an RCD.
RCDs will help for L-E faults, but will do nothing if the L-N impedance is too high.
I'm aware of that, but my thinking was that the thermal cutout will eventually get it.
The requirement for breakers to switch off instantly comes (also) from preventing dangerous touch voltages in case of a L-E fault, which the GFI would prevent.
There seems to be some discussion over here if the requirement to switch off within 0.4s is only applicable to L-PE or also L-N.
One way to get around this problem might be to use fusible element type fuses instead of breakers in combination with a GFI to achieve higher inrush current tolerance in high impedance circuits.
VDE100-600 says if there is a GFI you generally don't even have to measure the loop impedance, make of that what you will, I'm not much further towards understanding it.
The differnt standards in each country don't exactly make things easier.
Since 2017 in Germany Z_I has to be measured and Riso has to be tested between L&L and L&N. The Others important fact is, If the RCD ist used for "Basisschutz" (earth fault L-PE) or "Zusatzschutz" (earth fault L-Person) ...... In some cases the required tripping time (L-N) can be 5s instead of 0,4s. Because of is wird Situation i allways choose the Type according to 0,4s -> Z_I
Thank you
The majority of breakers found in domestic installations tend to be B type, whether or not this is by design or by the fact that that’s what comes with the fuse board I don’t know
If it did not trip on a fault current due to high impedance it would still trip eventually on overload i assume ? But the cables might be over heated before this. Is that correct ?
Yes - the overload part relies on a metal strip heating up so cables could overheat if that was the only thing which disconnected a short circuit fault.
Why is TNS Ze a high value up to 0.8 ohms ? Is the supply earth conductor smaller than the supply neutral ?
merci 🌹🌹💚💚
we have 110v phases in my country, I want to buy a 40A MCB, but I noticed that everybody sells these 230/400 volts MCB's no 110v breakers, so it would work properly?
Yes they will work, they are current operated, the voltage isn't particularly relevant as long as the maximum voltage isn't exceeded. Check with the MCB manufacturer to confirm the voltage range.
Very informative, thanks. One odd thing is the vertical (magnetic) part of the MCB graphs in Appendix 3, for example graph (and associated table) 3A4 and similar to your example in 21:04. 18th ed. Appendix 3A4 shows that for a 6A type B, trip time at 30A will be anywhere between 10ms and 12s (or 10ms to 5s in the associated table). If that is in fact the case, how are we to design to achieve 0.4s disconnections from Appendix data? Of course the table 41.3 defines a Zs value for 0.4s, and these data correspond to 0.95x the calculated impedance to achieve the breaking current shown in appendix 3A4, but how can we state 0.4s or better when appendix data suggests 5s (or 12s in the graph) or better, not 0.4s or better? This isn't the case for type D, which are specified separately for 0.4s and 5s. Seems there is a disparity between table 41.3 and the way data is presented in Appendix 3A4.
At 13:35 Table 41.4 there are 2 rows of Zs values for MCB type D for 10In and 20In. The 10In row of Type D has the same impedance values as a Type C MCB. Please explain. Also i am confused by 0.4 and 5 seconds. I thought all the MCB's trip almost instantaneously ? This is really confusing.
We get some violent thunderstorms here on our farm in western southern Thailand. Couple nights ago there was a local strike and fired the house RCD with a bang but not the one serving our well pumps about 10 meters away in a box on the service pole? Can you offer any explanation.
Are these Zs values the same for RCBO's . With type D is it written on the breaker if its 10ln or 20ln
Yes, they are the same. The overcurrent part of an RCBO is the same as an MCB.
Good video. How can I get the handbook that you're using? And website where I can purchase it?
Small on site guide: amzn.to/2Je3CxY
Large BS7671: amzn.to/2Jf8umv
Links also added to the video description.
John Ward awesome thanks. Keep up the videos.
Is there a way we could reduce the "Z" in order to install a type "C" or "D" breaker when Zs is none compliant?
Hi, Ningis21. If normally you use the "Z" type MCB?
Use bigger conductors for the circuit. The majority of Zs is provided by the supply though.. in a decent installation, so you are always limited to the installation loop as a maximum current. Most domestic circuits in the UK can't meet the psc or pfc for type D devices.
👍🏻👌🏻👌🏻 cheers.
Hello, if we have a B type MCB (22:00) and we have a 4times the rated current the magnet will trip between 0.02sec to 1.5sec approximately?
Bit confused at 14:06. On one hand you are choosing a circuit breaker which should trip at a different time, but on other hand you are choosing the earth the fault loop impedance such that they all trip at the same time. What am I missing here? Are we talking about different scenarios?
The difference is between moderate overloads and a short circuit fault.
All of them need to trip near instantaneously if a short circuit fault occurs (which is where the loop impedance is important), but for some applications overcurrent of a short duration may occur in normal operation, such as when starting a motor.
For a motor as an example, the circuit breaker needs to be selected so that it will not trip for the high starting current of the motor, but the loop impedance needs to be low enough so that it will trip if a short circuit fault occurs.
Dear Mr. John. Would you like to help me tell some details information about Z type. As we know the Z type instantaneous tripping range is from 2In to 3In. But normally MCB make the short-time delay test is 2In or 2.55In. So now we meet the problem is the short-time delay test almost equal to the instantaneous tripping test. Would you like to tell me some details information how to use the coils and core springs to solve the prblem? thank you very much.
What breaker would you recommend for 4 x 100w 12volt solar panels in parallel ?
Derek Todd You should have them in series (if your solar panel control unit accepts enough high voltage)
Ones that are specifically designed for DC - using AC breakers on DC will destroy them.
I agree with Jako, 48V series @ 8.3Amps or 12v at 33.3Amps. DC breaker as JC said.
Thanks very much for your videos , but my question is when am having high readings on Zs , what is the solution?
Are the Zs values high on each circuit you test or certain circuit's?
John Can I use a breaker that is only thermal? Let`s say a 40A breaker and a current of 420A. Would the bimetallic strip bend very fast and trip in less than .5 sec., or would the strip be melted?
No, thermal is too slow to disconnect on short circuit faults.
How Can I Get English Mediumboo?
Actually Type A exists. I've holded some MCB-s that are Type A. Extremely rare.
John, I can send you a photo of one I've held :)
Yes please - email and other contact details here: www.flameport.com/youtube_channel_info.cs4
@@jwflame Sorry, I forgot. I've sent the email right now.
Thank you. Are RCD`s and MCB`s coordinated? If there is a heavy L-E fault on a circuit, do I lose only this circuit, or the whole busbar because of a faster RCD?
Not usually. A high current L-E fault could result in either device disconnecting, but usually it's the MCB as they are much faster on high current than an RCD.
One RCD for multiple MCBs is a poor design anyway, if it's undesirable for the RCD to disconnect multiple circuits then individual RCBOs is a much better option.
I see some with type L, what is that for?
Hi John. I am having a TT type system. With reference to minute 13:00 of this video, the table is suggesting a system impedance which is not achievable by a TT system. How do we then go about this? Is the table not applicable for a TT system.
Or will therefore all TT system require a RCD for the MCB to work? But then the selection of the MCB type could be of any kind if the impedance value is irrelevant for a TT type system.
Appreciate your help..
That table and the rest of 411.4 only applies to TN systems. TT are covered further on starting at 411.5
RCDs are almost always needed to ensure disconnection on L-E faults for TT systems.
MCBs are still required to cover faults between L&N and overloads, as RCDs do not detect those.
Is the curve type of breaker is dependent on the length of cable.i
In a way. Each type has a certain trip current to ensure disconnection, and therefore the impedance of the circuit must be below a certain value to ensure the fault current is high enough. Circuits that are too long will have an impedance that is too high, so the length must be kept short enough to ensure the impedance is low enough.
In my industry, the caravan industry we us type B and type C, predomantly it is type C
What is the temperature rating of the lugs?
Usually 70C, same as PVC insulated cable.
Why does it just give Zs values. What about R1+Rn as you mention this must be low enough also for breaker to trip
Impedance between L&N will be the same or lower than the earth loop impedance, so if Zs is low enough, the other one will be as well.
However it's important to confirm R1+Rn and to also measure impedance L-N where possible, as problems such as high resistance or open neutrals can occur.
@@jwflame Thank you very much. I was looking for this explanation.
hello John Ward
Yours video is highly helpful however i encountered a MCB from Brown, Boveri & Cie (BBC) which is a very old defunct company which is of Type L and that type of classification is very old and i cant find any discription of it anywhere do you have any information about the same???
www.galco.com/techdoc/abbg/s252-l6_gi.pdf
@@jwflame the pdf was very helpful thankyou very much but would it be correct to assume this L type breaker comes under 1,2,3,4 classification???
Great video, you say there is no Type A, but what are the type A C and Type A B i've seen on sale? is there a video on these?
RCBOs, which are a Type A RCD combined with a Type B or Type C circuit breaker.
@@jwflame thanks John. Do you have a video about DC leakage and RCBO types?
How to get that yellow onsite guide. Kindly share link if possible
electrical-shop.theiet.org/books/guidance-notes/on-site-17th-ed-amd3.cfm. That said, I'd hang on for the 18th Edition which is due out next month. That way you'll only be buy once.
Available from Amazon here: amzn.to/2Je3CxY
John Ward many thanks
cjmillsnun perfect! Thank you
John Ward, thanks John
Hi l have just seen a consumer unit where 6 combined instant shower heaters each having a rating of about 15 amps are connected to only one type c 32amp mcb. Is this correct or safe!!!???
The breaker is thee to protect the wiring. Essentially, if the wiring is all rated for 32amps (i.e. about 4mm or more in most cases) and the impedance (Zs) at the far-end is low-enough for C32 breaker, then thats' fine. This arrangement does mean you should expect the MCB to trip if you use more than 2 of the showers at once, which is probably fine. The shower-units themselves may mandate a maximum rating of breaker. See video on "diversity". th-cam.com/video/Wq0uODypaGI/w-d-xo.html
I doubt that there is any upper value to the tripping range. It would mean that if you got beyond this colossally big value, there is no result (except to melt something).
The upper limit is the breaking capacity, which is normally printed on the device in a box, such as 6000 or 10000. Fault current exceeding that may damage the circuit breaker or weld the contacts closed.
So.. I have a B16 in my consumer unit feeding my Garage through a 2.5mm cable. On occasion, my compressor will trip the house fuse, even though I have a 16 amp fuse in the garage? If I fit a C type breaker will this cure the issue safely? I was advised by a "mate" to fit a 20A fuse but I feel that may be not the done thing?
A type C circuit breaker may resolve the tripping problem, but the circuit and supply must be tested first to ensure the impedance is low enough. The maximum impedance for a type B is double that of a type C, so it's entirely possible that a type C may not be permitted on that circuit.
@@jwflame thanks John.. I'll get it tested and go from there.
how many videos must i watch for someone to properly explain 3 fucking numbers on a MCB???
HIoT
How can a 6A type B still be a 6A if it is type C or D. Surely, it's not a 6A breaker anymore. Does not compute.
Yes. It's just got a higher surge tolerance before it trips
The 6AMP's rated MCB is for the thermal cut off which is the same for B, C,D rated. Not the trip current.
Talk alil bit slower..
Once again,thanks
Thanks John
Dear John, this video is graet. Regards, from Hungary
And a Hammond L solemnly sits in the background
What type will you recommend for Airconditioning unit
That depends on the specifications of the AC unit.
nice top where can i get one