Great video - I think 3 phase systems seem to be avoided by most TH-cam creators. Excellent knowledge and understanding building platform given here. 👏👏
Thank you 🙏 I agree, it's avoided. Il do some big stuff versions and perhaps some parallel conductors. It's been a while since I did those in real world so should revise first 🤭👍
Cheers Craig, you have a knack of making a seemingly complex design calculation easy, by breaking them down and explaining every step of the way. Great video, keep them coming👍
Interesting video, but note that re thermal constraints / checking the cpc size, the method you show of V/Zs is for fuses, whereas the EIDG says (don't have it to hand, but think it's chapter 8) that for CB's and PEFC of up to around 3kA, the CB trip rating can be used, whereas over 3kA, A2S's are used.
Yep, Section 8 and a little bit of 4. Figure 41b shows how the plot gets a little bit whacky after 3KA. This is an intro video, always tricky to decide what to put through and what to dive into. Should prob also check 434.5.2 after that level........
Great video. Was discussing the other day what you mentioned with the formula Zs=Ze + (R1+R2) and it seemed bizarre that you could add resistance and impedance to equal impedance 🤔! Would be interesting to see a cable calculation with cables greater than 35mm2 where you allow for reactanance as that's not something I've calculated! Thanks
To be honest, ive only ever calculated it for my own curiosity and I discovered how hard it would be to get an accurate result. In the real world I just use the data sheets from the cable manufacturer who state impedance per meter values. 😉
some would describe that as in rush current. happens during the first few moments of starting the motor. Once the magnetic fields and resistance has been established through heat the current drops to lower levels.
Something that has just crossed my mind is how to size cables for ev chargers. Is it just simply a case of selecting a cable that can handle the rating of the outlet? Could you show a worked example for this situation? Cheers Craig👍
It would be a similar process yes. So a 3 phase would be sharing the total rated load but there are more things to consider. But yeah, il stick it on the list. 👍
With regards to Cg, grouping is a lot more nuanced & is full of pitfalls for design such as notes 8 + 9. Note 8 significantly changing the current rating choice depending on temperature of cables in the group.
hi boss, in the beginning of the video the circuit is a 400v three phase system, i follow along for the calculations there. why when we go to calculate the CPC for the circuit are you then using 230v for the maximum Zs? should this value not still be 400? TIA
3 circuits in conduit. What does this mean exactly. Are we looking at supplies to 3 motors. That would be 3 phase and earth times 3 (12 single core cables) ? Are they single core or multicore cables ? Please explain
3 circuits means single or 3 phase or a mix. There is guidance shop.theiet.org/electrical-installation-design-guide-5th-edition on how to calculate these for various scenarios page 51 onwards but i usually stick to simple circuits in these videos. It would be 3 similarly loaded circuits. If a circuit is only carrying a small amount of current it can be ignored. Guidance value is around 33% of its capacity in the installation conditions.
Like you do a vid on voltage drop for large cables where you have the r x z values . I don’t know which one to pick with these and exactly what they mean or how you know which one to use
Yes it does effect Power. Star is approx 1/3 of Delta. We start in star to build up speed then switch over to delta. Think of a car starting in 1st gear then switching to 2nd gear.
why don't you use 0.4 for disconnection time? just started learning this and I have calculated it with 0.1s and it complies but when you do it with 0.4s it doesn't if you use 1.5mm2
Hello, the protective device would disconnect in 0.1s according to manufacturer as long as Zs complies. A D type may be 0.4s. We are allowed a max disconnection time of 0.4s as per table 41.1 bs7671. Any circuit outside of that scope would be 5s on TN earthing arrangements. Tt would be 0.2s or 1s accordingly. There is an argument to say you perhaps should design for the max allowed rather than actual disconnection times in case someone changes the type of device. But, that's really up to them to check and confirm suitable really. Some breakers achieve better than 0.1s! It's information from appendix 3 bs7671 but manufacturers can provide much more detailed information.
Unfortunately these books are copyright protected. However the cable manufacturers and protective device manufacturers will have their data available free of charge. I will do some videos on the cable factors soon and will show the tables there but there are other ways to get some of the common factors so the table won't be required. Most countries regulation books are based on iec60364 and some countries have theirs for free. So to get an idea of how it's written you could try looking for that.
@@cestemshow This is what i can use docplayer.nl/8187348-Normen-formules-tabellen.html page 9-4 the table that is landscape "Normen, formules, tabellenOverstroombeveiliging van kabels en leidingen" Also look at 2 pages before this table. May i email you, about the procedure to select a motorprotection on a circuit that is able to do starcircuit to deltacircuit at startup. How to calculate Ib, In proberbly in worstcase delta ? Shortcircuit current calculation, how do you determine this for a delta and for star, and is this shortcircuit current neccesary to select a motorprotection device? Is the basic procedure step 1) determine In, the maximum current of the motor at maximum load, if this is not on the motorplate then do use factor x I from kW then step 2) at startup a motor will pull 6 x In and look in the specification of the motorprotection device if you need type B or type C and select an appropriate device that is able to do 6 x In ? at the end you do the cable/wiring size calculation with cos phi the last part cable/wiring selection is clear, but the motorprotection selection is confusing and difficult, proberbly since it differs from DOL and star to delta. Also i found this, check this the WOLF method th-cam.com/video/sjQV2A9bjcc/w-d-xo.html
@@cestemshow I have response message, i would like to know how to select the MCB , the type is that realy based on the Ib, and ib is the current in the motor coil?
Yes by all means email me. Sounds like you know loads 👍. I left out efficiency in the design current calculations because I was mainly focusing on the cable selection bit for my students. Dol is easy and protection usually comes within the motor itself. Star delta is simply about the connections and usually a couple of contactor can handle that with 2 sets of wires coming from motor to contactor enclosure then depending on the motor you set up a timer to activate them into delta connection. Hard to teach this stuff over this forum because it's complicated and depends on which type of motor etc. Ultimately I'd say get in touch with some motor manufacturers as they have the best knowledge for this stuff and in the real world I've always consulted with them before finalising any design. Email is completelyelectrical@gmail.com
A square root function is the opposite of squaring a number so for example 4 "squared" is 16 and the square root of 16 is 4. or 9 "squared" is 81 and the square root of 81 is 9. Is that what you meant? or more specifically as to why we use the square root in some our calculations?
It's splitting the power equally over the 3 phases. At any one time the majority of rms value is only present in 1 phase at a time so to deliver the power you need to consider the delivery of all 3. 123 123 123 123 etc. If you zoomed in and looked at the characteristics for each nano second it would look very different but to get an averga power split over 3 phases we essentially are saying power diveded by 3 x 230v.... Ish. 😁
Just use the Z value instead in place of the usual mv/a/m The r x values are the resistive and reactanctance components for the cable per m and the z is the impedance so just use that 👍
Great video - I think 3 phase systems seem to be avoided by most TH-cam creators. Excellent knowledge and understanding building platform given here. 👏👏
Thank you 🙏 I agree, it's avoided. Il do some big stuff versions and perhaps some parallel conductors. It's been a while since I did those in real world so should revise first 🤭👍
really usefull breakdown of the 3 phase design principles. Thank you for this master class
Cheers Craig, you have a knack of making a seemingly complex design calculation easy, by breaking them down and explaining every step of the way. Great video, keep them coming👍
Glad to help!
Excellent! Just what I was looking for, many thanks for a clear no nonsense video.
Thank you 🙏
Superb video and workings, just well well presented.
So nice of you
Interesting video, but note that re thermal constraints / checking the cpc size, the method you show of V/Zs is for fuses, whereas the EIDG says (don't have it to hand, but think it's chapter 8) that for CB's and PEFC of up to around 3kA, the CB trip rating can be used, whereas over 3kA, A2S's are used.
Yep, Section 8 and a little bit of 4. Figure 41b shows how the plot gets a little bit whacky after 3KA. This is an intro video, always tricky to decide what to put through and what to dive into. Should prob also check 434.5.2 after that level........
Great video.
Many thanks 😊
Great video. Was discussing the other day what you mentioned with the formula Zs=Ze + (R1+R2) and it seemed bizarre that you could add resistance and impedance to equal impedance 🤔! Would be interesting to see a cable calculation with cables greater than 35mm2 where you allow for reactanance as that's not something I've calculated!
Thanks
To be honest, ive only ever calculated it for my own curiosity and I discovered how hard it would be to get an accurate result. In the real world I just use the data sheets from the cable manufacturer who state impedance per meter values. 😉
Could you do a video on motor calculation with locked rotor current and explain what this is also?
Thanks
some would describe that as in rush current. happens during the first few moments of starting the motor. Once the magnetic fields and resistance has been established through heat the current drops to lower levels.
Something that has just crossed my mind is how to size cables for ev chargers. Is it just simply a case of selecting a cable that can handle the rating of the outlet? Could you show a worked example for this situation? Cheers Craig👍
It would be a similar process yes. So a 3 phase would be sharing the total rated load but there are more things to consider. But yeah, il stick it on the list. 👍
With regards to Cg, grouping is a lot more nuanced & is full of pitfalls for design such as notes 8 + 9.
Note 8 significantly changing the current rating choice depending on temperature of cables in the group.
hi boss, in the beginning of the video the circuit is a 400v three phase system, i follow along for the calculations there. why when we go to calculate the CPC for the circuit are you then using 230v for the maximum Zs? should this value not still be 400? TIA
Hello, For the cpc we are concerned with line to earth fault. Generally this will only be 1 line touching cpc so 230v approx.
@@cestemshow thankyou so much for taking the time to reply!
3 circuits in conduit. What does this mean exactly. Are we looking at supplies to 3 motors. That would be 3 phase and earth times 3 (12 single core cables) ? Are they single core or multicore cables ? Please explain
3 circuits means single or 3 phase or a mix. There is guidance shop.theiet.org/electrical-installation-design-guide-5th-edition on how to calculate these for various scenarios page 51 onwards but i usually stick to simple circuits in these videos. It would be 3 similarly loaded circuits. If a circuit is only carrying a small amount of current it can be ignored. Guidance value is around 33% of its capacity in the installation conditions.
Like you do a vid on voltage drop for large cables where you have the r x z values . I don’t know which one to pick with these and exactly what they mean or how you know which one to use
Great video, really helped me. Thank You !
Cheers very good video
A 3 phase motor can be wired in star or delta. Does this affect the power ? Does it affect cable sizing. Please advise
Yes it does effect Power. Star is approx 1/3 of Delta. We start in star to build up speed then switch over to delta. Think of a car starting in 1st gear then switching to 2nd gear.
(table 4D1B): sir if we have three phase cable cross section size 25mm2 or 120mm2, then what we should do to get volt drop?
th-cam.com/video/vl1RE32W5lg/w-d-xo.html
bloody good vid
why don't you use 0.4 for disconnection time? just started learning this and I have calculated it with 0.1s and it complies but when you do it with 0.4s it doesn't if you use 1.5mm2
Hello, the protective device would disconnect in 0.1s according to manufacturer as long as Zs complies. A D type may be 0.4s.
We are allowed a max disconnection time of 0.4s as per table 41.1 bs7671. Any circuit outside of that scope would be 5s on TN earthing arrangements. Tt would be 0.2s or 1s accordingly.
There is an argument to say you perhaps should design for the max allowed rather than actual disconnection times in case someone changes the type of device. But, that's really up to them to check and confirm suitable really.
Some breakers achieve better than 0.1s! It's information from appendix 3 bs7671 but manufacturers can provide much more detailed information.
Great explanation. Well done!!
Thank you!
Are you sure you divide and not multiply the factors to the nominal current?
yes, i showed both methods.......there are 2 ways to get the same answer.
What free table or book may i use in the Netherlands? Or English downloadable FREE book?
Unfortunately these books are copyright protected. However the cable manufacturers and protective device manufacturers will have their data available free of charge. I will do some videos on the cable factors soon and will show the tables there but there are other ways to get some of the common factors so the table won't be required. Most countries regulation books are based on iec60364 and some countries have theirs for free. So to get an idea of how it's written you could try looking for that.
@@cestemshow This is what i can use docplayer.nl/8187348-Normen-formules-tabellen.html page 9-4 the table that is landscape "Normen, formules, tabellenOverstroombeveiliging van kabels en leidingen" Also look at 2 pages before this table. May i email you, about the procedure to select a motorprotection on a circuit that is able to do starcircuit to deltacircuit at startup. How to calculate Ib, In proberbly in worstcase delta ? Shortcircuit current calculation, how do you determine this for a delta and for star, and is this shortcircuit current neccesary to select a motorprotection device? Is the basic procedure step 1) determine In, the maximum current of the motor at maximum load, if this is not on the motorplate then do use factor x I from kW then step 2) at startup a motor will pull 6 x In and look in the specification of the motorprotection device if you need type B or type C and select an appropriate device that is able to do 6 x In ? at the end you do the cable/wiring size calculation with cos phi the last part cable/wiring selection is clear, but the motorprotection selection is confusing and difficult, proberbly since it differs from DOL and star to delta. Also i found this, check this the WOLF method th-cam.com/video/sjQV2A9bjcc/w-d-xo.html
@@cestemshow I have response message, i would like to know how to select the MCB , the type is that realy based on the Ib, and ib is the current in the motor coil?
Yes by all means email me. Sounds like you know loads 👍. I left out efficiency in the design current calculations because I was mainly focusing on the cable selection bit for my students.
Dol is easy and protection usually comes within the motor itself.
Star delta is simply about the connections and usually a couple of contactor can handle that with 2 sets of wires coming from motor to contactor enclosure then depending on the motor you set up a timer to activate them into delta connection.
Hard to teach this stuff over this forum because it's complicated and depends on which type of motor etc.
Ultimately I'd say get in touch with some motor manufacturers as they have the best knowledge for this stuff and in the real world I've always consulted with them before finalising any design.
Email is completelyelectrical@gmail.com
th-cam.com/video/km8MSWm39Z0/w-d-xo.html
Great vid for star delta simple explanation.....
I don’t seem to get my head around the square root, can you explain it to me
A square root function is the opposite of squaring a number so for example 4 "squared" is 16 and the square root of 16 is 4. or 9 "squared" is 81 and the square root of 81 is 9. Is that what you meant? or more specifically as to why we use the square root in some our calculations?
Yeh I had a brain storm ,I was squaring it sorted now
Thanks @@cestemshow
Why isn't it 230Vx√3 as that equals 400V?
It's splitting the power equally over the 3 phases. At any one time the majority of rms value is only present in 1 phase at a time so to deliver the power you need to consider the delivery of all 3.
123 123 123 123 etc. If you zoomed in and looked at the characteristics for each nano second it would look very different but to get an averga power split over 3 phases we essentially are saying power diveded by 3 x 230v.... Ish. 😁
where do you find out the power factor from?
The manufacturer would state it on the motor plate as "cos theta" value usually.
Did u forget to factor in ambient temperature?
Yeah kinder did 🙂. What factor would you use? BS7671 on goes down to 20 degrees and would only have a beneficial effect the colder it is.
what's the name of the book ?
BS 7671. Sometimes I use this shop.theiet.org/electrical-installation-design-guide-5th-edition
how to calculate voltage drop from x, y and z table
Just use the Z value instead in place of the usual mv/a/m
The r x values are the resistive and reactanctance components for the cable per m and the z is the impedance so just use that 👍
Learning how to use my calculator watching this video.
Glad it was helpful!