LIVE Testing on a 3 Phase Dis-Board - External Earth Fault Loop Impedance Ze, PEFC, PSCC AM2 & AM2S
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- เผยแพร่เมื่อ 5 พ.ค. 2024
- Live testing for external earth fault loop impedance, prospective earth fault current PEFC and prospective short circuit current PSCC (PFC tests). These tests are demonstrated on a live 3 phase distribution board and will help with AM2 and AM2S exams. We use the rule of thumb for calculating the PSCC test by taking the highest reading form the line and neutral tests and doubling it and then we go on to show you how some instruments can measure PSCC between line conductors. As always preparing for your end skills test AM2, AM2S or AM2E requires time testing at college and on-site experience of testing electrical circuits.
NOTE- for AM2 etc you may have a remote main earth terminal (MET) if the is the case this could have the bonding connecting in it (best to check). This will mean the earthing conductor could be removed and tested from this point for the external earth fault loop impedance or you can remove the bonding from the MET and test as shown in this video.
NOTE 2- Your end point assessment AM2 and AM2S will require you to have the main switch locked off, sign in place and key In your pocket during this test 👍🏻.
🔵 Testing for External Earth Fault Loop Impedance (Ze) When You Have a Main Earthing Terminal (MET) • Testing for External E...
🔵 First Live Test AM2 & AM2S - Check Polarity of 3 Phase Supply, Using an Approved Voltage Indicator • First Live Test - Chec...
== 🕐 Time Stamps - Cut to the action 🕕 ==
00:00 - Ze and PFC tests
00:54 - Isolating the 3 phase distribution board
01:58 - Disconnecting the earthing conductor to remove parallel earth paths created by the bonding
02:55 - External earth fault loop impedance test Ze test on a 3 phase dis-board
05:11 - Reconnect the earthing conductor
05:19 - Prospective earth fault current PEFC test (PFC)
06:34 - Prospective short circuit current PSCC test (PFC)
08:00 - Rule of thumb double your highest reading from PSCC test for a 3 phase supply
09:48 - Testing PSCC between the 3 line conductors of a 3 phase supply
Videos are training aids for City and Guilds (C and G) and EAL courses Level 1, 2, 3 plus AM2, AM2S and AM2E.
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Not sure if you guys will see this but just wanted to say a massive thank you, passed my AM2 first time and your videos absolutely carried me through, thank you!!!
Fantastic news 👍🏻 congratulations from team GSH
Yes, thanks guys, about to undertake this myself and your videos are invaluable 👊
@@GSHElectrical He should have done Zs at DB as well...
@@democracyforall isnt that only relevant if this is a sub main ?
Thanks guys make it so much easier to understand seeing it 👍🏼
Great video!
Lots of real world training missing online.
H&S… I wear VDE gloves when working/testing live. Just mitigates the risk. Easy enough to fall forward on to the live terminals, especially so on older 3ph boards & working off a ladder, etc..
Short but sweet. Well put together video with no gimicks, just the settings and procedures needed to carry out the tests! more videos like this are needed!
👍🏻thanks
Great Video Guys, very well explained
Thank you guys for all test. Some of them I wasn't sure 👍👍👍
Thanks for the support and watching
Another great video and demonstration, much appreciated
Thanks 👍🏻
Thanks ,you make it easy to understand
Thanks for commenting and watching 👍🏻
Having failed Section B on 'Prospective Fault Current' and knowing for a fact that I failed to remember to double that highest figure I'd say it probably is enough to give an overall fail on Section B. Pretty certain my method of test was correct so goes to show just how important it is to multiply that reading by two!!
So what is the safe value to measure then?
Thank you for the explanation
Thanks for watching 👍🏻
My level 3 teacher is currently drilling me with three phase testing and fault finding as Iv handed my design project in well early. I’m so glad because once you start doing the three phase it’s so much different. I can honestly say I feel confident to do my 2391 and am2 and watching these videos now make a lot more sense than when I watched it without doing three phase.
All the best and thanks for commenting 👍🏻
Thank you!
Brilliant
It was more than helpful, God bless u
Thanks 👍🏻
massive thanks !
👍🏻
Plz do many more videos. Great job chaps
Thanks! Will do!👍🏻
Thanks very much, been looking for a good ze, pfc vid in a 3p DB. Getting ready for my fica at the end of this year👍🏾.
Thanks
Brilliant guys
Thanks
Thank you so much for these videos. Really helpful information!
One question. Why we take the PFC measurement with the main switch off and on the source side? When using the system all breakers etc are on. Why take the rest of the system out of the equation? the PFC surely would be different when the whole system is connected and turned on?
Thank you
2 kings ❤
Great video, once again. Could you tell me how too test a 3phase rcbo please?
Thanks
== 🕐 Time Stamps - Cut to the action 🕕 ==
00:00 - Ze and PFC tests
00:54 - Isolating the 3 phase distribution board
01:58 - Disconnecting the earthing conductor to remove parallel earth paths created by the bonding
02:55 - External earth fault loop impedance test Ze test on a 3 phase dis-board
05:11 - Reconnect the earthing conductor
05:19 - Prospective earth fault current PEFC test (PFC)
06:34 - Prospective short circuit current PSCC test (PFC)
08:00 - Rule of thumb double your highest reading from PSCC test for a 3 phase supply
09:48 - Testing PSCC between the 3 line conductors of a 3 phase supply
Great video, possible to do video on 3 phase rcd 300mA
I’m assuming as it’s a live test you’d need the tails to have voltage to actually get a reading on the Ze and PFC tests? For example on the AM2 rig if they’ve isolated it remotely, I’d need to lock off the main switch on the board, then energise the isolator?
Good video, informative.
After 29 years of data cabling/engineering a flooded market of poor quality engineers the last few years reducing rates I started an electrical training course a month ago and enjoying it (should of started years back).
Would the incomer earth be better with a ring crimped connector?
I do believe the highest L-L reading has to be divided by 0.87 to get a simultaneous 3 phase fault PSCC.
Someone else also mentioned this. Was there a reason you didn’t mention it in this video?
Ma'am bahut accha padte hai m
Great video guys! Not sure how strict and to the book the assessors will be in the am2 but GN3 does recommend dividing the line to line value by 0.87 if measuring Ipf between phases.
Edit:
After some research online I believe this figure is a guide to working out a simultaneous fault between all phase conductors with a fault of negligible impedance.
Great feedback 👍🏻
What about if there is an rcd when taking the pscc, is there a way to test this on a 3 low setting?
Should the right hand side dial be set on zmax when doing pscc 2lead high?
Sorry if this is silly question as I’m still a beginner adult learner etc but why do we have to use a,,3lead high or 3lead low? what’s difference and why do it etc 👍👍
I didn’t double the figure and I failed on the PFC test so I had to resit the full inspection and testing segment
Thanks for your feedback 👍🏻
Don’t you have to actually times by square root of three and not double it For three phase PFC? It’s not double to work out single to three phase?
great video , big thumbs up and i want that red car , where is this filmed
Thanks for the support 👍🏻
Does that earth wire go back to supply transformer or is it just linked to the neutral at the cut out. Is 3 phase the same as single phase domestic in this regard. Thanks
On a TN-S the earth goes all the way to the transformer separately from the neutral,. They're then connected together at the transformer.
On a TN-C-S (shown in the video) the earth and neutral are joined at the cutout, and continue as a "PEN" conductor to the transformer (protective earth/neutral).
On a TT the earth doesn't go to the transformer at all. Instead it connects to the consumer's earth electrode.
for the am2s would we need to test between line conductors for PSCC or is testing between line and earth and line and neutral and doubling it enough ? Also would the reading from line and earth ever be higher than line to neutral ?
Should be times by square root of three I thought becuase of the different between Line and Phases?
👍👍👍👍👍👍
Hi thanks for this I didn’t realise you have to double the PFC, is this just on a three faze board?
Yes 👍🏻
@@GSHElectrical thank you! is the PFC is the only one you write down on the schedule of tests?
@@OllyDunne24 you write down the highest reading you get out the two I believe
Show how to measure insulation and RCD.
Theoretically the value is x1.73. However is much easier to double it
👍🏻
In guidance note 3 the PEFC shows a 3 lead test. does it matter if you do a 2 or 3 lead test?
i have my AM2 in 2 weeks. Thanks
I’ve always done a 3 lead test, seeing this has thrown me and I have my AM2S in a week and a half. How did yours go?
Would you double it on a domestic install as well?
Only on 3 phase installation 👍🏻
Only on 3 phase Because of the potential between 2 different phases
do you have to test between L1-L2 and so on or can you just do the L’s -N and double it?
If your tester can test between line conductors you take that as the heights reading if not it’s line neutral and double it 👍🏻
Would you fail if you measure PSCC on the load side of the main switch?
if its locked off you cant
Just failed my 2391 because i got lost at the PEFC testing. Isnt there a 3 lead test with this megger or thats just for single phase
pfc requires a 2 lead test
Hi, why do you bother testing the PEFC on 3 phase if it doesn’t get recorded?
Great point 👍🏻
What is AM2 ?
An end point assessment for apprentice electricians 👍🏻
I saw a test where the pfcc was 20ka, with out doubling it, it came straight from the Mccb board to the 3phase board, all connections were tighten correct, the pfc was 3ka, 6ka when doubled. Was this because the main intact was only 1.5 metres away? Trying to understand why it was so high, and what effect it would have as I know the the circuit breakers were at 10ka so they would be ok as the pfc was 7ka once doubled. The person just said the nic guy just wants a pfc so don’t worry about it, but I’m intrigued to know more if it happens to me.🤔👨💻
In the UK, the maximum design fault level for the DNO's LV network is 25MVA for a three-phase symmetrical fault. Distribution transformers are still manufactured to a spec' with the secondary winding rated at 433V no-load volts (250V 1-ph), so a typical secondary substation transformer may have a rating of 1000kVA, voltage ratio 11:0.433 kV and impedance volts rating of 4.75%.
So, what does all this mean? Well, the design maximum fault level of 25MVA (3ph fault) at 433V would equate to 33.3kA per phase at the transformer LV terminals. In the real world, however, the actual fault levels are quite a bit lower due to the upstream network impedances (unless there is an unusual parallel supply arrangement with more than one secondary transformer). In most situations, the maximum fault levels (or PSCC/PEFC if you prefer) you should encounter are -
three phase fault: 18.7MVA (24.9kA per phase)
phase-to-phase fault (PSCC): 9.4MVA (21.7kA per phase)
phase-to-earth fault (PEFC): 6.5MVA (25.9kA)
I did a wee head-tilt at the requirement to **double** the L-N PSCC to record the Ipf value on the test paperwork, but I realise the guidance is intended to build-in a factor of safety when considering the PSCC in the context of the equipment rating.
If you are concerned about the PEFC or PSCC readings you measure, you can request the DNO to supply the 'prevailing' fault level data for the point of connection - note that this may not be exactly the same as the point you are testing at, but likely to be close enough. Some DNOs may try to fob you off with simply stating the design maximum value. To an extent, they have a get-out, which is simply that the LV and HV network configuration can be altered without any reference to you or your client and so the test results you just recorded could change in 10 minutes after some switching. That's why I referred to the 'prevailing' fault level data, which would be calculated by the DNO based on the 'usual' network configuration. Chances are you would have to pay for them to do the calculations, though and so I guess that it wouldn't be worth it most of the time.
@@protectiongeek so it is to high, so the DNO would have to be called as it’s too high because its meant to doubled it would be 40 ka, if I’m reading this right. 🤔 doesn’t give you a reading L-N I noticed.
@@sugardaddyxxx tbh any time I was calculating fault levels, I made no distinction between L-N and L-E. There will be slight differences depending on whether the supply was TN-S or TN-C-S but not really that significant to the DNO network.
If the guidance to electricians is to record a fault current of twice the measured L-N PSCC, I can only assume that is to ensure a factor of safety in the rating of the switchgear. Faults close-in to a supply transformer will have a high peak asymmetric current, which modern switchgear - having fast operating times - may interrupt. If you double the value you have measured and it appears to exceed the DNO design values, there’s probably no point in contacting the DNO. Unless there is something unusual about the DNO supply arrangement or network config’ they will be unlikely to do anything. I guess the main consideration for the test electrician is the compatibility (so, the rating) of the installation switchgear, cables, etc with the recorded fault current.
@@protectiongeek I’ve always known to record the highest reading, but I’ve never seen it that high, but a remember accessor saying no point in measuring both as it’s the fault current, you really need so the breaker breaks in time, do you agree with that?
@@sugardaddyxxx if I understand you correctly, you are making the point that a PSCC would normally be expected to be higher than a PEFC simply due to the PSCC measurement being made with the main earth conductor connected to the installation, which is likely to have multiple earthing paths and hence a slightly lower loop impedance. Selecting the highest of the recorded currents is important in ensuring the installation components are adequately rated. When considering the correct operation of protective devices within maximum clearance times, other assumptions are made to derive a realistic worst-case scenario that would include the minimum available fault current and perhaps dividing that by a further factor of safety. I have to make it clear as a former DNO engineer that I am not as familiar with the specific requirements of BS7671 in terms of protection settings as you and other electricians will be - but I am learning!
On the am2 you don’t test for the zs you calculate it, this can fail you
This test is external impedance Ze 👍🏻.
Why double why not tripple...surely if the armoured was destroyed and 3 phase was shorted with the netural it would be higher than doubled?
If I'm right you can only sort between 2 lines so line voltage is 400V giving highest fault current possible. E.g 400V ÷ 0.10ohm =4000A
I can hear you Clem. Technically if you measure line to line you should then divide by 0.87 to account for the bolted fault shorting all lines at the same time that you describe! Doubling the line neutral pscc accounts for this already. Hope that helps. 👍
Even if you had a three way fault - which is a two fault situation so we don't usually consider these. But the three phases are like the corners of an equaliateral triangle - so each is 400V from each other. When you short all three you'd get approximately the same fault current on each line conductor as the additional current would be balanced across three instead of two conductors.
@@keirstitt8277 not according to the iet you wouldn't... It's in GN3 👍
@@travoltasbiplane1551 you must have a different GN3 because it doesn't say any such thing in there.
Appendix 14 of BS7671 maybe.
No lock on your board. Safe isolation .
great video guys, and surprised me how fluentJean Reno in english
Thanks