During this test all short circuit protection between you and the local transformer has been removed apart from 100A incoming fuse, so do a risk assessment first. In reality the fuse/dist board may be in an inaccessible, unlit location or you may have to work from steps/platform. The double pole isolation switch may be in a different location and DURING SET UP this should be padlocked OFF.
Great video, your content is so helpful for apprentices like me. Quick question, how would you perform this test on a sub main? Just R1 + R2 of the live and CPC going between both boards, and record it as Zdb?
any chance you can do some testing videos with a Fluke 1664fc? Ive bought one and maybe i made a mistake and should have bought a ,megger. I cant find many videos using a fluke
Why wouldn’t the Ze be taken from the external double pole switch? I understand if it’s for the purpose of the video to show how it would be undertaken from inside the CU. But surely in this scenario a Ze would be taken from the external DP switch and then a Zdb from the CU.
Hi, is this one of the tests that you have to take when doing the level 2 diploma in electrical installations? Or is this for the level 3 diploma? Thanks.
Hello Admin @GSH electrical. Please I need your assistance with a power supply problem. 1. Please what are the causes of negative power factor registered on a MD meter for a distribution installation. 2. How can this be corrected.
I still don’t get why the breakers have to be off. I know he mentions “It wouldn’t have that earth fault loop path” but you have the main switch off so I don’t see the reason behind it.
The breakers don't have to be off to get a proper Ze reading, however they should be off as part of the isolation procedure (breakers off in sequence, then main isolator/switch off)
Sorry if this is a dumb question, but why is it higher for TN-S than TN-C-S? I understand the difference between the earthing methods, I'm just not twigging why that might lead to a higher impedance being acceptable for TN-S.
In a TN-S the earth is ran from the transformer separate from the neutral wire. The earth conductor will be a lower CSA (smaller) than the neutral which is why it has a higher resistance. The earth is not designed to carry current under normal operating conditions, it just needs to be large enough to ensure circuit breakers will operate in the event of a fault. In a TN-C-S the earth and the neutral are the same cable up to the fusehead. Since the neutral is required to carry current in normal operating conditions, it's sized appropriately and so should have a lower resistance than a TN-S earth. Since the TN-C-S uses protective multiple earthing, a higher reading might indicate a failure in the system.
