gregmcc:

Lastman:

gregmcc:

Lastman:

gregmcc:

There’s plenty of You Tube videos demostrating just that but I’ll start by saying that RCDs are making ELFI somewhat redundant because you are not required to do one to test a circuit protected by an RCD. An actual physical test of the RCD trip is all that is required. I’m happy to provide a link for that if you require.

I never said the man in the street should be able to do electrical work. He will not have a meter to do an ELFI test, just that we should remove some of the archaic structures around these professions.

 

Thank you for proving that you really don't know what you are talking about, the question was never about RCD's, not all standard domestic power point circuits have RCD's the reason for EFLI is about ensuring protection devices trip in the correct time. This is the kind of skill that is learnt on the job.... the stuff apprenticeships are made of

 

 

 

 

https://www.electricalforum.co.nz/index.php?action=more_details&id=1510655103

 

 

I guess you forgot that I did say the test was *never* about RCD's, it was about how to preform a EFLI test with power and without power and what a pass result would be and what a fail result would be

 

Ok, I'll play the game ( haven't looked at other replies)...and give a longish answer. I don't have access to the standards (nor the time) so it will also be a general answer.

The NZ power system is predominately a TN-C-S system (or strictly described as a MEN-multiple earthed neutral), earth and neutral (PEN) come from the transformer as a single wire. At the distribution board the PEN goes to the earth busbar which also has a earth wire connected to an earth stake. The earth busbar is connected via a link to the neutral busbar and earth and neutral then go their separate ways in the building. Phase comes in via a single wire or three for 3-phase.

An earth loop impedance test is to ensure that the earth (and neutral) are A) actually connected and B) that the fault impedance is less than a certain value so that there is sufficient current in a fault condition that the circuit breaker will trip. That circuit is the journey from the point tested all the way through the transformer, back through the relevant return wire to the testing point.

Ze is the external impedance ie tested from the switchboard with power to the building off (and may require other earthing ie plumbing earths, to be disconnected). For TN-C-S you don't need to test N and E separately ie L to N fault as they are the same wire, for other earthing systems you may do.

Zs is the impedance at the final circuit e.g the power point. I don't now the exact details or the ohm value (again I don't have access to the standards). I assume though the meter tests the E and N paths (as they are now seperate) and uses the maximum of the two and that value would need to be less than a specified amount. This might depend on the specs of the circuit breaker as well or it might be standard.

I don't know the test for no supply available (but it is explained in the standards). I assume the impedance back to the switchboard is measured and added to a standard or general value of Ze to give an approximation. That is just a guess. This test is generally for electricians putting in new supplies where they don't yet have power. 

I did do brief research basically to remember some of the terms.

 

 

 

Fantastic, looks like a copy and paste from a standard, some of which is incorrect for NZ. Looks like you really don't have an understanding of why a ELFI test is done, or what a pass or fail test may be.

You did say "The electrical trade, especially in regard to house installations, is intellectually trivial. You could teach anyone the basis of it in a lazy weekend."

I am thinking that you really don't know much about the electrical trade. But if you do want to learn, the domestic electrical is a good starting point.