circuit breakers going off??

[steve snakeman]

Ive just finished testing a small domestic board.Everything fine untill I test the lighting circuits.Readings are as follows

R1+R2 0.89
Insulation resistance >299
Polarity OK
Earth continuity OK

These readings are for the first lighting circuit,the second circuit was similar.

so far so good,however when I come to do an earth fault loop impedence test(Zs)the test starts off ok but then the circuit breaker switches off after a few seconds(not the RCD).I move to the second lighting circuit and the same thing happens.I have removed all the pendant covers and switches and can find nothing wrong anywhere .....why is this happening???

 

[Edd]

When you do an Earth loop test it pushes about 20A down the circuit, most of the time 6A MCB's can handle this but sometimes they trip. link across a couple of mcbs to do the test (single phase only) or move the circuit to a higher rating for the test.

 

[roukel01]

I have no idea if what I'm about to say is true, but I have just read that when performing an Earth Loop test a 25A pulse is used during the test, although only for a short period of time, it can cause some MCB's to trip.

Again, its only what I've read.

 

[steve snakeman]

thanks guys,what you are saying appears to be true but this is the first time it has happened to me in ten years lol. This however appears to be plaussible .I will try again in the morning and let you know

 

[Deleted member 9648]

thanks guys,what you are saying appears to be true but this is the first time it has happened to me in ten years lol. This however appears to be plaussible .I will try again in the morning and let you know

Cant believe you've been testing for 10 years and not had 6a type B's trip on a Zs test....It's VERY common.

 

[Risteard]

It is true but really you shouldn't ever bypass the circuit breaker but calculate your Zs instead.

 

[telectrix]

or teat using no-trip.

 

[spark 68]

It is true but really you shouldn't ever bypass the circuit breaker but calculate your Zs instead.​

Or, open the MCB, join L to E at the furthest point, do the test across the open MCB​

 

[Les Macaulay]

ok Guys, but I was taught that we should not be using a live earth loop test on lighting circuits, but should measure R1+R2 and add to Ze to give Zs, i.e. avoid live testing except where it's essential, eg for Ze.

 

[Engineer54]

ok Guys, but I was taught that we should not be using a live earth loop test on lighting circuits, but should measure R1+R2 and add to Ze to give Zs, i.e. avoid live testing except where it's essential, eg for Ze.

You've already been told, that's a load of crap, when you're talking about testing procedures...

 

[Knobhead]

Not only is it crap, it's 11 month old crap.

 

[High Tower]

Not only is it crap, it's 11 month old crap.

Lmao.

U doing M&S adverts now mate