Rcd's fail trip test on new consumer unit

[sidekick]

I have just replaced a consumer unit and have one or two problems.
The first is taht on testing RCD trip times they will not trip. On x 1 tester reads 310ms but no trip, On x 5 tester reads 50ms but no trip. Thers are four rings with 2 on one RCD and 2 on the other and none of them trip.
The light circuits all work fine until I switch on the landing lights then both RCD's tripped. At the thought of borrowed neutrals I changed layout so all lights on same RCD but landing lights still trip that RCD.

Will investigate further to find fault on lights, but as this proves RCD's work does any body have an idea why sockets will not trip test ??

 

[Spudnik]

From the sounds of it, you problem could still be borrowed neutrals.

I suggest to start with, turn off all the MCB's and main switch etc and carry out a 250V IR test between the neutral bars, with the circuits still connected as they were intended.

If its flat, remove them one by one from the second bar until it clears.

That should identify which circuit is causing the probs.

Good luck, and take your time otherwise you WILL be going in circles.

Let us know how you get on.

 

[SirKit Breaker]

Here is a tip which can save a lot of grief. When you install a new CU build it up, connect the tails, main earth and your bonding conductors. Install the RCD's and then power it up. Carry out the RCD trip tests, then you know that they work, and if they don't you can do something about it without having to strip down the whole CU. If you know they work, then after installing MCB's and wiring everything up it all goes t**s up you will know it is something you have done, or a problem with the fixed wiring. Same applies to RCBO's trip test before terminating the circuit into it.

Cheers...........Howard

 

[Spudnik]

Wasnt my help good enough then Howard?

 

[SirKit Breaker]

Wasnt my help good enough then Howard?

I couldnt have put it better myself Jason. I have been where he is years ago, and that tip has saved me hours. An Elecsa assessor told me it in the days when i thought you had to do RCD tests on every circuit.:biggrin5:

Cheers...........Howard

 

[sidekick]

Thanks Jason. I assume that will identify the fault on the light circuit.
Why are the RCD trip tests on x1 and x5 not tripping on any ring? The first RCD only has 2 circuits on it and both are seperate rings.

 

[Geoffsd]

Well, difficult to say from here (other than sounding really patronising) especially on both RCDs.

Try removing a socket and shorting N & E.

Is your meter ok? Have you tested on other circuits with it? You didn't say.

 

[sidekick]

Is your meter ok? Have you tested on other circuits with it? You didn't say.

Not done an RCD test with it for a week or so but it did just fine when I did and this is the first time it has given readings x1 310ms and x5 50ms but not tripped on any ring. Not sure what to do next ??

 

[SirKit Breaker]

Not done an RCD test with it for a week or so but it did just fine when I did and this is the first time it has given readings x1 310ms and x5 50ms but not tripped on any ring. Not sure what to do next ??

I dont want to sound patronising or imply that you are stupid, but 1, is the install energised, and 2, are you testing the RCD on the load side?.
I have made both mistakes more than once.

What make of CU is it. if my memory serves me correctly i think Square D had links in their boards in the 16th days, and to make them 17th compliant you had to remove a link between the 2 neutral rails and one between the load side live of the main switch and the adjacent MCB, if you didnt then the RCD was effectively by passed.

Cheers............Howard

 

[Spudnik]

The amount of times i have tested the supply side, especially on Starbreakers

 

[Geoffsd]

Not done an RCD the first time it has given readings x1 310ms and x5 50ms but not tripped on any ring. Not sure what to do next ??

This is what it does when the RCD doesn't trip. Try the N to E 'short'.