dual RCD CU unusual tripping

DirtyDog368 · Aug 17, 2015

HELLO ALL

i am changing over a cu.

i have conducted basic testing before deciding to change over to a dual RCD wylex 17th ed board.

The board's RCDs and main switch were prewired.

The neutral cable comes out of one rcd and into another and out again from the same terminal and directly back to main switch.

Although i prefer to have the neutral wires fixed directly to the no protected neutral bar and from their to the main swtich i decided to go with the wylex set up.

with all mcb off i energize the board and one by one engineered both RCDs,
then started to energize each mcb.
However weirdly 4 out of 6 of the mcbs tripped the RCD which was not protecting them?

Is this a phenomenon that any one else has encountered?

Tomorrow i will retest each circuit to confirm integrity of insulation resistance and confirm no current leakage to earth and confirm i have wired all circuits correctly to each protected neutral bar.
Also Ill probably seperate the neutral cables and connected them all to the unprotect bar and then back to the main switch.

However i would like to know your ideas as to what may be causing this weird tripping?

thanks very much for you time in this matter.

DD368

R G · Aug 17, 2015

All testing should have been carried out before attempting to install the board also check for borrowed neutrals between circuits as well , with all appliances unplugged and other equipment isolated , could you post a picture of the board internals ..

Leesparkykent · Aug 17, 2015

Neutrals in the wrong bar?

Octopus · Aug 17, 2015

Bang test anyone? Hope you've not charged your customer for your mess up!

Weird tripping as you describe suggest you've got your circuits, RCD's and neutral bars mixed up!

davesparks · Aug 17, 2015

Don't alter the factory fitted wiring inside the CU. Wylex have designed and tested the assembly in the configuration it was supplied to you and there is no reason for you to interfere with it.

The symptoms you have described are very common and exactly what you would expect from either incorrectly connected circuits or a N-E fault within the installation

Deleted member 9648 · Aug 17, 2015

DirtyDog368 said:
HELLO ALL

i am changing over a cu.

i have conducted basic testing before deciding to change over to a dual RCD wylex 17th ed board.

The board's RCDs and main switch were prewired.

The neutral cable comes out of one rcd and into another and out again from the same terminal and directly back to main switch.

Although i prefer to have the neutral wires fixed directly to the no protected neutral bar and from their to the main swtich i decided to go with the wylex set up.

with all mcb off i energize the board and one by one engineered both RCDs,
then started to energize each mcb.
However weirdly 4 out of 6 of the mcbs tripped the RCD which was not protecting them?

Is this a phenomenon that any one else has encountered?

Tomorrow i will retest each circuit to confirm integrity of insulation resistance and confirm no current leakage to earthand confirm i have wired all circuits correctly to each protected neutral bar.
Also Ill probably seperate the neutral cables and connected them all to the unprotect bar and then back to the main switch.

However i would like to know your ideas as to what may be causing this weird tripping?

thanks very much for you time in this matter.

DD368

I'll have a wager on that one!

Toonlad · Aug 17, 2015

I had a fault on a new board a few weeks ago, done all my tests, happy with them,carried on and replaced the board. Then I had a reverse polarity on my socket circuit i was testing. Then after some head scratching even though my initial testing was correct,you start to over think it. haha

long story short,the manufacturer had assembled 1 rcd in reverse polarity. Simple remedy swap the feeds to correct polarity. Just goes to show they dont alway check there cu for polarity.

DirtyDog368 · Aug 26, 2015

Thanks all....
I didn't alter any wiring but found a neutral to earth fault which made the RCD trip weirdly. Personally I think it's the way wylex wired up the box. Instead of each neutral from RCD going to the main neutral bar and then to the main switch wylex wired it so that RCD 1 neutral goes to RCD2 neutral and then out to neutral of main switch.
The current leakage came apparent after spots were reinstalled into the ceiling recess. I guess the builder was a bit rough when he put em back.

Dave OCD · Aug 26, 2015

Glad you found the fault but those neutral links you describe are the feeds to the RCDs so perfectly ok and perform exactly the same function as the other configuration you mention.