trouble with newly installed MK c/u

[jenions]

recently changed an old fuseboard to a new MK consumer unit with 2rcbo's and then RCD with 5 mcb's on it, now i IR all the circuits and all came out at <299Mohm but since day 1 the rcd has tripped whenever a high load is switched on? i tried the up and down ring and the fridge radial on 1 of the rcbo's (40A) and they worked fine but if i put them back on the rcd side they trip. anybody got any ideas? also the test button on the rcd isnt working, now this is the 2nd rcd ive tried as i changed the 1st 1 just incase that was faulty.

 

[ezzzekiel]

try removing all the neutrals from the bar and test the rcd alone see if it tests out ok.

 

[vernam616]

Did you test for an earth?

seems like a odd one, one of them " have to be there ones " haha

Good luck, try the above suggestion though

 

[egginyourface]

seen something similar once before, could be reverse polarity somewhere.

everytime customer used hoover rcd would trip. located mixed connections in thermostat which plumber had connected

 

[vernam616]

Good call "egginyourface", try removing circuits one by one and trying it, just to pinpoint

 

[telectrix]

have several times found where customer has replaced a socket face and has reversed N/E. as soon as a load is applied, the RCD will trip.

 

[egginyourface]

easier way would be to interconnect live and earth and do r1 + r2 test at board and locate fault like that. you'll soon find where its been connected wrong

 

[jenions]

annoying thing is, the rcd dont trip if you plug small loads in

 

[vernam616]

Go round with a martindale before removing all the socket fronts, to check for polarity

 

[platty1005]

it may sound obvious but make sure the neutrals for the circuits connected to the RCD are indeed connected to the RCD it sounds as if a neutral is in the wrong place in the CU.
Test button should work if L and N are connected correctly check polarity at the incoming main switch on the CU. If LN ok and test button not working take it back and exchange RCD as faulty.
What type of earthing system is it?
What was the Ze ?
Did you carry out a full PIR and schedule of tests before changing the CU?

 

[Octopus]

Go round with a martindale before removing all the socket fronts, to check for polarity

But don't forget that a Martindale can't "see" a N to E reversal

 

[Mark_Burgess]

Did you notice anything strange about those boards?

Like the main switch has to be levered into the off position but flicks on!!

I had a similar problem last night, it was the fish pond pump.

 

[Guest123]

You say the RCD only trips under 'high loads', is it just one particular item??? was there an RCD present beforehand???

 

[egginyourface]

if its a borrowed neutral both rcds would trip???

 

[Guest123]

if its a borrowed neutral both rcds would trip???

I read it that he has used a 16th ed style split load CU with 1 x 100A main switch hence the RCBO's & 1 x 30mA RCD with the MCB's on???

 

[vernam616]

If tripping under heavy load , id very much doubt its N-E reversed

 

[jenions]

no rcd before hand jus old wylex fuse board, got a borrowed neutral but sorted that at the moment by putting them in same rcbo till i can run a new cable. i tried numerous high loads such as tv, fridge, 3kw heater even me sds drill but all tripped it. i got a low ze cant remember reading i wrote it down and its with all me gear on a job, its just thrown me as this is the second rcd ive tried which makes me think its something on the installation.

 

[platty1005]

When you carried out IR test I assume all loads were disconnected. It seems that there may be a leakage problems on the loads rather than fixed wiring, the old CU would not detect earth leakage on loads. PAT testing of the appliances that trip the RCD might help. If you cannot isolate one load as the cause it may be a cumulative effect IE 15mA leakage on more than one load.

 

[jenions]

but surely not every "high load" has a leakage problem? everything works on an rcbo but whack the rcd in instead and it trips

 

[egginyourface]

how many socket circuits are there?have you tried rcbos on every circuit??

 

[topquark]

Assuming that the RCD is OK, there's something wrong with the way the CU is wired if the test button isn't working (pressing it introduces a neutral -> earth fault at the RCD). That's what I'd be fixing before looking elsewhere. Check through all of the CU cabling connections (particularly the neutral and earth).

I assume that the IR readings where >299M Ohms

 

[alanl]

"the test button isn't working (pressing it introduces a neutral -> earth fault at the RCD)."

Are you sure about that?
I always thought it was a purely mechanical test.
Alan.

 

[topquark]

"the test button isn't working (pressing it introduces a neutral -> earth fault at the RCD)."

Are you sure about that?
I always thought it was a purely mechanical test.
Alan.

Positive, thanks. What would be the point in testing quarterly an electronic device via mechanical means ?

 

[topquark]

Here's a little quote from the MK datasheet:

Where connection of a neutral supply is not
possible, then an alternative method of
ensuring that the test button is operational is
to fit a suitable power resistor (rating 4W)
between the load side neutral pole and a
phase pole not associated with the normal
test button operation

 

[nickblake]

you could have a fault in a socket or an intermitant N to E fault it could be on any circuit not just the heavy load circuit as all the N's and E's are joined together on there bus bars they are common so although on low loads it doesnt trip on the higher it could increase the loading around the fault although just a tad but enough causing the RCD to trip ,oh and watch the main switches they have a habit of flipping on

 

[Knobhead]

The clue may be in the OP, “even the test button doesn’t work”. Change the RCD. The test button should work irrespective of any load.

 

[topquark]

The clue may be in the OP, “even the test button doesn’t work”. Change the RCD. The test button should work irrespective of any load.

That's a good point, so it must be phase->earth when the test button is pressed, oops!

 

[ezzzekiel]

i suspect a n-e fault somewhere, had one recently where rcd wouldnt trip and zs testing on ring failed with a trp message, found a low n-e fault to an outside light.

 

[platty1005]

The test button does NOT introduce a L - E fault on an RCD
The test button is connected to the Line conductor on the load side of the RCD this is connected via an internal resistor to the feed neutral. Pressing the test button allows current to pass through the RCD in the line conductor through the test resistor and back to neutral on the feed side so the RCD sees a difference in line and neutral current inside the RCD and trips out. If the test button is not working check supply polarity is correct L-N if yes Take the RCD out and change it again ?

 

[nickblake]

i suspect a n-e fault somewhere, had one recently where rcd wouldnt trip and zs testing on ring failed with a trp message, found a low n-e fault to an outside light.

agree with you check the outside lights dont have water in

 

[Knobhead]

Where the hell do outside lights come in to it!

For gods sake it’s not difficult if the RCD fails to trip on test, the faults in the RCD.

View attachment 7289

 

[jenions]

no outside lights apart from 1 on a plugtop and that isnt plugged in, can see this being 1 of those jobs

 

[jenions]

think is this is the 2nd rcd ive tried surely 2 in a row arent broke

 

[Knobhead]

No wonder I need tablets for my nerves!

 

[platty1005]

Good drawing Tony
Bottom line There are 2 faults

1) The RCD wont' trip on test button operation - check supply to RCD - Test RCD on a known good installation (own house) If RCD wired correctly it should trip SEE Tony's post
If not tripping change it again

2) The RCD trips when loads are switched on
but not when no loads connected - appliance/load problems

PS long distance fault finding is proving quite difficult

 

[mickys86]

Where the hell do outside lights come in to it!

For gods sake it&rsquo;s not difficult if the RCD fails to trip on test, the faults in the RCD.

View attachment 7289

Or the wiring beforehand

 

[sparkinlee]

I agree with Tony and others... if the test button is not tripping the RCD, that needs sorting before any other fault finding, and the test button not working would be caused either by a faulty RCD unit, or incorrect wiring configuration within the CU (but I can't think what!).

 

[Knobhead]

I’ve just re-read this thread.

I’m sorry but for professional electricians some of you should sign yourselves as “Hop-a-long Cassidy”. You condemn cowboys, but then give advice that is so off target it’s a wonder you’ve got two feet left!

A RCCD is a simple thing to figure out, if what’s going in doesn’t equal what’s going out then you’ve got a down stream fault and it trips. If it doesn’t trip on the test button then the RCCD is faulty (unless you’ve used a 4 pole 440V unit).

Sort your testing in to logical order, it’s the only way to fault find.

Sorry but people rely on you to get things right, I wouldn’t be impressed with someone constantly on their I-Pad asking advice.

Don’t get me wrong, I’ll help anyone, but you have to have the basics. Not just being able to quote regulations ad nauseum.

 

[RomRobi]

I quite agree with Tony and patty1005. I've had similar problems in the past. The RCD detects an imbalance between the line and neutral on the load side and pressing the test button simulated this imbalance to cause RCD to trip. I guess a few guys were right too, in carrying certain test and in particular trying the RCD in a complete different CCU to check its functionality.

 

[nickblake]

Where the hell do outside lights come in to it!

For gods sake it’s not difficult if the RCD fails to trip on test, the faults in the RCD.

View attachment 7289

Sorry Tony , but i have come across this before RCD trips on high loads brand new install ,the fault was caused by an incorrectly fitted lid on an outside light ,the light was half full of water ,replaced the fitting fault gone , this was the reason i mentioned outside lights

 

[ezzzekiel]

im sorry also Tony,

had a rcd that wouldnt trip, swapped for another exactly the same, swapped for the rcd in other bank which worked on one side but not the other.
removed all neutrals and it tested fine, replaced one at time until it stopped working when an old heating supply that had been fused down to supply an outside light caused the rcd not to trip and zs tests to fail, repaired the cable and then all tests came back fine.

But obviously I AM WRONG and as you say it was the rcd, next time ill leave it and tell customer the cu will only accept one rcd as all the rest in the world are broken................

and as a wise man once said and im inclined to agree with

I’m sorry but for professional electricians some of you should sign yourselves as “Hop-a-long Cassidy”. You condemn cowboys, but then give advice that is so off target it’s a wonder you’ve got two feet left!

 

[mickys86]

im sorry also Tony,

had a rcd that wouldnt trip, swapped for another exactly the same, swapped for the rcd in other bank which worked on one side but not the other.
removed all neutrals and it tested fine, replaced one at time until it stopped working when an old heating supply that had been fused down to supply an outside light caused the rcd not to trip and zs tests to fail, repaired the cable and then all tests came back fine.

But obviously I AM WRONG and as you say it was the rcd, next time ill leave it and tell customer the cu will only accept one rcd as all the rest in the world are broken................

and as a wise man once said and im inclined to agree with

Ok try that and if that don't work I'd go with the wiring beforehand haha

Maybe try the rcd connected with none of the mcb's connected? ( can't remember if this has been tried and am not re-reading all the posts again )

And as for the above..... Looks like a lot of us has learned something today

When removing all neutrals I'm guessing you mean with mcb's switched to off with the main breaker on?? Otherwise the neutrals would become live.
(just an apprentice and I like to be sure of these things!) hahaha 

 

[timo1]

RCBO's - They are the future!!! I got so fed up with RCD's and shoddy quality I only fit new boards decked out with RCBO's now, cost has come down so much its not all that much extra IMHO.

 

[topquark]

Well I'm not sorry ... well apart from the heath robinson explaination of the test circuit

 

[Knobhead]

Please supply a better drawing.

William Heath Robinson was a fantasic guy, using his methods I’ve got umpteen industrial plants going. What’s wrong with a brush stale holding a circuit breaker closed?

 

[nickblake]

Just to make i clear Tony when i replied i was in no way having a go . it was just a scinario that i have come across , and the reason i mentioned the outside lights , electricity can do wird things and with the addition of RCD make the whole job more intresting

 

[JamesBrownLive]

RCBO's - They are the future!!! I got so fed up with RCD's and shoddy quality I only fit new boards decked out with RCBO's now, cost has come down so much its not all that much extra IMHO.

But don't you need an RCBO for each circuit, as opposed to having a single RCD that covered a few? Or can you get RCBOs that can cover more than one circuit?

Cheers

 

[ezzzekiel]

Just to make i clear Tony when i replied i was in no way having a go . it was just a scinario that i have come across , and the reason i mentioned the outside lights , electricity can do wird things and with the addition of RCD make the whole job more intresting

cant see why not

this is one of the worst statements ive ever read lol

For gods sake it’s not difficult if the RCD fails to trip on test, the faults in the RCD.

 

[topquark]

But don't you need an RCBO for each circuit, as opposed to having a single RCD that covered a few? Or can you get RCBOs that can cover more than one circuit?

Cheers

You can, as with MCBs, put more than one circuit into an RCBO but it's not good practice. There's nothing wrong with mixing RCBO's, MCB's and an RCD(s) in a consumer unit if you want to achieve that (and have the necessary module space).

 

[jenions]

i know the wirings messy inside, but ive got no slack on any cables to try neaten it up so its the best i can get it. still havent got job sorted only just got access to property again