17th edition Split board issues.

[SafetyFirst]

Hi guys n gals, i've fitted another general electric 17th edition split board. It's the 3rd one i've fitted and the 3rd one that i've had problems with.
Haven't changed many boards over, only ever done so for friends or family who've needed/wanted too, i still have my rewireble box taking care of things in my bungalow without any probs

The first board change i did after much head scratching i found a borrowed neutral with the lighting from down/upstairs after grouping lighting circuits onto one RCD. Also the two way switch was dodgy, all fixed and no problems reported six months down the line-all good.

Second board change, everything worked bar upstairs lighting, megga tested and found a very low reading between E-N so needed further investigating. Haven't had the time to sort that one yet but there's no rush as buildings going to be redundant for sometime yet.

Both jobs for my sis and bro in law.

Moving onto todays, for a friend of mine, currently living there. Moved in just before christmas, have changed all the lights over to new shiney one's. Changed all light switches to chrome and awaiting to do the same with all sockets.

Anyways the building is fairly modern, built in '98, old hrc fuses with 2 30A MCB's protected by a 30mA RCD. They served a ring for upstairs/downstairs general bedroom/living room sockets.
The other ring serves kitchen/utility/garage sockets.

The way i setup new 17th edition board was to split the rings onto either RCD's and what this results in is having just upstairs lights and kitchen sockets on one RCD that trips when powered. The other RCD (1) has downstairs lights/smoke detectors/genereal sockets/cooker (only oven 10Amps)/water heater (13Amp). Doesn't trip and all working fine.

After much head tearing the RCD (2) doesn't like the kitchen ring or the upstairs lights individually.

Have used old boards copper to create a temporary by-pass for the two circuits that are not liked by the RCD till i have time next weekend to megga those cables and further investigate this problem. Whats baffling me is the fact there wasn't a problem with the old RCD protecting the kitchen ring.

Imbalance issue?

What a mare eh!

These fully loaded RCD boards can be a blessing in disguise as there has to be a few issues with the wiring on the kitchen ring and upstairs lights. I just wish i could have one that goes straight forward for once!!

 

[ringer]

Did you try swapping the RCDs to see if one is faulty?

 

[SPARTYKUS]

Yes they can be a pain in the bum the dual rcd boards. Prefer now to stick with one Rccb like the 16th boards and rcbo the other half. Or all of it.

 

[Engineer54]

Personally i don't like the modern split CU's or the philosophy behind them.

Where you have 2 X RCDs looking after multi MCB protected circuits, is always going to lead to problems, when one circuit develops any kind of fault that will trip the RCD device. It's basically a cheaper alternative to how a CU should be configured. Which to my mind should consist of all circuits being protected by RCBOs. On CUs for TT derived systems the RCBOs being backed up by an upfront S type RCD device, incorporated in the main CU switch...

Yes quite a bit more expensive than these split CUs, but oh so much better all round, and totally adaptable to various and future needs...

 

[SPARTYKUS]

Or the way i suggested!

 

[Hawk81]

My advice is that you do all your tests like insulation resistance (megga?) etc before starting your board change. Rectify any issues then change the board. When you say you used copper from old board to get it working tempory do you mean some circuits are not RCD protected at the moment?

 

[SafetyFirst]

My advice is that you do all your tests like insulation resistance (megga?) etc before starting your board change. Rectify any issues then change the board. When you say you used copper from old board to get it working tempory do you mean some circuits are not RCD protected at the moment?

Yes but my mates aware there's a problem somewhere and have told him don't overload the ring for now, ie just do one thing at a time, kettle, microwave etc. I know it's not ideal but i can only try again next wknd. The thing thats baffling me is as i say, the old board had the kitchen ring protected by an old RCD with no tripping issues.

Tbh the job has taken quite a while upto now, changed all lights, added new spots in kitchen (lighting cct), changed all switches and now board, would have been done sooner if i'd have rewired the place but moneys tight for this young couple and tbh the wiring's only as old as the house (13yrs) so thought it'd be fine just to straight swap stuff. Obviously not!

 

[SafetyFirst]

Did you try swapping the RCDs to see if one is faulty?

Yep i did and it made no difference thanks anyways! Oh on that note, i also tried the old RCD which was originally protecting the kitchen ring before which never had a tripping issue whilst in the old board. Guess what, it tripped in the new board which really confuses me!!!

 

[SafetyFirst]

Btw just for info's sake, the system is PME, luckily the good guys at the REC installed an isolator at the mains incomer so didn't need to cut the tag for the fuse and it's much easier to switch off/on than pull in/out ....ohhh errrr!lol. Go REC guys!!!

Bonding to gas and water.

Cables into board are clipped direct and i've not caught any insulation replacing the board, installed pretty much like for like position wise, aint modified any circuits barring changed setup inside board. Ie downstairs lights were for some reason split into two seperate cct's i tallied up wattage load and found 6A breaker was more than enough to combine them as one downstairs cct.

Earthing to cct's fine, however as said before haven't megga'd owt yet so i'll see where i go next week with this.


Any helpful advice from you guys is always appreciated thanks very much.

 

[Engineer54]

I agree with Hawk 81, in that any future CU changes you undertake, you use your test equipment ''Before'' you start undertaking any changes. Knowing of the existing faults you will face first and getting them sorted, will save all the problems your now facing.

Now your trying to trace faults with the RCDs in place and hindering your progress.

 

[ringer]

Sounds like you've got an interconnection between circuits - possibly two interconnections. Have you tried taking out all conductors from the kitchen ring and checking for continuity between each of those conductors and all earth and neutral bars? And the same with the upstairs lighting circuit? Have you checked for continuity between those two circuits as well?
Are you sure the RCD is connected to the main switch properly and RCD(2) busbar is isolated from all other busbars in the board?
Did you remove the link between neutral bars?
Have you tried isolating RCD(1) to see if RCD(2) will then hold in? Perhaps RCD(1) only holds in because RCD(2) always trips first?
Have you done all RCD tests x1, x5, < with RCD(2) live but mcbs off?
What order are the RCDs from the mainswitch?
A picture paints a thousand words - how about a photo of the board?

I'm a bit surprised that you didn't IR the circuits in question before now. There are lots of things you could/should be testing. Perhaps you just need time to sit back and assess what is going on. Sometimes with faults like this it is easy to get overloaded with ideas. Think back to basics, and work out a test strategy that covers all bases - and stick to it - do not go off on tangents because you will lose track of what you have and haven't tried. I'm sure you'll suss it out in the end - just be methodical.

And get back to it before next weekend if you can - leaving those circuits without additional protection is not good!

 

[SafetyFirst]

Aye don't i just know it. Still doesn't answer the fact that why all of a sudden would there be an issue with the kichen ring when there wasn't before when it was protected by an older version RCD??

Any idea's?

Bare in mind now that i also tried that said RCD in the new board and it now trips!

 

[1shortcircuit]

Bare in mind now that i also tried that said RCD in the new board and it now trips!

It would seem that you have made an error somewhere. Rip it all out separate each circuit and start again :thumbsup

 

[spark 68]

Ie downstairs lights were for some reason split into two seperate cct's i tallied up wattage load and found 6A breaker was more than enough to combine them as one downstairs cct

I would be looking at this bit, as this bit you did change.

Why were they split ?

 

[SafetyFirst]

It would seem that you have made an error somewhere. Rip it all out separate each circuit and start again :thumbsup

I taped each leg up, it's as was wired before. If i'd have mixed the rings up surely the other RCD would spot the imbalance on the other side and that too would trip?

The sockets stay on till there's load getting pulled, ie the fridge is swithched on or kettle or owt else, they run a few seconds and trip. As for the upstairs lights, it just doesn't go on full stop. Yet without the RCD no issues.

 

[Engineer54]

I taped each leg up, it's as was wired before. If i'd have mixed the rings up surely the other RCD would spot the imbalance on the other side and that too would trip?

The sockets stay on till there's load getting pulled, ie the fridge is swithched on or kettle or owt else, they run a few seconds and trip. As for the upstairs lights, it just doesn't go on full stop. Yet without the RCD no issues.

Well, ....There's a clue for you , Surely??

 

[SafetyFirst]

I would be looking at this bit, as this bit you did change.

Why were they split ?

Well there had been obvious DIY parts to the downstairs lights. Looked like to me that the kitchen/utility had been extended/altered in the past. The old fittings were badly overheated but i have replaced and made good all lights including well before old terminations.


The downstairs cct's aren't causing the issue, which i've joined into one 6Amp breaker. It's the upstairs, gonna place that on same RCD before i test next week see if its a borrowed neutral.

 

[SafetyFirst]

Sounds like you've got an interconnection between circuits - possibly two interconnections. Have you tried taking out all conductors from the kitchen ring and checking for continuity between each of those conductors and all earth and neutral bars? And the same with the upstairs lighting circuit? Have you checked for continuity between those two circuits as well?
Are you sure the RCD is connected to the main switch properly and RCD(2) busbar is isolated from all other busbars in the board?
Did you remove the link between neutral bars?
Have you tried isolating RCD(1) to see if RCD(2) will then hold in? Perhaps RCD(1) only holds in because RCD(2) always trips first?
Have you done all RCD tests x1, x5, < with RCD(2) live but mcbs off?
What order are the RCDs from the mainswitch?
A picture paints a thousand words - how about a photo of the board?

I'm a bit surprised that you didn't IR the circuits in question before now. There are lots of things you could/should be testing. Perhaps you just need time to sit back and assess what is going on. Sometimes with faults like this it is easy to get overloaded with ideas. Think back to basics, and work out a test strategy that covers all bases - and stick to it - do not go off on tangents because you will lose track of what you have and haven't tried. I'm sure you'll suss it out in the end - just be methodical.

And get back to it before next weekend if you can - leaving those circuits without additional protection is not good!

All connections were checked and tightened inc factory terminations. I've re-arranged board to suit temporarily. Will test during daylight when i'm off on saturday.

 

[spark 68]

Is it possible that part of the downstairs lighting is on with the upstairs lighting (hallway maybe) ?, and this is why it was split, rather than anything to do with current rating.

It is still possible that you have an incorrectly placed/borrowed neutral,

The sockets stay on till there's load getting pulled, ie the fridge is swithched on or kettle or owt else, they run a few seconds and trip.

I have seen this before, usually on a TNC-S system, as the imbalance is not always great enough to trip until a certain amount of loading takes place.

 

[Engineer54]

Well there had been obvious DIY parts to the downstairs lights. Looked like to me that the kitchen/utility had been extended/altered in the past. The old fittings were badly overheated but i have replaced and made good all lights including well before old terminations.


The downstairs cct's aren't causing the issue, which i've joined into one 6Amp breaker. It's the upstairs, gonna place that on same RCD before i test next week see if its a borrowed neutral.

That would have been my First check i would have made, with the conditions you have described... even to if it was only eliminate the borrowed neutral senerio. So, what are you going to do, if the lights upstairs suddenly start working again, when you combine all the lighting circuits??