Just changed Consumer unit - Having problems with RCD

[DaveZetec]

Hi
Today I changed the consumer unit at a relatives house - It was "rewired" in the mid seventies, so a lot of the wiring was fairly shonky.

I was doing some renovation to the house and had to add a few sockets and wiring for a Spa Bath - as soon as I saw the existing consumer unit I pretty much condemned it. The entire houses plug sockets were running from a single 15 amp fuse, which apparently "blew all the time" and I noticed the holder was noticeably hot when I removed it!

Back to the important stuff - I checked all the existing wiring as best I could, and replaced around half of it where accessable. I connected this back up to the old CCU and it all worked fine.
Today I came to swapping the CCU for the new unit. Connections are as follows

100A main breaker
16A breaker running to cooker socket alone (Its only an electric oven, just over 10A draw thing not a proper electric hob)
32A breaker on the kitchen and utility socket ring main
16A breaker on rest of house sockets (8 sockets in total)
6A breaker on one lighting circuit
another 6A breaker on the other lighting circuit (this is as it was before exactly)

then, on the RCD protected bus bar (63A, 30mA) there is just a single 16 amp breaker running the Boiler, the shaver socket in the bathroom and spa bath. pump.

I have no problems at all with the sockets, but the RCD will trip whenever a light in the house is turned on, which, incidentally don't actually work
All I can really think of is that the lighting circuits are using earth as a neutral which is upsetting things The lights aren't even connected through the RCD but still trip it off.
All wiring on the output side of the RCD was installed by myself and has been double and triple checked, and doesn't even run near any lighting circuits.
The central heating was recently totally replaced, Perhaps the earths weren't re-connected?

I had to leave it as we had no light left - Will be back over tomorrow and replace as much of the rest of the houses wiring as possible, take the brute force approach to it as I really should have just done this in the first place, but along with fitting a bathroom and kitchen and re-plumbing the hot water it was the last of my priorities!


Thanks in advance for help from any sparkies with more experience than myself

Dave.

 

[Lectrician]

Sounds as though a lighting neutral is connected to a neutral on the rcd side somehere - check your lights - pay attention to wall lights.

Your sockets should be on the RCD side!

Why 16amp for the house sockets after rewire? Wouldn't a 32amp ring be better?

What about the main and supplymentary bonding - have you upgraded / replaced this?

Have you re-wired ALL the lighting circuits, and ALL the circuits after the RCD??

Have you accidently put the neutral of the lights to the RCD Neutral in the CU??

 

[DaveZetec]

Sounds as though a lighting neutral is connected to a neutral on the rcd side somehere - check your lights - pay attention to wall lights.

Your sockets should be on the RCD side!
Will Swap these over tomorrow

Why 16amp for the house sockets after rewire? Wouldn't a 32amp ring be better?
They were on a 15 amp before, the wire looks to be 32 amp stuff but I was going for "better safe than sorry"

What about the main and supplymentary bonding - have you upgraded / replaced this?
Not touched it - Any reccomendations?

Have you re-wired ALL the lighting circuits, and ALL the circuits after the RCD??
The only circuit on the RCD goes straight to the shaver socket and then bath, and straight to the boiler - all these were installed by me.
Have you accidently put the neutral of the lights to the RCD Neutral in the CU??
I think this is my problem - It was fairly dark when I was at this stage, and i was working by candle light

Thanks for your help

 

[Lectrician]

Hope you get it sorted.

Search on here for bonding etc.

 

[ban-all-sheds]

Your sockets should be on the RCD side!
Will Swap these over tomorrow

Why didn't you know that this was how they should be?

Why 16amp for the house sockets after rewire? Wouldn't a 32amp ring be better?
They were on a 15 amp before, the wire looks to be 32 amp stuff but I was going for "better safe than sorry"

1) There is no such thing as "32 amp stuff" - how much do you know about cable sizes?
2) If it's a 2.5mm² radial then you cannot put a 32A breaker in - 16A, or possibly 20A depending on circuit length and installation method etc, is the limit.

What about the main and supplymentary bonding - have you upgraded / replaced this?
Not touched it - Any reccomendations?

Plenty of info here, and in the OSG.

Another recommendation:

Will be back over tomorrow and replace as much of the rest of the houses wiring as possible, take the brute force approach to it

I really think you should slow down, plan things properly, and find out a lot more about what you should be doing. Sounds to me as if you don't know enough to be doing a rewire, particularly in someone else's house.

 

[DaveZetec]

To be honest this is my first CCU change. I'm not an electrician, but an electronic engineer.

I've never really had any experience with a CCU with an RCD in it - Looking in to how they work i figured I'd just put the bathroom stuff on it. Sockets in every other house I've worked on arent on an RCD so its not exactly a death trap!

The wiring in the house was atrocious before - We can't afford to get anyone in to do it, So I'm having to do it. You are probably rightm I need to plan things more - Its not as simple as I envisaged, but I'm perfectly capable of doing it - with time, and help!
I'll pick up a book on it.

The existing sockets are connected with 2.5mm in an unknown configuration. 2.5mm says 24amps max to me, hence the 16 amp breaker.
although I was under the impression yesterday that 2.5mm was 32 amp max. Bugger!

 

[ban-all-sheds]

To be honest this is my first CCU change. I'm not an electrician, but an electronic engineer.

Ah.
The supply isn't a TT one is it (earth rod, rather than earth from the incoming supply)?

I'll pick up a book on it.

Useful books, from which you can learn a great deal:

http://www.amazon.co.uk/exec/obidos/ASIN/0852028172

http://www.amazon.co.uk/exec/obidos/ASIN/0863413749

http://www.amazon.co.uk/exec/obidos/ASIN/0953788539

The Electricians Guide shown above is a good explanation of the regs, but if you fancy one with a bit more of the electrical engineering theory behind it all, I can recommend this:

http://www.amazon.co.uk/exec/obidos/ASIN/0852962371

The existing sockets are connected with 2.5mm in an unknown configuration. 2.5mm says 24amps max to me, hence the 16 amp breaker.
although I was under the impression yesterday that 2.5mm was 32 amp max. b*****r!

It is if used in a ring circuit, as 2 cables then supply each socket.

 

[DaveZetec]

Thanks for the help everyone, I'll put an order in for a couple of books right now

It was the lighting neutrals connected to the RCD neutral rail rather than the plain jane one, Swapped it over and everything works right now , I also put my stuff onto a 16 amp breaker as I ran a spurred ring (it was physically much easier to install this way)

ban-all-sheds - On inspection the installation uses an earth from the supply (nice chunky wire from the main service fuse box to a connection block with a host of ~10mm earths coming from it, one going to the CCU and another to a gas pipe etc. Do I need to alter this in any way? I'm planning on connecting this to the water pipes that run by the box.

I read of somone earthing the pipes at several places, and running an earth direct to the metal kitchen sink and whatnot. Surely the copper pipes themselves will have a comparable resistance to a decently hefty earth wire, and arguably have a greater current capacity (All joints are soldered so provide a good electrical connection)


Many thanks again!
David

 

[ban-all-sheds]

Do a search here for words like:

• bonding
  [*]supplementary
  [*]equipotential
  [*]bathroom(s)
  [*]radiator(s)

you'll soon find lots of info.

 

[Damocles]

Getting your bonding sorted is nearly as trick as doping silicon.

Nice to see someone with a pragmatic approach thinking about safety rather than regulatons. Though the regulations are designed so a monkey could do if he could follow the instructions and it would be safe.