Adding a spur from c/u

[Scoby_Beasley]

This one has me confused!!
Our computer is next to the c/u but no sockets handy, so I put in a spur (this is ages ago) to the d/stairs ring main from c/u. Guess what ? Kept popping !! So I wired it into the immersion heater m.c.b (15amp). and have no problems (heater not used in three years, on gas) any ideas?
The way I'm looking at it a spur is a spur wherever it comes from, or have I got that wrong ?

 

[paulfromswindon]

Hmm, could be tricky, but I have one idea..

Do you have a split board? ie, one that has an RCD feeding some of the circuits, and the rest just fed from the main switch?

If so, there are two Neutral Bars in your consumer unit, one for the circuits fed just from the main isolator, the other for circuits fed by the RCD. If you connected your live connection to the ring MCB (which would be on the RCD-fed side) then connected your neutral to the Neutral bar that was for the isolator fed circuits, the MCB will trip every time, without fail. Swap the Neutral to the correct Neutral bar and it will work. I'm guessing when you connected it to the immersion one, you just moved the live wire, then it started working?

Please let me know if I can officially declare myself a smart-Alec!!

PS, don't leave a socket wired off the immersion heater circuit - it's against regulations - or disconnect the heater from the CU - you could still use it if your boiler goes down...

Hope it helps

Paul

 

[Scoby_Beasley]

Please let me know if I can officially declare myself a smart-Alec!!


Paul

Sorry Paul, I only the other day discovered what a split c/u was for but ours is a single way. As you say I just moved the live from the ring main to the old immersion m.c.b. and its worked fine, (don't worry, it's only a short extension, surface mounted, immersion disconnected,if we move it's coming out). just couldn't understand why it trips the ring main, is it 'cos of three cables ? if so, how does it know?
P.S. I did re-wire my previous house so I'm not forward in going backwards (or something like that !!)

 

[paulfromswindon]

Hmm, that's a mystery then. Shouldn't happen, can't think of another reason.

Oh, hang on, not beaten yet...

Even though you have non-split board, is the MCB feeding your sockets actually a combined MCB/RCD - ie does the breaker that kept tripping have a test switch on? It may also be marked 32A and 30mA.

If so, you will probably see that the there is an outgoing neutral terminal on the MCB/RCD where the neutrals are actually connected for this ring circuit, as opposed to the neutral block. If so, the live and neutral of the spur must both be connected directly to the MCB/RCD. If my theory holds water, and you have a combined MCB/RCD, you may have connected the live to the MCB/RCD, and the neutral to the neutral block. This fits with the fact that you only moved the live to fix it.

Same problem, different layout. If the live for a circuit goes through an RCD but not the neutral, it immediately throws the earth out of balance and trips the RCD. Every time.

If it was a short circuit or something, the trip would probably be accompanied by a bang. In this scenario, no big bang, the trip will just keep tripping. Was there a bang when you turned it on?

What you describe is a classic symptom of this scenario, but I will try and come up with something else if not.

Have fun

P

 

[Scoby_Beasley]

No bang, just a click next to my ear (thats how close).
BUT I WILL NOW CALL YOU ALEC !!
It is a combined mcb/rcd, do I move the neutral (and live) to sort this out? As you say I would like to reconnect immersion just in case ( you smart b+s+a+d !!! )

 

[paulfromswindon]

Scoby,

I feel good, baby, yeah! I was getting worried - thought you had me there for a minute!!

Move both the Neutral and live of your spur to the outgoing neutral and live terminals on the MCB/RCD that feeds the ring circuit - you should see where the two blacks and two reds of the existing circuit are connected. Just leave the earth in the main earth block. The outgoing side is usually on the top of the breaker, but it depends upon the make, it should all be labelled though.

Hey presto - job done!

Glad I could be of assistance

Mr S. Alec

 

[Scoby_Beasley]

MMMMMMoiiii XX

P.S. put a "p" in responsibility, Cheers Paul
(or r u taking the p ?? )

 

[Scoby_Beasley]

Job sorted, cheers Paul, if I'm in Swindon I.O.U a beer, cheers pal.

 

[paulfromswindon]

No problem, matey, glad it's sorted.

Must fix that signature, thanks for pointing it out..

Have a good one

P

 

[Gees]

Hey Scoby.. Have you seen the price of beer in the trendy wine bars in Swindon....... get your credit card out...

 

[Scoby_Beasley]

I said I owed him one, didn't say I'd pay for it, especially as he can afford to go abroad on holiday !!
Bloody rich sparkies !!

 

[paulfromswindon]

Trendy Wine Bars? Swindon? Ha Ha!

If I was rich, I'm certainly not now! Still, had a real good holiday.