MCB tripping on lighting circuit

[bleach]

Hi

Two lighting circuits (A&B) side by side, each feeding 1 gang of 2 gang switch, then onto lights.

circuit A works fine.
circuit B works fine if mcb A is off...MCB B holds ok if MCB A is on until light switch turned on for circuit B.

Yet to look at this job but thinking must be short circuit on outgoing switchline B to Neutral A. Maybe in switch or next jb if exists.

Any thoughts chaps

 

[Plonker 3]

What test results did you get when you tested the circuit?

 

[plugsandsparks]

SP or TP? - what conductors do you have in the 2G switch?

 

[bleach]

sphase, all conductors as cable feeding into switch first then straight on to lights. Will test later tonight on arrival.

 

[Plonker 3]

Why didn't yo carry out any tests on your initial visit to the job?

 

[Andy78]

I don't think he has even been there yet, judging by his OP. Maybe he is hoping someone on here has ?

 

[GMES]

Why is this place becoming like a helpline, I am all for helping people but only if the op has bothered to exhaust all his options 1st !!

It seems we are now being asked to diagnose problems before the site visit.

 

[GMES]

Sorry Andy missed your post / same kind of reply as yours.
It is getting ridiculous with some of the questions being asked! I am no mechanic, but if my van doesnt start in the morning I will at least check several basic things, battery,diesel levels etc before I consider ringing a mechanic out.

 

[Octopus]

Why was the OP there? Who has been tampering? What other work has been done?

So many questions!!

 

[amckay]

^^^ as Murdoch says there are a lot of questions.
It could be as simple as the (presumably) homeowner has done a bit of diy and maybe has a crossed neutral.

 

[telectrix]

you need to go and see it. could even be customer's got it wrong and it's a RCD that's tripping on a borrowed N. i'd tell you the exact fault over the net, but my crystal ball is in harry potter's for a service

 

[Octopus]

My crystal ball sees a shiny new CU, no invoice, a cash payment, no cert, a pile of horse poo outside the gate and a borrowed neutral!

 

[uksparks]

Well, without looking and knowing the full picture, somewhere along the line both circuits are clearly linked together, and more than like a borrowed neutral and some DIY work along side.

 

[Plonker 3]

How would a borrowed neutral cause a MCB to trip?

 

[uksparks]

Maybe the op has moved one of the light circuits around the board and now not on the same rcd possibly and it's not the MCB tripping but the rcd? Just a guess.

 

[Lucien Nunes]

My thoughts exactly. I reckon the fault is reported wrong - in an SP installation one side of all MCBs is connected together, so turning one ON can't realistically cause another to trip in the event of a cross-connection, it can only stop it tripping by shunting it, unless there are relays or similar involved which is unlikely here.

So even without any test results, we can look into the crystal ball of physics and give the OP some advice. Amazing!

 

[Octopus]

The OP does say "yet to look at the job" so he's going on what the customer has said......

 

[uksparks]

True, so it probably is the big switch thing in the board not the one with the little lever.

 

[Plonker 3]

But terminology is important in this job, if we are told MCB then we should take it as a MCB, you can't afford to guess in this job.

 

[telectrix]

why not? it works for doctors. mine told me that my back pain was caused by beer and worn-out knees due to smokes. all over the phone. brilliant.