Lights, Camera - No Action

[Zarian2013]

Ok so I am old and forgetful, but here is the problem,

I had a bulb blow in one of my landing lights. It is an E27 ( Edison thread) holder. When removing the bulb the glass came away from the threaded connector. So I isolated the circuit at the CP and tried to remove the offending bulb base, only to find that is was sort of welded to the holder. Not good. So I thought I would replace said crappy E27 with a GU10 Halogen lamp holder, better light anyway. So I removed the old E27 and found some fairly hard baked cable for about 2 inches back. Suggests heat wouldn't you agree?. Anyway I cut supply cable back to reveal normal soft Insulation and pliable copper cores. Wired in new holder, checked with my DVM for connectivity, lamp out and in. Fitted brand new GU10 50W and switched back on. On switch on the circuit tripped immediately, suggesting short. Isolated circuit at CP, closed switch ( double sure) and removed lamp and holder. Rewired, refitted, same result. So tried circuit with new holder and no lamp. Circuit stable and operating across all other lamps on Upstairs Lighting. Tried another GU10 lamp ( new ) and it tripped immediately on switch on. Isolated ( again) removed lamp and holder and fitted another lamp and holder ( both new) with same result.

What I don't get is that there is obviously a short for it to collapse the circuit so fast, yet it is only present when there is a load, but we know the load device is a good unit, so it suggests that the short occurs ONLY with a load.

Only thing I can come up with is that the removal of the original unit has created this condition as it was working up until the bulb went.

Ergo, could this be a "proximty short" in the wiring that only occurs when the current flows , thus suggesting a bared wire within the sheath that is arcing when the current is present?

Any ideas ?

 

[ban-all-sheds]

CP?

What's tripping - an MCB, an RCD or an RCBO?

 

[securespark]

Maybe CB?

 

[Zarian2013]

It is a Merlun Gerin K60 MCB 16A / 30ma.

Was working and is working fine without the offending lamp holder having any load. Once loaded it trips the circuit immediately.

My CP is fairly standard configuration,

Ring main sockets ground floor, Lighting Ground Floor. Ring Main Sockets 1st floor, Lighting 1st Floor.

Additional out to garage which in turn has a small CP installed off this limb to isolate sockets and lights therein.

CP Covered by RCD .

What am I missing?

 

[Taylortwocities]

What is a CP?
Cricket pavilion?

Or do you mean a consumer unit?

re

It is a Merlun Gerin K60 MCB 16A / 30ma.

Is that the device that is tripping?

 

[bernardgreen]

If it doesn't trip the RCD when switched ON but no lamp then it is 99% certain to NOT be a cable fault. Most likely you have connected the "earth" to the lamp instead of the neutral. Then when ON and a lamp in the holder current flows to ther earth from live via the lamp.

The 1 % is a cable fault where the earth and neutral have become shorted.

 

[Zarian2013]

Consumer Panel/Unit

This circuit has no earth it is twin only.

 

[Zarian2013]

Consumer Panel/Unit

This circuit has no earth it is twin only.

There are 3 lamps on this branch to illuminate the landing area. 2 Working fine, this third one only causes problem.Thus I think they may be individual stems off the 1 supply line ( more like europe than UK ) . So with only live and neutral ( Yes I know, but I didn't wire it ) connected the fault must lie in the cable. It is unusual though is it not, to only get a short in the cable with a load . After all if it is a L - N short, should it not trip irrespective of what is , or is not hanging off the end?

I am not an Electrical Installation Engineer, but I did do my HND Electronic Servicing a while ago, ( No it was not on stone tablets either) so I do have some understanding of current flow etc.

But I for one will admit I am stumped here.

 

[ban-all-sheds]

Ah.

Lighting ground floor.

Lighting 1st floor.

Landing light giving RCBO trip problems.

I'd move Bernards 99% to picking up the wrong Neutral - how was the old lampholder connected to the circuit - was there a rose or junction box?

 

[viewer]

From a non-electrician:
If it is X/30mA then it must be a RCB.
Is the fitting/holder metal and connected to anything (I know you said no CPC)?
It is on the landing, so is there a two way switching; i.e. is anything controlled from downstairs?
Is there anything else apart from the two wires (L&N) which go to the fitting, e.g. is there a type of rose/block connector etc?
The suspicion is that somehow the neutral on this lamp is not the same as on the others and so is connected to a different bar in the consumer unit - if you had a choice of neutrals this would be possible. Colour is no help here.

 

[Zarian2013]

There is no confusion over the choice of wires into the lamp holder as there are and always has been only two. BLACK/RED. No other wires here.

The removal of the original lamp holder was to change an Edison thread unit to a GU10 halogen one.

I am pretty sure that a two wire input to a two terminal fitting means polarity is incidental.

This is not on a 2 way switched circuit because it is for the landing area only not the normal 2 way switched circuit that one would normally find on stairways or long corridors.

The GU10 fitting is a ceramic base ( no metal ) and fits into a terracotta housing so no conductivity in either of those materials.

To the best of my knowledge all "1st floor lights go to the consumer panel to one mcb , which must be the case otherwise how would it trip that unit.

There is no visible rose/multi block/terminal block. Just the wire from the wall into the wall mounted light fitting.

All of which was working prior to changing the lamp holder as specified earlier.

So I appreciate all the input but there are no confused wires, dodgy terminals, only this dammed short that only manifests itself when a bulb is inserted into the holder and he circuit switched on.

The only thing I come back to is a breakdown in the cable that is not a permanent short but sufficient to allow current to arc when the load is activated.

Unless anyone knows of anything I have failed to consider...

 

[securespark]

You have tried isolating, removing the lampholder, putting a terminal block on the wires, then resetting the switch?

 

[sparkwright]

Have to ask, are you certain it is a GU10 lampholder and lamp, 230 volt?

 

[Zarian2013]

Definitely, I do not have any low voltage halogen units so I don't have the lamps, that said I did check ( twice ) on the packet.

Yes as we speak ( type) there is a terminal block on the end of the wiring and the other lights are fine and the circuit stable.

As stated it only happens when there is a load on this limb,

I even rewired a new Edison holder ( original config) back onto the wiring with a 40W E27 bulb and it still tripped and this was an " as was" state.

So whilst there appears to be no obvious "Shorts" , incorrectly wired nuetral, touching conductive materials, poor wiring, quite obviously there must be for it to trip the circuit.

I guess realisation is dawning that this has to be a cable fault, probably pre existing that has manifest itself due to the movement involved with the rewiring of the new GU10 lampholder.

Oh joy I feel a chisel coming on.....

 

[viewer]

Right, you've covered all bases (to my limited knowledge). I can't see how there could be a short L to N in the wiring or it would do it all the time, however, if, at some point the neutral was cut and the section to the common neutral (JB/switch- not clear from the info) was not in any connection and the section from the lamp was touching earth, then the RCD would trip. Possible for it be in the wall but hardly Ocam.
Where is the link to the other fittings? This would be a more likely starting point than the wall. If you found that point you could check continuity and resistance to/from the fitting.