Strange goings on with a wall lamp.

[88v8]

Baffled.
Wall lamp, single 25W incandescent bulb.
Controlled through nearby wall switch, one-way, not a dimmer.
Been working OK for months.

Switched it on one evening, bulb gave a little flash, then nothing.
New bulb. Nothing at all. Dead.
Checked new and old bulb, both OK.

Yesterday, looked at switch, continuity OK. Took it off wall, had a good look, it's OK. Nevertheless, put in another switch, also OK, still no light.

Checked the power at the feed wire - 99V (ninety-nine volts).
What????
Checked another light, different circuit but same j-box, 230V, so meter is OK.
Checked again, now I have 230V at the wall light, so I put the bulb back in. Flash, then nothing. Checked the bulb, still OK.
Arrrgh.

I find that if I leave the light half an hour or so, it goes Flash, then nothing. If I switch it again immediately, no flash no nothing. If I leave it half an hour, I can get one flash.
The voltage at the light is either nothing, or 99V, or 230V.
Nothing else in the house wiring had changed when this malarkey began.

All the other lights in the room and elsewhere in the house work normally.

Have RCDs, they're not tripped when the light works or doesn't.

Can't rewire the light because the room's all decorated, and anyway the wiring is not old.

Baffled. Any ideas please?

 

[riveralt]

Probably a loose connection - since you have ruled out the switch - then either at the power source - ceiling rose? or at the light fitting itself.
I take it you have checked the latter two?
What is the arrangement at the light switch?
Is it a live in - switch live out arrangement or does the switch have a neutral in the backbox?

 

[stillp]

Checked another light, different circuit but same j-box,

There's a loose wire in the circuit somewhere downstream of the junction box.

 

[88v8]

Probably a loose connection - since you have ruled out the switch - then either at the power source - ceiling rose? or at the light fitting itself.
I take it you have checked the latter two?
What is the arrangement at the light switch?
Is it a live in - switch live out arrangement or does the switch have a neutral in the backbox?

Hmmm, I haven't checked the light fitting. I'll take it off tomorrow and have a look. Switch is live in/out.
I'll report back.
Thankyou.

 

[Taylortwocities]

Have RCDs, they're not tripped when the light works or doesn't.

I don't think you mean RCDs. MCBs, perhaps?

Untitled

• Taylortwocities
• 27 Mar 2010
• 43

 

[88v8]

Have RCDs, they're not tripped when the light works or doesn't.

I don't think you mean RCDs. MCBs, perhaps?

Oops, yes.

And a right pain in the neck they can be, if there's fiddly wiring to do in a confined space. Bring back the fuse box, I say, lol.

 

[ban-all-sheds]

And a right pain in the neck they can be, if there's fiddly wiring to do in a confined space. Bring back the fuse box, I say, lol.

In what way is it easier to connect wires to a fuse carrier than an MCB?

 

[88v8]

And a right pain in the neck they can be, if there's fiddly wiring to do in a confined space. Bring back the fuse box, I say, lol.

In what way is it easier to connect wires to a fuse carrier than an MCB?

The advantage of fuses is that when working on the wiring in the house, if one switches off the circuit, the fuse doesn't mind when you touch the ends together, but the blasted MCB imagines there's a problem and plunges the whole house into darkness.
I realise this is supposed to be progress, but like so much progress, it seems to me that it's in the wrong direction.

 

[ban-all-sheds]

The advantage of fuses is that when working on the wiring in the house, if one switches off the circuit, the fuse doesn't mind when you touch the ends together,

Neither does an MCB if it's turned off, which it *(&%$&!£) should be (as a minimum)

but the blasted MCB imagines there's a problem and plunges the whole house into darkness.

Sounds more like you're describing an RCD operating when you create a N-E fault.

Which:

A) Means you were working live (N is a live conductor).

B) Would happen in exactly the same way if you had fuses instead of MCBs.


Not sure you should be doing electrical work...

 

[88v8]

The advantage of fuses is that when working on the wiring in the house, if one switches off the circuit, the fuse doesn't mind when you touch the ends together,

Neither does an MCB if it's turned off, which it *(&%$&!£) should be (as a minimum)

but the blasted MCB imagines there's a problem and plunges the whole house into darkness.

Sounds more like you're describing an RCD operating when you create a N-E fault.

Which:

A) Means you were working live (N is a live conductor).

B) Would happen in exactly the same way if you had fuses instead of MCBs.


Not sure you should be doing electrical work...

Perhaps it's the goon who installed the rcd/mcb board - before my ownership - who shouldn't be doing electrical work, because I certainly turn off the relevant circuit -= not that's it's always easy to identify as we have upstairs lights on the downstairs circuit, and vice versa, some even in the same room - but even with the circuit turned off, if I touch L/E or N/E then the main breaker trips and everything goes off. If that's how they're meant to work, B ridiculous.

 

[plugwash]

The problem is that the devices we use for circuit protection for only isolate the line conductor, not the neutral conductor. This applies to BOTH fuses and MCBs. Put a RCD upstream of those devices and it can be tripped by a neutral to earth fault even if the MCB is switched off.

BAS's point is that the MCB isn't "imagining" anything and it would make no difference if you replaced the MCB with a fuse and that the fact you think that it being a MCB rather than a fuse has anything to do with it shows a clear lack of basic electrical background.

He is also claiming that working with only single pole isolation is "working live". In theory double pole isolation is preffered when working on electrical installations but in practice our standard CU designs don't allow for that and turning off the entire installation is a significant inconviniance. On TN installations working with only single pole isolation seems to be widely accepted practice even if not strictly ideal.

 

[ban-all-sheds]

if I touch L/E .. then the main breaker trips and everything goes off.

You sure about that?

If that's how they're meant to work, B ridiculous.

It is how they are meant to work, and it is not ridiculous - they do that because of how they work, and they are doing what they are designed to do.

 

[stillp]

they do that because of how they work, and they are doing what they are designed to do.

And in doing so, they might just have saved your life!

 

[securespark]

On TN installations working with only single pole isolation seems to be widely accepted practice even if not strictly ideal.

Indeed this is correct.

Only on TT installations is it imperative to isolate both poles.

 

[plugwash]

if I touch L/E .. then the main breaker trips and everything goes off.

You sure about that?

Touching neutral and earth on a single pole isolated circuit is almost certain to trip the RCD. Touching live and earth may or may not trip the RCD depending on what if any load that is connected to the isolated circuit and what the local voltage difference between neutral and earth is.

If that's how they're meant to work, B ridiculous.

It is how they are meant to work, and it is not ridiculous - they do that because of how they work, and they are doing what they are designed to do.

IMO it is pretty crazy that RCDs were thrown into our electrical systems without providing a way to isolate circuits in a RCD compatible manner making the installation trickier to work on and meaning that a single fault in a final circuit can render the whole installation unusable. SPSN MCBs exist but are almost unheard of in the UK.