Put lamp in holder and the power dies... WHY?

[Ladders]

Hi all. So called out to a domestic properety as light fell off ceiling. Put it back together and power all shows good. L/E, L/N power 230v no reading N/E. But no power when connected to fitting? So swapped fitting for 6" pendant and did same? So took the lamp out of pendant and power readings back to normal? Any offers on what is going on? It looks like the lamp is acting as some kind of switch and cutting the power but who knows with out further investigation...

 

[i=p/u]

but very likely the jb is supplying other lights...

 

[telectrix]

if there is rcd in does this not detect anything before a fire could start

if that were the case, then smoke alarms would be redundant.

 

[Marvo]

Agreed, I've seen several occasions where an RCD hasn't prevented a fire.

 

[KFH]

He has a 30mA RCD on the whole installation. The lights are on rewirable fuses. I have quoted for plug in MCBs but still waiting, they are £10.00 each, no room for a new CU. What is more worrying is approx 3m of 16mm tails run somewhere in a wall and possibly under a floor between the meter and the RCD. TNCS so I cannot stick in an S type RCD at the meter. He is happy it is working and does want disruption to fix. I am still working on him.

 

[telectrix]

well, see if you can get a business card from a fire extinguisher company and give him that. might make him decide.

 

[Ladders]

bad connection upstream. with no load you are seeing the 230v. as soon as the load tries to pull current, the bad connection fails, dropping the volts. could be either L or N. easieat way to tell is use a voltstick at the fitting with load applied. if it goes out, the fault is on L. if not, it'son N

That makes sense. As did test with N and E connect to pendant and L hanging out and power was good all round. Only when the L then connected did power disappear. So probably the L feed... Cheers.

 

[telectrix]

could still be the neutral. check L-E with voltage tester with lamp connected. if you get 230v then it's the neutral.

 

[mechelec]

People take the mickey out of me for using one of these but it will only give a full light when 230V present. You can soon trace bad connections. Test-meter.co.uk sell them

 

[i=p/u]

if its such asmall load it might still take it where if bigger might not, but im sure you know better than me and im talking ,,aaa,aa s
hit

 

[mechelec]

if its such asmall load it might still take it where if bigger might not, but im sure you know better than me and im talking ,,aaa,aa s
hit

The lamp is a 15W 240v pygmy. So yes it is only a small load but if you have the same type of fault the OP mentioned it will load the circuit enough to show it.
I have had 240V reading on DMM, I have then used the test lamp and the voltage has disapeared.
Try one if you get the chance and prove it to yourself.

 

[i=p/u]

money have spent , your ok il stick with the voltage stick prototype.lol if was fault on one of the conductors would a continuity test show up a bad reading in a nicked conductor (method 2)

how much is a test lamp could i not just use a pendant with a bulb in.. maybe 6mm solid core

 

[mechelec]

money have spent , your ok il stick with the voltage stick prototype.lol if was fault on one of the conductors would a continuity test show up a bad reading in a nicked conductor (method 2)

how much is a test lamp could i not just use a pendant with a bulb in.. maybe 6mm solid core

Tight ar#se, you yougsters just wont listen to good advice LOL

continuity test probably wouldnt show the sort of fault described that is basically a high resistance fault, it would need to be loaded to show its-self.
The danger of course is every time it is loaded it will get hot and arc with the associated fire risk.

 

[i=p/u]

i do listen to the man on the ground, had same fault in cctv one time i think now .. continuity was there but when loaded up wouldnt work

 

[Bul]

If you use an analogue tester (a non-digital one that has a needle) you probably won't get the 230v reading with the lamp removed. This would make it easier to trace the fault.

Can someone explain this. I don't quite understand.

 

[telectrix]

the input impedance of the analogue meter is less than the digital one. hence the meter will pull a small current, hopefully enough load to show up the fault.