Multiple Halogen bulbs blowing! (at the same time)

[mark3178]

Hi, I have recently moved in to a new house, it has 10 gu10 50w halogen downlighters, in the kitchen. I've had no issues with the bulbs since i bought it about 3 months ago, however today the lighting circuit triped, When I switched it back on 4 of the ten bulbs appeared to have blown. I have checked one of the bulbs and it has blown as apposed to some other issue.

I know they can be temperamental, but 4 in one go can't be right? The lighting circuit should be on two separate loops but the lights only go off when BOTH trip switches are down???

If its an overload issue, can I simply change the bulb wattage as a temporary solution, will this help or will they blow even quicker?

All help gratefully received!

 

[sparkyspike]

Are you saying that you have to switch off two different mcbs to turn off the lighting circuit? This is very wrong. There must be a link between two circuits, e.g. in the switch, which shouldn't be there. This must be sorted first.

 

[mark3178]

Right ok any clues on where to begin looking? Should i check if all lights operate on both mcbs? Or if they are crossed as you say, i guess they will be. I had a sparky in to run some outside lights, he took his source from an existing ceiling rose, could this have been the cause, as I don't recall the mcb's being a problem prior to this. He also changed the entire consumer unit, do you think this could have been an issue?

 

[flameport]

I had a sparky in to run some outside lights, he took his source from an existing ceiling rose, could this have been the cause

No - there is no way to link 2 separate circuits by working on a single ceiling rose.

He also changed the entire consumer unit, do you think this could have been an issue?

Very likely. What documents were provided when the consumer unit was replaced?

 

[sparkyspike]

Right ok any clues on where to begin looking? Should i check if all lights operate on both mcbs?

Check that your lighting circuit will work with either of the mcbs on, and that it will only turn off if both mcbs are down. The cause will be a) a link in a 2 gang switch, (which can be removed) b) a cable connecting two lights on two different circuits, like a ring (this can be removed), or c) a cable returning to the CU.

The way to deal with this depends on whether you are supposed to have two circuits on two mcbs, or one circuit on one mcb. Count the number of watts of lighting you have (pendants are counted as 100W) and check the total. Allow 1200W per circuit. If you need two circuits, you need to find the offending link somewhere in the middle of the circuit, hopefully in a switch. You can use a tester to see if the neutrals are also linked in a ring. This will tell you if you have the link via a cable or at a switch. If you need one circuit, you can remove the cable at the CU and blank off one of the mcbs. You'll probably need a sparky in to test the circuits properly.

 

[electronicsuk]

Of course, once the lighting circuit itself has been sorted out, you'll still need to attend to the faulty downlights. If they are 12v then there will be a transformer or multiple transformers somewhere. It may be that four of the lights are fed from one transformer, and a dead short on the lamp has taken out a thermal fuse inside the unit, in which case you need to locate it in the roofspace and repair/replace.

If the fittings have mains lamps then it's more likely there is a loose/open circuit connection somewhere.

 

[mark3178]

Cheers, for the advice, I had a look at the 2 way switch the sparky put in, noticed he had put in a small "bridge" between probably 2 lives, i thought i'd see what happened if I removed it and funnily enough, not only did it solve the mcb issue it didn't have any effect on either of the lights it was switching! For once a job that was solved quicker than expected. I now have two lighting circuits working independently!

Can I assume that this potential overloading was the cause of the lights blowing? They are 240v lights (no transformer) I didn't get chance to test working bulbs in the blown downlighters, guess that will tell me if theres a problem in the circuit?

 

[sparkyspike]

Perhaps one bulb failed and as the mcbs failed to trip at 6A it took out the others on a surge. Hopefully removing the link has solved the problem. BUT you need to be sure that you have removed the right link. I mentioned it could be a 2 gang switch link, but also it could be elsewhere. Firstly you can count the number of lights on each (now seperate) circuit and see if they are roughly the same, or at least with neither exceeding 1200W. Secondly you need to test the neutral and earth conductors end to end to ensure they aren't still linked. You can do this with the power off and with a multimeter.

Or call the spark who did the work. Even if it wasn't his link that caused the mcb problem, he must have noticed the problem and should have corrected it. Either way, he has been a naughty boy.