New Light Sometimes trips Circuit


Postby Feanix » Sat Sep 06, 2008 8:23 pm

I've just installed a replacement light fitting in my hall. It's looks a bit like the death star and has about 20 12v 20W halogen bulbs on it. Every couple of times I switch it on it trips the breaker on the lighting circuit. Sometimes it comes on fine, sometimes it trips. As the light was a display model I didn't get any installation instructions and so just wired it into the existing lighting ring.

Can anyone help or offer any advice as to why this could be happening? Do I need to put it on a separate circuit as it has so many lights?

Any help appreciated.

Thanks
Feanix
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Joined: Sat Sep 06, 2008 8:16 pm

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Postby BLAKEY1963 » Sun Sep 07, 2008 11:59 am

[quote="Feanix"]I've just installed a replacement light fitting in my hall. It's looks a bit like the death star and has about 20 12v 20W halogen bulbs on it. Every couple of times I switch it on it trips the breaker on the lighting circuit. Sometimes it comes on fine, sometimes it trips. As the light was a display model I didn't get any installation instructions and so just wired it into the existing lighting ring.

Can anyone help or offer any advice as to why this could be happening? Do I need to put it on a separate circuit as it has so many lights?

Any help appreciated.

Thanks[/quote]

FEANIX.
TURN OFF POWER AT MAINSWITCH AT MAINS BOARD.
Check your connections 2 the light u have made and examine
for any trapped wires against any associated metalwork ( if any)
and any possible short circuit between live , neutral and earth.
IF CLEAR and above is not the case , u could have a faulty
fitting , without seeing it its hard 2 judge.
I would advise to get someone in

BLAKEY1963
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Joined: Wed Jun 13, 2007 10:57 pm


Postby TOPSPARK » Sun Sep 07, 2008 5:58 pm

As you say 12v 20 watt lamps i assume this has an inbuilt transformer this could be faulty but on whole i have to agree with Blakey1963 check for the wires pinched or any loose connections but would advise if this keeps happening to call in an electrician just to be on the safe side
regards
Topspark
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Joined: Fri Jul 25, 2008 9:44 pm


Postby ericmark » Sun Sep 07, 2008 7:36 pm

Feanix,
All lights of this type use more power on switch on than on run. Switching so many on together is likely to exceed the 18 to 30 amp instantaneous tripping current of a B type 6 amp MCB when combined with lights already in use.
Cure.
1) Swap at least some of the bulbs for lower wattage bulbs.
2) Split the circuits so not all the bulbs are switched on together even a few millisecond gap where two switches are used can reduce the inrush to below critical level.
3) Use some form of soft start this could be a electronic transformer or a dimmer switch but of course the type where it always switches on low and builds up power.
4) The type of MCB could be changed from a B to a C which would allow a bigger inrush but the circuit would need testing first to ensure it will still comply with the regulations once changed not a DIY job it would come under Part P.
Please remember both myself and BLAKEY1963 are guessing and we may be wrong only a site visit can really find the problem but with 20 lamps removing say half and seeing if that cures the problem would be a good pointer as to if faulty fitting or too much load. But in case it is faulty fitting I would switch off the mains before handling the fitting.
Eric
ericmark


Postby Feanix » Sun Sep 07, 2008 8:27 pm

Thanks for the advice. I fully understand that its just advice and that you'd need to be here to offer a solution. Thanks to both of you. Eric your point is interesting as it only trips on switch on, once it actually makes it on it happily stays on without tripping.

The MCB is a B type as you predict.

Unfortunately I can't use 2 switches as all the lamps are wired internally within the fitting. I'll try removing half the bulbs and see what happens then.

As an alternative, would wiring the fitting into the socket ring via a fused connection unit also offer a potential solution if load proves to be the issue?

Thanks for all your help.

Feanix
Feanix
Posts: 5
Joined: Sat Sep 06, 2008 8:16 pm


Postby Feanix » Sun Sep 07, 2008 8:45 pm

Tried it with half the bulbs and it worked for a few goes and then tripped again. It does share a circuit with the kitchen which has a few spotlights and the lounge which has 5 candle bulbs but it even trips when just on its own.

I've come to the conclusion that there must be a fault in the fitting - although this seems odd as it was the display light in the store and seemed to be fine when it was on there, although i suppose it could have been damaged when the guy from the store took it down, or even by me when I put it up! Although I'm not convinced of that obviously.

I'll call the manufacturer tomorrow and see what can be done - I don't want to have to replace it with something else as its quite a big fitting and I've had to re-inforce the ceiling and drill some new fixing holes due to the transformer being in the base of the fitting. So annoying as when it works its rather nice.

Is it unusual for it to work some of the time and not the rest?

Feanix
Feanix
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Joined: Sat Sep 06, 2008 8:16 pm


Postby ericmark » Sun Sep 07, 2008 10:41 pm

You say transformer built in and one would have thought a version giving a soft start would have been fitted as original fitting. Did it have any details on the transformer watts, amps etc. Wonder if wrong size bulbs fitted.
With transformer you can't use dimmer unless matched to it. Also removing bulbs it may not affect inrush where a transformer is used.
Yes using a 5 amp fuse instead of a MCB will more likely deal with inrush.
Talking to manufactures may help they may recommend how the supply should be protected.
Eric
ericmark


Postby Feanix » Tue Sep 09, 2008 2:47 pm

Spoken to manufacturer and they've said it is likely to be caused by the inrush and recommended a 10A type C fuse to protect the circuit. Sounds a bit hardcore to me but its what they recommend. Looks like I'll need to make a call.

Just out of interest what is the difference between a B and a C? Also if the circuit proves to be unable to take the upgrade what does that mean? A rewire or just a change on the circuit required - we have had an extension and so have a mixture of older wiring (probably 20yrs old) plus 2 yr old wiring I assume the more recent one is more likely to be able to take the additional current.

Thanks
Feanix
Posts: 5
Joined: Sat Sep 06, 2008 8:16 pm


Postby ericmark » Tue Sep 09, 2008 9:25 pm

I will try to take you step by step but please ask if I lose you on the way.
1) In the British regulations called BS7671:2008 you are allowed up to 16 amp to lighting circuits 559.6.1.6 but also manufacturer’s instructions must be complied with 559.4.1 and 134.1.1 and most ceiling roses are rated at 6 amp so as a result in the main 6 amp is the largest overload (MCB/RCBO) or fuse we can use. And with this in mind I am very surprised that the manufacturer of this luminaire has recommended a 10 Amp protection device.
Now I will try to explain the difference between a fuse and MCB/RCBO. A fuse will blow at the rated amps but only after a long time. And graphs and charts are produced to tell us how much extra current is required to make a fuse blow in a set time. A 13 amp fuse as found in a standard 13 amp plug needs 95 amp to make it blow in 0.4 seconds. And when an electrical circuit is designed we have to plan for this and we calculate or measure the earth loop impedance to ensure if there is a fault that the fuse will blow in time not to injure a person. This is what limits the length of cable that can be used.
With MCB/RCBO devices however there are two or three independent systems to trip the device and for a long period of overload it uses a thermal device but for short period overload it uses a magnetic trip. This magnetic trip will allow 3 to 5 or 5 to 10 or 10 to 20 times the rated current to flow for a very short time and are given letters B, C, and D. So a B6 MCB will trip at 30 amp even if it only flows for 0.08 of a second (Two cycles) a C6 with trip at 60 amp and a D6 at 120 amp.
I have not got the details for a 5A BS 1362 fuse but at 0.1 seconds looking at something like 30 A and at 5 seconds 14 A. Although it would seem it acts just a quick as a MCB because the inrush for both bulbs and transformers takes place in first milliseconds fuses do not tend to be so affected by inrush as a MCB.
Back to reality changing the B6 to a C6 or D6 will likely cure the problem but before doing this one must be sure the circuit will trip in time if the MCB is changed and the meter used to measure EFLI is expensive plus to change the MCB will require alteration within the consumer unit. Because it could cause danger the government introduced Part P which means it will cost you more to DIY than to get a registered electrician to do the job. Who will issue certificates you will need if you ever sell your house.
I know this seems complex and this is why Part P was introduced. I don’t like Part P but I can’t ignore it.
Eric
ericmark


Postby Feanix » Tue Sep 09, 2008 9:52 pm

Eric thanks for a superb explaination. Basically I need to get an electrician in to check the circuit for me and swap the MCB. I don't suppose you live in Surrey and fancy popping round do you?
Feanix
Posts: 5
Joined: Sat Sep 06, 2008 8:16 pm


Postby ericmark » Tue Sep 09, 2008 11:34 pm

I live in North Wales sorry. I have worked away in the past like 5 months in Hong Kong but not really worth it for the work you have.
Eric
ericmark


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