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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Tripping Lighting Circuit https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1104417029 Message started by AndyOlds on Dec 30^th, 2004, 2:30pm

Title: Tripping Lighting Circuit
Post by AndyOlds on Dec 30^th, 2004, 2:30pm

I have three separate lighting circuits, one for each floor of the house, each connected to a 6A type B MCB in the consumer unit. We have some ceiling mounted light fittings consisting of 3 and 5 lamps each. When a bulb goes in one of these fitings, the whole circuit trips out.

Could I get round the problem by replacing the MCBs with Type C (I've read another topic somewhere on here that states the disconnection time is slightly greater for Type C and can therefore combat this poblem). Someone else also suggested that I try repacing with 10A MCBs - is this a good idea?

Title: Re: Tripping Lighting Circuit
Post by Lectrician on Dec 30^th, 2004, 2:35pm

This problem is due to mass produced cheap bulbs.

Older bulbs always used to have a fuse in them of a very low rating for when the lamp blew.

I have seen numerous plug top fuses blow on table lamps, and 3036 fuses blow aswell.

A type C may help, and 10 also. A 10amp should only really be used if 1.5mm cable is installed, although 1.0mm will take the 10amp current, it will not for all installation methods.

Stick an emergency light near the CU and get used to it ;D

Title: Re: Tripping Lighting Circuit
Post by L.Spark on Dec 30^th, 2004, 5:18pm

I would suggest trying 6A Type C MCB's, you can't just upgrade to 10A withought having an inspection to ensure all the cable will take the load.

You should really have the circuit tested to ensure a Type C will meet disconectiont times, however if it meets type be which it should do, then it's likely that Type C will meet, They are quite close in relation to maximum impedance.

Title: Re: Tripping Lighting Circuit
Post by plugwash on Dec 30^th, 2004, 11:56pm

even on a worst case TN-S you can throw well over 50 meters of 1.0mm on a C6

iirc a B10 should be ok with 1.0mm provided the cable is either away from insulation or on one side of it (rather than in it) with similar cable length limitations to a C6

you have to take more care when using C10 breakers though.

Title: Re: Tripping Lighting Circuit
Post by L.Spark on Dec 31^st, 2004, 12:56am

Yea, not much need for a C10 on a domestic lighting circuit tho, unless your circuit is using close or near to 10A and you want that surge discrimination.

Title: Re: Tripping Lighting Circuit
Post by AndyOlds on Dec 31^st, 2004, 12:57am

Thanks for the advice - I'll try a 6A Type C first and see if that makes any difference. Cheers.

Title: Re: Tripping Lighting Circuit
Post by L.Spark on Dec 31^st, 2004, 1:01am

No problem andy

I think you will find it cure's it, altho you may have to wait awhile till a bulb blows ;)

Title: Re: Tripping Lighting Circuit
Post by ban-all-sheds on Jan 4^th, 2005, 11:19pm

Plan B - replace the MCBs with fuse carriers, or of these are not available for your CU, put in a higher rated MCB, and where the cable leaves the CU go through an FCU with a 5A fuse.

Title: Re: Tripping Lighting Circuit
Post by AndyOlds on Feb 7^th, 2005, 1:01pm

Thanks to everyone who replied.

I actually got some Type C MCBs (from ToolStation - miles cheaper and more stuff than Screwfix by the way). Waited a good couple of weeks then lo and behold, like buses, three lamps have gone in the last week! Circuit didn't trip out!! Woohoo!!

Only cost me about 12 quid for the new MCBs so am very chuffed (so is the missus as she now doesn't suffer a blackout when I turn the lights on during her morning shower!).

Thanks again.

Title: Re: Tripping Lighting Circuit
Post by L.Spark on Feb 7^th, 2005, 1:22pm

Happy to hear that Andy, great news

Done lot's of experimenting so know the way's to get around this problem now

Didnt know Toolstation did Type-C MCB's but that's good, there about double the price of Type B, but worth it for the lighting circuit ;)