I have fitted a new light wich trips the B6 mcb, apparently this is because of a millisecond surge from the light. is it ok to replace it with a B10 or should i use a C6?
MCB on a lighting circuit
- Thread starter jamiedodger
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no checked the wiring and put another light up in its place and that worked ok. its a big light with 10 bulbs and has a transformer. the trip switch goes when you turn it on but when you reset the trip switch it works fine.
jamiedodger said:
A slow acting MCB is needed or a means to reduce the in rush current which occurs when the voltage is first connectd to the transformer
What type ( electronic, toroidal etc ) and wattage is the transformer ?
You may need to use a "zero crossing point" switch. This turns on the power when the AC mains is at a zero voltage (100 times a second the voltage is zero) and results in a greatly reduced in-rush current which means the MCB doesn't trip.
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Before changing a breaker for a different type you must ascertain that its operating characterisitics will not jeopardise the safety of the circuit it is protecting.
AFAIK this can be done by measuring a few things with a sparks meter, or by a few calculations (and assumptions).ricicle said:
p.s. i dont think johnd owes you 50p as you forgot to mention you were powering a big transformer that in turn is powering the lights -was quite significant!
sm1thson said:
Care to enlighten us?
thanks guys, i tried to buy a slower acting mcb which would have been a C6, however they didnt have any so i got a B10 of the same brand as the original. do you think this will be ok?
jamiedodger said:
Try Bernard's solution, you need to know if it is safe, before you can upgrade to a B10 (cable size etc.)
You should note that its not actually slower acting (though I accept that there will be a little difference in reality), but we assume 0.1sec for them all (they actually go faster than this but we can't count on it unless me ask the maker)
What is different is the current level that triggers the magnetic trip, B type must be 3-5 times rated current, 5-10 for C, and 10-20 for D
The problem with replacing it with a less sensitive one, is you are not sure its going to be sensitive enough to trip when it needs to unless you measure Zs, Also with changing it from a B6 to a B10 instead of a C6 you have also changed the current rating, so the rateing of cables as they are installed, and also of lampholders need to be considered
What is different is the current level that triggers the magnetic trip, B type must be 3-5 times rated current, 5-10 for C, and 10-20 for D
The problem with replacing it with a less sensitive one, is you are not sure its going to be sensitive enough to trip when it needs to unless you measure Zs, Also with changing it from a B6 to a B10 instead of a C6 you have also changed the current rating, so the rateing of cables as they are installed, and also of lampholders need to be considered
replace that huge toroidal tranny with an electronic soft start one - problem solved. 
Out of interest, my mother bought a light with 10 GU9 capsules on it, and a transformer. The base of the light was round, so i thought "toroidal", but i looked inside and theres a small electronic tx in there.
Out of interest, my mother bought a light with 10 GU9 capsules on it, and a transformer. The base of the light was round, so i thought "toroidal", but i looked inside and theres a small electronic tx in there.
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Yeah, you have to be careful.
C types are half the values of B's and D's half of C's.
C types are half the values of B's and D's half of C's.
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