Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, about which type of MCB to use for lighting circuits, is answered by ABB:
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| An ABB Type B MCB. |
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Question: It has come to my notice that many of my customers are complaining that when a light bulb blows, it takes out the lighting fuse - even if it's the only light on.
All these boards are wired with a Type B 6A
MCB, which is standard practice in this area. Should this practice be changed so that the lighting has a Type C or Type D MCB?
What is best practice in this area and would it stop this fault?
Answer: In general, the 6A Type B MCB is the accepted norm for standard domestic duty; normally one MCB for upstairs and one for downstairs, with no great problems occurring.
The lighting load, type and estimated inrush current all have a part in determining the size and type of an MCB. It is possible in domestic situations that, when a filament lamp fails, the components that make up the filament fall across the internal contacts, causing an arc which can trip circuit the MCB.
You need to ascertain what is causing the breaker to trip as it is obviously seeing an inrush, but is this being caused by the lamp blowing, or by whatever is feeding/controlling the lighting?
With regard to best practice, you need to refer to BS7671 - ie: has any allowance been made for the lamp type, such as discharge lighting, wattage, associated gear and their harmonic currents?
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http://www.voltimum.co.uk/consult.php?universe=consult.index.questions
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