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New Light Fitting - blows MCB

Postby lectricwire » Sat Apr 19, 2008 10:30 am

I have just fitted a new light and it keeps blowing my MCB

There were only three wires coming from the ceiling and therefore I am certain it is connected properly but this new light has a transformer and 21 x 10W bulbs.

If I turn the light on and then turn on the MCB it works fine.

If i switch on the light at the switch it blows the MCB

The rated voltage of the new light is 240V ~ 50Hz
bulb type 12V G4
rated watt 21 x 10W
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Postby sparx » Sat Apr 19, 2008 4:37 pm

Hi, 210Watts! do you issue guests with sunglasses?
Seriously tho' 210W running plus transformer losses is quite a high load going on at once and cold halogen bulbs draw several times their running load at switch on, if your circuit is suitable ie low enough earth loop impedance the answer may be a change of circuit breaker type from usual 'B' to 'C' type,
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Postby lectricwire » Tue Apr 22, 2008 4:23 pm

Are there likely to be other options - like
adding in a transformer and a dimmer so that it would draw less power when cold?
or something even easier like
low energy halogen bulbs that start off slowly and dont drawer all the power at once?
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Postby ericmark » Tue Apr 22, 2008 11:12 pm

There are many options easy one is two transformers and two switches with some transformers you can use dimmers which would also reduce the in-rush but I would not use them myself matching types can be a pain. So much relies on the exact type of transformer or inverter used. Changing type of transformer or inverter could also help. Many inverters have in built protection from in-rush.

A transformer is just a couple of coils of wire around a former but an inverter has electronics which turn AC to DC then back to AC at high frequency then transform to output voltage with often a feed back to correct the electronics to give a stable output even when the input voltage varies. They look the same but inverters are often lighter.

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