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ian.settle1

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Had a phone call the other day regarding a dimmer switch and 5 x 50watt dichroic lamps.

Caller said that when switching off the lights which are on a dimmer switch the was a flash from one and all the lights went out plus MCB tripped.

They reset the MCB but the lights in that room would not come back on, when I went round I checked out light fittings found them all to be ok including the one that the flash had come from but the lamp had blown.

I have known when incandescant lamps blow they can take out the MCB but never heard it take out a switch.

Only reason I can think it took out the switch, is that the dimmer switch was rated 400w max(approx 1.6A) and with the MCB being a B type it needed 18-30A to trip thus 10-20 times current rating of switch flowing through it for an instant.:eek:
 
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S

Shakey

Had a phone call the other day regarding a dimmer switch and 5 x 50watt dichroic lamps.

Caller said that when switching off the lights which are on a dimmer switch the was a flash from one and all the lights went out plus MCB tripped.

They reset the MCB but the lights in that room would not come back on, when I went round I checked out light fittings found them all to be ok including the one that the flash had come from but the lamp had blown.

I have known when incandescant lamps blow they can take out the MCB but never heard it take out a switch.

Only reason I can think it took out the switch, is that the dimmer switch was rated 400w max(approx 1.6A) and with the MCB being a B type it needed 18-30A to trip thus 10-20 times current rating of switch flowing through it for an instant.:eek:
I'v never heard of this either - the dimmer and switches are underated by about 5 times rated current normally, to allow for temporary current surges - but hey, if its blown, its blown!!!
 
M

MacSparky

the dimmer and switches are underated by about 5 times rated current normally, to allow for temporary current surges
You've lost me here, i don't understand why you would underate the switches/dimmers, or come to think of it anything electrical:confused:

A little help would be appreciated here:eek:
 
S

Shakey

its the FOS (factor of safety) built into ALL engineering equipment

A switch rated at 10A does not melt at 10.1A or even 11A

or 12A

in fact it can take quite a bit more

so by rating it at, say, 10A that is what you will work to. the fact that it will probably take 30A without immediately becoming a molten lump is why it is under rated, as all things are

What would happen if 2.5mm installed at method 1 (or method 100, 101 or 102: 117th edition) melted at 27.1A? we would have houses all of the country going up in smoke.

No of course it can 'take' a lot more, but we 'rate' it at 27A to allow for all the un-known's, temorary overloads, design errors etc etc etc

thats why most things (not just electrical) are under-rated
 
M

MacSparky

Thanks shakey, it was the wording that threw me. Didn't know about FOS though...great stuff.;)
 
B

Bane

I know mate... I know.

But hey, you know me... Always willing to help out and not wanting to take the credit.

Modesty is my first name, discretion my surname ;)
 
S

Shakey

I know mate... I know.

But hey, you know me... Always willing to help out and not wanting to take the credit.

Modesty is my first name, discretion my surname ;)
your name is Modesty Discretion?

so how do you get called Bane?

and are you related to Soul-of Discretion?

you know, dark hair, his dad used to wear a belt to work?
 
B

Bane

That's the one! You know him then?

Bane? A polite form of being called a pain in the ar*e.

(Bane of your life)
 
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