Circuit breaker question

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Cspirit

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We have just fitted new bulbs and wiring all round to our mast (Westerly Corsair). All is well apart from the deck light - we fitted a 50watt halogen bulb. This gives a lovely bright light, much better than the original 10 watt, but unfortunately, this means that the circuit breaker trips out after about one minutes' use. The wiring in the mast is heavy duty - not sure about the original wiring from the switch panel to the mast step. My question is this: assuming that the wiring is OK, and that the circuit breaker is under-rated, what size of CB should I install for this 50 watt bulb? I know that I could fit a smaller bulb, but I'd really like to keep the more powerful light if possible.
 
Remember that the Circuit breaker must trip before the cable's de-rated current carrying capacity is reached.
 
It's precisely the bit of cable you don't know about that you <u>do</u> need to know about, as well as the connections
 
unless there's a partial short in the cable, it's just the lamp that's drawing current, and, as above, you need something over 5 amps to feed it. If the cable was below spec it would heat up, reduce the current, and the existing trip would probaly not blow until the cable melted. also, the light would be dim and you wouldn't be so pleased with it, so just fit the bigger CB.
 
Which switch panel is fitted ? the Corsair deck lights should have a 8 amp circuit breaker fitted to that circuit.
If this is tripping with only a 50 watt bulb, this must be the starting point.

Brian
 
my experience is that breakers trip earlier as they age. I have seen a 10 year old 15 amp breaker trip at 12 amps.
 
My interest is partly that we made most of the switch panels that went on the Corairs. We are still serviceing them, and am intereseted in why the circuit is tripping for ref, and customer support.
These breakers have been in use now for 23 years, and I have noticed no drop in trip amps from them. But will keep an eye them in future out of interest.

Brian
 
[ QUOTE ]
unless there's a partial short in the cable, it's just the lamp that's drawing current, and, as above, you need something over 5 amps to feed it. If the cable was below spec it would heat up, reduce the current, and the existing trip would probaly not blow until the cable melted. also, the light would be dim and you wouldn't be so pleased with it, so just fit the bigger CB.

[/ QUOTE ]

Not quite right. If the cable is under size then there will be more resistance which would increase the amps... Bad connection, under size wire would all cause more resistance and more amps....

The volts would get less so the amps would go up...
 
Sure?

[ QUOTE ]
Not quite right. If the cable is under size then there will be more resistance which would increase the amps... Bad connection, under size wire would all cause more resistance and more amps....

The volts would get less so the amps would go up...

[/ QUOTE ]That's an interesting theory! Seems contrary to Ohm's Law.
 
Re: Sure?

Working on the theory that volts x amps = watts, thus reduce volts increase amps.

Trouble is that the cable size and joints increase resistance, volts remain the same, amps = volts / resistance, so as resistance goes up, amps come down.

At the moment we have a lack of info, as that circuit should have a 8 amp breaker fitted.

Until the owner comes back it's only guess work.

Brian
 
Three months ago following similar confusion in a thread I posted a wee poll to which half the responders got the answer wrong. Let's try another:

A circuit is controlled by a switch. The switch contacts become dirty, introducing additional resistance into the circuit. All other conditions remain the same.
 
[ QUOTE ]
Who decides the right answer,

[/ QUOTE ] Georg Simon Ohm would have been a good choice but he died in 1854!
 
There is only one right answer, but three options, but as Georg Simon Ohm is dead, who picks the correct one, after all they could have the wrong one.

Brian
 
Ask the experts...

According to paulburton44, more resistance equals more amps. So that might be the right answer - after all, his profile says he's an electrician... /forums/images/graemlins/wink.gif
 
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