"Evan Gatehouse" writes:

I've been considering the use of Polyfuses (made by Raychem among others)
instead of circuit breakers in an electric panel on my boat. They are a
lot
cheaper (like $0.50 each) and smaller than a breaker. The specs say "100A
maximum current" for a typical 5-10A fuse. This is the maximum fault
current that can be used to trip such a device.

The typical C series Carling hyd./magnetic circuit breaker has a
interrupting capacity of 7500A @ 80VDC. This is the toggle type circuit
breaker that you see on most new boats.

My question: is 100A interrupting enough? If there is a short in a
typical
wire, will fault currents exceed that?
snip

What you are asking is really, "What is the short circuit available on this
boat?"

The answer is dependant on the size of the house bank.

5,000 amps DC would not be considered unusually large.

BTW, what you are asking is the answer to a coordination study, something
consulting electrical engineers do for a living for large industrial
facilities.

For the device in question, you need to determine the maximum let thru
current under a bolted fault condition.

The manufacturer can provide this info.

HTH


--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
Visit: http://home.earthlink.net/~lewhodgett for Pictures

"Lew Hodgett" wrote in message news:Zsnvc.19148

What you are asking is really, "What is the short circuit available on
this
boat?"

The answer is dependant on the size of the house bank.

5,000 amps DC would not be considered unusually large.


Thanks Lew and all, I think you're right. I sure wasn't comfortable with
just the 100A interrupting capability.

What about the idea of a 40A or similar size main breaker (like a Carling)
feeding the polyfused panel board? If there is a fault such that the
polyfuse doesn't trip, the main breaker would trip. This would black out
the boat, but I can live with that in the short term, until I could manually
switch off the circuit that was shorting out the main breaker?

With about 15 circuits on my boat, even ebay DC breakers add up in cost
fast.


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)