I have a Series2 FHC with factory air conditioning. There is an in-line fuse that keeps blowing. The fuse is a 10 amp but that seems low to me. Does anyone know the proper fuse amperage?

Submitted by mfrank@westnet.com on Tue, 07/31/2012 - 21:59

The exact current draw on this circuit is difficult to measure, not because of the complication of wiring an ammeter, but because it's a very 'noisy' circuit. This is due to compressor cycling.

A Lucas 25A fuse is designed to blow at 50A continuous, but can sustain spikes of up to 60A. Whatever the correct rating may be, the fuse holder wasn't up to it. Fuses aren't rated like this today, but a 50A ATO is going to be close. At least the holder doesn't overheat.

Submitted by bonnettoboot@e… on Tue, 07/31/2012 - 21:14

THIS IS ALL A LITTLE CONFUSING. A LUCAS FUSE STAMPED AT 50A IS MEANT TO CARRY A 25A LOAD AND IT WILL BLOW AT 50A ? cfb150. A LUCAS 25A FUSE WILL CARRY A 12A LOAD CONTINUOSLY BUT BLOW AT 25A. A 17 AT 35 ETC. MANY OTHER TYPES OF FUSES SHOW ONLY THE AVERAGE CURRENT FLOW AND BLOW SOMEWHERE ABOVE THAT, PROBABLY THE SAME AS LUCAS. THEY ARE ALL DESIGNED TO DEAL WITH CURRENT SURGES THAT OCCUR.

Submitted by MikeEck@optonl… on Tue, 07/31/2012 - 20:40

Josiah, the American fuses have a different rating system than the British fuses. A British 25 Amp fuse is designed to be used in a circuit that passes 25 Amps, and the fuse will carry that current for years. An American 25 Amp fuse is designed to BLOW if 25 Amps is exceeded. For an equivalent fuse, the American rating is about 1.8X the British rating. Using a 50 Amp American fuse in place of a 25 Amp British fuse is about right.

Submitted by tvtom@sbcglobal.net on Tue, 07/31/2012 - 12:02

I would suggest that someone measure the actual current flow in this circuit. It's a little bother to place an ammeter in series with the circuit but there are clamp-on ammeters that will measure DC flow with sufficient accuracy for this application. I don't have AC.

Submitted by joshbartlett@r… on Tue, 07/31/2012 - 09:54

Please explain to me how British AMPS are different than American AMPS. An ampere is a SI measure of electrical flow. Is it the way the devices are rated, or some magical way the two units become different?

Thanks for continuing my education....
Josh

Submitted by mfrank@westnet.com on Mon, 07/30/2012 - 23:33

George:

I know what the book says, and I know what it took to fix the problem. I did this long enough ago for there to be some NOS parts available...a new compressor and several used fan motors were at hand. I replaced the Lucas fuse holder because, after blowing my way through a whole box of fuses, the spring melted into the plastic housing. After amodern nylon fuse holder did the same, I went to the big ATO fuse. The right size might be 35 or 40 amps,but I've just been happy to not have it blow every time I use it. This system was designed as an afterthought, and I'm certain that the stock wiring was inadequate.

Submitted by SE98-32482CJ on Mon, 07/30/2012 - 23:16

My guess is that it is 25 amp US as the part number is 147 which is not in sequence with the Lucas fuses. As far as it being enough I think when the fuse holders were a lot newer than now there was no issue. Over time heat, vibration, and power load weakens both the spring and holder. More resistance brings more heat. I do know that 25 British is not 25 US but neither is 10!