In a message dated 30-Mar-00 23:11:48 Eastern Standard Time,
amdickin@ucalgary.ca writes:
> So what is the diference. Are the Lucas ones fast blow?
>
Here is my answer to the list after consulting with Dan Masters. This was on
the 6th of Feb.
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>From Arthurk101@aol.com (6 Feb 2000)
Those of you who remember Dan Masters from the list -- He is well and still
working on his electrical book for Triumphs. Says he will be back to us
shortly and that he misses the "lists."
I sent him a message regrding the Lucas fuse question. Here is my message
and his reply. Do as you wish; I will follow the advice given.
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My comment to Dan
> A question has come up again about the ratings on Lucas fuses. The usual
> mis-information and half facts have surfaced. I have to admit that I
started
> it when I said that I was going to replace my Lucas fuses with Buss fuses (
> because I didn't want to wait to get the Lucas'). I said that I would use
1/2
> the ratings called for in the fuse charts in the car's shop/owners' manual.
>
> My understanding is that Lucas fuses are rated for "quick blow" at the
> marked rating. For example, a Lucas fuse with a rating of 35A will blow
> IMMEDIATELY at 35A. BUT it will also heat up and eventually blow if the
> continuous current exceeds 17.5A, depending on how long the current exceeds
> that amperage. This will protect a circuit rated at some amperage above
17.5 >amps by allowing a short time surge up to 34.5A but would cause an
> immediate open for surges at 35A.
>
> Have I got the right explanation and is 1/2 the proper ratio to use when
> using Buss fuses?
Dan's answer:
You have it right. The newer Lucas fuses have two ratings printed on them. 35
amp in large print, and "17.5 blow" in smaller print. As with most things,
it's a bit more complicated than that, but it's also true that there is a lot
of leeway, both in the ratings of the fuse, and in the current carrying
capacity of the wires, so the 1/2 factor is more than sufficient as a
criteria. Unfortunately, you won't be able to find 17.5 amp Buss fuses, at
least not readily, so you will have to split the difference. My
recommendations are to use a 10 amp for the "red" fuse (the fuse feeding the
parking, marker, and gauge lights), 15 amp for the "purple" fuse (feeding the
horn, high beam flasher, and courtesy lights), and 20 amp for the "green"
fuse (feeding all the loads that are on only when the key is on - wipers,
reverse lights, brake lights, gauges, heater fan, turn signals, etc). If you
find that the 10 or the 15 amp fuses blow often, move up to a larger size,
but I would NEVER go over 20 amp.
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Cheers.
Art Kelly '64 TR4 CT33118L (original owner/factory pickup), '73 Stag
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