Fuses

Here's an item for conversation. The E-type list recently included the following excerpts:

>>A long time ago I believe I saw, probably on the Jag-Lovers list, a
>>conversion for Jag era fuse ratings to US current. Anyone know where I
>>can find that info? I have to say I've never known European Amps to be
>>any different than anyone else's amps.- Ed Scripps

>Same AMPS, different reference point. The difference between the two
>systems is in which characteristic is 
>being described. In the US system,
>the rating is the holding current.  
>Holding current is the maximum
>current which the fuse can pass for a 
>long, long time without failure.
>The UK rating is peak current, or the 
>current which the fuse will sustain
>for a very short period of time, but 
>which it cannot sustain for a longer
>period of time.

>>Generally speaking a standard metal fuse of a given design would have
>>about 1/2 the rating under the US system as it would under the UK system
>>(i.e. 10 AMPS US ~ 20 AMPS UK). John Horner

With that explanation out of the way, can anyone advise the recommended fuse ratings 
for the numbers 1, 2, 3 and 4 fuses in the 120 fuse box. Is there a reference?

I recently had a problem with intermittent headlight operation which I traced 
to dirty/lightly corroded fuse holders. After removing the fuses, and cleaning 
the clips, I realized that I really didn't know, nor could I find any reference 
to, which size fuse was specified for each holder.
Thanks for your input. - Dick Cavicke

Would you believe it, the Mark V service manual comes to the rescue!
Quoting from page P13: "All six fuses are 35 amp. capacity."

Naturally one asks the question "are the two models close enough that the 
assumption can be made?" Well, the circuits protected by each fuse are listed 
in this manual just as they are in the 120/Mk7 manual, and they are nearly identical 
to the 120. The difference is with MkV the headlamp main and dip circuits run through 
the same fuse, with foglights on another fuse, whereas with 120, not having foglights, 
they separate the main and dip circuits through two fuses.

So I'm willing to go out on a limb and say 35 amp (UK system) should be ok for all 
six fuses in the FHC/DHC (5 for OTS). Thanks to the E-type list member for 
enlightening us.

That said, what do we use in the US since we don't have 17.5 amp? 15 or 20?
The US fusemakers sell both fast-acting and Slo-Blo time delay types ranging from 
10 milliamp up to 30 amps. Any idea which would be equivalent to the Lucas 35 amp? 
- Rob Reilly

I was looking through some old books that came along with all the baskets of parts 
with the purchase of my XK150 DHC and found what appears to be an original 120 
service and spares catalog. On page 82 in the spares books it list part #270 Fuse, 
35 amps. (188218) So, Rob it looks like you have it. - Skip Smith

Most of the US Jag parts suppliers (XKs, etc.) offer the correct Lucas fuses. That 
is what I would buy. - John Horner

Rob Reilly and Skip Smith, ..thanks for the answers to the 120 fuse question. Skip, 
once again I'm reminded just how complete the Parts Manual really is and how I 
should have thought of looking there myself. Regards - Dick Cavicke

added 1/10/99...

I've finished rewiring my car and when replacing the fuses I noticed there
are three 75 and one 35amp. I've looked in the parts book and they list 35
amp only. Some of the suppliers offer 35 and 50 amp as needed for the 120.
Can anyone help sort this out? - Thanks, Jeff Kelley-Day

Jeff, I asked a similar question a while back when I couldn't find a chart
in either the Handbook or Service Manual listing the recommended fuse
sizes. I think it was Rob Reilly who steered me to the (all-knowing) Parts
Book and the 35 amp fuse answer for all 6 fuses (in the fuse box and the
control box). My experience with other cars led me to assume that the 120s
35 amp fuses were likely the largest of several sizes it used, not the only
size. I have used 20 amp fuses in the fuse box without a problem. Fuses
larger than 35 amps could, I believe, invite a fire, wiring meltdown or
component failures in the presence of a short circuit. I would stay with 35
amps maximum and not over-tax the senior citizen Prince of Darkness. -
Regards,  Dick Cavicke

If you have any questions or comments send e-mail to: ted@jag-lovers.org
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