Yeh amazing that there's only one fuse in the entire electrical system, right? As you know British fuses are rated at the ampereage that they will immediately blow. USA (Buss) fuses are rated at the max amperage they can carry for a period of time before blowing.

reposting:
Automotive Electrical Fuses -- British Vs American (Tim Engel’s opinions – use at your own discretion)
British and American standards for rating electrical fuses are different. Both provide an “Amp
Rating” for very similar looking fuses, but the two ratings mean very different things. The US
system rates the fuse based on the continuous load it can handle for a specified period of time w/o
blowing, whilst the British system expresses the load at which the fuse will immediately blow.
That’s a significant difference! As an example, the 35 Amp fuse called out for many 1950’s/ 60’s/
70’s vintage Britcars (Lotus Elan & Europa for sure) is roughly equivalent to a US-spec BUSS
AGC 17 Amp fuse. Install a US 35 Amp fuse into your LBC fuse box and the wiring harness will
melt down before the fuse blows.
DO NOT use a USA rated 35 amp fuse in your vintage British car!
The complete rating for the specified 35 amp Lucas fuse is…
“17 AMPS CONTINUOUS / 35 AMP SURGE”
Early British fuses were simply marked with the quick-blow rating, but later fuses are given two
ratings in an effort to minimize the confusion. For instance, the 35 Amp fuse is often marked as
“17 continuous/ 35 blow”, or simply 17/35. In that case, use the lower “continuous” rating as the
one to which you try to match an American BUSS fuse rating. Or, better yet, proper British fuses
are available from your favorite independent Britcar / Lotus parts dealer. Purchase a supply and
keep them in your Lotus' glove box.
The comparison/ substitution looks something like this...
British Lucas Fuse ~ American BUSS Fuse
Fast Blow Dual Rating ~ Continuous (AGC) Alternate Opinion (SFE ?)
50 amp 25/50 amp ~ 25 amp 25 amp SFE
35 amp 17/35 amp ~ 17 amp 20 amp SFE
30 amp 15/30 amp ~ 15 amp 15 amp SFE (too short ?)
25 amp 12/25 amp ~ 12 amp 15 amp SFE (too short ?)
20 amp 10/20 amp ~ 10 amp
15 amp 7.5/15 amp ~ 8 amp
10 amp 5 /10 amp ~ 5 amp
5 amp 2.5 / 5 amp ~ _____ 3 amp
2 amp 1 / 2 amp ~ 1 amp
Unfortunately, there’s no extra data marked on either the fuse body or on the package to tip-off
the user that the ratings are different. It’s very important that USA owners of British cars be aware
of the issue and make wise choices when using USA fuses in them. The best choice is to make
the effort to source proper British fuses for your LBC. In an emergency, the loose Rule of Thumb
is to use a USA BUSS fuse with an Amp rating equal to no more than one half of the British
Lucas fuse rating.