Fuse rating

[jimj]

On the Sprint I`ve had one of the fuses blow, the bottom one. The problem was traced to the bonnet spring damaging the electric fan connection. It took a while to find but was a simple fix. My question is; what rating should the 2 fuses be? I can`t find anything in the workshop manual or Brian Buckland`s tome.
Jim

[Foxie]

There were only two 35A fuses in the early Elans, similar to many other British cars of the period.

The Plus 2 has practically identical electric equipment

In the1970 +2S there are three fuse boxes, each of four fuses.

All the fuses are 35A, except rear fuse, centre box which feeds the indicators /hazards, which is 5A.

[jimj]

35 amps seems a lot.
Jim

[Foxie]

35 amps seems a lot.
Jim

That's what the man says.....

[draenog]

35 amps seems a lot.
Jim

I imagine the fuses are 17A continuous, 35A blow.

[Esprit2]

British and American standards for rating electrical fuses are different. The US system rates the fuse based upon the continuous load it can handle for a specified period of time without 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 Lucas fuse called out for many 1950?s/ 60?s/ 70?s British cars (Lotus Elan & Europa for sure) is roughly equivalent to a US-spec BUSS AGC 17 Amp fuse. Install a USA BUSS 35 Amp fuse into your LBC fuse box and the wiring harness will melt down before the fuse blows.

The complete rating for the specified 35 amp Lucas fuse is actually ?17 AMPS CONTINUOUS / 35 AMP SURGE?. These proper British fuses are available from your favorite independent Lotus parts dealer. Purchase a supply and keep them in your Lotus' glove box. Don't abuse the electrical system by trying to make whatever fuse you can find in US auto parts, hardware or electronics stores work.

The comparison/ substitution looks something like this:

__ British Lucas Fuse ______ ~ American BUSS Fuse
Fast Blow __ Dual Rating __ ~ Continuous (AGC)
50 amp ____ 25/50 amp ___ ~ 25 amp
35 amp ____ 17/35 amp ___ ~ 17 amp <<<< Common size in vintage Britcars.
30 amp ____ 15/30 amp ___ ~ 15 amp
25 amp ____ 12/25 amp ___ ~ 12 amp
20 amp ____ 10/20 amp ___ ~ 10 amp
15 amp ____ 7.5/15 amp ___ ~ 8 amp
10 amp ____ 5.0/10 amp ___ ~ 5 amp
_5 amp ____ 2.5/5.0 amp ___ ~ 3 amp
_2 amp ____ 1.0/2.0 amp ___ ~ 1 amp

Regards,
Tim Engel

[draenog]

https://en.wikipedia.org/wiki/Fuse_%28automotive%29#Lucas_type

Most automotive glass fuses sold in the UK only have a single rating. But is this the old Lucas-style blow rating, or the continuous rating?

Of the numerous listings on ebay, only one I found mentioned the blow rating (2x continuous) which implies the fuses are continuous rated:

https://www.ebay.co.uk/itm/263825329976

Which means the wiring will catch fire before the fuse blows (at least melt). Of the 12 fuses in my Elan +2S, 3 were modern replacements which I binned. I will only use fuses with dual ratings, such as:

https://www.ebay.co.uk/itm/132618606068