Please visit the Club's website https://www.dloc.org.uk/ to join, or visit https://www.dloc.org.uk/adhoc to DONATE towards the cost of running the forum.
Please don't post someone's email address. Some people don't want to risk it being harvested by spambots and GDPR regulations discourage it.
Always look at "ACTIVE TOPICS" which gives all posts in date & time order if you can't find a post as topics are sometimes moved; or look at "Your Posts".
Reg. nrs. Please add reg. nr. when posting a photo or anything about a car as this will help searches. Don't add punctuation next to nr. as this negates search.

SP 250 fuses

Crossley Stephenson
Posts: 252
Joined: Wed Feb 10, 2016 9:15 pm
Location: Victoria, Australia

SP 250 fuses

Post by Crossley Stephenson »

Can someone please tell me the amperage of the two fuse in a standard SP circuit. I have looked but can't seem to find this info.
Thanks in advance,
Michael

Ian Slade
Wise Man
Wise Man
Posts: 589
Joined: Sat Feb 13, 2016 9:54 am
Location: Scotland

Re: SP 250 fuses

Post by Ian Slade »

35 Amps same as any car of that vintage, cut down 6"nails or wrapping chocolate paper round them is no longer considered acceptable :D
Owner since the 70's, Genghis is slightly to my left.

User avatar
theoldman
Extremely Wise Man
Extremely Wise Man
Posts: 1108
Joined: Mon Feb 08, 2016 2:39 pm
Location: Bacton on Sea, Norfolk UK

Re: SP 250 fuses

Post by theoldman »

You ridicule all my best electrical repairs, Ian............................ :D :D :D :D
Normal for Norfolk

Crossley Stephenson
Posts: 252
Joined: Wed Feb 10, 2016 9:15 pm
Location: Victoria, Australia

Re: SP 250 fuses

Post by Crossley Stephenson »

Thanks. This will explain why the 15 amp fuse installed was not up to the job on a very warm day with the electric fan cutting in and out regularly. The fan needs a 30amp fuse. Surprised it hasn't blown before. Although the fan rarely comes on except on very warm to hot days.

Will correct the situation for next week and an approx 700 km run north (warmer).

Cheers
Michael

David S
Posts: 188
Joined: Sun Feb 21, 2016 9:23 am
Location: Forest of Dean

Re: SP 250 fuses

Post by David S »

I have fitted something like this on mine and feel if I have one fault the chances are that I will still get home.

http://www.ebay.co.uk/itm/CAR-MOTORCYCL ... Swx-9WzABW

I have an 'always live' set of 4 outlet fuses: Horn 10A; Electric Fan 15A; Radio; Cigar accessory 15A.
And 'ignition on' set of 8 outlet fuses: Indicators 10A; Reverse 5A; Lumenition 5A; Fuel Gauge 10A; Heater 10A; Wiper/Wash 10A; Stop Lights 5A; and a spare.

I just tagged 4 inputs together on one of the 35A live 'always on' wires, and joined 8 tags together for the 'ignition controlled' systems from the existing [mostly green] wires [and yes, 15A seems ok for the electric radiator fan on mine, which is off an old Astra].
......... it's worked well over quite a few years, is not a particularly big job and gives me peace of mind.

I often think of fitting relays for the circuits that draw heavy currents to prolong the lives of the switches, but that is for another day!

Christopher Storey
Posts: 312
Joined: Wed Mar 16, 2016 6:40 pm
Location: Cheshire

Re: SP 250 fuses

Post by Christopher Storey »

David S ; anyone fitting a modern spade fuse setup needs to bear in mind that the fuse ratings are not comparable. The old Lucas fuse ratings were blow ratings ie a 35 amp fuse would blow if more than 35 amps was carried instantaneously. Spade fuses are continuously rated fuses and their ( unstated ) blow rating is approximately double their nominal rating - so a 15 amp spade is broadly equivalent to the old 35 amp, and a 30 amp spade will not blow until about 60 amps is carried . The danger of fire is considerable if this fact is not taken into account in selecting fuses

David S
Posts: 188
Joined: Sun Feb 21, 2016 9:23 am
Location: Forest of Dean

Re: SP 250 fuses

Post by David S »

Thanks Christopher... maybe I should lower the values of each of the spade fuses to suit the application?

David

JSabah
Posts: 108
Joined: Mon Feb 15, 2016 9:27 pm
Location: Los Angeles

Re: SP 250 fuses

Post by JSabah »

I see earlier in this thread that Ian stated that the correct fuse size is 35 amp. Can someone please confirm that this is correct for BOTH fuses? I recently blew the fuse with all the green wires (fuel gauge, temp gauge, brake lights and turn signals). i think mine blew as a result if another issue with my light switch - it shorted out and burned up a wire that melted one of the green wires. The short issue is now resolved and I went to replace the fuse and see that I had a 25amp fuse... (my SP250 i as original - glass fuses in a 2 circuit lucas box, no additional equipment, no radio and no electric fan)
Sp250, Sunbeam Tiger, MGTD, Jensen Interceptor conv, Jensen Interceptor Coupe', '49 Plymouth Woody and now a '65 Jensen CV8 Mk3 LHD

Simon Hyslop
Posts: 314
Joined: Wed May 04, 2016 3:30 pm

Re: SP 250 fuses

Post by Simon Hyslop »

This is an "I can only tell you what it says" reply. Pitmans Automobile Electrical Maintenance, 5th ed, 1965:

" In many British cars two fuses, only, are fitted, namely a 35 ampere fuse to protect circuits controlled by the ignition switch and a 35 - 50 ampere fuse for circuits which operate when the ignition switch is either On or Off". There is also a little drawing showing a fuse box with one fuse marked 35 amps and the other marked 50 amps.

I am aware that in clearing out various collections of electrical bits over the years, some from garages, I do have a fair quantity of original 50 amp Lucas fuses and so someone thought they were a useful thing to have on their shelves.

Added 24/11/20
In looking up something else, I've dragged out my parts book for the 1952-55 Riley RME which lists the two fuses as both being 50 amp.
Last edited by Simon Hyslop on Tue Nov 24, 2020 8:32 pm, edited 1 time in total.

Ian Slade
Wise Man
Wise Man
Posts: 589
Joined: Sat Feb 13, 2016 9:54 am
Location: Scotland

Re: SP 250 fuses

Post by Ian Slade »

The fuses are there to protect the dynamo and wiring from over current, not the electrical components, the dynamo has a designed max current of 30Amps it normally will supply at 25Amps regulated. Most generators have an over current capability of between 10 to 20%, 35 Amps the SP dynamo sits safely in this bracket, obviously higher output dynamos and alternators have a higher current rating so can have higher rated fuses, the SP dynamo is rated at 30Amps so is protected by 35Amp fuses.
Owner since the 70's, Genghis is slightly to my left.

Post Reply