[steve roberts]

Does anybody know the correct fuse amperage for a 1952 MKV1 Bentley MAIN FUSE. I know it is "3 strands of 28swg wire twisted together' (Handbook) but what IS that as a fuse rating? (10, 12, 25...?)

 

[Jeff R 1]

I don't believe there is one, all the fuses do is protect against shorts.
I've had my MK VI for 20 years, and the only time when the main fuse blew is when the regulator for the generator was acting up.
One of the big resistors underneath the regulator was an open circuit and it's voltage was spiking at over 120 volts, it may have been higher then that if memory serves.
The whole car just stopped working when it blew.

If a circuit is drawing too much current, then they will blow before any damage is done.

The problem with these cars is the main wiring harness that passes through the fire wall, or bulk head.
All there is, is this big rubber grommet to keep the wires from chafing on the sharp edge where the wires pass through.
The grommet is over 70 years old and has either turned to mush, or is hard and crumbly.

This is a source for many dead shorts, and very often can cause fires.

I'm sure others will post with more knowledge then me.

 

[steve roberts]

THANKS JEFF. I traced the problem to the foot dipswitch earthing on the floor panel. I replaced the MAIN FUSE per the handbook which said "3 strands of 28swg twisted together" which works perfectly. But what I want to know is what, exactly, do those 3 strands represent as a fuse rating? (eg 10 amps, 15? 25 etc?)
This is so I can obtain that wire just in case it happens again by whatever short appears next! Flying Spur don't know - so who does?
Steve

 

[Wraithman]

First, measure the resistance of all 3 wires. Your voltage is 6 volts. I=V/R in other words: Current(amps) I = volts divided by resistance

 

[Jeff R 1]

Search results for: 'fuse wire' | IntroCar

This is interesting, I never knew they had different kinds with amps rating.
I don't think this was available when I got mine.
The question is, what rating is used in each circuit, I would think the highest for the main fuse.

 

[steve roberts]

ALL the other fuses use 28swg per the handbook. This was suppl;ied by the factory on a card in all MKV1s (bottom L in fuse box) This Main Fuse is "3 strands of 28swg twisted together" (from handbook) But I am trying to discover what that is as a fuse? i.e. how many amps? Then I can carry the appropriate wire or use a modern cartridge type with adaptor.
Steve MK6

 

[Wraithman]

Steve, did you read and understand my post? It's basic Ohm's Law. When you find the amperage using the formula, you can build a clip-on type emergency fuse.

 

[steve roberts]

Hi Wraithman!
Thanks for your input. I read your post but am as baffled by simple electrics in the way that my dog is baffled by quantum mechanics. I guess what I am hoping is to get an answer from somebody who has resolved the equation - or just has a (10,20,25 amp fuse sitting in his MK6?)
I have done the 3strand trick as suggested by Crewe, and it works perfectly, but still would love to know just what its fuse rating IS. What is 3 strands of 28swg expressed as a fuse value?

 

[Wraithman]

If you have a voltmeter, something that can measure resistance, you are closer to your answer. You must know someone that has one. If you work on your own stuff, this should be as common as a screwdriver in your toolbox. They can be purchased for the cost of 3 Latte's from Starbucks. Seriously.
Once you know the combined resistance of the wires, divide the 6 (volts) by the resistance figure and that will give you the amperage rating.

 

[steve roberts]

Will do. Headed for Starbucks right now.
I'll post the result in case anybody else wants to know what main fuse RR/Bentley used. Seems to be as mysterious as the horsepower.
I drive my MK6 between Vancouver BC and Los Angeles regularly and without fuss until this short reminded me of the electrical demons of Mr Lucas, Prince of Darkness. The fix was easy. The theory and practice may be familiar to his acolytes not humble oily persons like myself.

Moderator's note: Steve, please note that you do not need to quote a previous post in your reply if you are following the train of thought in the thread.

 

[David Watts]

Robert - just wondering about the dividing the 6 (volts). A Mark VI is a 12 volt car. Would you still divide 6?

 

[Wraithman]

No, divide by the correct voltage. It was my wrong assumption the car was 6 volts. The formula remains the same. Have an appliance that has no amp rating, but has watts instead? Divide the watts by house current and it will give you the amps that it pulls. Watts divided by volts will give amp rating. Example a 1200w toaster on 120v house voltage pulls 10 amps from the outlet.

 

[Jeff R 1]

I didn't think any RR/Bentley was 6 volt.??