Fuses again

[Robbie693]

Hello,

I know this was discussed amidst another thread recently but I thought I'd start a new one to get some opinions.

I was at Paul Matty yesterday and asked about what ratings the fuses in the dash (late S/130) should be. They agreed it was unclear from the manual and said that they fit 35A fuses in all positions..

Does this sound a bit high?

Also, could someone explain to me - when a fuse has a continuous and a blow rating, what's the difference to one with just a continuous rating? And are they marked with both?

Thanks

Robbie

[steve.thomas]

Hi Robbie,
I also have a late 130/S with the 4 fuses in the dash. Mine are all 35amp except the 2nd from right when viewed from driver seat (not sure if that is referred to as number 2 or 3) - this one is 50amp ! From the wiring diagram this seems to protect stop lights, reverse lights, fog lamps and battery gauge so it sounds too high to me, but having recently acquired the car I haven't found if there is some reason for this......
Cheers
Steve

[robertverhey]

Clearly for those times when you hit the brakes while reversing in the fog, while checking the battery gauge

[billwill]

A continuous rating of a fuse is the maximum current it can take continuously, It can exceed that a bit but the fuse will deteriorate over time.

The blow rating would be the current which will melt it quickly.

[neilsjuke]

Pull the fuse and check current with a dc ammeter / multimeter with every thing on and go for the next fuse up do take the 50 amp out way to high ,A white 35 amp was rated as 17 amp continuous.
Neil

[gerrym]

I agree with Neil, that 50A fuse must be way too high.

Do you have any idea how thick a wire has to be to carry 50A with over heating and possibly starting a fire?

Regards

[terryp]

I have 4 x 25amps!

Surely someone should know what they should be!

Terry

[Galwaylotus]

The purpose of a fuse is to protect the wiring downstream. If you can determine the wire gauge and look up the amp rating, you're well on the way to determining which fuse to use.

[Robbie693]

Thanks everyone,

Yes 50A sounds scary!

So, I'll try as Neil suggests and take the fuse out and measure the current. Just have to figure out which accessories run through which fuse..!

Once I've found out the current draw, should I be using continuous fuses or continuous/blow fuses?

Cheers

Robbbie

[neilsjuke]

Turn every thing on with the engine running pull the fuse and put the ammeter on and go for the next nearest car glass fuse are rated at the max blow

Continuous...........blow or fusing what you will have marked on the fuses
1A ..................= fuse 2A
2.5A................= fuse 5A
5A...................= fuse 10A
7.5..................= fuse 15A
12.5................= fuse 25A
17.5................= fuse 35A

50A WOULD BE OK FOR ABOUT THREE ELANS TOTAL current drain
Neil

[Robbie693]

Thanks Neil, very helpful.

Would the reading be the same with the fuses in and just measuring across the contacts?

Robbie

[alan71]

No, you need to take the fuse out to measure the current.

Alan.

[billwill]

Thanks Neil, very helpful.

Would the reading be the same with the fuses in and just measuring across the contacts?

Robbie

Er, no.

To measure the current, your amp meter takes the place of the fuse, so that ALL the current flows through the meter.


Just putting two prods across the fuse, will not have the right effect, most current will flow through the fuse and only an indeterminate (*) portion through the meter, so it will show an incorrect reading.

(*) depends on the resistance of the fuse and the resistance of the meter, neither of which you will know accurately.

[neilsjuke]

No the current need to flow through the meter
Neil

[neilsjuke]

So thats a no three times then