Uprating from 100amp to 125amp fuse
Uprating from 100amp to 125amp fuse
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Discussion

LaserTam

Original Poster:

2,183 posts

248 months

Monday 19th October 2009
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Recently had the 100amp fuse failure on my Tam. All fixed, replacement 100amp fuse is in, but I have heard people talk of uprating to 125amp. Other than the obvious that this will hopefully prevent another failure, before I order one and fit it, just questioning the what the potential downfalls might be.

Surely 100amp was put in for a reason, would I not be opening the possibility of some sort of electrical damage if the higher rated fuse is installed? Overloading battery/alternator perhaps? I'm no sparky, so dont get too technical.

Also, if I do it, just it fit in the same holder as the 100amp fuse, or do I need to change that too?

TIA.

T350 Al

624 posts

220 months

Monday 19th October 2009
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I went through the same thought process as you and we decided it wasn't worth it.

We imagined what our insurance company would say if something went wrong and they found out we had increased the fuse rating by 25%! Can the existing wiring carry that sort of current for prolonged periods? I know the chances might be minimal that:
a) a fire/catastrophic event might be caused by the fuse not blowing when it should
and b) the insurance company attributing it directly to the higher-rated fuse.

I worry about such things too much so for us, it was a no-no.
We just keep spares handy in the glove box and I'll be relocating the fuse holder over the winter months to make it easier to replace when it pops!

shep1001

4,620 posts

218 months

Monday 19th October 2009
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LaserTam said:
Recently had the 100amp fuse failure on my Tam. All fixed, replacement 100amp fuse is in, but I have heard people talk of uprating to 125amp. Other than the obvious that this will hopefully prevent another failure, before I order one and fit it, just questioning the what the potential downfalls might be.

Surely 100amp was put in for a reason, would I not be opening the possibility of some sort of electrical damage if the higher rated fuse is installed? Overloading battery/alternator perhaps? I'm no sparky, so dont get too technical.

Also, if I do it, just it fit in the same holder as the 100amp fuse, or do I need to change that too?

TIA.
Had mine changed when in for the 12K service recently. You will also need a new fuse holder. Only had it changed at the garage said it was a good idea. Don't the newer cars come with a 125amp fuse as std?

KillerJim

972 posts

232 months

Tuesday 20th October 2009
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I`m trying to understand why putting a 125amp fuse in, rather than 100amp's is such a "bad" idea..

A fuse is designed to prevent more than a specified current from travelling through a (in this case, large) wire. If there is a fault then the flow of current (usually to ground somewhere) will cause the fuse to pop..

Now 100amp's is alot of current and there's very few wires in the car capable of handling that current. If any fault occurs is it not likely that a) the smallers wires that are channelling the 100amps+ (to ground) are going to burn up quickly given that it can`t handle 100amps+ or b) even if the wire supports the current for a 'while' its going to pull way more than 100amps (so 125amps will pop just as much..)

I`m just trying to think of a situation where an electrical fault will pull (specifically) between 100 and 125 amps (also given that other fuses will pop too)

J

Targarama

14,784 posts

312 months

Tuesday 20th October 2009
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IMO The design of the standard 100A fuse is not great - it could fracture through movement rather than current overload. The 125A version looks much more rigid. If you keep having to replace the fuse then perhaps this is a mod you should consider. However, if it hasn't gone then leave it alone IMO - carry a spare for the AA man to fit if needed.

In 5.5 years of ownership I have not ever needed to replace this fuse, nor any other fuse or even a bulb on my car. About a year ago I 'went in' to have a look at my 100A fuse (more to make sure I knew how to change it if it goes) - it looked OK, but I replaced it anyway since I had two spares. (I once nearly needed a reverse light bulb, but it turned out to be the switch.)

VARLEYHYD

2,244 posts

236 months

Tuesday 20th October 2009
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Just replace it with a 100A MIDI fuse (not strip fuse)

G

T350 Al

624 posts

220 months

Tuesday 20th October 2009
quotequote all
VARLEYHYD said:
Just replace it with a 100A MIDI fuse (not strip fuse)

G
Should've said in my original reply that this is what I did; got the Midi fuses and new holder from Steve Heath IIRC.

LaserTam

Original Poster:

2,183 posts

248 months

Tuesday 20th October 2009
quotequote all
Thanks for the coments guys. I think maybe the midi fuse might be the way to go.

Is it a straight forward task to change out the holder to the midi type? Assuming its just a matter of disconnecting cables at end of existing holder, then reconnecting the new one.

Edited by LaserTam on Tuesday 20th October 22:04

LaserTam

Original Poster:

2,183 posts

248 months

Thursday 22nd October 2009
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Any ideas?

T350 Al

624 posts

220 months

Thursday 22nd October 2009
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It's an easy enough job to do, you just have to either disconnect the battery before changing it or be very careful not to short out the terminal on the chassis/engine when changing the holder over!

I did it in about 20 minutes once the airbox was off.