Blown 40A fuse

[Bonsaiman]

Hi electrical wizards
Any ideas what would cause my 40amp fuse adjacent to my hab battery to blow
TIA

 

[pappajohn]

Doubtful you overloaded it at 40amps so maybe a dead short to earth.
Have you replaced it yet, if so what's the outcome.

 

[Bernie P]

First guess would be a short to earth somewhere

 

[Bonsaiman]

Doubtful you overloaded it at 40amps so maybe a dead short to earth.
Have you replaced it yet, if so what's the outcome.

First guess would be a short to earth somewhere

Thanks for the replies
Have all the smaller fuses for appliances etc but not a 40A so will get some and see what happens

 

[pappajohn]

If a new one pops straight away you have a dead short.
If it blows after a while or when you start driving it could be an intermittent short circuit caused by vibration....live wire chaffing on earthed metal.

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[Bonsaiman]

So changed the fuse and didn't pop straight away and have been for a two hour drive on various condition roads (some smooth, some bumpy) and not blown, so non the wiser

 

[Stealaway]

Is there any sign that the old fuse connection were getting hot?
At 40amp you would want a very tight fit

 

[jockaneezer]

I had the red 50 amp mega fuse blow on my van 3 years into owning it (we woke up freezing) I did a cursory check, but found nothing and it's been ok for the last ten years.

 

[donkey]

Study the old fuse. Has it blown, sometimes they go open circuit without actually blowing. If so a new fuse should cure the problem.

Geoff

 

[pappajohn]

Study the old fuse. Has it blown, sometimes they go open circuit without actually blowing. If so a new fuse should cure the problem.

Geoff

Exactly.....that's the reason I suggest using a meter rather that type 1 eyeball

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[BillandHelen]

Sorry, for my education, what’s a dead short to earth and what would cause it? Still learning!

 

[pappajohn]

Sorry, for my education, what’s a dead short to earth and what would cause it? Still learning!

A live wire with damaged insulation touching a vehicle earth....chassis, metal bodywork etc.
Live wiring can rub on a sharp metal edge or similar until the live wire is exposed and touches an earth.

 

[Dorwyn]

I think sometimes they can just go duff!

 

[autorouter]

A live wire with damaged insulation touching a vehicle earth....chassis, metal bodywork etc.
Live wiring can rub on a sharp metal edge or similar until the live wire is exposed and touches an earth.

Another possibility is that mice can chew the insulation, so that when there's vibration, while driving for example, the bare wires can touch other wires or the metal chassis, which can cause a short and blow the fuse. Depends where you store the motorhome, town or country, I guess.