Circuit breaker in place of fuse

sighmoon

sighmoon

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This is perhaps a stupid question, but can I use a domestic (i.e. 240V AC) 6A circuit breaker in place of a 6A fuse in a 12V DC circuit?

We keep blowing the fuse for the domestic water pump, trying to empty the tank now and again to keep the water drinkable.
 
sighmoon said:
This is perhaps a stupid question, but can I use a domestic (i.e. 240V AC) 6A circuit breaker in place of a 6A fuse in a 12V DC circuit?

We keep blowing the fuse for the domestic water pump, trying to empty the tank now and again to keep the water drinkable.
Click to expand...

Innit better to find out 'why' it keeps blowing?
 
sighmoon said:
This is perhaps a stupid question, but can I use a domestic (i.e. 240V AC) 6A circuit breaker in place of a 6A fuse in a 12V DC circuit?

We keep blowing the fuse for the domestic water pump, trying to empty the tank now and again to keep the water drinkable.
Click to expand...

Yes you can, but the small freshwater pumps I've fitted come with 10amp fuses, that may be the problem.
 
alant said:
Innit better to find out 'why' it keeps blowing?
Click to expand...

The compartment the pump in gets a little damp from condensation - which may be a factor.

'Keeps blowing' may be an exageration. It blew twice this year. The third time, I couldn't get a 6A fuse, so put a 5A one in. It was fine until we wanted to run it for a few minutes, when (I suspect) the fuse overheated.

Lazy Kipper said:
Yes you can, but the small freshwater pumps I've fitted come with 10amp fuses, that may be the problem.
Click to expand...

The pump says 'fit 6A fuse' on the label.
 
There is no technical reason not to fit a domestic MCB other than physical size and maybe its construction materials for use in damp salty conditions, a smaller 50v DC rated one may be more appropriate, or possibly simply try a 6a slow blow fuse if you are using fast blow one currently.
 
+1 for the slow blow fuse, it is designed to cope with starting surges and so forth on a circuit which is nominally 6A. Trouble is, your average shop assistant won't know which type they are selling...

Rob.
 
AC circuit breakers may not be appropriate

as

AC removes and then deposits contact material

DC circuit breakers may be more robust
 
ianabc said:
AC circuit breakers may not be appropriate

as

AC removes and then deposits contact material

DC circuit breakers may be more robust
Click to expand...

Very good point. Switch contacts generally have a very much lower current rating for DC than they do for AC.

OTOH switches would be expected to operate hundreds of thousands of times in their life. A circuit breaker used only as an over-current protection device very few times.
 
pvb said:
The purpose of the fuse is to protect the wiring.
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Maybe, maybe not, there may already be a higher value conductor protection fuse installed upstream and the subject of this discussion a 6a load protecting fuse located closer to the pump. It is not clear from the OP if that is the case or not. The manufacturer is calling for a 6a fuse to protect their product so a slow blow fuse would be my instinct as a first call.
 
nigelmercier said:
No, they are calling for a 6A fuse to protect the wiring in their product.
Click to expand...

Yes, and that is part of the product, I was reffering to the boat's supply cabling which is very clear from my post.
What I was trying to establish is if there is (say) a 2.5mm2 supply cable from a distribution point to reduce volt drop which would be protected by a much higher value fuse and then (possibly, we don't know) a 6a inline fuse close to the product to protect it including its internal cabling and windings. If so then I still believe a slow blow 6a fuse is a better first call than using a fuse higher than the maker specifies.
 
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David2452 said:
Yes, and that is part of the product, I was reffering to the boat's supply cabling which is very clear from my post.
What I was trying to establish is if there is (say) a 2.5mm2 supply cable from a distribution point to reduce volt drop which would be protected by a much higher value fuse and then (possibly, we don't know) a 6a inline fuse close to the product to protect it including its internal cabling and windings. If so then I still believe a slow blow 6a fuse is a better first call than using a fuse higher than the maker specifies.
Click to expand...

As far as I know, there is no other fuse protecting it.

I bought the circuit breaker now. My first concerns were that it may flip on power rather than current (i.e. 6A @240V becomes 120A @12V), but that seems not to be the case. When it dies from damp, It will be superceded by a slow blow 6A fuse - I had no idea there was such a thing prior to this thread.

As ever, thanks for the helpful replies.
 
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sighmoon said:
As far as I know, there is no other fuse protecting it.

I bought the circuit breaker now. My first concerns were that it may flip on power rather than current (i.e. 6A @240V becomes 120A @12V), but that seems not to be the case. When it dies from damp, It will be superceded by a slow blow 6A fuse - I had no idea there was such a thing prior to this thread.
As ever, thanks for the helpful replies.
Click to expand...

Look at what is fitted.
A slow blow (time delay) fuse may be identified by a T in the marking and a quick blow fuse by an F

Normally you'd fit a time delay fuse to a pump or other motor driven device so that it does not blow due to a surge when starting.

If your fuse is blowing when the pump has been running for a while i would think perhaps it is in need of some attention.

For the reasons given already it would be a little unwise to fit a larger fuse than specified.

It would be interesting to actually measure the current the pump draws esp if that can be compared with a specification figure.
 
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FWIW I've had MCBs in my 24v for the last 20 years: no problems as far as I know, and when I installed a large heavy draw sounder the MCB tripped as required, had to get a bigger one. Advantage is you can instantly see which circuit has tripped and its no fiddling about to try it after repair.
 
fisherman said:
FWIW I've had MCBs in my 24v for the last 20 years: no problems as far as I know, and when I installed a large heavy draw sounder the MCB tripped as required, had to get a bigger one. Advantage is you can instantly see which circuit has tripped and its no fiddling about to try it after repair.
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Are yours Dorman Smith Loadmaster MCB's? The reason I ask is that this is what is fitted to my Rival 41C, also 24V. In keeping with this thread I believe that they are rated to quite high voltages and not just 24V. Where do you purchase yours from as I need some additional MCBs and would like to keep the panel looking the same.
 
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