# Blowing Fuse



## Deleted member 39993 (Feb 15, 2020)

Hi..we have a Burstner Nexxo and having problems with the 15amp fuse blowing which is on a 12v permanent live feed, the circuit feeds the fridge, awning light and the interior entrance light, the fuse can be fitted and works fine for all the above but it seems after driving for a few minutes the fuse pops, (it can then be replaced and if the van dosen't move all ok) have wiggled wires here, there and everywhere thinking maybe a loose connection somewhere but nothing? The 15 amp fuse is in reserve 4 slot rated at 25amp...anyone with electrical knowledge help please..


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## jagmanx (Feb 15, 2020)

So when you say moving is the fridge then being powered by 12V ?


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## Deleted member 39993 (Feb 15, 2020)

Yes the fridge only runs on 12v when engine running, if fridge on battery without engine running alarm from fridge goes off..


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## Fisherman (Feb 15, 2020)

What appears to have happened is the socket on your fuse box has loosened.
But I see from your photograph that you have spare sockets. So a simple solution would be to transfer to another socket and use this. It would be advisable to remove all power from the fuse box before gaining entry to the inside of the fuse box. It’s a simple case of removing a single positive connection from the faulty socket and connecting to a spare.


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## r4dent (Feb 15, 2020)

As jagmanx implied the fridge could well draw only a few amps when fridge on gas or EHU but over 15a when fridge is in 12v.
This fits your description of the problem.

Has the problem as always happened (or the van is new to you) ?
Simple question if reserve 4  is "rated" 25 amp, why are you using a 15 amp fuse?
Have you modified the wiring in any way?  Please don't just fit a larger fuse unless you understand basic electrics.

If you have a handbook for fridge please check current draw, otherwise try and find handbook on net. (or check the label for detals) 
N.B. if the book/lable quotes power in watts just divide wattage by voltage to get amps (e.g 60watt / 12 volt = 5amp).


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## Deleted member 39993 (Feb 15, 2020)

Had the van from new and have had the problem for a few months, when we had the problem last year it took a while to identify the faulty fuse as we were on a site in Yorkshire, problem is I can't remember what fuse was in place and whether it was replaced with a 15amp because that was all we had (stupid I Know) ideally someone with a Burstner Nexxo with the same fuse box could check what fuse they have...anyone?? please.


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## Fisherman (Feb 15, 2020)

Apologies I miss understood your post.

My thetford fridge draws 10amps when mobile.
I would have thought 15 amp would be ok.
The fridge only draws full current when travelling, hence your problem.
When the fuse blows is it broken, or has it vaporised.?
If broken possibly a 20a fuse may prevent this.
But be careful if fitting a larger fuse.
If vaporised it would suggest a serious short circuit.
The short circuit could be due to a fault in your fridge,
Creating a short circuit. Hope this helps,


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## maingate (Feb 15, 2020)

The 12 volt fridge element could be suspect, causing a spike in voltage. Try checking the connections, you should get access by removing the lower grill.

Alternatively, if you have a manual selector knob on your fridge, set it to gas when you are travelling and see if the fuse still blows.

Somewhere at home I have the full schematic wiring diagram, I will see if I can find it to check what 'reserve 4 ' is for.


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## Deleted member 39993 (Feb 15, 2020)

Thanks for all replys, much appreciated....the fuse when blown has a black mark around the break wouldn't say it was 'vaporised'...I think it needs a bigger fuse but a bit wary as don't want to fry the wiring...just need some one with Burstner Nexxo with same Elektroblock (EBL99) and see what fuse is in reserve 4 to put my mind at rest...cheers all


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## Fisherman (Feb 15, 2020)

Warwickwelsh said:


> Thanks for all replys, much appreciated....the fuse when blown has a black mark around the break wouldn't say it was 'vaporised'...I think it needs a bigger fuse but a bit wary as don't want to fry the wiring...just need some one with Burstner Nexxo with same Elektroblock (EBL99) and see what fuse is in reserve 4 to put my mind at rest...cheers all



That’s your fuse box, 



			http://ourbumble.com/wp-content/uploads/2016/01/Electrobloc-EBL99K.pdf
		


what model of fridge do you have


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## Deleted member 39993 (Feb 15, 2020)

yes thats the fuse box, the fridge is a Dometic..


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## 2cv (Feb 15, 2020)

Warwickwelsh said:


> yes thats the fuse box, the fridge is a Dometic..



Reserve 4 certainly looks to be 25 amp, so maybe that’s the problem.


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## Fisherman (Feb 15, 2020)

From what you have described a 15a fuse blowing but not being vaporised would suggest an overload on the fuse. In my experience a dead short always induces such a large current as to vaporise a 12v fuse. So I would try a 25a fuse and see how you get on. If there is a dead short in either the circuit or in the fridge a 25a fuse will blow anyhow before any damage is done. After driving for say 15-30 minutes see if the fuse is still holding, and check the fridge that the fridge is ok. No smell of burning.* I have checked and reserve 4 is 25amp.*


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## Deleted member 39993 (Feb 15, 2020)

Should be off down Devon/Cornwall tomorrow, (all depending on the weather in the morning) so will try a larger fuse at some point..


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## Fisherman (Feb 15, 2020)

Warwickwelsh said:


> Should be off down Devon/Cornwall tomorrow, (all depending on the weather in the morning) so will try a larger fuse at some point..



Another point.
The fact that the fuse does not blow on EHU or gas suggests an overloaded fuse.
I would replace the fuse now, then turn on your engine for 15 minutes or so and see what happens.


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## r4dent (Feb 15, 2020)

maingate said:


> Alternatively, if you have a manual selector knob on your fridge, set it to gas when you are travelling and see if the fuse still blows.


   I think I would set the selector to "off".  I know some people travel using gas, but it makes me very nervous.

I still think the issue that the "reserve 4" is rated 25 amp but the OP uses 15amp fuse. 
Best thing is to check the fridge specification, but although we know what make it is we still await the model number or  specifications.
Just putting a 25amp fuse in is a potentially risky solution.


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## maingate (Feb 15, 2020)

The '25 amp rating' is the maximum permissible size, not necessarily the correct size. If the fault is related to a failing 12 volt Element in the fridge then installing a bigger fuse could be dangerous.

How many members on here have swapped their lights over from Halogen to LED and not fitted a smaller fuse in the circuit? The fuses are sized by the manufacturer for a reason.


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## Fisherman (Feb 15, 2020)

r4dent said:


> I think I would set the selector to "off".  I know some people travel using gas, but it makes me very nervous.
> 
> I still think the issue that the "reserve 4" is rated 25 amp but the OP uses 15amp fuse.
> Best thing is to check the fridge specification, but although we know what make it is we still await the model number or  specifications.
> Just putting a 25amp fuse in is a potentially risky solution.



I agree about the Gas.
I have checked and from what I can see domestic fridges normally run on 15a.
but the model would help


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## Fisherman (Feb 15, 2020)

Got this from the manual for the fuse box

The refrigerator does not work during mobile operation
Defective alternator No voltage on D+ input Defective electrobloc
No power supply to the refrigerator
Defective electrobloc Defective refrigerator
Check the alternator Check the fuse and wiring
Contact the customer service department
Check the fuse (20A of the supply; possibly 2A of the D+ signal) and wiring
Contact the customer service department
Check the refrigerator


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## Tezza33 (Feb 15, 2020)

r4dent said:


> I still think the issue that the "reserve 4" is rated 25 amp but the OP uses 15amp fuse.


I would think the 25A rating is because the cable thickness on reserve 4 is capable up to that amount so that is the maximum for that circuit not the minimum, I have the same elektrobloc (Hymer though) and reserve 4 isn't used for anything.
I would let my van idle with the fridge on 12v for a while and see if it still blows, if it doesn't but then blows while driving I would suspect a loose or corroded connection causing a spike


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## QFour (Feb 15, 2020)

I would have thought the sensible thing to do was fit a 20A fuse first and see what happens. 25A fuse is a bit big for thin wiring.


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## r4dent (Feb 15, 2020)

maingate said:


> The '25 amp rating' is the maximum permissible size, not necessarily the correct size. If the fault is related to a failing 12 volt Element in the fridge then installing a bigger fuse could be dangerous.



Which is why  say we need to know the Fridge specification.

It the fridge does draw 15a as Fisherman suggests and Reserve 4 circuit contains wiring cable suitably sized for 25 amp (the implication from that being the recommend size ) then he symproms are explained and the solution is a 25a fuse.  But for the umteenth time we did to know what the fridge spec is.


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## r4dent (Feb 15, 2020)

QFour said:


> I would have thought the sensible thing to do was fit a 20A fuse first and see what happens. 25A fuse is a bit big for thin wiring.


The reserve 4 is specified 25 amp and the wiring protected by this should be a suitable gauge.  The OP can't tell us the power usage of the fridge, I don't fancy asking him about wire gauges and run lengths.


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## Fisherman (Feb 15, 2020)

I know that uprating the fuse can be dodgy.
But I have been around 12v alarm installations for over 30 years.
In my experience if a fuse breaks its due to simple overload.
If it’s more serious the fuse is vaporised.
I think under careful supervision a larger 20 or 25a fuse should be fitted.
Such a fuse would still be the weakest point within the circuit, and would blow before any damage was done. But supervision is important.


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## Deleted member 39993 (Feb 15, 2020)

Info from inside of fridge..


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## Deleted member 39993 (Feb 15, 2020)

on earlier post it was stated that 170W divided by 12v = 14.16

does anyone agree with this...15amp fuse not big enough ??


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## Fisherman (Feb 15, 2020)

Warwickwelsh said:


> on earlier post it was stated that 170W divided by 12v = 14.16
> 
> does anyone agree with this...15amp fuse not big enough ??



you need at least a 20a fuse, but I suspect a 25a.
your calculation is correct.


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## Deleted member 39993 (Feb 15, 2020)

Fisherman said:


> you need at least a 20a fuse, but I suspect a 25a.
> your calculation is correct.



Thanks for your input today, I think I may have learned something...everyday a school day...thanks again.


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## Deleted member 5816 (Feb 15, 2020)

Surly it’s a simple matter try the 20A fuse,  if you have a short on the wiring  it could cause damage.
Many car fuses are of inferior quality a poor fuse blade and socket can cause overheating at 14+ amps plus the poor connection would suggest a 15A fuse would take a short time to blow.
Try a 20;A if OK and you feel confident swap the cable to one of the spare fuse holders.
Please take care in buying replacement fuses.

Alf


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## Fisherman (Feb 15, 2020)

Warwickwelsh said:


> Thanks for your input today, I think I may have learned something...everyday a school day...thanks again.



That’s why the fuse was broken rather than vaporised, try a 20a first, but that may be a bit light. Contact the manufacturer or supplier for advice.


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## Fisherman (Feb 15, 2020)

Found the manual for your fridge.
you should have a 20a fuse see page 34



			https://magnummotorhomes.co.uk/wp-content/uploads/2018/08/RML9335-Install-Instructions.pdf


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## Fazerloz (Feb 15, 2020)

As Alf says do not buy cheap fuses they are thinner in the blade and make poor contact in the holders causing overheating.


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## jagmanx (Feb 16, 2020)

Useful info all round including the recommendation to get "Good quality fuses"
Reminder to self to check my Fridge details and relevant/all fuses.
I have a Calira Power Unit but the manual has the details.

Where can you get quality fuses ? Halfords ? (obviously not Poundland or the like !)


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## Fisherman (Feb 16, 2020)

jagmanx said:


> Useful info all round including the recommendation to get "Good quality fuses"
> Reminder to self to check my Fridge details and relevant/all fuses.
> I have a Calira Power Unit but the manual has the details.
> 
> Where can you get quality fuses ? Halfords ? (obviously not Poundland or the like !)



Halfords sell only fuses that meet EN and BS standards.


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## trevskoda (Feb 16, 2020)

Poor man will be conFUSED.  a 20 fuse seems right buy the maths to me though a slightly higher 25 will cover better and should be good to go.


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## Bardotbongo16 (Feb 16, 2020)

Hi everyone
Does anyone have knowledge of Mazda Bongo campers, the heating & air conditioning not working, it's digital not Manuel. 
It's freezing cold so no trips until get resolved, longing to be out in Bongo.. 
Cheers  
BardotBongo


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## Wooie1958 (Feb 16, 2020)

Bardotbongo16 said:


> Hi everyone
> Does anyone have knowledge of Mazda Bongo campers, the heating & air conditioning not working, it's digital not Manuel.
> It's freezing cold so no trips until get resolved, longing to be out in Bongo..
> Cheers
> BardotBongo



Hi and welcome, start a new thread and you`ll get a better response.


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## Fisherman (Feb 16, 2020)

trevskoda said:


> Poor man will be conFUSED.  a 20 fuse seems right buy the maths to me though a slightly higher 25 will cover better and should be good to go.



Yes Trev a 25a fuse should be fine. Manufacturers recommend a 20a. Better stick to that for insurance reasons.


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## shortcircuit (Feb 16, 2020)

A word of caution.  The fuse is there to protect the wiring and not the appliance.  Keep on increasing the amperage and you could have serious consequences as alluded to in previous posts. Far better to find out why it is blowing.


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## Fisherman (Feb 16, 2020)

shortcircuit said:


> A word of caution.  The fuse is there to protect the wiring and not the appliance.  Keep on increasing the amperage and you could have serious consequences as alluded to in previous posts. Far better to find out why it is blowing.



It was blowing because a 15a fuse was used in error.
A 20a fuse is recommended by domestic.
the fridge draws 170w at 12v.


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## runnach (Feb 16, 2020)

I was always taught the simple rule was watts / volts = amps ......so eg 60w/12v =5 amps so you then select the fuse next size up so in my example 7.5 amps .

In practice people seem to fit what’s at hand with no thought given to good practise 13 amps typically fitted to any domestic appliance I have seen that often 

In this case and with my understanding a 20. Amp would be the correct fuse,


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## shortcircuit (Feb 16, 2020)

That’s good, the “why” was determined.


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## harrow (Feb 16, 2020)

But a quality 15 amp blade fuse is designed to allow 15 amps continuously and will fail at a load of 20 to 30 amps.


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## winks (Feb 16, 2020)

harrow said:


> But a quality 15 amp blade fuse is designed to allow 15 amps continuously and will fail at a load of 20 to 30 amps.



It's all coming back now from electrical principals in 1969 City and Guilds. Coarse protection vs. Close protection. Thought I'd put all that behind me. Another vote for 20A though and keep a close eye on the fridge wiring.

Cheers

H


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## Fazerloz (Feb 16, 2020)

Do not forget though that fuse is carrying other loads as well, not just the fridge.


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## Fisherman (Feb 16, 2020)

Fazerloz said:


> Do not forget though that fuse is carrying other loads as well, not just the fridge.



I wondered about that to, but when you think about it the Awning light, and interior door lights will be leds and using little current. Also the fridge only draws 170a when moving, and these lights would be off then.


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## shortcircuit (Feb 16, 2020)

Fazerloz said:


> Do not forget though that fuse is carrying other loads as well, not just the fridge.


The fuse is there to protect the cable and not to cover the total current of the various appliance attached, which logically would be under its rating


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## Fazerloz (Feb 16, 2020)

Fisherman said:


> I wondered about that to, but when you think about it the Awning light, and interior door lights will be leds and using little current. Also the fridge only draws 170a when moving, and these lights would be off then.



True but the lights are a unknown figure and what if he were to run his engine when parked up to charge batteries wouldn't the fridge automatically go onto 12v. I also thought fuse ratings should be 20% above actual load for continuous use. I could well be wrong but that's how i've always worked it.


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## Fisherman (Feb 16, 2020)

shortcircuit said:


> The fuse is there to protect the cable and not to cover the total current of the various appliance attached, which logically would be under its rating



Which is why I reckon a 25a fuse would be ok if required.

Lets not forget that the fridge has its own internal fuses a 20a fuse for the fridge, and a 2a fuse for the fridge lighting.


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## shortcircuit (Feb 16, 2020)

Fisherman said:


> Which is why I reckon a 25a fuse would be ok if required.
> 
> Lets not forget that the fridge has its own internal fuses a 20a fuse for the fridge, and a 2a fuse for the fridge lighting.



 And the size of the cable is capable of taking a load of 25A??????????????


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## Fisherman (Feb 16, 2020)

shortcircuit said:


> And the size of the cable is capable of taking a load of 25A??????????????



yes it’s connected to a 25a slot.


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## maingate (Feb 16, 2020)

Fisherman said:


> yes it’s connected to a 25a slot.



The EBL leaves the factory marked up with fuse recommendations. The motorhome manufacturer does what it likes with the wiring fitted to the EBL. Manufacturers are noted for undersizing wiring on motorhomes .... that is why it is best to disregard electrical norms when talking about motorhomes (unless you have a selfbuild).


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## Markd (Feb 17, 2020)

I'm afraid we may all be barking up the wrong tree.
The OP tells us that the circuit is permanently live - so it won't be supplying the fridge element.
From the description it is probably the supply for fridge light.
None of the loads should get anywhere near 15A.
The OP tells us that a larger fuse blew first and originally only 15A available.
It may be worth trying a higher fuse but I suspect that the issue will continue.


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## Nabsim (Feb 17, 2020)

@Markd the OP may have meant that it isn’t turned off when you turn 12voff at the control panel. I believe the wording is similar for my EBL but may say permanently available. It is a circuit to provide fridge 12v, one internal light, electric step and I think maybe something else on mine.
With my setup you turn 12v off at control panel when you are going to move then turn it back on when you arrive. Never looked closely at circuit diagrams to see why but it may be to disable some battery equalisation circuit or switch mains availability on.
Needs the OP to say though


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## r4dent (Feb 17, 2020)

[QUOTE="Fisherman, post: 1050321, member: 62221 "... the fridge only draws 170a when moving..."[/QUOTE]

I think this is a typo !


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## in h (Feb 17, 2020)

harrow said:


> But a quality 15 amp blade fuse is designed to allow 15 amps continuously and will fail at a load of 20 to 30 amps.


Not really. You should rate the fuse 30% above the normal current. Fuses are to protect cables from overheating. If the cable doesn't have a 30% overhead, fit a thicker cable.


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