melted 10 amp fuse

[mrlee]

hello i’m very new to owning a caravan.
i picked up fendt platin malpet which my son and his girlfriend are using on our driveway whilst they save up for a house.
whilst going over it finding out how it works i noticed on the main fuse box in the wardrobe that the 10amp fuse had melted but. not blown, so replaced it and again this evening checked to see that it had melted again.
the wires seem cool to touch and are. not melting i think the 12v system may of been moved to the bedroom area under the bed.
any idea what could be causing the fuse to melt because i’m not to keen on letting them sleep in it if there is a chance of it setting on fire.
below is an image of the fuse box.
tomorrow i’m going to go over all the 12v setup, under the bed is an old car battery which we are going to replace for a leisure battery a 12v charger which i’m replacing tomorrow for a more modern trickle charger and the unit that moves the wheels via a remote..
any advice would be appreciated.
Lee.

 

[Woodentop]

They are not fuses but rather miniature circuit breakers (MCBs) which are effectively resettable fuses. However such devices are normally found in the mains supply circuits and conventional fuses (i.e. car-type fuses) are used in the 12V circuits.

Given you are having an overheating problem and mains kills, I would suggest you get someone who knows what they are doing with mains - better still but not mandatory with caravan mains - to check it over.

 

[ProfJohnL]

I am concerned when you say there is a 12V battery under the bed. Lead acid Batteries should be in a room sealed box such that any escape of gas is only vented out side and not into the living space of the caravan. The 12V wiring should be protected by a correctly rated fuse (typically 15 to 20Amp)

As Woodentop has stated the devices in your picture are Miniature Circuit Breakers (MCB's) and are rated for use on 230V ac circuits. They may not function correctly on 12Vdc circuits.

You are correct to be concerned about th e problem your having, as whilst 12Vdc does not heave enough potential to give anyone an electric shock, but the current available form a battery is more than enough to to cause a fire.

My advise would be not use the caravan until the 12V wiring has been fully sorted out and at least checked by a professional caravan engineer.

 

[mrlee]

Thanks for the reply’s .
today we are changing the battery for a correct leisure battery..
in the image above yes there are 3 mcb which are fine, but if you zoom in and look under where the grill part is you will see 2 slots, one is empty and a type of blank area, the other in the right is where a 10 amp blade fuse is, and that’s the one for some reason that keeps melting but not blowing.

 

[ProfJohnL]

Do you mean the coloured plastic moulding around the the metal blade fuse link is melting?

If that is the what happening, then clearly the something is getting too hot, and its most likely a poor connection of the wires to the fuse holder, or the fuses contacts with the fuse holder.

 

[mrlee]

yes it’s the red plastic around the blade fuse that is melting, the metal part of the fuse stays intact and doesn’t pop,
later today i’m going to trace the wires from the fuse box in the wardrobe back to the battery and see what is actually running of the 12v , i think it’s just the taps and the internal water pump and some lights around the roof vents.
i shall look out for some loose connections as the actual box that the blade fuse go into is a tight fit and doesn’t look damaged from heat or anything.

 

[mrlee]

just for the record the battery is in a grey plastic box with a lid and a vent tube running outside.

 

[Beardy]

yes it’s the red plastic around the blade fuse that is melting, the metal part of the fuse stays intact and doesn’t pop,

I agree with ProfJohn on this one. First thing to do is clean the contacts on the fuse holder. Try folding a small piece of emery cloth and work it in and out of the fuse holder where the fuse legs go in. Next check the connections on the back of the fuse holder. It's likely to be a couple of spade connectors and if one or both of them is a poor connection you'll know straight away as it will be discoloured.

It's possible that you are close to the limit of the fuse carrying capacity. If you don't have a meter to check this try replacing the 10 Amp fuse with a 7.5 Amp fuse. If it blows you're on the limit and the fuse itself is getting hot. If it doesn't blow but the plastic still melts you have a bad connection.

 

[Woodentop]

Most caravans these days have a fuse in line with the battery to protect the battery if the charger throws a wobbler. The in-line fuse is usually around 20A - it is only there to protect the cables - so if the 7.5A fuse lights up like a firework as it expires, temporarily try a 20A fuse in it and see what happens.

 

[mrlee]

ok thanks for the advice,
i been out there this afternoon, been tidying up the connections at the battery end as some of them going into the emove was not good so crimped some proper connectors to it, and tightened down all the terminal connections,

tested having the lights on for an hour or two because i think the bedroom spot lights run on 12v and the fuse was fine,
i’m thinking maybe if there is a bad connection that it could be either the taps or the internal pump, but they are only used for a minute at a time if that, i don’t think they are running long enough to generate enough power to melt the plastic,
i have swapped out the 10 amp for a better quality fuse, as the ones in my garage where poor quality.

they are going to stay in it tonight and use it as normal but keep an eye on the fuse to see if they can notice at what point it looks like it’s melting., i got them fire extinguisher and a fire blanket just in case.
also i have just noticed that the toilet has stopped pumping water out but the pump makes a noise, this was also a test i was doing to check for the fuse getting hot, but holding the flush for over a minute again the fuse was fine, but just watching youtube i think the toilet has its own fuse in the cassette area. this i need to check tomorrow,i just need to figure out why no water is now coming from the toilet.
i may take a photo of the tap in the toilet area for you to check out the wiring and see what you think .
Thanks for your time.

 

[ProfJohnL]

I personally don't think it's a case of the current being drawn exceeding the fuses rated value, becasue the actual fuse wire has remained intact. It's perfectly possible for a modest current that is well within the rating of the fuse to generate heat if it encounters a (relatively speaking) high resistance.

Such as corrosion on a contact or loose or damaged wire. localised heating will occur, so for it to affect the fuse carrier the fault ahs to be close to th e fuse carrier, and a high probability it will be the fuse receptacle connection as they will be close enough to transfer the heat to the fuse and melt the carrier.

One of the risks is the localised heating may have annealed the contacts and they may no longer grip th e fuse blade properly. Th e fuse receptacle should be treated as suspect and probably need changing.

 

[mrlee]

a little update,
so just now after earlier putting in the better quality 10 amp fuse , my daughter in law used the tap in the toilet , (they use the toilet tap for now as the tap on the sink i’m waiting for a new cartridge to arrive as it leaks) she went to fill the kettle and used the tap on the hot side and it blew the fuse rather than melting.
so i went out there looked at the wiring under the sink all seem ok except for the 2 thin wires coming off the tap where just twisted together, so i have crimped them together, whether this makes a difference i do not know, but they look safer now atleast.
tested the tap but only on the cold side for now because it’s dark and will test hot side tomorrow.
would this suggest a problem with this taps wiring or something to do with trying to pull water from the hot side.
i haven’t really got round to figuring out the hot water side of things yet, don’t even know how to get hot water yet.

 

[ProfJohnL]

This is getting more complicated rather than simple. we are at a major disadvantage as we cannot see the situation first hand, and test items in situ.

Thin wires from taps are usually micro switiches in the taps which can be used to control the water pump, but that fact tn pump seems to work without them suggests your caravan may have a pressure switch system.

Its time to call in a professional.

 

[mrlee]

the tap or pump did not work when the thin wires from the tap were disconnected as i tested it to see what happens when they are not connected.

i think today i will put my attention to the water heater, which i think is the white mini tank thing under the sofa next to the water storage and submersible pump.
getting a pro in would be nice but i think it would be quicker for me to go to college and learn electrical.
everything seems to be ok, they are using the caravan as normal,got it on saturday, and it’s not set on fire. none of the wires are getting hot, the wiring that i can see seems to be ok,
i think i’ve narrowed it down to having the tap running hot water seems to make the fuse pop.

 

[Buckman]

This is getting more complicated rather than simple. we are at a major disadvantage as we cannot see the situation first hand, and test items in situ.

Thin wires from taps are usually micro switiches in the taps which can be used to control the water pump, but that fact tn pump seems to work without them suggests your caravan may have a pressure switch system.

Its time to call in a professional.

Perhaps they have a reason for not wanting to call in a professional? This is very much a safety issue and does need a professional.

 

[mrlee]

no reason for not calling a pro, if anyone can recommend a pro in the cambridgeshire area that would save me having to faff around each day.
or would i just contact a electrician from local paper do they deal with caravans?
i have never owned a caravan before, only campervan that were simple to wire up.

 

[otherclive]

no reason for not calling a pro, if anyone can recommend a pro in the cambridgeshire area that would save me having to faff around each day.
or would i just contact a electrician from local paper do they deal with caravans?
i have never owned a caravan before, only campervan that were simple to wire up.

If you search Approved Workshop Scheme you will find the locations of AWS technicians who will do mobile work. These techs are widely used by Forum members even for keeping caravans in warranty.

 

[Buckman]

See https://www.approvedworkshops.co.uk/find-approved-workshop

 

[mrlee]

Thanks for the info i appreciate it.