Light Shorting out

gazzeroo

gazzeroo

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Sep 14, 2014
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Norwich
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33,337
MH
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I`m a newbie
Has anyone had this problem or know of a solution? My bathroom light blew the 10amp fuse recently, when I turned it on. I thought it might be the light itself so I got a new one and installed it, but it was only on a few seconds and blew the fuse again. I have taken it out again, taped up the exposed wires and all the other lights work ok. Could it be that one of the wires has chaffed somewhere and exposed the inner core thus shorting out? I cannot easily get to the wiring as it is behind the bathroom panel. Any suggestions would be most welcome
kind regards
gary
 
Hopefully no mice lol.Check for water under the bath 10 amp fuse seems a bit big for a light ,not that that would would be the problem .don't forget to turn off at the mains if your messing with the wires under the bath.lol.
 
You state you have taped the exposed wires and all the other lights work OK?
If you leave the bathroom light on, even with the missing light will the fuse blow after a few seconds? .... If I'd does then the problem is in the wiring leading to the light, if it does not blow then the problem is obviously in the light unit. Put a H7 bulb in situ, if it lights and works ok then your light fitting is obviously the issue.
 
May also be worth checking wiring behind the switch that terminals and wiring secure.
The lighting in the bathroom should be 12v only in MH.
With switch in off position, use a test meter to check between resistance between the +ve and -ve of the feed to the light fitting. It should be open circuit, if there is a low resistance reading, then there is a short on the feed.

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Thanks for all that, just to explain further! The light is fixed to the bulit in corner shower unit. The light has an integral switch so I have removed the whole unit. There is now just a red and white wire coming thru the hole in the plastic. These are now taped up and secured to the cubicle and all the other lights work ok. I replaced the light with a brand new one and it still blew the fuse. I am sure it must be the wiring but am confused as to what would make it faulty. It is all 12v on the lighting, I have replaced the fuse like for like and the information on the cover of the fuse box says 10amp so I am certain that is correct. We were parked up when the fuse blew, all I did was turn it on, previous to that it worked fine. The new light is a 12v led, but I wouldn`t have thought that would be a problem. Again any advise much appreciated
gary
 
Gary, is the switch part of the new light fitting?
What we're trying to establish/rule out is where the "short" is.
We will assume for now the switch is separate from the light fitting, remove the light fitting, tape up the wires, SWITCH THE SWITCH ON..... See if the fuse blows now ?.... Are the other lights working?
If the fuse still blows then a problem exists somewhere else but NOT the light fitting.
If the fuse remains intact the problem IS in the light fitting.

Your problem is that the circuit is demanding more than the fuse can deliver, actually a draw of over 120 watts (12volts x 10amps) which is considerable, the only scenario this really can happen is there is a short in the circuit somewhere, either in the light fitting or the switch/cable run.

Have you hooked the new LED up with correct polarity? LED's are polarity dependant i.e... + & - need to be connected to the correct terminals.

Hope this helps.
 
Gary, when you say 'a new light' , do you mean a new bulb or a new complete fitting? If you've replaced the old fitting with a new one are you sure that perhaps the mounting screws or part of the fixings aren't touching something in the wall that could be shorting out the +ve to the chassis or something else? If you're just replacing the bulb in the old fitting then the fault is obviously in the fitting if all works OK with the wires taped up. (incidentally, 'bulbs grow, lamps glow) - it helps to get terminology correct!)
 
Just in order to clarify things in my mind, the light fitting you have completely removed contains an integral switch. Therefore the 2x wires you have taped up are the 12v +ve & -ve. If the fuse does not blow now, the fault is within the light fitting, as I would presume the fuse protects the whole of the habitation 12v lights.
If the above is all correct as I understand it to be then using a test meter set for continuity if it has that feature with audible buzzer. If not set it to Ohms, Omega sign on the tester. Remove the lamp from the fitting.
With the unit in the off position, put probes of test meter into the +ve -ve connectors of the fitting. If using continuity feature with buzzer it should remain silent. Switch the fitting on, the tester should remain silent if it sounds, there is a short circuit in the fitting. If the test meter is set to Ohms, then the reading should be infinity as there should be nothing there to make a circuit. If there is a reading, then something is shorted so you then need to open up the fitting and check all wires for chaffing against each other or metal frame.
Hopefully you should be able to identify the problem. (y) Are you able to take a picture of the fitting at upload it so as to give an idea what circuitry is involved? May then be able to assist further. Lance.
 
Wickolad said:
Just in order to clarify things in my mind, the light fitting you have completely removed contains an integral switch. Therefore the 2x wires you have taped up are the 12v +ve & -ve. If the fuse does not blow now, the fault is within the light fitting, as I would presume the fuse protects the whole of the habitation 12v lights.
If the above is all correct as I understand it to be then using a test meter set for continuity if it has that feature with audible buzzer. If not set it to Ohms, Omega sign on the tester. Remove the lamp from the fitting.
With the unit in the off position, put probes of test meter into the +ve -ve connectors of the fitting. If using continuity feature with buzzer it should remain silent. Switch the fitting on, the tester should remain silent if it sounds, there is a short circuit in the fitting. If the test meter is set to Ohms, then the reading should be infinity as there should be nothing there to make a circuit. If there is a reading, then something is shorted so you then need to open up the fitting and check all wires for chaffing against each other or metal frame.
Hopefully you should be able to identify the problem. (y) Are you able to take a picture of the fitting at upload it so as to give an idea what circuitry is involved? May then be able to assist further. Lance.
Click to expand...
Excellent,
We "dilbert" minds think alike !

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Forgive me for jumping in here but if the switch only has 2 wires going through it, it is either switching pos + or neg - and the light fitting is connecting the opposite.
 
bertiebasset said:
Forgive me for jumping in here but if the switch only has 2 wires going through it, it is either switching pos + or neg - and the light fitting is connecting the opposite.
Click to expand...
Correct,
So it the fuse blows when no light fitting is in situ then the problem lies elsewhere other than the fitting... of course that's assuming the +ve is switched. The -ve should be irreverent unless the +&- are shorting before the switch/light fitting.
 
Jonkil,, I agree,, one way to try, as the OP seems to have stated the fuse remains ok and the rest of the lights work ok it the lamp is removed,, would disconnect the lampholder and see if there is a short across the contacts. if so then there is the problem, if not then the fault lies after the lampholder. IMHO
 
Thank you very very much for all your replies, you really are a very helpfull lot. I will try all of the suggestions at the weekend and will let you know how I get on. Just to reiterate, the old and new lamp both have integral switches, both blow the fuse when connected, but all the others lights are ok when the bathroom light it not connected. The only thing I am not sure about is if I got the polarity right when I connected the new led light, would this blow the fuse if I got it wrong?

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gazzeroo said:
The only thing I am not sure about is if I got the polarity right when I connected the new led light, would this blow the fuse if I got it wrong?
Click to expand...

The new light is LED you state. If the new light has a circuit internally then there may be a protection diode to prevent reverse polarity and if so then yes it is designed to protect the circuit and may well blow the fuse
 
I thought with most Led's that if connected the wrong way around they just did not work ?
 
Thanks Jonkil, I think I`ll check that first.
 
Jonkil said:
The new light is LED you state. If the new light has a circuit internally then there may be a protection diode to prevent reverse polarity and if so then yes it is designed to protect the circuit and may well blow the fuse
Click to expand...
A protection diode to prevent reverse polarity will normally stop any current flow if connected wrong way so not likely to blow fuse.
 
Borderland said:
A protection diode to prevent reverse polarity will normally stop any current flow if connected wrong way so not likely to blow fuse.
Click to expand...
When a protection diode blows it will cause a short across the input +ve and -ve terminals.

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As a diode will only allow current to flow one way I thought the idea of a protection diode was so that the current couldn't flow the wrong way. If the protection diode blows and goes short circuit does that suggest the protection diode was the wrong spec.
 
watching with interest as my lack of technical skill often embarrasses me, still keen to learn though

looking at the basics of the OP, is it not extremely unlikely that 2 light fittings could both be faulty, there must be something wrong in wiring

quite what, how you find etc would be my next nightmare, all my problems seem to be behind something impossible to move

for my own sanity I think I would attach wires to the light inputs and hold onto my leisure battery terminals, just to prove the light works, that would presumably confirm a wiring issues as well

very best of luck from an enthusiastic amateur (y)
 
Your problem is that the circuit is demanding more than the fuse can deliver, actually a draw of over 120 watts (12volts x 10amps) which is considerable, the only scenario this really can happen is there is a short in the circuit somewhere, either in the light fitting or the switch/cable run.

Hope this helps.[/QUOTE]


As mentioned by Jonkil the fuse is delivering more than it is capable of.
What other circuits are connected to this fuse, have you changed anything recently that could be adding to the loading. Are you able to measure the current through the fuse without the light fitting connected.
It could simply be that the fuse is already delivering close to 10 amps in other circuits and switching on the light is just enough to take it over its limit and causing it to blow.
 
The more I think about this problem the more convinced I am that it has nothing to do with your bathroom light or wiring. As stated above I think the bathroom light is just enough to take the fuse over its limit.
Out of interest, you say you changed the fuse like for like, was it a standard quick blow fuse or slow blow, or time lag fuse. I am not sure what type should be fitted in your situation but some devices when first switched on will take a higher initial current and a time lag or slow blow fuse would help in that case but I would always be sure to check that it is the correct type specified.
 
Hi all, just to update all those who have been kind enough to offer me advice. I have replaced the light with the LED light and all seems to be well. I checked the polarity with a meter and it seems that I did put the new one on correctly, so I am bemused as to why it blew the fuse, the wiring came up with a reading of 12.9v so that seems ok. I will just have to wait and see if it happens again. Once again thanks for all the advice
Gary

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Pleased to hear it is sorted. It might still be worth checking the total load through the fuse as it may be that you are on the limit. If that is the case then you may get the problem again.
 
Daifuse said:
incidentally, 'bulbs grow, lamps glow
Click to expand...
Correct on both counts....the correct name is lamp, not bulb.....but the correct name for a car is an automobile.
when did you last hear someone say "im just nipping to the shop in the automobile" ?

Even some manufactures label their packaging 'LIGHT BULB'

on-aldi-mini-compact-fluorescent-light-bulbs-box-package1.jpg
 

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