Electrical Diagnosis: Fuse Blows Immediately

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Author Topic:   Electrical Diagnosis: Fuse Blows Immediately

strbrst posted 05-31-2008 03:13 PM ET (US)
When I hook up to the battery in my travel trailer I have power to the water pump and that is it. I checked the fuses and the fuse for the main lights in the trailer was blown so when I went to replace the fuse it would blow every time. I then tried disconnecting the battery and then putting a new fuse in and as soon as I hooked the battery back up the fuse blew. Any suggestions.
seabob4 posted 05-31-2008 03:36 PM ET (US)
A direct short. In other words, a ground wire is touching a hot wire somewhere. Now, to find that short look in areas that possible chafing has taken place, areas where wires pass through openings, something like that. But you definitely have a direct short.
jimh posted 05-31-2008 10:09 PM ET (US)
Do you own a multi-meter?
Chuck Tribolet posted 06-01-2008 09:59 AM ET (US)
Turn off all the lights. Does the fuse still blow? If yes,
you have a long row to hoe, and as seabob suggests, it's likely
chafing somewhere. If no, turn them the lights on one at
a time. If it blows when you turn on a fixture, there's likely
a dead short to ground in that fixture. (or between switch
and fixture if the switch is remote).
Don't even think about using a bigger fuse.
Listen as you plug the fuse in. You might hear some arcing
at the short.
Have a water hose handy. The arcing might start a fire.
Chuck
jimh posted 06-01-2008 01:10 PM ET (US)
You are going to go broke troubleshooting this problem with fuses.
Take a blown fuse and modify it so that there is a small 12-volt incandescent lamp wired across the fuse. Insert the fuse back into place. The lamp will light at full brilliance as long as there is a short in the circuit. When you clear the short the lamp will go out or its illumination will reduce to much less. This is a way to test without blowing $20 in fuses.
Jerry Townsend posted 06-01-2008 01:34 PM ET (US)
Or - disconnect the battery and use a multi-meter between the suspect line and ground with the multi-meter set on continuity/resistance. The meter will show some resistance and you can then move/tweak the wires and connections until the meter shows no resistance - at which time, you have just identified where the problem is. Doesn't cost a cent - unless you don't have a multi-meter - or don't have a friend with one - and knows how to use it. ---- Jerry/Idaho
swist posted 06-03-2008 08:48 AM ET (US)
An old telephone worker's alternative trick if you are working alone and the wiring extends a distance from the fuse panel is to hook a small buzzer or bell in series with a battery across the (empty) fuse holder. The buzzer will sound if there is a short and will stop when you've found the problem. If you can't keep a light bulb or multimeter in constant view, you could easily miss the tweak that identifies the problem.
Also some DVMs and multimeters have a beep or buzzer type continuity signal, but I wouldn't buy a new one just for that.
jimh posted 06-03-2008 08:58 AM ET (US)
All good advice. Is it reaching strbrst?
knothead posted 06-03-2008 05:04 PM ET (US)
We probably won't know, but I just learned a few handy tips,which is why I keep reading this site.
Keep up the good work.
regards---knothead

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Author	Topic: Electrical Diagnosis: Fuse Blows Immediately
strbrst	posted 05-31-2008 03:13 PM ET (US) When I hook up to the battery in my travel trailer I have power to the water pump and that is it. I checked the fuses and the fuse for the main lights in the trailer was blown so when I went to replace the fuse it would blow every time. I then tried disconnecting the battery and then putting a new fuse in and as soon as I hooked the battery back up the fuse blew. Any suggestions.
seabob4	posted 05-31-2008 03:36 PM ET (US) A direct short. In other words, a ground wire is touching a hot wire somewhere. Now, to find that short look in areas that possible chafing has taken place, areas where wires pass through openings, something like that. But you definitely have a direct short.
jimh	posted 05-31-2008 10:09 PM ET (US) Do you own a multi-meter?
Chuck Tribolet	posted 06-01-2008 09:59 AM ET (US) Turn off all the lights. Does the fuse still blow? If yes, you have a long row to hoe, and as seabob suggests, it's likely chafing somewhere. If no, turn them the lights on one at a time. If it blows when you turn on a fixture, there's likely a dead short to ground in that fixture. (or between switch and fixture if the switch is remote). Don't even think about using a bigger fuse. Listen as you plug the fuse in. You might hear some arcing at the short. Have a water hose handy. The arcing might start a fire. Chuck
jimh	posted 06-01-2008 01:10 PM ET (US) You are going to go broke troubleshooting this problem with fuses. Take a blown fuse and modify it so that there is a small 12-volt incandescent lamp wired across the fuse. Insert the fuse back into place. The lamp will light at full brilliance as long as there is a short in the circuit. When you clear the short the lamp will go out or its illumination will reduce to much less. This is a way to test without blowing $20 in fuses.
Jerry Townsend	posted 06-01-2008 01:34 PM ET (US) Or - disconnect the battery and use a multi-meter between the suspect line and ground with the multi-meter set on continuity/resistance. The meter will show some resistance and you can then move/tweak the wires and connections until the meter shows no resistance - at which time, you have just identified where the problem is. Doesn't cost a cent - unless you don't have a multi-meter - or don't have a friend with one - and knows how to use it. ---- Jerry/Idaho
swist	posted 06-03-2008 08:48 AM ET (US) An old telephone worker's alternative trick if you are working alone and the wiring extends a distance from the fuse panel is to hook a small buzzer or bell in series with a battery across the (empty) fuse holder. The buzzer will sound if there is a short and will stop when you've found the problem. If you can't keep a light bulb or multimeter in constant view, you could easily miss the tweak that identifies the problem. Also some DVMs and multimeters have a beep or buzzer type continuity signal, but I wouldn't buy a new one just for that.
jimh	posted 06-03-2008 08:58 AM ET (US) All good advice. Is it reaching strbrst?
knothead	posted 06-03-2008 05:04 PM ET (US) We probably won't know, but I just learned a few handy tips,which is why I keep reading this site. Keep up the good work. regards---knothead