What amp fuse for 12v lights?

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pprendergast

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My interior lights keep busting the 8 amp fuse. Autoshop guy says it probably should be a 16 amp fuse. The system is off the 12v car battery, that also starts the engine, so -although it would be on a different fuse-, I am a bit wary of doing anything that might be worse than just going through a lot of fuses. I have three lights on the fuse. The one causing the problem has two little incandescent bulbs on it probably 20 watt. (old style bulbs not the new long-lasting fluorescent ones). All advice welcome.
 
If all three lights come on at once you may get a power surge at startup (when cold filiment lamps breifly draw mor current. Even so 3x20w should only be 5 amps and standard fuses are 'slow blow' so will take more than there rated current. Does sound like you might have a fault, possibly a broken wire, cracked insulation or a switch fsult allowing periodic shorts. As paulburton says check the wire size before increasing the fuse rating.
 
Agree, fuse is fine sounds like an intermittent short. Wires on boats do fracture and what we do (since most cable runs are a nightmare) is run run new wires straight from the fuse to the appliance(s). If it works we then do the cable run. If it doesn't work the short is obviously elsewhere.
 
You certainly need to check the bulbs and understand exactly what the load on the circuit is. E qually you need to be sure the cable is adequate for the load as well. It is far too easy on a boat to just add more lights and end up overloading the original circuits.
 
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