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Old 22-06-2021, 06:50   #1
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Diagnosing electrical faults

Let me start by saying this is not something I am experienced in.

The spreader lights have begun blowing their fuse after I rebuilt the fuse panel. I've gone back and checked the continuity of the switch, the fuse holder and the circuit to the lights. The all showed a strong consistent tone showing continuity.

I also measured the resistance of each of the three.

Switch 2.8 ohms
Fuse 3.1 ohms
Circuit 3.4 ohms

It would make sense that the circuit would have slightly more resistance because it is roughly a 40 foot circuit (up and back).

Here's my conjecture. There is a fray/crack in either the positive or negative loop of the circuit, however its not actually touching another line (hence no increase in resistance); its arcing under load.

Now my questions:

1) Is my conjecture accurate?
2) how do you identify if its the positive or the negative that has the fray?
3) how do you track down where the fray is?

Thank you,

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Old 22-06-2021, 07:29   #2
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Re: Diagnosing electrical faults

To start with, you need a new meter.
The switch should measure zero ohms when ON and infinity when OFF.
Your meter should not be able to measure the resistance of the fuse which should be less than 0.01 ohms.
How did you measure the circuit resistance - - was the spreader light installed? The light should have an order of magnitude more resistance than the wiring.
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Old 22-06-2021, 07:36   #3
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Re: Diagnosing electrical faults

For spreader lights it's possible that the frayed wire is intermittently shorting in the mast. Your comment "after I rebuilt the fuse panel" suggests maybe not. Difficult to diagnose reliably diagnose. Yandina is correct in that the switch and fuse should either be 0 Ohms or infinity, but if you are testing them in circuit, you are probably measuring the circuit, not the switch/fuse.
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Old 22-06-2021, 07:40   #4
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Re: Diagnosing electrical faults

The the meter is fine. Its the operator that is the problem. I need to learn how to use the bloody thing.
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Old 22-06-2021, 08:07   #5
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Re: Diagnosing electrical faults

Most lengths of wire will show resistance. Not a lot though. Maybe a 1/4 ohm in 100 ft.
I would be checking the fixtures and wires passing through the spreaders up the mast. Also for corrosion.
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Old 22-06-2021, 08:36   #6
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Re: Diagnosing electrical faults

Disconnect and isolate the negative wire from the spreader light at the panel. Then measure the resistance between the positive wire and your battery negative/negative bus bar. If you don't have infinite/very high resistance then you have a short somewhere.
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