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Old 12-12-2017, 06:14 PM   #1
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Stray current and indicator lights

Two questions that may or may not be related.

I have a steel boat so galvanic corrosion and Electrolytic corrosion are a concern. I have been reading "Motorboat Electrical and Electronics manual" by John Payne trying to learn as much as I can. In the Electrolytic corrosion section under Ground Faults on page 212 it says; "In any area where a cable can contact grounded metal, leakage or fault currents can flow. Install a leakage test lamp unit such as a Mastervolt that handles both AC and DC. This allows the hull to be monitored continuously and any problems can be rectified promptly". Maybe you can Google better than I but I can't find a "leakage test lamp" anywhere on the internet.

Thinking through this issue brought me to my second question. My DC panel is large and wired such that just about everything has it's own circuit breaker on the panel and it has indicator lights next to each circuit breaker so when the CB is on there is a little red light next to it... I have noticed for some items when I turn off the CB the little light immediately goes out but for other things the light slowly dims then goes out taking 3-4 seconds. The indicator lights are wired directly to the output side of the CB and to a ground bus bar on the backside of the panel.

Are the lights next to the CB the "Leakage test lamp"? I always assumed they were just indicators saying the CB was on. Is how fast the light goes out linked to some type of ground fault or leak in the wiring?
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Old 12-12-2017, 06:31 PM   #2
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Cool boat by the way. I’d get some professional help from an ABCY Corrosion/Electrical Tech. Worth the money to make sure your boat is wired correctly and help answer some questions.
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Old 12-12-2017, 07:19 PM   #3
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So, by design, all of your current carrying circuit conductors should not contact the steel hull.
Now, imagine two 12v light bulbs connected in series, connected to your 12 v system. Take the middle connection and attach that to the hull. If no other conductor in the 12v system contacts the hull, you will see two dim lamps. Now, a short develops between the hull and + 12 volts. One lamp goes off and the other goes to full brightness.
That is a ground fault detector in its simple form. Iíve done some design work on electronic ones but hopefully you get the principle.

Your question on the action of the panel lights is unrelated. That is simply some stored energy discharging thru the lamp. Capacitive charge or sometimes a running dc motor will do that. A bilge pump will do that if its running and you kill the breaker.
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Old 12-12-2017, 07:38 PM   #4
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Quote:
Originally Posted by diver dave View Post
So, by design, all of your current carrying circuit conductors should not contact the steel hull.
Now, imagine two 12v light bulbs connected in series, connected to your 12 v system. Take the middle connection and attach that to the hull. If no other conductor in the 12v system contacts the hull, you will see two dim lamps. Now, a short develops between the hull and + 12 volts. One lamp goes off and the other goes to full brightness.
That is a ground fault detector in its simple form. Iíve done some design work on electronic ones but hopefully you get the principle.

Your question on the action of the panel lights is unrelated. That is simply some stored energy discharging thru the lamp. Capacitive charge or sometimes a running dc motor will do that. A bilge pump will do that if its running and you kill the breaker.

Very well put ( written ) ........ FB
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Old 12-12-2017, 08:13 PM   #5
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A few youtube videos:



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