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Old 24-02-2006, 01:01   #31
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Alan Wheeler once whispered in the wind:
Dang, the name has gone right out of my head. But it is a form of lightbulb and if you look closely, it has no filament. It has two probs inside that stand parrellel to one another. When it operates, the light flickers around one of those probs. Often seen as indicator bulbs on all sorts of AC equipment and were very common in the old days on Valve operating equipment.
From this description and the color of the light in the picture, I think it is a neon lamp. The voltage drop across a neon lamp is something like 70 - 80 volts, leaving me wondering why there is still 80 volts at the AC panel. (I have some speculations, but it probably isn't worth going in to.)

I wouldn't want one of these things in my boat. You could think that there was no power in the circuit because the fuse is blown, but in fact there is high voltage there that is leaking through the neon lamp. Yow!
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Old 24-02-2006, 01:36   #32
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Mark S (Coot)

You said you're tied up at a dock. So you own a boat. I noticed on your profile that you didn't list, that you own a boat?

What type of boat do you own?

I haven't filled out the profile yet. I have a Beneteau 42CC; it's mostly the stock configuration, though we upgrade the electrical system. My wife and I are out cruising, though we've been stopped in Baltimore for several months. For some reason, I just don't feel like being out in the cold this winter...

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I think what Mark was saying around the latter half of his post said.

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I'm not saying "don't inspect the wiring" -- just if you find anything, replacing the burned up part is not enough to fix the problem.
I believe he means, that if you find a burnt wire. You should replace the entire wire that has burned. And replace with a new wire?
Not exactly. Let me try again.

I should be able to hack the end off an extension cord, plug it in to any circuit in my boat, and touch the two ends together without causing any damage. The only problem that results should be a blown fuse or a tripped circuit breaker.

If a wire or connector was hot enough to get burned, it was hot enough to start a fire. If you put an identical new wire and connector there, the same problem will happen again next time. You don't want to almost-start-a-fire every time you blow a fuse.

So my point is this: If he found any burned wires, there is some OTHER unknown problem in addition to the short circuit that he knows about. That unknown problem would also need to be identified and fixed.


b.t.w. I don't have a problem with hacking off the burned end of a wire and using the undamaged portion, as long as I am sure that it really IS undamaged.

I never re-use burned power connectors; I've seen what is inside enough of them that I wouldn't trust one after it has been damaged.
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Old 24-02-2006, 03:01   #33
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Mark, the reason why they use those Neon bulbs for this purpose, is the very low current draw to make them operate. You can't get a shock from them. Ever seen one of those circuit testers where you stick a screw driver type looking probe onto a live wire and there is a light that glows in the handle? That's one of those bulbs. It produces light via the leakage through your body to ground. But it is so small, you don't feel a thing. The reason why the90V is seen on the meter, is if there is no load sinking away that minute current. He will on lyever see that volatage while the breakers in his main panel are OC. As soon as one is closed, the volatge will drop to zero and the little light would have bee glowing back at that other circuit breaker.

I agree with you that you only need to cut the wire back to good cable again. Burn't cable is a sure sign of a poor terminal connection. The resistance creates heat and the wire discolours and eventually can burn away. But it is usually localised at the termination. The entire wire length does not need replacing.
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Old 24-02-2006, 04:52   #34
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Wheels nailed it - its a Neon (negative) Glow Discharge indicator lamp c/w ballast resister.
This is somewhat archaic technology, and located out of sight in your case, is of little value.
Id remove it from the AC Panel Feeder circuit.
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Old 24-02-2006, 08:24   #35
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I did think about removing it... and I know it's old technology. But... there is one safety factor in having it. (just one)

Say there was a breech of the hot shore power wire as it runs from the shore power receptacle to the AC main...

in this case, the fuse located in this little neon doodad (a 30amp fuse, for this 30 amp service) would blow and save me from a fire.

Without a fuse in this line, it is completely unprotected from a short.

I think that was probably the logic in installing one.

The other 30 amp service I have (I have dual 30s) does not have this type of protection though, so I'm only half way protected. The 2nd 30 amp service was added later, for the air conditioning units. The primary 30 amp service that was factory installed has this little neon light.
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Old 24-02-2006, 14:54   #36
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What I would do Sean, is to get rid of that entire contraption. You don't want one of those glass fuses. They are not designed well for an AC supply. You want a resetable circuit breaker. I also suggest an RCD, GID (what ever you guy's call it) device. You need to b e able to reset the main breaker quickly and easily. You don't want to be rimmaging around for a fuse to replace and then find it blows again cause the fault wasn't removed. Plus, by their very nature, they work by heat/resitance, so a lot of loss is incured across that fuse when working at full load.
I would also consider changing the situation of that panel. I would have it in a n easy to access place, either where your shore supply cable connects to the boat system, or at the main switch board. Don't worry about fire or bad wiriung. It could happen anywhere and the shore box breaker should be the thing that trips in that event, so don't fret about wiring between.
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Old 24-02-2006, 16:15   #37
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That's good thinking, Wheels.

Why not simply replace the fuse with a modern circuit breaker? I think I'll do that. No harm in that, and it's a quick, easy fix.

Thanks!
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