AC Main Power?

[ssullivan]

Hello All,

Why do I have a feeling I'll be in this Power & Electricity section for the rest of my life??

I had a short today (bad wiring at the factory - left a hot wire dangling in an outlet).

This hot wire ended up grounding to ground (not neutral). Now, I don't appear to be getting power to my main AC panel bus/bar. I am, however, getting power to my shore power cable, and into the shore power receptacles up on deck.

So... somewhere between the shore power cord and the AC main bus on the AC main panel, I am losing my power.

Any ideas? So far, mine are:

1) Blown out shore power socket
2) Some kind of fuse between the shore power socket and the AC main
3) Fried cable between the shore power socket and AC main.

Are there any other variables involved? Anything I might be overlooking?

Interestingly enough... neither the main AC breaker or the smaller breaker to the outlet tripped. The power just went out when the short happened.

Basically, my question is: out of the 3 ideas I have above, do boats commonly have anything else between the shore power socket and the AC main that I'm missing?

I ask because I hope to shave some time off all of the Digital Multimeter fun I will be having in the AM.

[CaptainK]

Well Sean.

I'm no expert. But I'd have to say that you better break out that "Digital Multimeter." And spend some quality time alone with that device. And nermous wires and componants that you'll have to trace down. And find that spot, where you are losing your power.

Working on automobiles is very similar. And believe me. It's a pain in the ass to work with. I even admit hating to deal with it!! That's the only way of truily finding your little culprit in the act?

I would start by accessing the back of the shore power recepticle. Visibly inspect the recepticle for damage. ( Unplug the cord and check the outside as well). If no visible damage, check the voltage at the back of the recepticle. If all is in order, check the voltage at the main breaker, and buss bar. This will either eliminate, or identify these items as the problem. If no problem is found at this point, the breaker is probably bad. Check the output. Also try switching it off and check to see if it does in fact disconnect. It is uncommon, but not impossible that there is a fuse of some sort inline, but The above check should determine if the failure is between the breaker and the recepticle.
FWIW, I have had 2 of the 30amp recepticles fail over the years due to a reverse polarity issue in the dock. They melted away the potting between the terminals, and I did not discover them intill the power started to fluxuate.

[ssullivan]

Kai Nui once whispered in the wind:
I
FWIW, I have had 2 of the 30amp recepticles fail over the years due to a reverse polarity issue in the dock. They melted away the potting between the terminals, and I did not discover them intill the power started to fluxuate.

VERY interesting! My gut feeling tonight was that I will be looking at a weakened receptacle for shore power. It is from 1987, and my thought was that this current might have been enough to fry it (since it might have already been on its way out), but not enough current to trip my AC Mains breaker. As in... the weak shore power receptacle crapped out before the breaker could kick in.

With what you wrote above, I'll hone in on that in the AM. Thanks!

And captain K... I sure will spend plenty of "quality time" with my digital multimeter! ha ha

[Alan Wheeler]

Sean, I doubt it. Careful you don't go chasing Red hearings. Use some basic and logical fault finding skills. Yes you need a meter to test everything. OK,
First ,You need to confirm you have shore power. Ensure your meter is swicthed to AC and to a voltage high enough to do the test. Now place one leg of meter probe into the Active terminal of the shore socket. It doesn't matter which probe. Now the other probe can be placed in Earth and Neutral. You should get a reading of 110V(240 for NZ) between each and Active. You will get nothing between Earth and Neutral. If you can notget the correct voltage, then you don't have shore power. If the breaker has not tripped, you may have another safety device at the head of the Marina. It could be a ground fault interupter or Residual Current Device, (same thing different country) They seem to often become an expensive means of protecting your Circuit breaker
OK, so lets assume you have power at the shore socket. So lets suspect the AC cable to the boat. Set your meter to a continuity setting. A meter that beeps can be a big plus for this. (Oh and unplug the probes from the shore socket of course ) Now gather both plug and socket together and test the continuity between each. Earth, Phase and Neutral. This ensures you test for contiuity and for correct termintation. If a wire is swapped over, it should just blow the breaker or RCD. So the main point in the test is to ensure conituity. Not picking hairs here, but having a wire around the wrong way in an AC circuit is NOT out of polarity. Polarity is in a DC circuit. Neutral and Active swapped in a single phase circuit is called Out of Phase.
OK, so lets assume that all tests OK. Next is, how does the AC cable(lead or what you yanks call it ) connect into the boat. Now it is possible the recepticle could have an RCD device there and maybe a circuti breaker. With RCD devices, if power has failed, they don't reset automaticaly. You usually have to manually reset, so look for a button. There is often two. A test and a reset. (Good excersise to test once in a while as well.) Failing all that, you have a problem in the switch board. Lets see how we go with all the above, then let us know and I maybe able to talk you through some more.

[Alan Wheeler]

I kept this post seperate so as it doesn't cloud the view. OK, Kai I know you guy's have some weird power schemes, but I can't see how reverse phase(polarity incorrect term)will cause the failure of the plug. It should trip the breaker. If it doesn't, your system is not safe. So nin following on from that, Sean, a weakend socket should not be at fault either. Youy either have power or not. Any "weak" point means resistance. Resistance means heat and loss of voltage. Heat means melted plastic and loss of volatage means loss of power which equals a brown out.

I was simplifying. Switching the nuetral and hot in a 110v AC system will not necessarily produce a major issue, however, many of the AC panels available now ave an indicater that lets you know if the recepticle is wired backwards. The warning light is labeled reverse polarity. I realize this is an incorrect term but just like "head", I am going with the terms in the brochure so we can all be on the same page.
As for where I started, Sean said in the first post that he was getting power through the cord to the recepticle. The weak link beyond this point is from the recepticle to the output of the breaker.
FWIW, both times the harbor maintenance people claimed the problem was that the nuetral wire had come loose and was making contact with the ground wire when my plugs failed. I suspect it was making contact, not with the ground, but with the hot. We have a very unique system here. zincs last about 6 months at best.

[CaptainK]

Kai.

6 months? At that mairna you're in now?

That's not good!!

Living aboard is a factor. With all the stray currents from all the electronic goodies we use from day to day, electrolisis is much more of an issue. For instance, on Kittiwake, tha has not electrical on board, and is wood, the zincs are still in great shape after about 18 months.

[Alan Wheeler]

Yeah Kai, I wasn't trying to be...err...umm...you know. It was more for others ready than a correction as such.

I wonder though, was the wire coming loose the issue, or was it a result. My thought would have been a too high a load. It's one issue I have always had with the US system of 110V. The currents are huge. Here in NZ we have a 230V system (regulated to +/-10%) so say an electric jug(kettle) of 2400W would draw 10A on our voltage and 21.8A on yours. Now yes at the end of the day it is a total load of 2400W. But current doesn't like traveling across anything that provides a resistance. It produces heat very quickly on any dirty contact.Especially a salt corroded one. So connections on plugs and sockets can get hot very quickly and burn out and also cause terminations to become loose and the wires to burn out or fall out, which of course, equates to more resistance and thus more heat and so on.

No offense taken
Here it is more a matter of wiring done in the 1950's and not upgraded, combined with lots of boats with substandard wiring.
You are correct about the current. That is one reason a 24v system is far superior on a boat in comparison to a 12v system. Higher voltage leads to lower corrosion, and less heat. AC or DC.

[coot]

It's looking like you're going to spend a lot of time on electric. It could be worse -- I would rather work on electric than plumbing any day.


I assume what you're saying is this:

A bad 15 amp branch circuit shorted out. When it did, all your shore power went down. The 15 amp breaker in the panel did not blow. The 30 amp AC breaker in the shore power pedestal did not blow.

There is a 30 amp AC breaker between the shore power inlet and the distribution bus in your AC panel. (If there isn't, there should be!)

All you have to do is find it and reset it. If you think that you have found it already, look for another one closer to the shore power connector.


I think it is unlikely that you developed a new defect because of this event. A well implemented electrical system should be able to tolerate this kind of a fault without any damage. If you find a burned wire somewhere, it is important to ask: Why was it possible for this to happen, and what do I need to do to make my electrical system safe?

[ 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. ]


Here is a thing to think about with fuses and circuit breakers: The more overcurrent, the faster it reacts. 31 amps on a 30 amp circuit will take a while to get cut off. 35 amps will take a little less time. 100 amps will get cut off very fast.

Circuit breakers and fuses come in different speeds; the fastest one is the first to react.

In a normal 30 amp shore power connection, there is a breaker on the shore power pedestal and another in the boat. Normally only one of them will shut off for an overcurrent condition, because the other one will be a little slower. Where I'm docked right now, the breaker in the pedestal is consistently faster than the breaker in my internal wiring.

In your case, you had an instantaneous short circuit current of hundreds of amps. That triggered the fastest circuit breaker, and then all the slower circuit breakers saw the current drop to zero.

Your 15 amp breaker was too slow in responding. The 30 amp breaker shut the power off faster. If you just had a toaster and a hair dryer running at the same time, your 15 amp breaker would have responded.

[ssullivan]

I'll add for clarity that I do have power coming in from my shore power cord. I tested the cord and have the correct voltage. I do not know if this power makes it from my cord to the cable that runs from the shore power receptacle and my AC Main breaker panel. All I know is there is no power getting to the AC main (by testing the hot, neutral and ground busses finding no voltage at all). - plus, it don't work! ha ha

In 10 minutes, I was able to quickly find that out with the meter.

I am now trying to find the fault between them that is causing the power not to flow. The only items between are a large cable and the shore power receptacle itself. I was checking to see if anyone had heard of anything else between these two that might be at fault (pun intended??).

In this case, I know very specifically what caused the short. A hot wire touched ground/earth through a poorly wired outlet box.

Just wanted to be clear... I'll post some results in the AM. Oh wait... it IS the AM. 3AM. Wood heat. There is the one disadvantage!

[GordMay]

Get a “Non-Contact” Voltage Tester (GB Electrical “Circuit Alert” #GVD-504A, or GCV-206 - about $10) from your local Mega Mart (Lowes, Home Depot, etc).
This greatly simplifies tracking down open wires etc.
Note: Power indication is reliable, but power “off” indication is not.

[Alan Wheeler]

Confused I am now. So to clarify, you have a box on the jetty? Then you have a cord that connects the jetty box to the AC main panel in your boat? And if I understand correctly, that cord has power at the end of it and this then plugs into a boat recepticle? Sooooo? if I am on track here, there is nothing wrong with shore power, cord to boat recepticle, but there is a problem somewhere between the boat recepticle and your switchboard?? Or do I need to take a lesson in American