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MitchK 02-03-2018 09:44 PM

Strange AC voltage issue
 
All, Sorry in advance for the long post. I had a rather strange experience today. I have been in the process of upgrading the shore power system on our N28-2. So I get the old panel such as it was removed, enlarge the opening for the new Paneltronics panel, run a new 10ga wire from the shore power plug to the panel, and hook it all up. I temporarily hooked the old outlet wiring to the new panel for testing. Everything was looking good. Plugged in one of my power tools, and turned it on. The circuit breaker immediately tripped, as well as the main 30A breaker. As the breaker tripped, the reverse polarity LED lit. So , back to the shore power plug. Verified it was wired correctly. Checked the wiring at the panel, which was also correct, restored power, and tried again. Same result. Both the circuit and Main breakers tripped and the reverse polarity LED was lit. Got out the DVM., Thinking that the marinas power was faulty. Started checking voltages. Checked the voltage at the panel, saw 120 from hot to common, and also to ground. That looked good. Checked the voltage between common and ground, and saw about 60v. Now that should not be. So I scratched my head a bit, trying to figure out what was wrong. Checked the voltages at the end of the shore power cable, and got the same voltages. Ok, so I think to myself, that the marinas power has a problem. Check the voltages at the marinas plug in, and found 120v from hot to common, and to ground, just as it is supposed to be. Checked the voltage between common and ground, an it was 0v. Again just as it should be. I had brought a new shore power cable to replace the old cable that came with the boat. There was nothing visually wrong with it, but I had a new cable I had purchased for the CM26 I rebuilt last year that I wanted to use. Plugged the new cable in, and everything worked perfectly. Able to plug in power tools and run them without the breakers tripping. So with all of that said, there appears to be a high resistance short between the hot and either common or ground in the old shore power cable. The resistance is high enough that it does not trip the marinas shore power breaker, but it lets enough voltage pass to trip the voltage actuated breaker in the new AC panel. Anyway, I figured that you guys might want to know about what I discovered today. I will take the cable ends off in future and see if I can see what is causing the voltage issue.

BillMoran 02-04-2018 06:37 AM

Re: Strange AC voltage issue
 
That's some crazy shorting ... did you notice if the SP cable was getting warm when connected to power? It would also be interested to measure resistance between the different leads in the cable before you pull anything apart. Also, consider the possibility that it's one of those shorts that only exists if you bend the cable in just the right way.

I'm interested to hear if you learn anything additional.

MitchK 02-04-2018 01:01 PM

Re: Strange AC voltage issue
 
Bill,
I agree completely that it is pretty strange. The only thing I can think of at this time, it that the cable had just started to develop a burn track caused by dirt or corrosion between the hot lead and common/ground. I have seen similar things before, but not in a shore power cable. I have no idea how old the cable is. It came with the boat when we bought it last fall, and was stored inside the salon under one of the seats. It may well be original to the boat. Don't know. I di know the plug is not molded to the jacket insulation as most are made today. The first half of the boats life was in salt water (Puget Sound Area). The last 15 years has been in fresh water. Not that it should matter. What I am getting at, if the plug(s) were not sealed, then salt air/moisture could have made its way inside the plug and caused a corrosion path between connectors. Either way, once I am done with my inspection, the cable will be cut up and scrapped to eliminate any future risk to anyone.

I did re-use the existing onboard shore power receptacle. I did a through cleaning and inspection of it when I replaced the wiring. I will be replacing it with a new one in the near future.

When I get back to the boat today, I will take some pictures of the old wiring that I replaced. It definitely was not up to ABYC standards. It was also only 12ga wire without an outer insulation sheath.

The wiring to the outlets will also be replaced due to the way it was run. The outlet wiring used the same three conductor wire as was run from the shore power plug. This wire ran approximately three feet to where the wire was spliced to a sheathed version of the wire. This splice is covered in electrical tape. Not sure how the connections wee made. Then it runs a short distance to where the wires are again spliced together in a T configuration. one part of the T from the panel, one part to an outlet, the third continuing on to the next T splice. The splices were made using ring crimps on each wire end, then connected together with bolts, then just wrapped in a layer of electrical tape. Needless to say, this wiring needs to be replaced with properly run wiring. Also, the outlets are not GFCI. They will all be replaced with GFCI outlets.

Mitch

[email protected] 02-04-2018 03:52 PM

Re: Strange AC voltage issue
 
Quote:

Originally Posted by MitchK (Post 2051372538)
Bill,

I agree completely that it is pretty strange. The only thing I can think of at this time, it that the cable had just started to develop a burn track caused by dirt or corrosion between the hot lead and common/ground. I have seen similar things before, but not in a shore power cable. I have no idea how old the cable is. It came with the boat when we bought it last fall, and was stored inside the salon under one of the seats. It may well be original to the boat. Don't know. I di know the plug is not molded to the jacket insulation as most are made today. The first half of the boats life was in salt water (Puget Sound Area). The last 15 years has been in fresh water. Not that it should matter. What I am getting at, if the plug(s) were not sealed, then salt air/moisture could have made its way inside the plug and caused a corrosion path between connectors. Either way, once I am done with my inspection, the cable will be cut up and scrapped to eliminate any future risk to anyone.



I did re-use the existing onboard shore power receptacle. I did a through cleaning and inspection of it when I replaced the wiring. I will be replacing it with a new one in the near future.



When I get back to the boat today, I will take some pictures of the old wiring that I replaced. It definitely was not up to ABYC standards. It was also only 12ga wire without an outer insulation sheath.



The wiring to the outlets will also be replaced due to the way it was run. The outlet wiring used the same three conductor wire as was run from the shore power plug. This wire ran approximately three feet to where the wire was spliced to a sheathed version of the wire. This splice is covered in electrical tape. Not sure how the connections wee made. Then it runs a short distance to where the wires are again spliced together in a T configuration. one part of the T from the panel, one part to an outlet, the third continuing on to the next T splice. The splices were made using ring crimps on each wire end, then connected together with bolts, then just wrapped in a layer of electrical tape. Needless to say, this wiring needs to be replaced with properly run wiring. Also, the outlets are not GFCI. They will all be replaced with GFCI outlets.



Mitch


I may be naive but how do I know that my AC is properly grounded ? I am on a 1979 Cal 2-27. What and where should I look. My first thought is to start at the boat 30 amp breakers and back to the 30 amp dock breaker. And is that enough?





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MitchK 02-04-2018 04:09 PM

Re: Strange AC voltage issue
 
If I understand the question correctly, you are concerned that you have an actual ground path back to the marinas pedestal (ground), and that the pedestal is properly grounded? If you have a digital volt meter, it is easy enough to verify that you have a ground return path to the pedestal. Just measure the AC voltage between the hot leg of any outlet and the ground lug of the same outlet. If you see approximately 120vac, then your ground line back to the pedestal is good. Same for the hot to common slots on a receptacle. There should be no difference between the voltage readings between hot and common and hot and ground. There should be 0vac between the common and ground. If you have a galvanic isolator in the ground line, the voltage may be a slight bit lower due to the voltage drop across the diodes in the isolator. The ground and common should be tied together at the marinas service box.

[email protected] 02-04-2018 04:10 PM

Re: Strange AC voltage issue
 
Another thought is it might be in the plugs at either end. I go through beaucoup iPhone charging cable and it is almost always where the cable enters the plug on either end. I just bought the six foot long phone cable in the current ad above 5 cords for $44.and change. Postage and taxes. Iíll let you know how they last. Tapa talk isnít allowing me to drop in and correct a single letter. Where do we send complaints?


Sent from my iPhone using Tapatalk

[email protected] 02-04-2018 04:19 PM

Re: Strange AC voltage issue
 
Forgive me. I am in the middle of just having the Marina replace my dock side breaker. It was tripping and there seemed to be no issue on my boat.


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MitchK 02-04-2018 08:06 PM

Re: Strange AC voltage issue
 
2 Attachment(s)
Here is a picture of some of the wiring I am replacing. This is piece was the run from the shore power plug to the original AC panel. It looks to be 12ga, but there is no markings on it that I could read. Also attached is a picture of the new panel in place. I will be filling the holes in the bulkhead with some colored epoxy in the near future.

boatpoker 02-04-2018 09:39 PM

Re: Strange AC voltage issue
 
Quote:

Originally Posted by MitchK (Post 2051373114)
Here is a picture of some of the wiring I am replacing. This is piece was the run from the shore power plug to the original AC panel. It looks to be 12ga, but there is no markings on it that I could read. Also attached is a picture of the new panel in place. I will be filling the holes in the bulkhead with some colored epoxy in the near future.

Looks like solid core Romex (house wire) conductor. Wise to get that stuff off your boat. Don't forget to bond your AC and DC grounds.

MitchK 02-05-2018 11:20 AM

Re: Strange AC voltage issue
 
boatpoker,
Actually it is stranded. However it is a relatively coarse strand, and the insulation jackets are molded together into a flat assembly. It reminds me of something like boat trailer light wiring, but only much heavier. Again, it looks to be about 12ga. The existing push button breaker was only rated for 20A, and once the wiring makes the transition at the splice, it looks to be fairly good tinned marine grade wiring. The problem with the panel to outlet wiring is how it is run. A nut and bolt to connect three sets of wires together and covered in a thin layer of electrical tape for insulation is an electrocution waiting to happen. Also, none of these splices are in any sort of box, and at least one is located between the hull and liner where it is impossible to access for maintenance. I will have to cut the existing wiring and attach pull strings and pull it back towards the panel to be able to get the new wires in. Looks like it will be a pain in the rear, but at least it is doable.


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