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Old 27-05-2016, 21:06   #16
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Re: Question On Twin 30 Amp Shore Power Service

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Originally Posted by Blue Stocking View Post
10s of thousands of 125/250, 50 amp services use a single neutral, split at the panels for 125 vac. As do just as many generators.

and if you had 2 generators feeding the boat, the N's would be kept separate. same as his question with 2 shore power feeds.
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Old 27-05-2016, 22:14   #17
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Re: Question On Twin 30 Amp Shore Power Service

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it is much easier and cheaper to add a 2nd small 30a panel and plug to the boat, then to redo the whole existing panel to 240v
True, but a change to 50 amp 125 volt is pretty inexpensive and easy to accomplish.
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Old 27-05-2016, 23:26   #18
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Re: Question On Twin 30 Amp Shore Power Service

I use dual 30 amp when necessary if I am in a marina where I need my AC unit, which I connect to one of the 2 30amp shore power cables coming from my Y connector, or if 2 30 receptacles are available on the Dock Power Tower. In that way I am not connecting my (small but hard working) AC unit to the interior boat power "grid", and can use my frig or other AC appliances without fear of popping the boat's breakers. Thats the only reason why I would need 2 separate 30 amp feeds. Does anyone have an opinion on why this is NOT a good idea? Experience at Sea (and dock) is respected in our world!
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Old 28-05-2016, 05:12   #19
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Re: Question On Twin 30 Amp Shore Power Service

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Originally Posted by smac999 View Post
and if you had 2 generators feeding the boat, the N's would be kept separate. same as his question with 2 shore power feeds.
Not the same thing. His 2 shore current sources are coming from the same supply.
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Old 28-05-2016, 05:39   #20
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Re: Question On Twin 30 Amp Shore Power Service

Ok let me hijack the thread just a little...I have a reverse polarity detector on my 30a panel. I can't use a GFI shore source during the winter (it trips as soon as I load it). Anybody know why...


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Old 28-05-2016, 06:23   #21
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Re: Question On Twin 30 Amp Shore Power Service

Well the simplistic answer is "because you have current leaking to ground rather than going to the neutral during the winter," but you already know that. What is different about your load in the winter? Something in that load is shorting at least a little bit. Substituting a non-GFI source to overcome the problem is scary. First, you could get into that circuit, a shocking experience. Second, that little short could become a big short and start a fire. Third, you could be putting current into the water around your boat by that being the destination of the missing current. I have no real idea as to what is leaking, or why only in the winter, but it's time to disconnect each current user in turn until you find it.
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Old 28-05-2016, 07:23   #22
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Re: Question On Twin 30 Amp Shore Power Service

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Originally Posted by WaterfrontcplUS View Post
I use dual 30 amp when necessary if I am in a marina where I need my AC unit, which I connect to one of the 2 30amp shore power cables coming from my Y connector, or if 2 30 receptacles are available on the Dock Power Tower. In that way I am not connecting my (small but hard working) AC unit to the interior boat power "grid", and can use my frig or other AC appliances without fear of popping the boat's breakers. Thats the only reason why I would need 2 separate 30 amp feeds. Does anyone have an opinion on why this is NOT a good idea? Experience at Sea (and dock) is respected in our world!
If you are plugging in one 30 amp cord at the dock (likely with a 30' boat) you are not getting 2 30's but one divided by 2, with the 30 amp shared.
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Old 28-05-2016, 08:38   #23
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Re: Question On Twin 30 Amp Shore Power Service

i think the poster is talking about a pedestal with two 30A outputs.
BTW I have always found the cost of two 30A cord sets and terminals is less than the cost for a single 50A set.
I have two 30A inputs on my boat but rarely need the second 30A; I bought a 50A to twin 30A converter on sale after a marina had only 50A outlets and wanted to charge me $12 per day to "rent" their 50A to twin 30A converter.
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Old 28-05-2016, 18:24   #24
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Re: Question On Twin 30 Amp Shore Power Service

We have recently discovered that the neutrals from our two 30 Amp. shore power circuits are combined at a rotary switch. This switch is used to switch between shore power and the generator.

I am not doubting that it correct to have them separated . I am planning on installing a new switch which will keep neutrals separate. But am not understanding why being combined is dangerous.
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Old 28-05-2016, 19:19   #25
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Re: Question On Twin 30 Amp Shore Power Service

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We have recently discovered that the neutrals from our two 30 Amp. shore power circuits are combined at a rotary switch. This switch is used to switch between shore power and the generator.

I am not doubting that it correct to have them separated . I am planning on installing a new switch which will keep neutrals separate. But am not understanding why being combined is dangerous.
As the generator is a separate source of power, joining the neutrals at the generator is proper and within ABYC Standards ........... as long as the generator cannot supply power while connected to shore power.

If the neutrals are joined you could turn off one circuit and still have power to it through the joined neutrals. This could lead to electrocution if you work on a circuit on which you believe you have turned off the power. It can also cause problems with polarity indication.

I strongly recommend you make no changes without consulting an ABYC Certified Marine Electrician.
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Old 29-05-2016, 05:56   #26
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Re: Question On Twin 30 Amp Shore Power Service

Amen. AC 120, not to say 240, is just too dangerous in a saltwater, vibrating, corroding and flammable environment to mess with without an expert. These aren't houses or hunting cabins we're wiring.
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Old 29-05-2016, 07:01   #27
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Re: Question On Twin 30 Amp Shore Power Service

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Originally Posted by Greggegner View Post
Ok let me hijack the thread just a little...I have a reverse polarity detector on my 30a panel. I can't use a GFI shore source during the winter (it trips as soon as I load it). Anybody know why...


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Greg, there could be several things that can trip a GFCI without there being an an actual danger or ground fault problem.

Automatic transfer switches that switch between shore power and an inverter (either a stand alone switch or one built into a newer inverter) might do that as they switch from one source to another, since for microseconds the sources are connected. The switching speed is important when buying/installing one, and particularly older ones are slow since there never used to be GFCI protection at marinas.

Also, older (generation 2) galvanic isolators and zinc savers test themselves by pulsing into the system which is seen as a ground fault, even though it is intentional and brief enough not to cause problems.

you can read more here:

https://gilwellbear.wordpress.com/ca...fault-sensors/

good luck.
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Old 29-05-2016, 08:00   #28
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Re: Question On Twin 30 Amp Shore Power Service

Years ago living in a marina on the Chesapeake Bay I installed a second 30 amp service on my Cruising Cal 35. The reason for the independent service was to put all of the large resistive loads (hot water heater, cube heaters, oil radiator heaters) on an independent circuit.

I had recently installed a freedom 10 inverter and was concerned that if dock power went off one of these could drain the batteries if accidentally left on when leaving the boat.

In addition, at the time most shore pedestals in the Chesapeake Bay were single or dual 30amp service with unknown phase relation. One would often find hot and neutral swapped, etc. Single 50amp 125 plugs were very rare as we're 50amp 125/250 plugs.

In addition there had been some boat fires in the area from boat AC wiring which was not up to handling continuous 15 amps to a socket. Many boats came badly wired from the factory.

My physically separate second AC panel was run with #10 wire from the inlet to panel, then one breaker for each load or new gfci outlet. All run in #10 wire.

The goal was a bulletproof resistive loads circuit that if shore power went away would not power those loads.

Hot and neutral were obviously physically separate, each ground had an independent galvanic isolator before going to ships ground.

I did have a 30 amp splitter to two 30 amp plugs for summer use where I would use one 30 amp cord and split at the boat to run the hot water heater.

System was very robust and worked well.



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Old 29-05-2016, 08:06   #29
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Re: Question On Twin 30 Amp Shore Power Service

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Originally Posted by botanybay View Post
Years ago living in a marina on the Chesapeake Bay I installed a second 30 amp service on my Cruising Cal 35. The reason for the independent service was to put all of the large resistive loads (hot water heater, cube heaters, oil radiator heaters) on an independent circuit.

I had recently installed a freedom 10 inverter and was concerned that if dock power went off one of these could drain the batteries if accidentally left on when leaving the boat.

In addition, at the time most shore pedestals in the Chesapeake Bay were single or dual 30amp service with unknown phase relation. One would often find hot and neutral swapped, etc. Single 50amp 125 plugs were very rare as we're 50amp 125/250 plugs.

In addition there had been some boat fires in the area from boat AC wiring which was not up to handling continuous 15 amps to a socket. Many boats came badly wired from the factory.

My physically separate second AC panel was run with #10 wire from the inlet to panel, then one breaker for each load or new gfci outlet. All run in #10 wire.

The goal was a bulletproof resistive loads circuit that if shore power went away would not power those loads.

Hot and neutral were obviously physically separate, each ground had an independent galvanic isolator before going to ships ground.

I did have a 30 amp splitter to two 30 amp plugs for summer use where I would use one 30 amp cord and split at the boat to run the hot water heater.

System was very robust and worked well.



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+1 Sounds like you did it right.
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Old 29-05-2016, 08:31   #30
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Re: Question On Twin 30 Amp Shore Power Service

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Originally Posted by Greggegner View Post
Ok let me hijack the thread just a little...I have a reverse polarity detector on my 30a panel. I can't use a GFI shore source during the winter (it trips as soon as I load it). Anybody know why...


Greg S/V Sweet Dreams
Pearson P385 out of Racine Wisconsin
There is the possibility of an even simpler issue here. The polarity at the shore power pedestal source may be, in fact, reversed. That would then carry to your boat. I'm not sure why that might happen only in the winter and not in the summer. You could also have a boat nearby which is "leaking" AC in to the water which is then being picked up by your boat through its water fittings. This would rapidly destroy your zincs if so but could also cause a GFCI to see an imbalance and shut down. You should take your voltmeter and carefully check the polarity of the juice at the end of your shore power cord and then at the pedestal itself. If the shore power cord had been repaired it could have been miswired. I've seen that dozens of times when troubleshooting polarity problems on customers' boats. Your shore power cord MUST be 100% in all ways, always.
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