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Old 09-23-2014, 09:56 AM   #1
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Another electrical question

I watched a U-tube on water electrocutions and one data point the presenter made was that 13% of the boats investigated had the neutrals tied together.

My boat has the neutrals switched with each of the hot phases. However, when switched from shore to generator the breakers are by-passed and the generator and boat wiring goes to single phase 120V and combines the hots into the same phase so the whole boat has AC power. Switching back to shore power separates the hot wires in two banks so the incoming split phase 220 will work without shorting. Obviously my neutrals are tied together. Is this wrong?
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Old 09-23-2014, 11:05 AM   #2
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You can't put anything on the Internet that's not true, right?

I would check the ABYC specifications to see if your boat is in compliance. If you can't do that, have an ABYC certified marine electrician check the boat's wiring for compliance.

I can't say from your post if your neutral conductors are connected together on the boat but once you plug into shore power they are connected together either at the pedestal or at the marina's electrical panel.

I don't think you have anything to worry about unless an unqualified person has been working on your electrical system.
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Old 09-23-2014, 11:14 AM   #3
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Originally Posted by rwidman View Post
I can't say from your post if your neutral conductors are connected together on the boat
The neutrals are connected on the boat because my generator is set up as 120V and it has only one neutral and one hot, and all the 120 AC works when on generator.
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Old 09-23-2014, 11:25 AM   #4
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That is a new one on me, but I understand why and it could be more prevalent than I think.

Your shore power supplies 240V with two hots, common neutral and a ground. Typically this is 50 amp service. Your AC panel has two 120V busses, each fed by one of the hots.

When you switch to generator power, your generator is wired to make 120V power. So the hots on your panel are combined and fed from hot side of the generator. This allows the total KW capacity of the generator to feed the 120V power.

The other way to do this is to mimic the shorepower, wire the generator to produce 240V and feed each buss separately. But this scheme may limit the use of all the KW that the generator puts out. Each leg can only produce half of the KW and if all of the active loads are on one buss that may overload the generator. The other leg may be loafing in that case.

So your wiring scheme works and it maximizes the loading of your generator.

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Old 09-23-2014, 11:28 AM   #5
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Originally Posted by obthomas View Post
The neutrals are connected on the boat because my generator is set up as 120V and it has only one neutral and one hot, and all the 120 AC works when on generator.
That's the way mine was wired also...

I'm still thinking through the obvious safety issues pointed out by the video and Boatpoker...the only issue I can see is if you do have some electrical issue where power is still feeding through to a neutral and if tied toether it isn't interrupted when you cut that buss off (main breaker).

In our case where the genset is both hot and neutral and feeding both sides...probably the main breakers don't matter...just the breaker from the genset that if cut cuts everything anyhow...not just one buss.

When on a 120/250 system and cutting off one buss...I'm assuming any issue would go back to landside and not backfeed anything on the boat.

Again..Ive been too bust to pen it all out to fully understand all possibilitis and "Y" cords..but I can see the basic ABYC assumption.
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Old 09-23-2014, 11:33 AM   #6
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djmarchand

You got it exactly right! That is how my boat is set up electrically. Unfortunately the video I watched about water electrocution only inferred that connected neutrals is wrong and did not explain why.
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Old 09-23-2014, 11:40 AM   #7
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Originally Posted by djmarchand View Post
The other way to do this is to mimic the shorepower, wire the generator to produce 240V and feed each buss separately. But this scheme may limit the use of all the KW that the generator puts out. Each leg can only produce half of the KW and if all of the active loads are on one buss that may overload the generator. The other leg may be loafing in that case.

So your wiring scheme works and it maximizes the loading of your generator.

David
David

As you describe for genset use, ours and many others are set up this way. To prevent one leg from loafing, the ACs, washer and dryer are one leg and pull about 45 to 50 amps when fully loaded. The other leg is kept below 50 amps by assuring stove, microwave, water heater, chargers and hair dryers are not all running at same time.
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Old 09-23-2014, 11:45 AM   #8
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Psneeld

I haven't got my mind around the possible safety issues either. I do know that my generator main breaker is a two pole and breaks the generator neutral at the same time as the hot. I think there is some extra switching going on in my ship shore switch that prevents the generator from powering the shore connection. I have had my boat 4 years now an I still do not have a really good electrical diagram. Every year it is getting better though.
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Old 09-23-2014, 11:47 AM   #9
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Quote:
Originally Posted by obthomas View Post
I watched a U-tube on water electrocutions and one data point the presenter made was that 13% of the boats investigated had the neutrals tied together.

My boat has the neutrals switched with each of the hot phases. However, when switched from shore to generator the breakers are by-passed and the generator and boat wiring goes to single phase 120V and combines the hots into the same phase so the whole boat has AC power. Switching back to shore power separates the hot wires in two banks so the incoming split phase 220 will work without shorting. Obviously my neutrals are tied together. Is this wrong?
Are you 2 -30A shore power or a 50A 125/250V shore power? I think someone may have made a wrong assumption.
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Old 09-23-2014, 12:04 PM   #10
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Are you 2 -30A shore power or a 50A 125/250V shore power? I think someone may have made a wrong assumption.
I have one 6/4 cable 50A/125/250 into my boat. The neutral splits, and follows the split phase hots to 2 separate double pole breakers. These breakers then feed through the ship to shore switch and then to the panel. The neutrals go on to a common buss.

When I switch to generator the shore power is isolated and the generator then feeds both panel busses. The generator neutral is also landed on the common neutral buss. The generator has a 2 pole breaker that switches both the hot and neutral.

I could be making a little of this up because I am not sure I fully understand my ship shore switching.
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Old 09-23-2014, 12:57 PM   #11
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http://www.paneltronics.com/technica...grams/3310.pdf

This has the neutrals connected but I think the problem is connecting the neurals AFTER the cutoff breakers...in other words..if you had 2 separate busses with separate cutoff switches like you have and connected the neutrals AFTER the main double pole breakers...then all the neutrals would be active. If they are split (as in a "y" connector...before the main double throws....cut the power to one leg and there should be no way to backfeed the neutrals on the other buss.
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