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Old 12-04-2011, 15:17   #1
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Shore Power Question

I know that if you plug into true shore power at a marina, and something on your boat, or the marina's power set up is not grounded correctly, over time can cause damage to the boat. Or kill someone working on the boat in the water.

This is mainly when the shore power is being used to charge the boat's battery's???

If while living in a marina, I run a power cord from the power box and power my 110V mini fridge, 110V fan & lights, but DO NOT have a battery charger hooked up, will I avoid the posable issues of a typical shore power set up?
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Old 12-04-2011, 15:22   #2
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Re: Shore power question??

maybe. Do you have any DC circuits at all? Where is your AC power green safety ground attached inside the boat?
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Old 12-04-2011, 15:42   #3
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Re: Shore power question??

use a good quality power board with serge protection keep the AMPs under the max (10amp in Australia) and you will not be using you boat earth.

And keep it out of the water even with cable ties as short as from the power point to to your boat so if you forgot to unplug it would pull out before touching the water.
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Old 12-04-2011, 15:50   #4
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Re: Shore power question??

[QUOTE=sctpc;665391 keep the AMPs under the max (10amp in Australia) and you will not be using you boat earth. [/QUOTE]

what?

Maximum amperage draw has nothing to do with safety ground; a dead short will go to ground at any amperage.

What do you mean by "boat earth"? Are you referring to the bonding system or the grounding system?
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Old 12-04-2011, 16:54   #5
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Re: Shore power question??

Quote:
Originally Posted by doug86 View Post
what?

Maximum amperage draw has nothing to do with safety ground; a dead short will go to ground at any amperage.


What do you mean by "boat earth"? Are you referring to the bonding system or the grounding system?
Keeping it a separate plugin system a short if there was one uses the marinas earth
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Old 13-04-2011, 04:00   #6
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Re: Shore power question??

Ocean Roads, I am not an electrician but what you want is a Galvanic Isolator wired into the boats circuit and ensure there is an RCCD too.

Have a read of this:

SmartGauge Electronics - Galvanic Corrosion

Please don't just use an extention lead, the above isn't expensive and much safer way to power your boat.

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Old 13-04-2011, 05:29   #7
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Re: Shore power question??

Quote:
Originally Posted by doug86 View Post
what?

Maximum amperage draw has nothing to do with safety ground; a dead short will go to ground at any amperage.

What do you mean by "boat earth"? Are you referring to the bonding system or the grounding system?
Doug... "Earth" is Eurospeak for what we call a "ground"
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Old 13-04-2011, 06:08   #8
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Re: Shore power question??

My previous boat had no AC system at all. I ran an extension cord to the dock, as you described, to run a small heater in the winter or fan in the summer. It was safe enough... It had no risk at all
to divers in the water, but relied on the docks ground, which I tested whenever I plugged in at a different marina. (You can get a little plug in device at the hdw store, for testing reverse polarity & ground faults).

When I had a larger boat with a proper AC installation, circuit breakers and Hubble connectors... I did also have a galvanic Isolator. This neither improved nor made worse the "safety", but kept our boat's green ground wire isolated from the other boats in the marina for reduction of zinc consumption and protection of underwater metals...

I have always done the diving on my own boats, and professionally on occasion. I turn off the pedestal when in the water, just for good measure.
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Old 13-04-2011, 06:30   #9
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Re: Shore power question??

Quote:
Originally Posted by capngeo View Post
Doug... "Earth" is Eurospeak for what we call a "ground"
Yeah, I know. But, was he referring to the boat's AC safety ground (aka the green wire), or the underwater metals that can allow a shorted AC circuit to go to ground when the AC green wire is missing, broken or intentionally disconnected?

The post also said "you will not be using your boat earth". In any fault free system, you are not using boat earth aka: ground. The ground is only used when something is wrong - as a safety valve so the electricity doesn't use a person as a path to ground, and wiring a boat so that it won't have a ground is dangerous.
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Old 13-04-2011, 07:01   #10
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Re: Shore power question??

Quote:
Originally Posted by doug86 View Post
as a safety valve so the electricity doesn't use a person as a path to ground, and wiring a boat so that it won't have a ground is dangerous.
the mains wiring may not be connected to earth using just an extension cable, but have a short and touch a metal part of the boat and you are now the earth cable.

This isn't big ticket items, should be done properly if you are living on board.

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Old 13-04-2011, 07:30   #11
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Re: Shore Power Question

When I was referring to an extension chord (preferably with # 10 wire), being "safe enough" the way I did it 25 years ago, the chord was not connected to the boat in any way at all. (I had no AC system). It ran down a crack in the hatch and plugged into a plastic housing fan. I tested the "dock ground" at the far end of the extension chord, knew it was grounded, and there was no more risk than if the fan were in a house. It had no risk component to divers in the water either... It was however MUCH less "padded" than a proper boat cable with Hubble connectors, so not up to years of dock cart and foot traffic.

A proper system is safer in this respect, more utilitarian, and many marinas will not allow the "extension chord" thing.

Over the long haul, I'd put in a proper Hubble connector, AC panel, and galvanic isolator. It is bound to give more utility.

BTW... One should NEVER use an automotive battery charger on a boat with an inboard engine!!! (They are banned in most marinas) Unlike boat chargers, automotive chargers can send stray current from the connected battery, down the - wire to the engine, then down the shaft and into the water. It can wreck havoc on your zincs & then under water metal. It can do the same to the boats next to you too!

M.
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Old 13-04-2011, 09:25   #12
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Re: Shore Power Question

Quote:
Originally Posted by Mark Johnson View Post
It ran down a crack in the hatch and plugged into a plastic housing fan. I tested the "dock ground" at the far end of the extension chord, knew it was grounded, and there was no more risk than if the fan were in a house.
Are you sure? Did you use an adapter to plug into a 30A outlet? What fuse/breaker value was used? The standard household extension cords are not rated for 30A so they need a 11A or 13A breaker, which I have never seen as part of an adapter. Also, the fan or heater construction assumes it plugs into an outlet that has a 11-13A fuse/breaker for protection.

If you use a standard extension cord, fans or heater on a 30A outlet, you risk fire.

cheers,
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Old 13-04-2011, 09:37   #13
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Re: Shore Power Question

Running an extension cord is a hazard. All appliances need to have a ground in the boat. The appliance must be connected to the boats earth ground. This has nothing to do with the DC ground except they need to be tied together. This is for safety as you can become the ground if there is a fault. If there is a fault on the marina ground you are at risk as well. Please consult an expert on this, the advice you are getting here is wrong for the most part. AC can be very dangerous around water. Just because some have gotten away with it does not make it safe
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Old 13-04-2011, 10:46   #14
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You're right about the advice on this thread being suspect , especially your comments about " ground on the boat"

As to automotive chargers mentioned in another post just exactly what is the problem with them. ( are you referring to the fact they sometimes are constructed using auto transformers, which have nothing to do with cars BTW) I wait for explanations ?

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Old 13-04-2011, 11:01   #15
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Re: Shore Power Question

Dave the difference between the automotive chargers and marine is the way the windings are isolated from each other. Marine chargers the ]high and low voltage circuits are isolated from each other. They are also required to have a fault current path to ground. Automotive chargers and inverters may have the fault path to ground and neutral connected together, this can cause a current flow to your boats ground or worse to you if you touch the case. This is why I keep saying use only marine approved chargers and inverters. Also why using an extension cord is so dangerous. ABYC writes this stuff not to raise the cost of products but because people have died.
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