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From: (no name) (no email)
Date: Sun Dec 03 2000 - 18:00:35 EST
In a message dated 12/02/2000 12:46:17 PM Eastern Standard Time,
writes:
>
> It's very simple and yet seems to be very mystifying.
>
> When a boat is connected to shore power, it receives power from the
> utility company and must comply with all the provisions of NEC which
> include having only one ground point per service entrance point.
I have never heard before that a boat must comply with the NEC and simply do
not believe it.
>
> You might think of the boat as nothing more than a toaster or other
> appliance connected to the nation's power grid.
>
> OTOH, when the boat is at sea, operating on an engine-generator, solar
> cells, wind generator or any other type of self contained power
> generation, the boat must comply with ABYC who grounding procedures, of
> necessity, are in direct violation of NEC.
This is simply not true. A yacht, once sold, does not have to comply with
any standards other than the usual Coast Guard boarding checklist and COLREGS
requirements. It may be that insurance companies require ABYC standards for
their policies to be in force, but there is no statute requirement. I am
free to construct my boat any way I wish.
>
> The only way to satisfy these conditions is to have a transfer switch
> that transfers the earth ground as well as the power conductors between
> the NEC and the self contained system.
In every requirement I am aware of the grounding conductor is never broken by
any switch or overcurrent device.
>>>
The following quote is from Randy...
following is from the Heart User Guide:
"Neutral Bonding
For safety purposes and NEC code
requirements, the Freedom Combi unit
internally bonds the AC output neutral (white)
to the AC output ground (green), when the unit
is OFF or in the inverter mode. When
incoming AC power is applied and the transfer
switch is engaged, the internal neutral-to-ground
bond is automatically lifted.
When external AC power is applied, the
grounding system is connected to the source
power ground (by the shore power cord - Norm), where neutral and earth ground
are bonded together. This technique insures
safety in all conditions and conforms to the
requirements of the NEC."
Regards....Randy
>>>>
What Randy describes is the "bond" connection, that is the one-and-only wire
in any neutral-grounded system that actually makes the neutral to ground
connection. There must be only one to avoid a ground loop which can make
normally safe grounding wires become above ground potential. The Heart relay
opens the "bond" wire inside the Heart unit when the unit is receiving shore
power because then the one-and-only connection between neutral and ground is
made by the shore wiring.
The grounding conductors remain untouched and unbroken.
> If you have a chance, you might want to wade thru the sections of the NEC
> that apply to standby emergency generator systems equipped with automatic
> transfer switches.
>
> The type used by hospitals, police, certain chemical plants, and other
> critical load applications.
>
> These systems all switch the earth ground from the incoming utility
> service to the engine-generator service when the engine-generator is
> operating.
>
I don't have a copy of the NEC, but have read many discussions of the
pertinent parts in Home Power magazine which deals with interties between the
grid and homeowners who make their own electricity. When wiring a house, the
ground is not brought in from the powerline, one can simply look and see but
three wires at the service entrance (neutral and two hots), but from the
water service pipe, a ground stake driven in below the frost line or a bare
wire buried in a wire trench.
> It is pretty well defined, although like everything else in the NEC, the
> cross referencing can drive you nuts before you get thru it all.
>
> BTW, if you chech out a Heart inverter schematic, you will find an
> internal relay that automatically switches the earth ground conductor
> when the inverter is energized.
I don't have access to a Heart inverter schematic, but on my 2.5 KW Trace all
the grounding wires go to one terminal on the chassis and are not switched
anywhere.
Norm
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