Re: [K3] Why fuse the negative lead from a battery?

Posted by James Maynard-2 on Apr 02, 2011; 10:40pm
URL: http://elecraft.85.s1.nabble.com/K3-Why-fuse-the-negative-lead-from-a-battery-tp6233377p6235338.html

Right, Bob.

What you say is true of AC residential wiring.

Boats are different.  The so-called "main" AC breaker on a correctly
wired boat breaks both the "hot" wire(s) -- black or in 120/240 VAC
single phase, black and red) and the "neutral" (white) wire -- coming
from the boat's shore power inlet. Also, boats are required (by ABYC
E-11) to have a reverse polarity indicator or alarm to alert the user if
he plugs his shore power cable into an incorrectly wired shore power
pedestal outlet at the marina.

The marina's shore power outlet at the pedestal near your slip is, from
the point of view of the requirements for residential or factory wiring,
a BRANCH outlet, and one in a particularly damp and hazardous location,
where a Ground Fault Circuit Interrupter would be appropriate.  (Most
marinas lack GFCIs however.)  The shore power coming on board a boat at
its shore power inlet has its neutral and safety ground conductors tied
together only at the main power inlet for the whole marina.  At the
shore power pedestal at your slip, there is usually a noticeable
different in AC voltage between the neutral and safety ground.  (If
indeed, there *is* a safety ground -- too often marinas are wired
incorrectly!)

This can be a particular hazard in marinas in fresh water.  If there
were a wiring fault aboard your boat - or a nearby boat - there can be
an AC potential gradient in the fresh water surrounding the boats, and
anyone swimming nearby can be electrocuted by that AC voltage gradient.  
(People are more conductive than fresh water, but less conductive than
salt water. So-called ESD -- electro-shock drowning -- can and does occur.)

So I am wiring my boat acccording to the current ABYC E-11 standard
rather than according to the National Electric Code that applies to
residential wiring.  I am installing ELCIs (Equipment Leakage Circuit
Interrupters) for each shore power inlet, and I am also installing an
isolation transformer, wired according to E-11, with the case connected
to the boatside ground, and the shield between the windings connected to
the shoreside neutral (white wire coming from the marina's shoreside
pedestal).

You are correct, Bob, in describing residential wiring.  But boats are
different!

Jim Maynard, K7KK

At 2011-04-02 05:14 AM (Pacif Daylight Savings Time), Bob Naumann wrote:

> Jim,
>
> You said:
>
> " Likewise, AC branch circuits are on the other side of a "main" circuit
> breaker which cuts both the "hot" conductor ("ungrounded", black in US,
> brown in EU) and the "neutral" conductor ("grounded", white in US, light
> blue in EU).
> The safety ground (green with yellow stripe) is never switched."
>
> The neutral or white wire in USA residential wiring is never "cut" by a
> circuit breaker.
>
> Both neutral and protective ground circuits are continuous and tie together
> only in the main circuit breaker panel (typically) and neither are "cut" by
> a circuit breaker.
>
> In the case of normal residential 120/240v single phase circuit panels, both
> "hot wires" are indeed broken by a "Main" 2-pole circuit breaker. 240v
> branch circuits (2 hots) also use 2-pole breakers. In 120v branch circuits,
> only the single "hot" wire(black) is "cut" by a circuit breaker.
>
> 73,
>
> Bob W5OV
> (retired electrician)
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html