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

Posted by Jim Brown-10 on Apr 04, 2011; 5:17pm
URL: http://elecraft.85.s1.nabble.com/K3-Why-fuse-the-negative-lead-from-a-battery-tp6233377p6239415.html

On 4/4/2011 1:40 AM, James Maynard wrote:
> Do you know, Jim, whether the definition of "premises" in the NEC would
> include an entire marina? Not the boats kept in the marina, but the
> wiring of such structures as floating docks?

I'm not enough of an expert on NEC that I could offer a detailed opinion
on that in the context of a marina, which is a rather special use, for
the reasons you and others have pointed out. BUT -- the generally
accepted, broad definition of "premises" in the context of NEC would be
a conventional land-based home or business. It would apply to the LAND
wiring, and of wiring connected to LAND-based wiring -- for example,
mains power outlets on the dock. Such outlets would be required to be
protected by a GFCI, which acts as a circuit breaker and cuts off power
if leakage current.is detected.

GFCI's are required to kill power if the leakage current exceeds 5 mA,
which is the current at which electrical shocks can begin to hurt you.
They work simply by comparing the currents on the phase (hot) and
neutral conductors.

If land-based power were brought onto a boat, the parts of NEC with
which I'm familiar would seem to require outlets on the boat for
land-based 120V or 240V power to be GFCI-protected (or a GFCI-like mains
breaker, which is widely used in the UK for premises wiring, where they
are called a Residual Current Detector, or RCD). There's a discussion of
this on page 22 of my Power and Grounding tutorial.

73, Jim Brown K9YC


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