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

[Jim Brown]

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