A note on sub panels. Yes the fault current does have to travel all the way
back to the main panel in order to trip a breaker, even one in the sub
panel. This is kind of a poor way to do it in my opinion but that is what
the NEC requires.
The reason for only having neutral and ground bonded in the main panel is so
that normal neutral current does not flow in the ground lead. If the neutral
and ground were also bonded in the sub panels then they would be parallel
paths for neutral current. However it would be a shorter, lower resistance
path for fault current to trip a breaker.
But do as the NEC says, bond neutral and ground only in the main panel as
neutral currents on the ground lead can be a hazard.
> ## The standard deal for the commercial grade joslyn units is just two
> big puck size movs.... and each mov is wired from each hot to neutral.
> The main 200A panel will have it's neutral and GRND bonded
> together... which by code... is the ONLY place you can bond the neutral
> and grnd together... via an internal cu strap. IF a sub panel is
> used... then the sub panel will NOT have it's neutral and grnd
> internally bonded. Reason is... in any sub pane, all fault current
> must travel from sub panel back to main 200A panel... via the grnd
> wire... and NOT the neutral.
> later.. Jim VE7RF
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