Codes vs. common sense (Was module grounding) [RE-wrenches]

Bill Brooks billb at endecon.com
Tue Nov 5 10:03:37 PST 2002


William,

You certainly are an inquisitive one aren't you? Your mamma must have had to
answer a million "why?" questions when you were growing up. The basic rule
has always been that if a fault can be sustained at or below the level of
the overcurrent protection, the ground wire must be able to handle that
current and have the ampacity of the current carrying conductors. It follows
that a PV source circuit can do that. Also an inverter input circuit can do
that.

However, the 2002 code revised that requirement and now allows sizing based
on 250-122 (AC equipment grounding conductor table) when a system has ground
fault protection (all units on the market today have that at least as an
option). Table 250-122 is a great help for larger circuits but requires full
size for smaller circuits (up to 30 amps).

Bill.


****snip****

Having said the above, I still don't understand why DC grounds have to be
sized to the largest current carrying conductor?!?!  this makes no sense at
all.  Bill Brooks, can you explain this?  Or better yet, leave me in
blissful ignorance....



Respectfully


William Miller

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