[CQ-Contest] Portable Generators

Gary A. Nieborsky PE k7fr at televar.com
Tue Jan 13 11:12:06 EST 1998


Article 702 of the National Electric code addresses this issue.  The big
hang up with what you are proposing is that under 702-6, in part:

"Transfer equipment shall be suitable for the intended use and so designed
and installed as to prevent the inadvertant interconnection of normal and
alternate sources of supply in any operation of the transfer equipment."

Having the main breaker open while feeding the panel from a branch circuit
would be acceptable only if there were means to prevent the closing of the
main breaker while the generator is running.  The Code does not
specifically address what this should be but from experience (I wrote our
corporate policy regarding standby generators used by customers) this needs
to be a system that is either automatic (closing the branch circuit breaker
automatically opens the main breaker) or requires a conscious effort
(manual interlocks) to achieve the desired configuration.

Our coporate policy requires that the backup generator have a  transfer
switch that isolates them from us. This installation can be installed by
the home owner but must be inspected and approved by the State Electrical

Our policy stemmed from a potentially fatal incident.  We had a micro-burst
event in our southern service area that snapped poles off at the ground. 
Service was out to a large area.  On one of the laterals that fed a dairy
our crews were clearing downed wires.  They came upon a storm dead-end (a
pole that is set and guyed to limit cascading failures) with a set of fuses
that were open.  They started to cleared the downed wire on the damaged
side when the foreman noticed that the blinking red light at the
intersection was happily blinking away!  Investigating this he found that
the dairy at the end of the line had a 75kW backup generator hooked into
their panel with the main disconnect closed! Had he not noticed the light
blinking the next action, installing grounds on the intact wires, would
have resulted in a very spectacular and very dangerous ball of fire.

Check with your local utility to see what they require.

73 Gary K7FR

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