[CQ-Contest] Portable Generators

[Eric Scace]

Pete --

   I am not a commerical electrician, but I have built a house with an
emergency generator system.  From my limited understanding, I know there
are several problems with this scenario:

-- Practical Problem:  the circuit breaker that guards this garage outlet
may not be large enough to carry the current that will flow into the rest
of the house.

-- Legal Problem:  This is against the National Electric Code and, almost
certainly, against the local requirements for habitable dwellings (which
are based on the NEC).  You may not care about legal niceties... but, if a
fire occurs while your house is powered this way, the insurance company
might have something to say which would make you very sad.

   There may also be other practical problems for some people (not you, in
this case).  Example: is generator running 240V/120V outputs (2 wires plus
neutral plus ground) or not.  If not, it will be powering only one side of
the 120V portion of the house.  All of the return current will come back
through the neutral side.  The neutral wire in the garage outlet feed may
not be large enough to handle the current safely (fire hazard).  Some parts
of the house will not be able to receive power.

   Most well pumps require 240VAC to reduce the current requirements for
the (frequently lengthy) wiring down to the pump.  The generator may not
produce 240VAC.  If the generator does produce 240VAC, a 240VAC outlet is
needed in the garage in the garage... but most existing garage wiring is
sure to be 120V.  [Pete - yes, you have a 220 outlet in the garage, so this
doesn't apply to you.]

   I am also aware that there is a technical requirement for the neutral to
be grounded at the point of "power generation".  I am not fully versed in
the details of this requirement nor the consequences for not adhering to
it... but I THINK it works as follows:  [I am explaining this part in my
own words -- there is, I am sure, a better set of technical terms in the
trade.]  Typically, at the last step-down transformer that generates the
240/120V feed for your house, the neutral of that transformer will be
grounded there.  In a normal generator setup, the generator's neutral wire
will also be grounded at the generator.  There would be a (big) transfer
switch that transfers neutral along with the other two power-carrying wires
between the generator and the power company feed... so that neutral is only
earthed at one point.  If neutral is grounded at multiple points, there can
be a ground loop (extraneous current flow) which can disrupt the proper
functioning of whatever else is plugged into the line (like your radios).
(When you pull the main breaker to off, it does not interrupt the neutral
line.)

   A safety hazard is the male plug required to plug into your garage
outlet.  If this plug falls out, or if the generator is running while the
plug has not been plugged in, the pins of the plug will be expose and HOT.

   If you (or someone else) EVER makes a mistake and leaves the main
circuit breaker on the house distribution panel "on", the power company
repair people will be very sad if they touch an unearthed cable... and your
generator will be very sad when the electricity is restored (or the
commercial power line is earthed by the repairpeople during the process of
repair -- a typical safety measure).

   These are the drawbacks of which I am aware.  There may be others...
but, to me, these are sufficiently serious.  I would strongly recommend
against the scenario you describe under any circumstances other than
life-threatening (i.e., someone will die unless electrical power is
provided in this building by some quick solution).

-- Eric K3NA

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