PSNet,
The US NEC is quite clear that no one appliance can use the entire branch
circuit capacity unless it is a dedicated circuit. This is what drives the
derating of the allowable current available to any appliance. It is
expected that another appliance will be connected into one of the outlets on
that circuit. This requirement is embedded into various safety standards,
but the root requirement is the NEC.
There is an exception allowed: A dedicated circuit may be supplied for a
particular appliance and, in that case, the appliance may use the entire
capacity of the circuit. A dedicated circuit is one that is specifically
run from the breaker box to a specific location and only has one outlet
available there. This is generally avoided in that one must hire an
electrician to install the dedicated circuit in order to put the equipment
into service; and most customers don't want to spend the money for the
electrician.
Note that you may UL/NRTL List equipment for such use, but you will be
required to specifically note the installation restrictions in the
installation manual; and you may be required to put a special tag on the
power cord with the same information. If the installation is inspected, the
inspector will specifically check for the dedicated circuit before passing
the installation. Avoiding inspection is more problematic in these times
when companies are working harder to have turn-key installations provided by
a contractor - who installs the equipment at the same time the construction
is being finished which draws the inspectors attention to all this equipment
which also must meet the code requirements (read: be Listed). If the
installation is not inspected, you should be so lucky, the customer will
probably have nuisance tripping of the breaker from any other significant
equipment installed on that circuit - which will lead to customer
dissatisfaction with you equipment since it isn't reliable and always
working when expected.
I have such a circuit in my garage specifically for the freezer; not so
much as the freezer needs the entire 15A available from that circuit, but
that I don't want some other appliance throwing the breaker and causing the
freezer to defrost whereby we would loose the entire store of frozen goods.
(That happened to us once before in another house - the circuit blew the
first day of a 3 week vacation, according to the neighbor who saw that the
full-time light we had left burning was out. Anyway, we had moldy meat in
the unit and berry juice running out over the carpet in front of the
freezer. We lost most of half a frozen cow plus a year's crop of berries,
and had to throw the rug out plus my wife spent most of a month getting the
rotten meat smell out of the unit so we could put it back into service. So
much for the war stories.)
br, Pete
Peter E Perkins, PE
Principal Product Safety Consultant
Tigard, ORe 97281-3427
503/452-1201 fone/fax
p.perk...@ieee.org
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