For industrial machinery, the NEC (NF{PA 70) requires an FLA marking on the
machine nameplate, and that the value "shall not be less than the sum of the
full-load currents required for all motors and other equipment that may be in
operation at the same time under normal conditions of use."
Large, complex machinery may have many, many loads fed from its internal power
distribution system (e.g., controllers, power supplies, robots, etc...). Each
of these sub-systems is usually a stand-alone commercial product with a
nameplate of its own indicating its own FLA rating.
More often than not, such large complex machinery is not operated with all of
its sub-systems running at full power (e.g., all set to '10'). In typical
operation it may be that many are set at 8, most at 5 and a few at 2 (for
example).
Does the 'may' in 'may be in operation at the same time' require that one
consider what *could* happen even if it is not how the machine would ever,
realistically, be operated, or is it acceptable to take some empirical
measurements for a 'typical' operating scenario and set the nameplate FLA
based on that?
Is there any commonly accepted position paper for US electrical inspectors on
this point?
The issue of course is whoever installs the machine has to design their
infrastructure to support the nameplate FLA. If a machine nameplate FLA must
be determined by the simple addition of sub-system FLA's, then there is
possibility for great waste (unneeded current carrying capability). If a
machine nameplate FLA can be set by some more empirical method (e.g., current
draw during intended use), then sensible infrastructure is possible.
==============
60204-1:2005
The question converts into the EU also since '204 has very similar criteria
for the full-load current marking of the nameplate.
"The full-load current shown on the nameplate shall be not less than the
running currents for all motors and other equipment that can be in operation
at the same time under normal conditions."
Thanks for any insight/advice.
Lauren Crane (Mr.)
Product Regulatory Analyst
Corporate Product EHS Lead
Applied Materials Inc.
Austin, TX 512 272-6540 [#922 26540]
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