In our experience it's a very good idea to observe the "don't operate a
circuit at more than 80% of rated capacity". We just had to replace a
150A 3-phase breaker which died after being operated a bit too close
(within 10A) of its rated capacity for a number of months.
Cheers,
Bruce
On Mon, 1 May 2006, Jim Lux wrote:
At 08:41 AM 5/1/2006, Mark Hahn wrote:
>
> We've being switching cabinets in one of our datacenters to 220volt
> service to support the sort of density we're seeing without running new
> conductors.
sure, there's no downside to 220 afaikt. one thing I don't fully
understand is where the 80% figure comes from. just a fudge-factor,
and what if you wind up always using that extra capacity?
presumably an L6-30 circuit is actually safe to run at 30...
The electrical code usually requires that a circuit be wired (and overcurrent
protected) so that the expected load is no more than 80% of the circuit
ampacity. If you don't have a specific design, then the expected load is
calculated by using a set of rules that turn square feet of floor space and
what that space is used for (offices are different than residential are
different than a parking lot). There's also rules for certain specific kinds
of loads and locations (i.e. you have to have 20 Amp circuits for a
refrigerator in a kitchen) and rules about what kinds of loads can be shared
(no combining the lights and the receptacles in a kitchen).
"L6-30" is a NEMA designation for a particular form of pins in the
plug/receptacle. "L" for locking. 6 for the particular configuration of pins,
and it's nominal usage: The 30 refers to convention for what that
plug/receptacle configuration is used for (i.e. a 30 Amp circuit, intended
for use at 24 Amps)
Bear in mind, also, that the various configurations will have designs
compatible with the nominal use. For instance, a configuration designed for
30A service will accomodate AWG10 or AWG8 wires, typically larger on the
receptacle (female) than on the plug (male). There's also voltage ratings
that apply to each configuration. That is, a connector designed for 480V
service will be rated for 600V, and have different clearances internally than
a connector designed for 120V service, rated for 300V.
It is not unheard of to have NEMA plugs and receptacles used on circuits with
ratings different than the nominal. For example, some of the other 4 wire
connectors for 277 or 480V are used on 230V circuits, just to provide
different, non-inadvertently-interchangeable pin configurations. For
instance, you might have a motor controller that is supplied with a L15-30
(30A, 3ph, 250V rating) from the wall, and the motor is connected using a
L17-30 (which is normally on a 480V 3ph line). This is why you should always
check before blindly plugging something in.
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875
_______________________________________________
Beowulf mailing list, [email protected]
To change your subscription (digest mode or unsubscribe) visit
http://www.beowulf.org/mailman/listinfo/beowulf
_______________________________________________
Beowulf mailing list, [email protected]
To change your subscription (digest mode or unsubscribe) visit
http://www.beowulf.org/mailman/listinfo/beowulf
