Electrical codes and plugs/sockets was Re: [Beowulf] Opteroncooling specifications?

[Michael Will]

And this is generally the message - short term it will work
but long term continuous load should stay at 80%. There are different
timeouts for breakers to be triggered at different over-80% levels.

Michael

-----Original Message-----
From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org]
On Behalf Of Bruce Allen
Sent: Monday, May 01, 2006 12:01 PM
To: Jim Lux
Cc: beowulf at beowulf.org; Mark Hahn
Subject: Re: Electrical codes and plugs/sockets was Re: [Beowulf]
Opteroncooling specifications?

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
>
>
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