Branch Circuit Calculation for computer labs

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steveng

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What code article covers how many computers you can have per branch ckt? the computer/monitor are rated @ <3amp
i have to power up 32 computers in a school lab, and a laser printer.

would 6 per ckt be allowed?
 
steveng said:
What code article covers how many computers you can have per branch ckt? the computer/monitor are rated @ <3amp
i have to power up 32 computers in a school lab, and a laser printer.

would 6 per ckt be allowed?
Click to expand...


Assuming 3A at 120v = 360VA per computer/monitor combo.

I would consider these to be continuous loads since it is likely they will operate for more than 3 hours continuously. 360VA x 1.25 = 450VA.

15A circuit @ 120v = 1800VA
1800VA / 450VA = 4 computers per 15A circuit

20A circuit @ 120v = 2400VA
2400VA / 450VA = 5 computers per 20A circuit.

Code reference is NEC Art. 210.19
 
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since they typically shut down into power saving mode when not in use, I would not consider them to be continuous.

In any case, I think the numbers make sense. you don't want to trip a CB because someone also plugged in a switch or a laptop at a station.

My preference would be a separate 4 banger on a 20A CB for each workstation. More money, but than they won't mess with each other.
 
petersonra said:
since they typically shut down into power saving mode when not in use, I would not consider them to be continuous.
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From NEC Art. 100 - Definitions
Continuous Load. A load where the maximum current is expected to continue for 3 hours or more.

Unless you know for certain that no computer will be in use for more than 3 hours continuously, how could you decide they are not a continuous load? I would expect the computers to be on and in use for most of the day continuously.
 
baddriver said:
From NEC Art. 100 - Definitions
Continuous Load. A load where the maximum current is expected to continue for 3 hours or more.

Unless you know for certain that no computer will be in use for more than 3 hours continuously, how could you decide they are not a continuous load? I would expect the computers to be on and in use for most of the day continuously.
Click to expand...

You are missing the part where the definition says MAXIMUM current. A computer could be on and in use all day, but they will not be using their maximum current continuously for 3 hours or more.
 
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