Thread: 80% rule in datacenters?
05-05-2012, 04:16 PM #61
If you have a 20 amp breaker, max continuous load is 16 amps. This is not questioned by anyone (20 / 1.25).
16 amps continuous load times 1.25 allowed spike load is, guess what? 20 amps - the size of the breaker.
If your datacenter doesn't define operating requirements in their environment stricter than those defined by laws / the NEC, then you should be able to spike non-continuous load to 20 amps without an issue.0
05-05-2012, 04:20 PM #62
Multiply continuous load times 1.25
add non continuous load
Result of the two added together must be less than rated circuit / breaker size.
In my case, I'm never using under 14a on that circuit, so there is no room for argument that my continuous load is under 14a. 14 times 1.25 = 17.5. If I'm using a 20a breaker, this means there is 2.5a "left over" for non continuous loads, which would mean, a total of 16.5a.0
05-05-2012, 04:34 PM #63
The 125% sizing of the Over Current Protection Device (or 80% loading) is only applicable when continuous loads are involved. Circuit Breakers and other OCPDs can be sized at 100% of their rating for noncontinuous load applications.
What this means is, if you mix continuous and non-continuous loads on the same circuit, the circuit must be rated for the larger 125% sizing, and not simply 100% sizing. You do not add these together to come up with 225%
It is extremely rare for continuous and non-continuous loads to be on the same circuit, which is why this isn't very clear from reading the NEC as it assumes you will use separate circuits for the different loads types. If you mix loads you use the stricter continuous load definition at 125%, otherwise you use the 100% definition. You don't use both definitions at the same time.
Last edited by ramnet; 05-05-2012 at 04:48 PM.0
05-05-2012, 06:23 PM #640
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