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Why is my APC by Schneider Electric UPS derated to 80% of the circuit's total capacity?
Issue
My APC by Schneider Electric UPS is derated to 80% of the circuit's total capacity.
Product Line
All UPS systems
Environment
All serial ranges
Cause
When installing an APC UPS or any electrical device, it is important to keep in mind the ampacity of the circuit into which it is connected. Per National Electric Code which is developed by the National Fire Protection Association, a circuit must be derated to 80% its capacity.
Users often have questions regarding the amperage draw of the load versus what the circuit is capable of supplying. According to National Electric Code, continuous loads (like an UPS operating continuously longer than three hours per day) must not exceed 80 percent of the branch-circuit over current device (e.g. fuse or circuit breaker) rating. The following is taken directly from Article 210-23 of the 2011 National Electric Code Handbook.
(a) 15- and 20- Ampere Branch Circuits. A 15- or 20- ampere branch circuit shall be permitted to supply lighting units, other utilization equipment, or a combination of both. The rating of any one cord- and plug- connected utilization equipment shall not exceed 80 percent of the branch-circuit ampere rating...
(b) 30- Ampere Branch-Circuits. A 30- ampere branch circuit shall be permitted to supply fixed lighting units with heavy-duty lamp holders in other than a dwelling unit(s) or utilization equipment in any occupancy. A rating of any one cord- and plug-connected utilization equipment shall not exceed 80 percent of the branch-circuit ampere rating.
If there are further questions on this documentation, please consult the National Electric Code Handbook or write to:
National Fire Protection Association
P.O. Box 9101
Quincy, MA 02269-9101
Resolution
APC UPS systems are either appropriately derated out of the box or, in the case that the UPS requires a hardwire connection, the input connection recommendations take into account the 80% rule.