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NEC in the Facility

Jan 4, 2010 4:36 PM

Retrofits, upgrades, and additions can result in a change to the "total load" used for sizing service conductors. Don't look only at the size of your service transformer(s) when adding equipment, upgrading HVAC, or making other configuration changes. Service conductors that were correctly sized with load diversification and other mitigating factors may suddenly be undersized.

Any time you add or change a load, you should recalculate the required ampacities of the conductors for the branch circuit, feeder, and service supplying that load. The service is the most critical, as loss of those conductors will shut down the whole area supplied by that service.

The ampacity of service conductors before any adjustment or correction factors must be at least the sum of the noncontinuous loads plus 125% of the continuous loads [230.42]. But if the service-entrance conductors terminate in an overcurrent protection device (and its assembly) listed for operation at 100% of rating, use the sum of noncontinuous and continuous loads.

Calculate each load per Art. 220, Part III, IV, or V as appropriate. Determine ampacity per 310.15.

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