Ten-foot inverter tap rule

240.21(B)(1), the ten-foot tap rule (for taps of ten feet or less):

• Tap ampacity > tap load

• Ampacity of tap conductor has to be greater than the load.

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Example:

• ten-foot tap rule

• 200A source breaker

• 16A inverter.

The tap conductor must be at least 10% of (source breaker + 125% inverter

current):

                                             16A inverter 3 1.25 = 20A

                                       20A + 200A source breaker = 220A

                                                   0.1 x 220A = 22A

Tap conductor must be at least 22A

Additionally, the inverter breaker must be less than 22A and for a 16A inverter;

we would use a 20A breaker (16A 3 1.25 = 20A breaker).

One more thing to check is the 230A feeder, which needs to be enough to carry

currents from the source and 125% of the inverter.