Point of Connection - Compliance with NEC Art 690.64.B2

[cuky2000]

NEC 690.64.B2 stipulates the sum of the ampere ratings of over current devices in circuits supplying power to a bus bar or conductor shall not exceed 120 percent of the rating of the bus bar or conductor.

Should this rule consider the circuit breaker frame size or the trip setting of the breaker?

_{For example:
a) If the switchboard rated for 3,200 A with 5-800 A breakers /1.20 = 3,333 This do not meet the NEC.
b) If all 800 A breakers frame are set to trip at 650 A (5x650 A/1.20 = 2708 A) this appears to be OK}

 

[rcw retired EE]

I believe it applies to the sum of the trip ratings. Implied intent is to prevent overloading.

NEC paragraph 690.64 was changed in the 2011 Code to refer to Section 705.12 which has the same rule, expressed a little differently. I still think it should be for the trip rating becaseu thatis teh "Ampere rating".

 

[RonShap]

Review the text in 240.6 with regard to whether the breaker is considered adjustable-trip or has restricted access to the adjustment. If it is only adjustable by replacing a trip plug or sensor, I would consider that restricted access and use the trip setting (ampere rating equal to the adjusted setting).