700.19 Multiwire Branch Circuits The branch circuit serving emergency lighting and power circuits shall not be part of a multiwire branch circuit.
This is a Code change from the “2014” NEC that came up this week at work. Multiwire branch circuits are no longer allowed for “Emergency Circuits”. Reason behind this change follows what was done in the 2011 Code for Hospital circuits in sections 517.18(A) and 517.19(A). This allows for a ground fault, short circuit, or an overload to occur without tripping a two pole or three pole circuit breaker which would take out other essential loads. Only individual branch circuits will be allowed.
For example reliability is certainly decreased when a short in a 277 volt lighting ballast takes out the other two poles of a three pole circuit breaker, knocking out the remaining 2/3 of the lighting. With this requirement only the 1/3 of the lighting on the affected pole is out, leaving 2/3 of the lighting in operation when using individual branch circuits. Makes sense!
Till next time be safe wear your mask.
Jake
PS Nice picture of box fill. Yeah we need to add dimmers!!!
