NEC 695.4

[anas ibrahem]

hello guys i Have a question

In Nec 695.4 B a (2) which talk about the overcurrent protection device of the fire pump if the source is the standby generator .... Why we dont size the breaker to carry the locked rotor of the fire pump motor same as the breaker of the utility ?

 

[ron]

Do you mean 695.4(B)(2)(b) ?
This requirement correlates with 695.3(D)(1) covering the required capacity of an on-site standby generator. OCPDs supplied by an on-site standby generator are not required to be sized to carry the locked-rotor current (LRC) of the fire pump(s) indefinitely. The on-site standby generator is not limited to supplying only the fire pump. Where other pump room loads such as lights or fans are supplied, the generator must have sufficient capacity to instantaneously carry the entire load supplied. The OCPDs are not required to provide overload protection and are required to be sized per 430.62.

 

[anas ibrahem]

yes ron i meant this article ... Therefore my question why we dont need to size it to carry locked rotor

 

[ron]

yes ron i meant this article ... Therefore my question why we dont need to size it to carry locked rotor

Because it is the second source and not practical in many cases for the generator to be oversized. It is nice to have the optional 2nd source at all.

 

[anas ibrahem]

i understood u but the requirement to sizing it not carry LRC same in multibuidling campus style complexes do you know the reason ?

 

[Canton]

i understood u but the requirement to sizing it not carry LRC same in multibuidling campus style complexes do you know the reason ?

Simply put…it’s a back up. If it had to meet the same requirements it would be way larger than needed

 

[anas ibrahem]

Thank u for your reply ... but how multibuidling is a backup source its a main source for the pump