What really gets my goat is that NFPA 130 won't allow me to use thermal overload protection in subway emergency ventilation fans. It seems a darn shame because most of the time they are used won't be for emergencies. I never got a clarification as to whether or not I can use overloads other than thermal.
{bold emphasis mine}
Joe, I think the reason is the same as for fire pumps (Art. 695, 1999 NEC, latest edition I have), in that it is far more important in that application to have the motor operate to failure than to have it shut down in the middle of an emergency situation, thus adding to the hazards created by the original emergency. In fact, a fire pump is one of the few exceptions that allows a tap
ahead of the service disconnecting means!
My local motor repair shop has shown me the results of a motor used in a fire pump that was operated to total failure (It was big, IIRC 25hp) and it had to be scrapped! The combination of eddy current heating and burning/arcing of the windings totally destroyed the laminations of the stator.
The rotor also showed some peculiar effects that I can't even describe.
Now as to the part I made bold here, isn't that a violation of NFPA and other codes? I had thought that those types/classes of fans (like in some large buildings) were to be used
only in emergencies? The whole point of those fans is to back up the primary ventilators in the event of fire or in your case, excessive fume build-up.
edited for spelling
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[This message has been edited by mxslick (edited 03-26-2006).]
[This message has been edited by mxslick (edited 03-26-2006).]
