Wire size for commercial locations

[lady sparks lover]

Re: Wire size for commercial locations

Question


I thought Lock Rotor Amps were 4 to 8 times the FLA or RLA??

Ed, are you taking the average between 4 and 8??

 

[Guest]

Re: Wire size for commercial locations

It seems the thread was hung-up on wire AWG. Motor protection devices should kick in before the wire fries. The devices are for motor protection but wire protection is a by-product.

../Wayne C.

[ September 25, 2003, 04:41 PM: Message edited by: awwt ]

 

[bennie]

Re: Wire size for commercial locations

Locked rotor current is dependant on the design letter. Generally 600% of the FLA, is a good figure.

A motor is protected based on the 600% of the FLA. A stalled motor should trip off line within 10 seconds. 600% would be considered a short circuit for practical purposes. Any amount of current above the normal load is a short circuit or overload.

A stalled motor with the 600% current increase will cause the magnetic trip of an inverse time/trip circuit breaker to actuate immediately. The thermal devices can and will take the entire 10 seconds to respond.

An HACR breaker actually has a designed delay in the magnetic trip to allow for starting inrush. This is the special feature that sets it apart from a standard thermal/magnetic breaker.

 

[jim dungar]

Re: Wire size for commercial locations

Bennie,

The industry has designated 3 classes of motor overload relay trip curves.

Class 10 = 600% current for 10sec
Class 20 = 600% current for 20sec
Class 30 = 600% current for 30sec

Class 20 is the standard for North American (NEMA) starters, while Class 10 is typical for European (IEC) ones.