motor control

[Porter]

Can anyone tell me why, in a motor control circuit its required we break the neutral unlike every other type of circuit ? :-?

 

[rbalex]

Can anyone tell me why, in a motor control circuit its required we break the neutral unlike every other type of circuit ?

Actually there is no general rule that prohibits breaking a grounded conductor. There are various specific prohibitions and requirements. For motor control circuits there is a conditional rule in 430.74.

NEMA ICS2, Section 7.3 - explains that locating the contact between the m-coil and the grounded conductor minimizes the potential of contact welding. Since the overload contact is normally closed a welded condition may go undetected.

 

[jim dungar]

Can anyone tell me why, in a motor control circuit its required we break the neutral unlike every other type of circuit ? :-?

The general rule is about not putting an overcurrent device in the grounded conductor.

 

[Smart $]

Can anyone tell me why, in a motor control circuit its required we break the neutral unlike every other type of circuit ? :-?

In basic motor control circuits, the overload is the only "break in the neutral". With the load of the circuit being the contactor coil, all other "breaks" are on the ungrounded side of the circuit.

Somehow you are getting the wrong impression if you are thinking all control switching must be on the grounded-side of the coil.

 

[don_resqcapt19]

Somehow you are getting the wrong impression if you are thinking all control switching must be on the grounded-side of the coil.

In fact, 430.74 prohibits control devices external to the starter on the grounded side of the circuit. As others have said it is common practice to have the overload contact in the grounded side, however I have worked on projects where the specs prohibited that practice.