Reversing Starter

[jap]

Is there any code requirement that a reversing starter would need to be both Electrically and Mechanically interlocked?

or,

Can a reversing starter be Electrically interlocked only?


Thanks,

JAP>

 

[kwired]

Is there any code requirement that a reversing starter would need to be both Electrically and Mechanically interlocked?

or,

Can a reversing starter be Electrically interlocked only?


Thanks,

JAP>

I don't think NEC even requires any kind of interlock here, though it is generally accepted as good design to have at least one or the other type of interlock.

 

[ptonsparky]

VFDs make that easy if you can think of additional justification.

 

[kwired]

VFDs make that easy if you can think of additional justification.

If you get both FWD and REV signal to a VFD, additional parameters will possibly determine which one gets higher priority or even other input conditions may be considered.

 

[Jraef]

There is no NEC requirement for it, neither is it required in UL or other design / testing specifications. But it falls under "prudent design considerations" because if you use ONLY the electrical interlocking, the result of a single failure of an aux contact is catastrophic not only to the starter, but the entire electrical system. Closing both contactors is a "bolted fault", meaning it will deliver the highest possible short circuit conditions when it happens, testing the withstand ratings of all components in the system. True, everything SHOULD survive if properly designed and coordinated, but how willing are you to take that chance?

What is the cost of the electrical interlock compared to the down time cost? The answer is... minuscule, no matter what you are doing with that reversing starter!

One place I see people leave out the mechanical interlock a LOT is in elevator controls. Why? Two reasons; they are cheap about how they build them and THE SERVICE CONTRACTOR BENEFITS from the call out to fix everything because elevator controls need certified technicians (in many cases).