Mechanical Interlocks On MCC's

[ElectricMech]

I'm trying to indicated where a mechanical interlock should be so the panel supplier knows where this needs to be tied to. I'm not really experienced in this area and all I know is that it needs to be either on the MCC or the stand alone breaker. How do I find the stand alone breaker on the one-lines? There are no other sparkys around here to help me so I'm hoping I can get my answer here.

 

[jraef]

Not totally sure what you mean, but here's a shot.
If you have an MCC, then I don't understand the reference to a "stand alone breaker". If the starter is in the MCC, the breaker must be in there with it. If you have a feeder breaker in the MCC feeding power to a remote starter, there would not necessarilly need to be another stand alone breaker in the starter again, just a disconnect switch would suffice, although a 2nd CB is OK, just a waste of money since it really is just a local disconnect at that point. So let's separate these scenarios.

1) Starter with breaker in MCC:
If you are referring to an interlock that prevents access to the MCC cubicle unless the power is off, the interlock mechanism is supposed to be a part of the circuit breaker operating mechanism. Depending on the manufacturer, some leave the operating mechanism attahed to the cubib\cle and latch onto a catch on the door, others mount the handle to the door and latch onto a shaft that operates the breaker.

2) Fedder in MCC, remote starter:
The feeder breaker in the MCC will need to have its own interlock with its cubicle door, just as described above. When the starter is remote, AND it has another disconnecting means in its own enclosure, then the disconnect at that enclosure must have a mechanical interlock as well, because there would nbe nothing else preventing someone from opening that box when live. An alternative to that is a padlocked remote enclosure with the key located inside of the MCC cubicle with the interlocked feeder breaker, because you cannot get the key without killing power, but not all inspectors accept this.

If the staerter is remote and it DOES NOT have a local disconnect / breaker in it's box, then the padlock rule applies. Access to the enclosure must be prevented unless the power is off.

Keep in mind that there are other requirements for local disconnecting means etc. not addressed here. You asked about "interlocks".

If I'm totally off base, explain your situation in better detail.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[dpc]

I'm going to make a guess that you are talking about an MCC that has two sources of incoming power and you want to prevent both sources from being energized at the same time.

You might do a Google search for Kirk Key. Basically both breakers need a lock that prevents operating the breaker when the key is removed. Then you have **one** key that is held captive when the lock is in a position that allows the breaker to be closed. This requires modification to both circuit breakers.

If you're talking about something else, maybe you can clarify, or maybe jraef's comments cover it.

When I think of "mechanical interlock" in an MCC, I first think about reversing starters that have a mechanical interlock to prevent closing both contactors at the same time (which is a big drag for everyone involved).

 

[LionelHutz]

I think you're talking about keyed interlocks. Last few times I've seen keyed interlocks on single-line drawings they were shown as a circle with a K1, K2 etc inside with the number representing the matched key sets. So, you'd have 2 or more K1's which are the ones keyed together. They were drawn with a line to the switch and a dotted line between the matched key sets. There was also a note on the drawing in the legend explaining what it represented. I hope this helps.

 

[UKpete]

LionelH, something like this perhaps:

http://www.castellinterlocks.com/machinep.htm

http://www.fortressinterlocks.com/

e.g. used on circuit breakers on utility changeover panels.