Kirk Key Required by NEC (or other applicable codes)

[jstpie5]

Scenario:
There is a MV VFD that is fed by MV SWGR (in the same room).

Is there any NEC (or other applicable code) that requires a Kirk Key interlock between the VFD and the contactor in the MV SWGR?

I say it is good practice to have an interlock between the two, but it can be address by administrative procedures and be in compliance with applicable codes.

What say you fine gentlemen and gentleladies???

 

[GoldDigger]

NEC requires disconnects for safety (sometimes lockable, if not in plain view) and isolation switching of some kind for alternate power sources which cannot be paralleled with the grid or other alternate sources.
But a Kirk Key system is only one way of achieving those goals and is not called out specifically in the NEC.

 

[charlie b]

I agree with GoldDigger.

But I am confused with your description. Are there two power sources to the motor? If power goes from something outside the room to the MV SWGR, then to the VFD, and finally to the motor, why would you need an interlock? I have only see Kirk Keys used to prevent two separate power sources from being inadvertently connected to each other.

 

[jstpie5]

I agree with GoldDigger.

But I am confused with your description. Are there two power sources to the motor? If power goes from something outside the room to the MV SWGR, then to the VFD, and finally to the motor, why would you need an interlock? I have only see Kirk Keys used to prevent two separate power sources from being inadvertently connected to each other.

@charlie - the MV SWGR has a contactor that feeds power to the VFD (located 10 feet or so away). There is only one source of power to the motor (no vfd bypass).

The AHJ has raised a concern (years after the installation) is that someone could open the VFD compartment where the power conductors terminate without first de-energizing the feeder. I certainly understand the safety concern.

I also get that AHJ has the final say on this, but I wanted to make sure there's no code requirement that requires an interlock system for this (and similar) installations.

From what I could find in the NEC the SWGR just needs to be lockable..

NEC 430.102(A) Exception No. 1 states “For motor circuits over 1000V, nominal, a controller disconnecting means lockable in accordance with 110.25 shall be permitted to be out of sight of the controller, provided that the controller is marked with a warning label giving the location of the disconnecting means.”

110.25 just says the disconnecting means (switchgear needs to be able to be locked in the open position.

Am I missing something? I don't mind learning something new; my main concern is that things are installed in accordance with the code.

 

[charlie b]

The cover to almost any electrical enclosure can be opened without first deenergizing the upstream power source. The code requires a method of turning off power, and you have that. But it does not command you to use it. Yes, opening the VFD compartment without first putting a LOTO on the source presents a safety risk. But an interlock is not the answer. Rather, the answer is a good LOTO process and qualified workers.

The Kirk Key installations I have designed work like this:
1. Turn off (e.g., open breaker for) the source presently feeding the load.
2. Only then can you remove the Kirk Key from that breaker.
3. That breaker cannot be reclosed until the key is reinserted into its lock.
4. Insert that same key into the other power source's breaker.
5. Only then can you close that breaker.

The fact that only one key exists and that it can only installed in one breaker at a time is what prevents inadvertent connection of the two sources. I can't imagine how such an interlock could work for a contactor in one enclosure and the cover of another enclosure.

 

[don_resqcapt19]

@charlie - the MV SWGR has a contactor that feeds power to the VFD (located 10 feet or so away). There is only one source of power to the motor (no vfd bypass).

The AHJ has raised a concern (years after the installation) is that someone could open the VFD compartment where the power conductors terminate without first de-energizing the feeder. I certainly understand the safety concern.

I also get that AHJ has the final say on this, but I wanted to make sure there's no code requirement that requires an interlock system for this (and similar) installations.

From what I could find in the NEC the SWGR just needs to be lockable..

NEC 430.102(A) Exception No. 1 states “For motor circuits over 1000V, nominal, a controller disconnecting means lockable in accordance with 110.25 shall be permitted to be out of sight of the controller, provided that the controller is marked with a warning label giving the location of the disconnecting means.”

110.25 just says the disconnecting means (switchgear needs to be able to be locked in the open position.

Am I missing something? I don't mind learning something new; my main concern is that things are installed in accordance with the code.

The AHJ does not get to make up rules, only the legally adopted code and any legally adopted amendments can be enforced.
As long as the power source can be locked out on the line side of the VFD, the installation is in compliance with the requirements of the NEC.

 

[jim dungar]

The AHJ does not get to make up rules, only the legally adopted code and any legally adopted amendments can be enforced.
As long as the power source can be locked out on the line side of the VFD, the installation is in compliance with the requirements of the NEC.

Unless the AHJ is also the customer, like happens on VA medical projects. The OP said the installation is several years old.

Charlie, keys are not just for sources. The key interlock scheme would require the feeder breaker to be locked open before the key can be used to unlock the VFD compartment.

Many decades ago I had to install a key interlock for the primary terminal compartment of a MV transformer to satisfy the state AHJ.

 

[charlie b]

Charlie, keys are not just for sources. The key interlock scheme would require the feeder breaker to be locked open before the key can be used to unlock the VFD compartment.

I understand that, Jim. But the OP was asking about a key interlock between the VFD compartment and an upstream contactor (i.e., not the upstream breaker). That is what confused me.

 

[charlie b]

By the way, there are five contributors (so far) to this thread. Four of us are retired. I don't know what to make of that.

 

[TwoBlocked]

By the way, there are five contributors (so far) to this thread. Four of us are retired. I don't know what to make of that.

Uh those that aren't retired work during the day.

 

[TwoBlocked]

I have seen Kirk keys used as described by Charlie for ties to another LV feed, but not MV. But I have seen Kirk keys used to insure the secondary of a transformer is open before opening the primary, both for MV and HV. For access, like the OP describes, I have seen Kirk keys used for accessing MV transformer primary disconnect fuses.

I have not seen a Kirk key used for the purpose the OP describes.

I have seen kill switches on access doors that will kill the power if opened. They are usually easy to spot. They are the limit switches with the zip tie holding the switch in the closed position.

For access, I don't see how the AHJ can have a say so. I take it the VFD is listed. And if installed according to the manufacturer, that's it.

 

[petersonra]

I think there are multiple ways to handle these kind of things and the code rarely if ever specifies a specific solution.

For instance, the code allows a switch or a breaker to be used as a disconnecting means, but does not require either.

 

[jim dungar]

I understand that, Jim. But the OP was asking about a key interlock between the VFD compartment and an upstream contactor (i.e., not the upstream breaker). That is what confused me.

The way to lockout a contactor is to open and lock out its feeder.

 

[Tulsa Electrician]

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