Does a Kirk key interlock need to be installed?

I

Isaiah

Senior Member
Location
Baton Rouge
Occupation
Electrical Inspector
We have a 480V SWGR that gets input from 2-500kVA Emerg generators when there is an outage.
There is no ATS and the two generators feeders terminate in 1600A CB. There is also a MCB that gets its supply from a normal 480V source.
They want to manually close 1600A CB when there’s a outage (which doesn’t lineup with Nec 700 or 701).
In addition there is no kirk-key interlock between the MCB and the feeder CB.
There seems to be multiple code issues here


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It doesn't sound like either 700 or 701 apply to this installation.
I believe 702 does, and 702.5(A) requires transfer equipment. The 2026 will also permit interlock equipment. Breaker interlocks are commonly used and accepted under the 2023 code and older codes.
I would require some type of interlock and for your example, about the only thing that would work is a kirk-key system.

It looks like you are paralleling two generators? What are you using for paralleling equipment?
 
don_resqcapt19 said:
It doesn't sound like either 700 or 701 apply to this installation.
I believe 702 does, and 702.5(A) requires transfer equipment. The 2026 will also permit interlock equipment. Breaker interlocks are commonly used and accepted under the 2023 code and older codes.
I would require some type of interlock and for your example, about the only thing that would work is a kirk-key system.

It looks like you are paralleling two generators? What are you using for paralleling equipment?
Click to expand...

Thanks Don
They’re having trouble syncing the paralleled feeders from the Generator CBs to the SWGR BUS…but are you saying that under 702, the breaker interlocks are not actually required?
Using the the 2020 NEC


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Isaiah said:
Thanks Don
They’re having trouble syncing the paralleled feeders from the Generator CBs to the SWGR BUS…but are you saying that under 702, the breaker interlocks are not actually required?
Using the the 2020 NEC


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Click to expand...
The 2020 & 2023 requires transfer equipment and does not permit interlocks. In the case of breaker locks, which accomplish the same thing as a kirk-key, most AHJs permit them.
702.5(A) General.
Transfer equipment shall be required for all standby systems subject to the requirements of this article and for which an electric utility supply is either the normal or standby source. Transfer switches shall not be permitted to be reconditioned.
Click to expand...

I would permit an interlock system of some type for this, but some AHJs would require actual transfer equipment as stated in the code.
 
don_resqcapt19 said:
The 2020 & 2023 requires transfer equipment and does not permit interlocks. In the case of breaker locks, which accomplish the same thing as a kirk-key, most AHJs permit them.


I would permit an interlock system of some type for this, but some AHJs would require actual transfer equipment as stated in the code.
Click to expand...
You know who pushed that through! Transferswitch manufacturers!
 
don_resqcapt19 said:
The 2020 & 2023 requires transfer equipment and does not permit interlocks. In the case of breaker locks, which accomplish the same thing as a kirk-key, most AHJs permit them.


I would permit an interlock system of some type for this, but some AHJs would require actual transfer equipment as stated in the code.
Click to expand...

Great feedback Don as always!


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don_resqcapt19 said:
The 2020 & 2023 requires transfer equipment and does not permit interlocks.
Click to expand...
Where does it specify key interlocked equipment as not being allowed?
Key interlocks are a type of mechanical interlock.
Relay/electronic interlocked paralleling/transfer equipment has been used for decades.
Neither of these types of transfer equipment are equal to simple electrical interlocks.
 
don_resqcapt19 said:
It doesn't sound like either 700 or 701 apply to this installation.
I believe 702 does, and 702.5(A) requires transfer equipment. The 2026 will also permit interlock equipment. Breaker interlocks are commonly used and accepted under the 2023 code and older codes.
I would require some type of interlock and for your example, about the only thing that would work is a kirk-key system.

It looks like you are paralleling two generators? What are you using for paralleling equipment?
Click to expand...

Since these two generators are paralleled and terminate in a single CB at the SWGR, I assume they must also conform to 705?


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don_resqcapt19 said:
The 2020 & 2023 requires transfer equipment and does not permit interlocks. In the case of breaker locks, which accomplish the same thing as a kirk-key, most AHJs permit them.


I would permit an interlock system of some type for this, but some AHJs would require actual transfer equipment as stated in the code.
Click to expand...
Is there a specific definition of transfer equipment that would exclude a kirk key system. I would not allow breaker locks because they don't force an actual transfer. Both can be on or off simultaneously. That is not anyone's definition of transfer.
 
jim dungar said:
Where does it specify key interlocked equipment as not being allowed?
Key interlocks are a type of mechanical interlock.
Relay/electronic interlocked paralleling/transfer equipment has been used for decades.
Neither of these types of transfer equipment are equal to simple electrical interlocks.
Click to expand...
It requires transfer equipment and interlocks are not transfer equipment. Interlocks have been used for years, but the actual code language does not permit that for connecting standby sources.

Yes the key interlocks are a mechanical interlock, but are not transfer equipment and the code language requires the use of transfer equipment. Yes, I am aware that mechanical interlocks have been used for this purpose for years. I submitted a PI for 702.5 that will add "interlocks" for the 2026 code. This is only an issue in 702 as 700 and 701 require listed automatic transfer equipment.

The relay interlocked paralleling and transfer equipment is probably listed as transfer equipment.
 
petersonra said:
Is there a specific definition of transfer equipment that would exclude a kirk key system. I would not allow breaker locks because they don't force an actual transfer. Both can be on or off simultaneously. That is not anyone's definition of transfer.
Click to expand...
The definition of a transfer switch says it is a single device, which does not include multiple devices with interlocks.
 
jim dungar said:
Yes, a switch is a single device. Does anyone make a MV transfer switch?
But doesn't the NEC require Listed transfer equipment?
Click to expand...
An interlock system involves two switches and is not a single device.
Articles 700 and 701 require the use of listed automatic transfer equipment, and since it must be automatic, it precludes the use of any type of interlock.
I know that there are automatic MV transfer switches as the utility had them on the feeds for a couple of different hospitals that I worked on.
However, not sure that there are any listed MV transfer switches.
 
don_resqcapt19 said:
Articles 700 and 701 require
Click to expand...
I think this is the important part.
I think MV transfer equipment are now only for 702 systems.

Proper wording versus industry slang is important.
All Listed transfer switches are Listed transfer equipment, but not all Listed transfer equipment are Listed transfer switches
 
don_resqcapt19 said:
An interlock system involves two switches and is not a single device.
Articles 700 and 701 require the use of listed automatic transfer equipment, and since it must be automatic, it precludes the use of any type of interlock.
I know that there are automatic MV transfer switches as the utility had them on the feeds for a couple of different hospitals that I worked on.
However, not sure that there are any listed MV transfer switches.
Click to expand...

Don do you think the feeders from two generators that terminate in the single 480V CB constitute “Transfer equipment” per NEC 702.5(A)? They want to do everything manually - not via auto transfer
Thanks


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