210.63 HACR outlet - tapped before unit's disco - violates code?

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Dark Sparky

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We've specified that a piece of 480V HVAC equipment - an RTU (rooftop unit) - come supplied with a receptacle to satisfy NEC (2011) 210.63. The specifications call for the 480V circuit that feeds the RTU to be tapped before the RTU's disconnect, to feed a control transformer, to supply the 120V convenience outlet on the RTU. (This type of outlet is a standard option available from some RTU manufacturers.)

We've had feedback that tying the receptacle to the 480V feeder before the disconnect is not allowable by code.

Can anyone explain why? Or if this is a common misconception?

Thanks in advance!
 
Mech contractor

Mech contractor

jumper said:
Pretty common install. Who is balking at the idea?
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The mechanical contractor. Perhaps that's my answer - they likely aren't familiar w/ electrical code.

Nevertheless - I would like to get some input on whether this should meet code. Thanks!
 
Xfmr size

Xfmr size

infinity said:
What size transformer?
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I will ask...not sure.

The xfmr does not exist yet, most likely: These RTU units were incorrectly spec'd by the contractor. Thus they are looking to add the receptacles now. Thus I do not believe the control power transformers are yet sized, but we may be able to find what a typical size one would be.

I would imagine that the xfmr would be simply large enough for a 20 amp receptacle - perhaps 2 kVA-ish?
 
jonathankpa said:
We've had feedback that tying the receptacle to the 480V feeder before the disconnect is not allowable by code.

Can anyone explain why? Or if this is a common misconception?
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I think the contractor has it backwards. Tying the receptacle to the feeder AFTER the disconnect is not allowable by Code (210.63.)
 
david luchini said:
I think the contractor has it backwards. Tying the receptacle to the feeder AFTER the disconnect is not allowable by Code (210.63.)
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The potential drawback would be if the disconnect normally used for maintenance is NOT the one which is part of or attached to the unit.
In that case opening a remote disconnect would kill the convenience outlet too.
The assumption made is that the tap and control transformer is there so that a tech can plug in equipment, not just to supply power to control circuitry that is part of the unit.

Note also that if the control circuitry is fed from a tap before the disconnect and does not have its own disconnecting means, it pretty much means that you have to disconnect farther up before working on the controls. And then you lose the receptacle outlet again.
 
jonathankpa said:
I will ask...not sure.

The xfmr does not exist yet, most likely: These RTU units were incorrectly spec'd by the contractor. Thus they are looking to add the receptacles now. Thus I do not believe the control power transformers are yet sized, but we may be able to find what a typical size one would be.

I would imagine that the xfmr would be simply large enough for a 20 amp receptacle - perhaps 2 kVA-ish?
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A 2 kva transformer would require a GEC for the connection to the building grounding electrode system. A violation I see quite a bit when using these setups.
 
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GoldDigger said:
The potential drawback would be if the disconnect normally used for maintenance is NOT the one which is part of or attached to the unit.
In that case opening a remote disconnect would kill the convenience outlet too.
The assumption made is that the tap and control transformer is there so that a tech can plug in equipment, not just to supply power to control circuitry that is part of the unit.

Note also that if the control circuitry is fed from a tap before the disconnect and does not have its own disconnecting means, it pretty much means that you have to disconnect farther up before working on the controls. And then you lose the receptacle outlet again.
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Thanks for pointing this out. Yes - the whole point of the disconnect is that one can kill power to the RTU, but still use the receptacle to service the equipment.

I believe the transformer in question is only for the convenience outlet, not for the controls. (Sorry if I obscured that by calling it a 'control transformer'.)
 
Xfmr ground

Xfmr ground

infinity said:
A 2 kva transformer would require a GEC for the connection to the building grounding electrode system. A violation I see quite a bit when using these setups.
Click to expand...
Thank you - that's a great reminder.


To everyone - unless I hear otherwise, I don't hear anyone saying why this would be a code violation.

The only thing I can see an inspector might want could be a sign stating that the disconnect does not kill power to the outlet, and noting the location of the outlet's 'disconnect' (breaker)?
 
New info

New info

New info on why they are saying that this does not comply (although I was not given a code reference that I requested). This is from the mechanical contractor - explaining why they feel that the "non-disconnectable" receptacle does not meet code. Is this true?

It appears that you are asking us to double lug the primary side of the disconnect, add a transformer to step down the voltage and wire the convenience outlet on the RTU. This methodology does not meet code and will not be allowed by the Local Authority Having Jurisdiction. This could be performed inside the termination box inside each unit, but as previously stated this would mean that it would lose power if the service disconnect has been moved to the off position.

The correct way to install receptacles for servicing units is to run a separate 120 volt circuit for these receptacles. Per general guidelines, the drawings should have receptacles located within sight of each piece of mechanical equipment on the roof and the electrician should know that this is required. We have achieved location of the receptacles by having them come factory with each RTU.

One option, as I understand it, is to add a junction box prior to the RTU disconnect, to add another disconnect and transformer to feed the convenience outlet.
 
jonathankpa said:
Thank you - that's a great reminder.


To everyone - unless I hear otherwise, I don't hear anyone saying why this would be a code violation.

The only thing I can see an inspector might want could be a sign stating that the disconnect does not kill power to the outlet, and noting the location of the outlet's 'disconnect' (breaker)?
Click to expand...
The branch circuit device for that receptacle is very likely going to be right in the same vicinity, you were tapping off the HVAC 480 volt circuit, supplying a transformer, and should need an overcurrent device somewhere in there, maybe even a primary and secondary device.
 
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