277V Lighting feeds 120V receptacle?

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gravy

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I have a retrofit suggestion by an owner, for comment by the forum. There is an existing 277V in-ground uplight that illuminate large metal sculpture located indoors. They want to install a 120V receptacle at top of sculpture but there are no 120V circuits anywhere close by to tap from. Suggestion is to tap the 277V circuit at base of sculpture and run 277V circuit in flex metal conduit up to a small transformer mounted and hidden at top of sculpture that would serve the receptacle. Transformer would be protected by fused switch at top of sculpture, and grounded via insulated copper ground to base of metal sculpture which is grounded. It looks inherantly wrong to me, and have been looking for code that would prevent this installation (210.6, etc) but have not found anything. I thought there was an article that prohibited 277V wiring under 8-0" height in public areas...but maybe that went away?

Any help appreciated.
 
Lets start with
450.13
Is this sculpture and the surrounding area going to permit ready access the transformer?



Based on your description, the transformer does not seem like it will be located in the open, therefore shall be readily accessible. See the definition in Art 100.
 

gravy

Member
Lets start with
450.13
Is this sculpture and the surrounding area going to permit ready access the transformer?



Based on your description, the transformer does not seem like it will be located in the open, therefore shall be readily accessible. See the definition in Art 100.
Yes, transformer would be accessible at the top, using ladder, and would have NEC code clearance.
 

gravy

Member
The owners do realize if the light is off there will be no power to the recep. :)
the receptacle is for plug-in holiday lighting....so yeah, they are fine with switching the 277V light and the receptacle from same lighting control relay.

the 277V wiring to fixture is run in MC cable...so no way to pull new circuit through any existing conduit.

my question is more if there is any code prohibiting them from doing the scenario in my original question.
 
the receptacle is for plug-in holiday lighting....so yeah, they are fine with switching the 277V light and the receptacle from same lighting control relay.

the 277V wiring to fixture is run in MC cable...so no way to pull new circuit through any existing conduit.

my question is more if there is any code prohibiting them from doing the scenario in my original question.

If this is residential there is a voltage limitation on occupancy NEC 2008 210.6(A)(B).
If this is a commercial installation, I would be concerned about the rating of the transformer, because receptacles are calculated at 180va per yoke. Be sure the transformer can handle the load.
110.27(A)(4) has to do with the height of live parts.
 

kwired

Electron manager
Location
NE Nebraska
Lets start with
450.13
Is this sculpture and the surrounding area going to permit ready access the transformer?



Based on your description, the transformer does not seem like it will be located in the open, therefore shall be readily accessible. See the definition in Art 100.

Read all of 450.13, transformer in this case is less than 600 volts and very likely less than 50kVA - does not need to be readily accessible
 

LEO2854

Esteemed Member
Location
Ma
I have a retrofit suggestion by an owner, for comment by the forum. There is an existing 277V in-ground uplight that illuminate large metal sculpture located indoors. They want to install a 120V receptacle at top of sculpture but there are no 120V circuits anywhere close by to tap from. Suggestion is to tap the 277V circuit at base of sculpture and run 277V circuit in flex metal conduit up to a small transformer mounted and hidden at top of sculpture that would serve the receptacle. Transformer would be protected by fused switch at top of sculpture, and grounded via insulated copper ground to base of metal sculpture which is grounded. It looks inherantly wrong to me, and have been looking for code that would prevent this installation (210.6, etc) but have not found anything. I thought there was an article that prohibited 277V wiring under 8-0" height in public areas...but maybe that went away?

Any help appreciated.

Read 210.6(C)(2)

?I thought there was an article that prohibited 277V wiring under 8-0" height in public ?
In buildings where 277volt lighting is used line voltage switches are at 4'
How about the panel that your feed is coming from that is below 8' right?
 

gravy

Member
Read 210.6(C)(2)

?I thought there was an article that prohibited 277V wiring under 8-0" height in public ?
In buildings where 277volt lighting is used line voltage switches are at 4'
How about the panel that your feed is coming from that is below 8' right?
good reference....looking at 210.6 (C) (2) it references allowing 277V for incandescent luminaires if the autotransformer is an integral part of the luminaire. I could not find any other code reference for our situation where the autotransformer just feeds a receptacle (for future use) to plug in holiday lighting. It appears this installation would satisfy code....although I probably need to look at tap rules (tapping the 277V circuit at base of sculpture and running about 20' up to the transformer/receptacle at top of sculpture).

I was also concerned about the secondary grounding of the transformer. For those small 200VA transformers, does secondary grounding even apply? If so, I would need to run an insulated ground conductor down the sculpture to base and ground to rebar.
 

kwired

Electron manager
Location
NE Nebraska
I did read all of 450.13. Maybe you should read what I wrote and then read 450.13(A) again.

Don't forget to read 450.13(B), then, if you still don't think this location would be acceptable, please tell us why.

(B) Hollow Space Installations. Dry-type transformers 600 volts, nominal, or less and not exceeding 50 kVA shall be permitted in hollow spaces of buildings not permanently closed in by structure, provided they meet the ventilation requirements of 450.9 and separation from combustible materials requirements of 450.21(A). Transformers so installed shall not be required to be readily accessible.

Transformer in this case is less than 600 volts (OP says 277:120) and very likely less than 50kVA (180 amp or more lighting circuit would be needed to exceed this, and that would not be allowed by 210.23(D)). Improper ventilation or combustible materials could be a problem but that likely could be easily solved.

There may be some other section not allowing this install but I don't see 450.13 having any effect on not allowing this.
 

gravy

Member
thanks all. seems like it is permissible by code. my only remaining question would be the transformer size that would be practical to install to feed this receptacle. The holiday lighting that is going to plug into the receptacle is less than 50VA. If I specify a 50VA 277V:120V transformer to serve this receptacle, couldn't somone plug in a load that exceeds the transformer rating? although I guess my primary fusing at transformer primary would protect the xfmr.
 

kwired

Electron manager
Location
NE Nebraska
Don't forget to check the load on the lighting circuit to make sure you don't overload it with whatever you do add.

You will have a separately derived system unless you use an autotransformer and will need a grounding electrode conductor run to your buildings grounding electrode system someplace. 210.9 should allow the use of an autotransformer.

Your overcurrent device on the separately derived system will likely need to be readily accessible. I may look into that a little more.
 
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kwired

Electron manager
Location
NE Nebraska
Don't forget to check the load on the lighting circuit to make sure you don't overload it with whatever you do add.

You will have a separately derived system unless you use an autotransformer and will need a grounding electrode conductor run to your buildings grounding electrode system someplace. 210.9 should allow the use of an autotransformer.

Your overcurrent device on the separately derived system will likely need to be readily accessible. I may look into that a little more.

After looking I would say 240.24(A) would require the overcurrent device to be readily accessible.
 

gravy

Member
After looking I would say 240.24(A) would require the overcurrent device to be readily accessible.
thanks. I did check to make sure the lighting circuit is not overloaded after adding the transformer/receptacle to the circuit.

if I provide a 200VA autotransformer to transform from 277V, 1ph to 120V, 1-ph....it appears I do not then have to worry about seperately derived system and grounding to electrode system if I read the code correctly.

I would plan on providing a fuse protection at the primary to the transformer at top of sculpture. The secondary of the autotransformer would feed the duplex receptacle that the holiday lights would plug into. Do i need secondary fused protection as well before hitting the receptacle?
 
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