120V receptacle without adding additional transformer and panel

[Fitzdrew516]

I'm in the strange position of only needing one 120V receptacle in an area where I intend to only have a 480/277 panel. I am hoping that I don't have to add a transformer and a panel just for one receptacle. The area will have a unit heater so I was looking around for a model that maybe has a receptacle on the side of the unit (similar to how RTU's sometimes have these). I've looked at different unit heaters for a while and can't find anything like this. Does anyone have any other ideas of how I could get just one 120V receptacle? Does anyone make a 277V to 120V plug in adapter/transformer? I couldn't find anything like that when searching either.

Thanks,
- Drew

 

[dkidd]

Look at Square D mini power zone or similar from your favorite manufacturer.

http://www.schneider-electric.us/en...ctrical-distribution&parent-category-id=53700

That would be my suggestion.

 

[Fitzdrew516]

Look at Square D mini power zone or similar from your favorite manufacturer.

http://www.schneider-electric.us/en...ctrical-distribution&parent-category-id=53700

That would be my suggestion.

Thanks! Yeah, I thought about doing a buck/boost set up, but was trying to avoid it. Looks like I may have to bite the bullet though. I've never done a buck/boost before. What are the OCP requirements when it comes to these? I assume it's not the same as the normal transformer requirements.
In other words - How are these wired up and are there any other factors I need to take into account? Or is it just running a 277V branch circuit to a buck/boost transformer and then wire straight out of the secondary to a 120V receptacle?

Thanks again,
-Drew

 

[iwire]

I don't believe you can buck 277 down to 120 anyway.

 

[Fitzdrew516]

I don't believe you can buck 277 down to 120 anyway.

Forgive my terminology as I always call small transformers buck boost transformers (I know this is incorrect). What I meant to ask about were the requirements for smaller transformers intended to be used for single loads. Are these to be treated in the same fashion as normal transformers?

 

[ActionDave]

Forgive my terminology as I always call small transformers buck boost transformers (I know this is incorrect). What I meant to ask about were the requirements for smaller transformers intended to be used for single loads. Are these to be treated in the same fashion as normal transformers?

In your case yes. Look at 250.30.

 

[Jraef]

You can't get from 480 or 277 down to 120 without a transformer somewhere, so even if you found a 'unit heater' with a receptacle on the side, there will still be a transformer.

What you don't necessarilly need however is the "panel" if it is just one receptacle. You can buy single pole free standing circuit breakers, such as a Sq. D QOU115, and use it on the output of the transformer to feed just that one receptacle. You can also just use a fuse.

The bigger issue will be the PURPOSE of that receptacle. If you want it so that anyone can plug anything into it that plugs into a 120V receptacle, then the transformer capacity will need to be 15A, which makes it a 2kVA transformer. But if the purpose of the receptacle is so that a service person can plug in a drop light or small power supply while working on the panel, you can use a smaller transformer and put a label above the receptacle warning them that it is a limited power source, then give them the limit. I do that on pump panels sometimes, telling them that it is limited to 5A max load and use a fuse, or if they insist on a CB, you can get a QOU110 rated at 10A, then use a 1500VA control power transformer in the 480V panel.

 

[Fitzdrew516]

You can't get from 480 or 277 down to 120 without a transformer somewhere, so even if you found a 'unit heater' with a receptacle on the side, there will still be a transformer.

What you don't necessarilly need however is the "panel" if it is just one receptacle. You can buy single pole free standing circuit breakers, such as a Sq. D QOU115, and use it on the output of the transformer to feed just that one receptacle. You can also just use a fuse.

The bigger issue will be the PURPOSE of that receptacle. If you want it so that anyone can plug anything into it that plugs into a 120V receptacle, then the transformer capacity will need to be 15A, which makes it a 2kVA transformer. But if the purpose of the receptacle is so that a service person can plug in a drop light or small power supply while working on the panel, you can use a smaller transformer and put a label above the receptacle warning them that it is a limited power source, then give them the limit. I do that on pump panels sometimes, telling them that it is limited to 5A max load and use a fuse, or if they insist on a CB, you can get a QOU110 rated at 10A, then use a 1500VA control power transformer in the 480V panel.

Thanks for the info! I'm aware that you always need a transformer to change voltages. My thought of having one on the unit heater was that it would be one less step I had to take because it would be inside the pre-fabbed unit. All I would have to do is wire the unit heater up and I would meet my requirement for a service receptacle.

Anyway - I looked up the free standing circuit breaker you referenced. Everyone seems to be calling them "Unit Mount C/Bs". I looked for images, but I don't see how they are usually mounted. Is there a common small enclosure that is typically used that would (in this case) sit next to the secondary of the small wall mounted transformer? I'm thinking something similar to a molded case cb.

 

[JFletcher]

I'm in the strange position of only needing one 120V receptacle in an area where I intend to only have a 480/277 panel. I am hoping that I don't have to add a transformer and a panel just for one receptacle. The area will have a unit heater so I was looking around for a model that maybe has a receptacle on the side of the unit (similar to how RTU's sometimes have these). I've looked at different unit heaters for a while and can't find anything like this. Does anyone have any other ideas of how I could get just one 120V receptacle? Does anyone make a 277V to 120V plug in adapter/transformer? I couldn't find anything like that when searching either.

Thanks,
- Drew

Why not just get a 277/480V heater?

 

[Fitzdrew516]

Why not just get a 277/480V heater?

I plan on doing that for the unit heater. The issue I'm running into is the fact that I have to have a 120v "service receptacle" within 25' of the equipment.

 

[hbiss]

Where does it say you need a service receptacle for that kind of equipment?

-Hal

 

[Fitzdrew516]

Where does it say you need a service receptacle for that kind of equipment?

-Hal

210.63

 

[iwire]

210.63

I don't know of anyone applying that section to a simple unit heater

 

[JFletcher]

210.63 seems to apply but I could swear Ive seen gas fired heaters in warehouse ceilings w/o a receptacle within 25'.

 

[iwire]

Is the unit heater located on a roof, in attic or in a crawl space?

 

[Fitzdrew516]

I don't know of anyone applying that section to a simple unit heater

The code language seems to encompass unit heaters in this category. I don't often consider this requirement when it comes to unit heaters because usually by default there's a 120V receptacle within 25'.

I think it's kind of picky to require this in this situation, but the risk/reward of not doing it for this one doesn't add up. If the inspector comes in and wants to see one then it's a lot more additional cost for the owner down the line and I know the finger will get pointed at me. So I figure I may as well include it now and not get burnt down the road.

 

[Fitzdrew516]

Is the unit heater located on a roof, in attic or in a crawl space?

Unit heater will be in the same room wall mounted.

 

[hbiss]

If the inspector comes in and wants to see one...

Well, how about asking the inspector before you do the job? This is going to be a considerable expense that should be clarified- unless you can convince your customer to do it anyway.

-Hal

 

[templdl]

I don't believe you can buck 277 down to 120 anyway.

32v is usually the limit for a std BB scheme. But a custom BB can be built to do it though it would be similar in cost to a std xfmr and there is no isolation with a BB.
One may consider a small 3kva 480(or 277v)-120/240 encapsulated transformer and parallel the sec windings which has a capacity of 25a @ 120v. Mount it to the exterior to the pnlbd. You could mount a fuse block on the inside for pri and sec protection and mount a box with a duplex receptacle on the outside or on the wall next to the pnlbd w/ conduit. You could even use a 2p15at breaker to feed the transformer as long as you have sec protection and forego the pri fuses.
I can't think of any violations of the NEC in doing so.

 

[Fitzdrew516]

Well, how about asking the inspector before you do the job? This is going to be a considerable expense that should be clarified- unless you can convince your customer to do it anyway.

-Hal

Problem being this AHJ is unresponsive. It's a real problem. Idk what they're going to do come inspection time. This job is out in the middle of nowhere and they don't have a city inspector so it falls to the state inspector who is half retired and doesn't respond to emails or voice mails. And as for the cost - in respect to the job size the expense to do it right is so minimal that it wouldn't be noticed. However, after the job is done and it's an additional, unknown expense is where it always seems to be an issue (understandably so).