Advice: 277V Lighting w/ 120V receptacle over a long distance

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MSMStannyl

Member
Location
Baltimore, MD
So I'm working on a design for low level pedestrian style lights along a section of bike trail that goes through the center of a town. Per the lighting calculations, we'll probably need about 74 light fixtures to cover this long stretch. I've broken these up into 3 segments (based on a bridge, and major road crossings) which will each get their own 277V/480 service.

Obviously for runs this long, I will design using the 277V single phase to the lights. However, the client has mentioned possibly wanting to add receptacles at the bottom of each pole. I'm not sure about the exact reason for this but I've started looking into this and am trying to figure out the best way. The receptacle obviously needs 120V power.

I've contacted one of our lighting reps to see if they make poles with receptacles that might have a built in step-down transformer. Something small that sits inside the pole. I've never seen one myself but I can't imagine I'm the first person with this dilema. My concern here is cost. I can't fathom this will be a cheap way to go, especially considering we would need 74 of them.

The other idea I had was to provide a transformer at each service (so we would have 3 of them) and run dedicated 277V lighting circuits out to the lights and then seperate circuits (for the receptacles) through the transformer and then out to the poles. The obvious problem here is that you're stepping down to 120V at the service location and then having to make long runs down the line to the poles. Voltage Drop would be killer and I'd need some pretty big wires.

Anyway, that's pretty much where I am right now. I'm trying to get definitive direction on these receptacles. I'm thinking that once the client realizes the cost implications, the receptacle idea will be scrapped. Just curious if anyone has dealt with something similar and what their solution was.

Thanks!
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
However, the client has mentioned possibly wanting to add receptacles at the bottom of each pole. I'm not sure about the exact reason for this but I've started looking into this and am trying to figure out the best way. The receptacle obviously needs 120V power.

In my experience this sort of request is usually done with Christmas decorations in mind. Not much of a power requirement, so you may be able to get away with the voltage drop of a dedicated circuit, since there is no code requirement on VD.
You might have a problem with putting 25 receptacles on one circuit though.

Or maybe it is so that a stranded electric bicycle rider could charge up and continue? :)
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I lean somewhat to what GoldDigger says. Without knowing what purpose the receptacles serve you could figure them at 180VA each allowing you 13 per 20 amp circuit.
Of course, if's shooting in the dark not knowing the distances, but I doubt your increase in wire size (IF you figure it on the limited load or load diversity) would outweigh the cost of transformers and associated OCP & bonding.
Ethically I think you would need to explain the situation and make sure they understand the system is not designed for a fair with
20 amp loads at every pole. With a 277 volt system, if you were to plan for significant loads, you would still be looking at a sizable increase in wire sizes.
 

broadgage

Senior Member
Location
London, England
I can not recomend a transformer at each pole, apart from the cost of the transformer, the customer will be paying forever for the iron losses in these transformers.

It might be worth putting lights and outlets on the same circuit.
Run a MWBC at 120/240 volts. Voltage drop with 240 volts on the lamps wont be much worse than with 277 volts.
Alternate outlets should be on each hot so as to reduce the neutral current.
The cost of the upsized wire would probably compare well with running a 277 volt circuit for the lights, and a 120 or 120/240 volt circuit for outlets.
If the load exceeds the limit of a single 20 amp MWBC, then consider say a 40 amp MWBC with a 15 amp fused disconnect or breaker for each outlet and lamp.

If the use of the outlets is unknown, a fair assumption might be a modest load of Christmas lighting on every outlet, 180VA would be reasonable, or use of power tools for any maintenance or repair works, in which case assume a full 15 amp load, but only on one or two outlets at a time.
 

Shoe

Senior Member
Location
USA
I'd work with the lighting manufacturer to see if they allow an option for receptacles in the base of their poles. Some do, as this is something I've seen in the past.

Along with this may be an option for fusing ahead of the receptacles to limit the input current, so you can calculate voltage drop based on the rating of the fuse.

Also, oversized terminations on the input to this assembly may be an option to account for larger conductors (again for voltage-drop considerations).
 

Saleh

Member
Location
Saudi Arabia
Lithonia

Lithonia

HID take time for restarting. So in the malls and shopping centers is advisable to have GLS lamp to use for immediate restarting.
Lighting manufacturers sell a HID 277V fixture operate two lamps 1- MH 2- Incandescent and it is mostly 120V.
So you can branch of the GLS lamp and wired down to your receptacle.
Please check with your vendor if you can achieve this? The Chinese will do it for you definitely.
 

iwire

Moderator
Staff member
Location
Massachusetts
HID take time for restarting. So in the malls and shopping centers is advisable to have GLS lamp to use for immediate restarting.
Lighting manufacturers sell a HID 277V fixture operate two lamps 1- MH 2- Incandescent and it is mostly 120V.
So you can branch of the GLS lamp and wired down to your receptacle.
Please check with your vendor if you can achieve this? The Chinese will do it for you definitely.

It would be very low capacity and likely not NEC compliant.
 

Electric-Light

Senior Member
I have a vague recollection of reading about single lamp sized 277 to 120v auto-transformer at each socket to feed incandescent.


Also, some ballasts have a 120v tap, but its not meant to be used for a receptacle. 277v or 480v is stepped down to 120v to power a backup incandescent after a power outage for 15 minutes or so it takes for HID to recover. The ballast's primary is used as an autotransformer.

If it's off of 277v, you'll get neutral to 120v, but if its off 480Y277V, you'll have one end that is 480v above ground even though line-to-line is 120v, which is fine for incandescent housed within the fixture, but totally unacceptable for a receptacle.
 

kwired

Electron manager
Location
NE Nebraska
I have a vague recollection of reading about single lamp sized 277 to 120v auto-transformer at each socket to feed incandescent.


Also, some ballasts have a 120v tap, but its not meant to be used for a receptacle. 277v or 480v is stepped down to 120v to power a backup incandescent after a power outage for 15 minutes or so it takes for HID to recover. The ballast's primary is used as an autotransformer.

If it's off of 277v, you'll get neutral to 120v, but if its off 480Y277V, you'll have one end that is 480v above ground even though line-to-line is 120v, which is fine for incandescent housed within the fixture, but totally unacceptable for a receptacle.

You are correct that this tap from ballast would likely only be designed to run the recommended lamps. Some maintenance or construction guy plugs in a big saw or something of similar load and probably toasts the ballast. There would also be some control involved somehow to shut the standby lamp off.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
the customer will be paying forever for the iron losses in these transformers.

I realize this is a little off topic, but I wanted to mention it since your statement brought it to mind.
We have had several customers that have complained about their electric bills being higher when we went from the old mechanical meters to the new electronic smart meters. The losses in the customers dry pack transformers weren't being picked up by the old mechanical meters. The new ones will record these. We have had some farm services with nothing more than a fence charger plugged in that never recorded the first kWh. With the new meters, they are now recording kWh usage.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I have a vague recollection of reading about single lamp sized 277 to 120v auto-transformer at each socket to feed incandescent.


Also, some ballasts have a 120v tap, but its not meant to be used for a receptacle. 277v or 480v is stepped down to 120v to power a backup incandescent after a power outage for 15 minutes or so it takes for HID to recover. The ballast's primary is used as an autotransformer.

If it's off of 277v, you'll get neutral to 120v, but if its off 480Y277V, you'll have one end that is 480v above ground even though line-to-line is 120v, which is fine for incandescent housed within the fixture, but totally unacceptable for a receptacle.

Sort of what kwired said, but that would only work at night, if at all. The photocontrol(s) won't have the ballast energized during the day.
 

MSMStannyl

Member
Location
Baltimore, MD
To start with, thanks everyone for your input/advice.


Unfortunately, as these things usually go, the scenario has changed somewhat. I had a meeting on site with the local power company. It would appear that asking for 277/480V services is just not going to work in terms of cost. The power company applies a significant rebate to each 277/480V service assuming that you meet one of three criteria. In our case, for lighting, the criteria is to have at least 50 KW per service. I'm nowhere even remotely close to that. As such, I've been instructed to begin looking into going with the much cheaper and readily available 120/240V services.

I believe this may end up being the better option, especially with the receptacles in mind. It definitely brings that cost down although I'll have to look into the voltage drop at 120V running those long distances.

Oh, and some of you had asked what the receptacles are for. It is my understanding that the town is asking for them to provide Xmas decorations as some of you had speculated. I would imagine the loads would be pretty insignificant but I'll have to run VD for a "worst case" scenario.

At this point, I'm moving forward with the assumption of running only 1 - 120V circuit per pole. In other words, 1 circuit will power both the light and receptacle. We were asked to do this so that the Xmas decorations will power on/off with the lighting. They have also requested timeclocks to run the lights.
 

MSMStannyl

Member
Location
Baltimore, MD
Oh, I do have a question though. Based on the scenario above, what would be an acceptable load to use for the receptacles on each light pole? Obviously I have to account for the 150W light but I would think the receptacle is what will make or break the Voltage Drop. Even if I know that the receptacles are for Xmas lights which probably barely pull 1-2 amps, do I need to calculate with a much higher load? I would think 20 amps per receptacle would be crazy. I was thinking of doing the VD calcs using 3 or 5 amps per receptacle. Thoughts?

Thx
 

hurk27

Senior Member
Oh, I do have a question though. Based on the scenario above, what would be an acceptable load to use for the receptacles on each light pole? Obviously I have to account for the 150W light but I would think the receptacle is what will make or break the Voltage Drop. Even if I know that the receptacles are for Xmas lights which probably barely pull 1-2 amps, do I need to calculate with a much higher load? I would think 20 amps per receptacle would be crazy. I was thinking of doing the VD calcs using 3 or 5 amps per receptacle. Thoughts?

Thx

The code will allow you up to 13 receptacles on a 20 amp circuit using the allowed 180va per strap.
 

kwired

Electron manager
Location
NE Nebraska
How much voltage drop can be tolerated will effect what drop you design to.


The use of MWBC's will help with voltage drop. You essentially want to have loads as balanced as possible and then you are looking at VD for 208 or 240 instead of 120. The only 120 VD will be related to the unbalanced load.
 
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