Illegal 277 volt medium-base lamp use

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SC-Retired>NEC-CMP

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Location
Los Angeles, California, USA
Powering a medium-base lamp socket with more than 120 volts is a violation of the NEC - 210.6. It is dangerous because following persons will screw in a 120 volt bulb "knowing" that the socket is 120 volt supplied - BOOM. The rating of the socket itself does not matter - the application does. The key is the medium-base.

A light fixture that was 277 volt rated due to its being a ballasted type DOES NOT allow the socket to be legally converted to direct supply from the 277 volt circuit.
UL certifying medium-base bulbs at more than 120 volt is a dangerous mistake - it is not a legal NEC installation, and it is dangerous.
 
SC-Retired>NEC-CMP said:
Powering a medium-base lamp socket with more than 120 volts is a violation of the NEC - 210.6. It is dangerous because following persons will screw in a 120 volt bulb "knowing" that the socket is 120 volt supplied - BOOM. The rating of the socket itself does not matter - the application does. The key is the medium-base.

A light fixture that was 277 volt rated due to its being a ballasted type DOES NOT allow the socket to be legally converted to direct supply from the 277 volt circuit.
UL certifying medium-base bulbs at more than 120 volt is a dangerous mistake - it is not a legal NEC installation, and it is dangerous.
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Is there a question here?
 
It is intended to be an answer which can reach anyone who is faced with using 277 volt rated lamps with medium-base sockets. I have seen multiple questions regarding fixtures with these illegally powered medium-base lamp sockets.
Hopefully a search for the subject will bring the person trying to deal with it to this explanation.
This illegal conversion is common in commercial facilities with originally 277 volt ballasted fixtures.
The availability of 277 volt rated medium-base LED lamps exacerbates the desire to make this illegal conversion.
 
Many small hid fixtures are medium base, ballast voltage to lamp far exceeds 120 volts. I have came behind people that stick and LED lamp made for 120 volts, not multi volt in the fixture. Ballast still connected. Usually the magic smoke is let out after a while.
 
In a lot of countries they use E26/E27 bases for 240 volts. They are manufacturing for the global market

Presumably, there are not a lot of untrained people working with 277. It's not like Joe Blow homeowner has a 480/277 WYE service
 
hillbilly1 said:
Many small hid fixtures are medium base, ballast voltage to lamp far exceeds 120 volts. I have came behind people that stick and LED lamp made for 120 volts, not multi volt in the fixture. Ballast still connected. Usually the magic smoke is let out after a while.
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do they operate at more than ~120 volts though if an HID ballast is involved? High starting pulse does happen but I seem to remember back in the day when HID were dominant you could always place a 120 volt incandescent lamp in a HPS luminaire and it would light up (and not be over driven to any extremes) regardless what the supply voltage was to the luminaire. This also was an easy way of telling the ballast was good but the "ignitor" was probably bad if it would light the incandescent but not a known working HPS lamp that is correct for the ballast being used.
 
In past I have seen 230 volt rated lamps with medium base. We sometimes even used them on 120 volts in some places to gain long life though at much less light output, so you had to factor that in in your design. Usually for exterior lighting that would run all night as low level light for security type reasons.

Also is 12 volt lamps intended for use in RV's. Might not be as common as it once was, but they definitely don't last more than a second or two if you put them in a 120 volt supplied socket.

I kind of don't see an issue with a 120-277 volt rated lamp with medium base. It will work in a 120 volt luminaire. If retrofitting some old HID with a mogul base and 277 volt supply, just use one those mogul to medium base adapters. should someone come along sometime later and not be able to figure out the deal, even though the chances are getting higher they will be replacing with 120-277 volt lamp anyway, they can just learn their lesson messing with something they maybe don't understand?
 
kwired : There is not a problem with the listed ballast in place; the ballast's input voltage does not directly power the socket. The problem comes when the ballast is bypassed and the socket is illegally fed directly by the 277 volt circuit. Because of the current-limiting autotransformer function of the ballast, many listed HIDs utilize medium-base sockets.

There is also no code problem or danger with putting a higher rated voltage lamp into a 120 volt supplied medium base socket. This is a very common approach for low light level requirements which want VERY long life bulbs, exactly as you say.

There is no problem using a 120-277 volt rated bulb in a 120 volt supplied medium-base socket.

It is powering the medium-base socket directly with 277 volt which is the code violation, and the creator of danger.

Joethemechanic : No code problem powering a medium-base socket at less than 120 volts. Only a problem powering it at more than 120 volts.

The danger exists within areas which are under the jurisdiction of the NEC where the maximum legal voltage supply to a medium-base socket is 120. Nobody working in a country using 240 volt as the common circuit is going to think that the medium-base socket has only a 120 volt supply.
 
That’s where that little phrase “Qualified person” comes in. 277 is not a household voltage, so it will not be Joe Homeowner servicing the fixture. Ceramic medium base sockets are usually rated 600 volts. With direct wire retrofit kits, a sticker is to be affixed stating fixture is direct wired.
 
I recently removed some 277V ballasts, connected the lamp holder to the 277 for LED lamps.
So I powered LED from the 277 medium base, did I violate code :unsure: I was kinda wondering..
They way I read 210.6(C) it is electric-discharge and or listed light-emitting diode-type
lamps are permitted on a 277V no restrictions on outlet type (lamp base).
A incandescent lamp is restricted to the output of a step down or a mogul base.
And any lamp can go in a mogel base.
I did contemplate using the old ballast coil as a auto transformer, but that seemed more of a hack?

Another building I work on has really old 240V delta and the lighting circuits are 240V off a 3-pole breaker and 3-pole lighting contractor. the lights are all Line - Line 240.
 
Notice there is some difference between an E26 base and an E27. There are also some differences in the sockets. I believe there is some additional distance between the screw and the terminal because the E27 is actually a 230 volt socket. All that being said they are used interchangeably all the time

Screenshot 2025-10-04 230325.png
 
hillbilly1 said:
With direct wire retrofit kits, a sticker is to be affixed stating fixture is direct wired.
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Though we are talking about screw shell sockets that does apply to linear type lamps as well. But I stopped putting in ballast bypass lamps in linear fluorescent luminaires because people don't understand or ignore this and put non bypass or an actual fluorescent in and I get called back to tell them they put in the wrong lamp. Meanwhile they have a box full of mixed lamp types in a storage room and a mentality of if it fits.....
 
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