480/415/240V. 3 phase high leg

[Russgary]

Hello I recently became the lead electrician for a concrete pipe, and products facility. Imagine my surprise upon finding this voltage spread throughout the plant. In 30 years as an industrial electrician I have never seen this exact setup.

Here's my dilemma : at this particular facility our stinger leg is just shy of 500 volts.
The plant is a nightmare of power quality issues, burned out vfd's blown MH ballasts etc.
None of our 480v panels are listed, or labeled for this voltage, and a junior electrician /handyman already employed by the company has attempted to use single phase breakers on many of the panels for yard lighting, there is no 277V available anywhere. I know on a technical level the power quality issues are more likely related to other issues
Is this type of voltage permitted by the NEC?, are there any special stinger leg marking requirements (orange marking )? Why would anyone use this type of service? 277V is deadly enough around unskilled workers, but now I have them handling wet concrete soaked SO cords that run the various moving equipment with one of the conductors at 498volts to ground .

Additionally I want to "fix" the MH yard lighting by using the two 240volt legs to feed multitap ballasts, one leg will be a grounded conductor, is this permitted?

 

[infinity]

Something sounds wrong, the high leg to ground should be close to what is in your graphic not 500 volts.

Welcome to the Forum.

 

[Little Bill]

View attachment 22652

How is there 240V here? I thought 277V would be there from 480V.

 

[texie]

How is there 240V here? I thought 277V would be there from 480V.

Take a closer look- this is a delta not a Y. Same thing as a 120/240 3 phase 4 wire service except double the voltage. Instead of a high leg of 208 volt you have a high leg of 416 volt.
Used to be very common in some areas for things like oil wells, irrigation pumps, etc.

 

[Little Bill]

Take a closer look- this is a delta not a Y. Same thing as a 120/240 3 phase 4 wire service except double the voltage. Instead of a high leg of 208 volt you have a high leg of 416 volt.
Used to be very common in some areas for things like oil wells, irrigation pumps, etc.

And to think, that pretty triangle was right there!:slaphead:
I'm used to 480/277 and didn't even think of delta even though it was right there.

 

[kwired]

Take a closer look- this is a delta not a Y. Same thing as a 120/240 3 phase 4 wire service except double the voltage. Instead of a high leg of 208 volt you have a high leg of 416 volt.
Used to be very common in some areas for things like oil wells, irrigation pumps, etc.

And still is, especially if using open delta for the source.

Yes you can run 240 volt single phase loads from the non high legs to the neutral.

Yes it is exactly the same thing as 240 high leg delta - just everything is doubled voltage wise.

No you can't connect 277 volt loads to it without transformation, autotransformer will work.

No you can't use breakers/panels that are rated 277/480, must be a straight 480 or even 600 volt rating, unless you only connect two the two non high legs and neutral with say a single phase panel, demand for such thing is usually not all that great though.

 

[iceworm]

480V, 3 phase, 4 wire Delta is sufficiently odd, I have never seen one. Never even heard of one - just seen the pictures. Leaves me completely blank why anyone would ever want one. However, I have not worked on oil wells or irrigation - maybe there is a reason.

As infinity said, the stinger voltage should be 415V to neutral - not 500V.

Suggest measuring:

all three phases to neutral
all three phases and neutral to ground.​

Is it possible the system does not have a grounded neutral? That could explain the high stinger voltage.

worm

 

[kwired]

480V, 3 phase, 4 wire Delta is sufficiently odd, I have never seen one. Never even heard of one - just seen the pictures. Leaves me completely blank why anyone would ever want one. However, I have not worked on oil wells or irrigation - maybe there is a reason.

As infinity said, the stinger voltage should be 415V to neutral - not 500V.

Suggest measuring:

all three phases to neutral
all three phases and neutral to ground.​

Is it possible the system does not have a grounded neutral? That could explain the high stinger voltage.

worm

Get out in middle of nowhere and don't already have all three phases on primary distribution system you can save some expense on conductor and necessary accessories to supply a limited load application and build an open delta bank supplied by two phases and the neutral.

If a small load - many irrigation machines around here that only need 30 amp supply max - often you still find open delta even if all three primary phases are available.

Larger loads - say 50 or more HP with all three primary phases available is usually going to be 480/277 around here. Most the open delta on 50 HP or more is older and existing, today they generally want to utilize all three primary lines so supply those loads. I can think of one 100 HP irrigation well that is supplied by open delta. Ironically it is only about a mile from the substation but there is no three phase line along the road it is supplied from - it has one phase and neutral from the north and another phase and neutral from the south to the transformer bank.

 

[iceworm]

Get out in middle of nowhere and don't already have all three phases on primary distribution system you can save some expense on conductor and necessary accessories to supply a limited load application and build an open delta bank supplied by two phases and the neutral. ...

Open D is fine. I'm baffled why one would not go with corner-grounded. I don't see any different in the expense. Same amount of steel and copper. The only reason I can see for the 4W - D is if there is an alien containment field requiring the 1ph-240V.

However, the OP's system is not Open-D, it has all three transformers.

The point:
The listed system is sufficiently odd that I would seriously consider investigating if the system is in fact 4W - D.

And if it is, I'm not much help

the worm

 

[kwired]

Open D is fine. I'm baffled why one would not go with corner-grounded. I don't see any different in the expense. Same amount of steel and copper. The only reason I can see for the 4W - D is if there is an alien containment field requiring the 1ph-240V.

However, the OP's system is not Open-D, it has all three transformers.

The point:
The listed system is sufficiently odd that I would seriously consider investigating if the system is in fact 4W - D.

And if it is, I'm not much help

the worm

The drawing he posted is. What he actually has at his facility - we still don't know.

His stinger leg should not be ~500 volts if line to line volts is nominal 480 it should be ~416.

If he has corner grounded delta then I could see misunderstanding ~500 volts to ground as a stinger leg - but there should be two legs that are ~500 volts to ground.

 

[iceworm]

The drawing he posted is. What he actually has at his facility - we still don't know.
Yes, we don't.

His stinger leg should not be ~500 volts if line to line volts is nominal 480 it should be ~416.
Yes

If he has corner grounded delta then I could see misunderstanding ~500 volts to ground as a stinger leg - but there should be two legs that are ~500 volts to ground.
Yes

yes

 

[ptonsparky]

The drawing he posted is. What he actually has at his facility - we still don't know.

His stinger leg should not be ~500 volts if line to line volts is nominal 480 it should be ~416.

If he has corner grounded delta then I could see misunderstanding ~500 volts to ground as a stinger leg - but there should be two legs that are ~500 volts to ground.

It is a curious situation. Too many WTHs.