Delta Distribution

[hecorp]

I have a 120-volt 3-phase Delta service from the utility company to the building. I have never seen this before and confusion is a great place to start.

Being a 120-volt 3-phase system (Delta) the distribution would be a 3-phase panelboard and only 120-volt loads could be connected.

My question is: all branch circuits will be connected using 2-pole circuit breakers - there is no neutral and polarity doesn't matter ???

Any discussion would be helpful

Thanks

 

[cadpoint]

I'm no transformer man, but Google is your friend go to Google, images. You get something like this.

120-volt 3-phase system (Delta)

Note - There are some sutter differences in these 3 sided images, and with out knowing exactly what you have. It almost a coin flip in respects to your type of power at point of service. There
are no three sided coins.

There are some Line workers that hang out here we'll see.

Welcome to the Forum.

 

[GoldDigger]

I have a 120-volt 3-phase Delta service from the utility company to the building. I have never seen this before and confusion is a great place to start.

How did you determine that it is 120 volt delta?
Because there are only three wires coming from the utility?
Or is there a fourth "ground" or "grounded" wire that you are not using?
Some point in the system is likely to be grounded, whether it is a wye or delta supply at the POCO side.

 

[hecorp]

I met with the power company. It is rare

There is no ground - ungrounded

 

[cadpoint]

So your in the warehouse district or on the end of a run.

Did they say that they want to maintain this? This is it, Good Luck?

You going to bring in a PE to get you some more or different power?

 

[GoldDigger]

I met with the power company. It is rare

There is no ground - ungrounded

Ungrounded systems, where allowed by NEC, must have a ground detector. And some types of loads, like standard Edison base light sockets, are UL listed conditioned on the conductor going to the outer shell being grounded.
Similar problems may be seen with other load equipment.

 

[iwire]

I met with the power company. It is rare

There is no ground - ungrounded

So you have three lines coming in with 120 volts line to line and 0 volts any line to ground?

 

[hecorp]

There is no ground

I have 120 volt on 2 phases to ground 70 volts on the 3rd. I checked with the engineer - he said that is correct

Trust me it is a 3-phase ungrounded 120-volt DELTA system.

 

[Hv&Lv]

There is no ground

I have 120 volt on 2 phases to ground 70 volts on the 3rd. I checked with the engineer - he said that is correct

Trust me it is a 3-phase ungrounded 120-volt DELTA system.

Still trying to get a handle on this..

There is no ground, yet you have 120 volts to ground?
What is the line to line voltage? 208?

 

[hecorp]

The line to line is 120-volt

The utility company said that they still have a few 120-volt Delta systems still operational in MA and RI

 

[GoldDigger]

Still trying to get a handle on this..

There is no ground, yet you have 120 volts to ground?
What is the line to line voltage? 208?

Chances are good that all measured line to ground voltages are just phantom voltage readings.

 

[Hv&Lv]

The line to line is 120-volt

The utility company said that they still have a few 120-volt Delta systems still operational in MA and RI

Is it a corner grounded delta?
Also how many transformers are there on the pole? Two or three?

 

[hecorp]

there are three transformers on the pole

 

[Hv&Lv]

there are three transformers on the pole

OK. Didn't think there was any call for 120 delta anymore. Is one phase grounded? if not treat it as you would any other ungrounded delta.

 

[hurk27]

I have a 120-volt 3-phase Delta service from the utility company to the building. I have never seen this before and confusion is a great place to start.

Being a 120-volt 3-phase system (Delta) the distribution would be a 3-phase panel board and only 120-volt loads could be connected.

My question is: all branch circuits will be connected using 2-pole circuit breakers - there is no neutral and polarity doesn't matter ???

Any discussion would be helpful

Thanks

In all my years working in many parts of the country and even being a member on this forum for well over 10 years I have yet to ever hear of a 120 volt delta in the sense of having 120 volts line to line between each set of phases, there are no 3-phase loads that I have ever heard of using 120 volts, for one it would not be a NEC compliant service without having a grounded conductor for 120 volt loads except in one certain case of what is called a technical power supply system but even then it is still a grounded system with a 60 volt center tap to ground.

Edited because many post have been made since I started this one

 

[kwired]

There is no ground

I have 120 volt on 2 phases to ground 70 volts on the 3rd. I checked with the engineer - he said that is correct

Trust me it is a 3-phase ungrounded 120-volt DELTA system.

Your voltages don't make any sense if this is a DELTA secondary. They do make sense for a wye secondary that is 120 volts phase to phase, the voltage to neutral in such a system would be about 70 volts(69.28). You maybe have a situation of a grounded phase, a second phase and the neutral conductor, but are missing the third phase for some reason?

 

[hurk27]

Your voltages don't make any sense if this is a DELTA secondary. They do make sense for a wye secondary that is 120 volts phase to phase, the voltage to neutral in such a system would be about 70 volts(69.28). You maybe have a situation of a grounded phase, a second phase and the neutral conductor, but are missing the third phase for some reason?

but in a WYE you would have 69.28 from any phase to ground or the X0 not 120 volts from 2 and one with 69.28??? this is why I pointed out the 647.5 in the NEC makes no sense unless there are three seperate windings each with a center tap and only the center tap is connected in a WYE giving you still stranger voltages if interconnected phase to phase, with a 60 volt center tap in the discription in 647.5 any connection from one winding (phase) to the next would give you only 103.92 volts, but you would have 120 volts from each individual winding.

To have a 120 volt phase to phase WYE you would have to have three 69.28 volt windings connected in a star?

 

[hurk27]

a 4-wire delta you would have 120 volts phase to phase but it would give you 60 volts from A or C to ground and 69.28 from B to ground, but still doesn't fit the OP's discription but is about closest I can figure it.?

 

[hurk27]

Ok after doing some searches I actully found another thread on here, it's used around ships:

http://forums.mikeholt.com/showthread.php?t=157388

maybe this will help

 

[texie]

There is no ground

I have 120 volt on 2 phases to ground 70 volts on the 3rd. I checked with the engineer - he said that is correct

Trust me it is a 3-phase ungrounded 120-volt DELTA system.

It is not clear to me, and I don't think to the others, what you are using for references of voltage. On one hand you are saying that it is an ungrounded system, but yet, you are referring to voltage to ground. If it is truly an ungrounded system you have no reference to ground and any measurement taken this way is meaningless.
It seems we need more specific info.