480 volt to ground service from utility

[woodduder]

Got an issue and need some input. I have been in electrical for 30 years and this is first time I have seen this voltage from the utility. I am a project manager for the issue below and I hold a master license in Florida.

I am building a small 100 amp 240/480 volt single phase service for temporary construction power and will be installing a 480 to 120/240 transformer to power the GC's construction office. I had discussed the voltage with the FPL (Florida Power and Light) engineer prior to designing the service and was told their transformer was a 240/480 output so that is how we have built our service.

I have a single phase meter socket and then a 2 pole fused 100 amp disconnect switch for my main. We had ran our service conductors from the utility transformer to our meter with 3#1 aluminum (I believe but cannot be sure since I am at home at this time) , 2 hot lines and one neutral.

FPL came out to hook us up today and they realized that they have a 240/480 transformer, but it has been modified or jumpered to produce 480 on one line to ground. FPL sees that we have 3 conductors and says "sorry, we cannot hook you up" because we (FPL) do not have 2 hot legs with 480 between them and 240 to ground. My foreman who is present with the power company is very confused with a 480 volt single line to ground service that he agrees there is a problem and FPL leaves.

My foreman calls me right after FPL leaves and explains the issue to me, but not ever having heard of this single line 480 to ground power from utility, I was scratching my head and wondering if it will work if we just eliminate one of the lines that we have pulled to the utility transformer.

So question is, if FPL does not have an issue, could I bring one line and one neutral (or grounded conductor) to my meter and then go from meter to fused disconnect with same (one line and one neutral) and then feed a 50 KVA single phase transformer (it is a Square D EE50S3H) with this 480 volt tied to H1 and H4 (which are the points to connect the 480 volt) and have it work fine? My man in field has connected a thousand transformers with 480 (line to line), but this is freaking him out that the 480 is one line to neutral and I have not run into this either so I cannot say that it will or will not work, but in my mind it should work just fine.

Also, being unusual to me I started to question if the 100 amp fuse on the single line would be adequate since we had figured we would be using 2 hot legs to get 480 but we now have only one single hot leg. The math says it should be fine, but again very unusual system and just second guessing myself.

Please give my your thoughts if you believe this will work just fine or not.

 

[augie47]

Obviously anything ahead of your transformer (meter socket, fused disconnect, etc) would need to be rated 480 (600v), but odd as it seems, off the top of my head, I see no problem with your fusing one leg of the 480v and using the grounded leg for your other phase. Means would have to be taken to meet 230.75 but that could simply be the grounded lugs in the disconnect

 

[electrofelon]

Obviously anything ahead of your transformer (meter socket, fused disconnect, etc) would need to be rated 480 (600v), but odd as it seems, off the top of my head, I see no problem with your fusing one leg of the 480v and using the grounded leg for your other phase. Means would have to be taken to meet 230.75 but that could simply be the grounded lugs in the disconnect

Yeah I agree nothing wrong with this, just Kinda odd. The one thing that weirds me out a little is the metering. I would just make sure you confirm what socket they want. I guess it could very well by your typical 4 jaw socket socket with nothing on one side, as they are rated 600 volts. Possibly they could want a three phase socket if that coordinates with their standard meter voltages. Check with them.

 

[woodduder]

Thanks for the replies. I am contacting the utility this AM to see if they have an issue with metering, but if they do not then I will be removing one of my ungrounded legs and having them come back to hook it up.

I was having trouble grasping that I could still receive enough VA from the single line to give me full (or very near) use of my 50KVA transformer. Math says all should be exactly the same.

50,000 / 480 = 104 amps

I need 200 amps at the 120/240 side. Looks like it should work.

I will let you know what the utility has to say later.

The utility is using this transformer to run street lighting in a subdivision.

 

[LarryFine]

I would think that both the hot and grounded conductors would feed through the meter, using all four terminals, not just one line using two.

 

[kwired]

Yeah I agree nothing wrong with this, just Kinda odd. The one thing that weirds me out a little is the metering. I would just make sure you confirm what socket they want. I guess it could very well by your typical 4 jaw socket socket with nothing on one side, as they are rated 600 volts. Possibly they could want a three phase socket if that coordinates with their standard meter voltages. Check with them.

I would think that both the hot and grounded conductors would feed through the meter, using all four terminals, not just one line using two.

All depends on what POCO wants to use for a meter. Possible they could want to use a three phase meter, then you would need to supply the meter with all three conductors, and then run just single phase to your service disconnect.

Oops, sorry EF I didn't read your post careful enough then said a lot of same things you said.

 

[texie]

Thanks for the replies. I am contacting the utility this AM to see if they have an issue with metering, but if they do not then I will be removing one of my ungrounded legs and having them come back to hook it up.

I was having trouble grasping that I could still receive enough VA from the single line to give me full (or very near) use of my 50KVA transformer. Math says all should be exactly the same.

50,000 / 480 = 104 amps

I need 200 amps at the 120/240 side. Looks like it should work.

I will let you know what the utility has to say later.

The utility is using this transformer to run street lighting in a subdivision.

I used to be from your neck of the woods. 480 volt 2 wire service is an FPL standard for street lighting service. I'm surprised they will let you use it for this but maybe because it is temporary.
Not the end of the world though, just use 480 volt straight rated, 2 pole, solid neutral equipment and not use 1 pole. You'll just have remove a conductor and do some re-configuring on your end. Been years, but I seem to recall they require cold sequence metering setup-better check with them.
I never understood why they don't just use only 240/480 3 wire services as a standard for this as it has other advantages.

 

[kwired]

Got an issue and need some input. I have been in electrical for 30 years and this is first time I have seen this voltage from the utility. I am a project manager for the issue below and I hold a master license in Florida.

I am building a small 100 amp 240/480 volt single phase service for temporary construction power and will be installing a 480 to 120/240 transformer to power the GC's construction office. I had discussed the voltage with the FPL (Florida Power and Light) engineer prior to designing the service and was told their transformer was a 240/480 output so that is how we have built our service.

I have a single phase meter socket and then a 2 pole fused 100 amp disconnect switch for my main. We had ran our service conductors from the utility transformer to our meter with 3#1 aluminum (I believe but cannot be sure since I am at home at this time) , 2 hot lines and one neutral.

FPL came out to hook us up today and they realized that they have a 240/480 transformer, but it has been modified or jumpered to produce 480 on one line to ground. FPL sees that we have 3 conductors and says "sorry, we cannot hook you up" because we (FPL) do not have 2 hot legs with 480 between them and 240 to ground. My foreman who is present with the power company is very confused with a 480 volt single line to ground service that he agrees there is a problem and FPL leaves.

My foreman calls me right after FPL leaves and explains the issue to me, but not ever having heard of this single line 480 to ground power from utility, I was scratching my head and wondering if it will work if we just eliminate one of the lines that we have pulled to the utility transformer.

So question is, if FPL does not have an issue, could I bring one line and one neutral (or grounded conductor) to my meter and then go from meter to fused disconnect with same (one line and one neutral) and then feed a 50 KVA single phase transformer (it is a Square D EE50S3H) with this 480 volt tied to H1 and H4 (which are the points to connect the 480 volt) and have it work fine? My man in field has connected a thousand transformers with 480 (line to line), but this is freaking him out that the 480 is one line to neutral and I have not run into this either so I cannot say that it will or will not work, but in my mind it should work just fine.

Also, being unusual to me I started to question if the 100 amp fuse on the single line would be adequate since we had figured we would be using 2 hot legs to get 480 but we now have only one single hot leg. The math says it should be fine, but again very unusual system and just second guessing myself.

Please give my your thoughts if you believe this will work just fine or not.

My first reply was presuming you had a corner grounded delta, now I'm not so sure what you have. Is it a single phase 240/480 unit but with un-utilized center tap and one side grounded or is it a corner ground delta constructed from three 240/480 single phase transformers?

 

[jap]

I have a hard time believing your going to get the voltage you want, or even what that voltage is going to be, out of the secondary of your transformer seeing as how you don't have 2 opposing phases on the primary.

From your description you only have one.

I don't see that working out.

Let us know though.

If it were me, I'd have them supply me with 480v single phase 2 wire with a neutral, not 480v on one leg to neutral. To me that doesn't compute.


JAP>

 

[electrofelon]

If it were me, I'd have them supply me with 480v single phase 2 wire with a neutral, not 480v on one leg to neutral. To me that doesn't compute.


JAP>

I don't think it matters how the 480 is arrived at, as long as one leg can be and is grounded. They could use a 480 with center tap, not use the center tap, and ground one side, as long as the center tap isn't factory bonded to the can. They cold also use a 960 with a center tap and connect to the center tap and one side (such a thing probably doesn't exist, just making an academic point).

 

[jap]

I don't think it matters how the 480 is arrived at, as long as one leg can be and is grounded. They could use a 480 with center tap, not use the center tap, and ground one side, as long as the center tap isn't factory bonded to the can. They cold also use a 960 with a center tap and connect to the center tap and one side (such a thing probably doesn't exist, just making an academic point).

It does because there's not a difference of potential to feed the primary with only a single leg of 480.

He's only going to have 480 on a single leg.

That would be like trying to feed the primary of a 208v to 120v transformer's primary with only the single high leg of a 240v delta primary.
I don't see that happening.

JAP>

 

[jap]

If one read between H1 and H4 on the primary input as the OP is explaining, it would not read 480.

It would read zero.

JAP>

 

[jap]

Then feed a 50 KVA single phase transformer (it is a Square D EE50S3H) with this 480 volt tied to H1 and H4 (which are the points to connect the 480 volt) and have it work fine? My man in field has connected a thousand transformers with 480 (line to line), but this is freaking him out that the 480 is one line to neutral

Tell your guy in the field he's not alone.
It freaks me out also.

Where is the difference in potential if your using a single leg of 480 jumpered between H1 and H4 to be able to produce the secondary you need?


JAP>

 

[jap]

Just for kicks, can you feed the primary of a 480 primary to 120/240v secondary transformer from (2) 1p breakers in a 480v panel if both 1p breakers are installed on the same phase and produce the output needed?

This is roughly what the OP has.

I say no.

JAP>

 

[electrofelon]

Just for kicks, can you feed the primary of a 480 primary to 120/240v secondary transformer from (2) 1p breakers in a 480v panel if both 1p breakers are installed on the same phase and produce the output needed?

This is roughly what the OP has.

I say no.

JAP>

Jap, I dont think he is proposing using the same leg/phase to feed both sides of the transformer. We are talking about single phase 480, one leg is a grounded conductor (it may be a neutral, but it may not be).

 

[jap]

Jap, I dont think he is proposing using the same leg/phase to feed both sides of the transformer. We are talking about single phase 480, one leg is a grounded conductor (it may be a neutral, but it may not be).

He said in his original post that it was a funky transformer that produced 480 from 1 line to ground.
Not 480 between 2 phases.

JAP>

 

[jap]

I see what your getting at now.

If that's the case , I take it he's actually going to have to take a line and a neutral to the transformer primary of the transformer.

Even at that, this is an odd duck.

Most of these transformers wired that way that the power company use for their street lights are usually a direct connection from the transformer to the street lights themselves without the meter in between.

It is very unusual that they are using this in the OP's scenario

JAP>

 

[texie]

Not meaning to be harsh here and intended to be gentle but some are making this out to be much more complicated than it is. This is a very common arrangement for street lighting with FPL and many other utilities. It is no different than an old fashion 120 volt 2 wire service to a home except that it is 480 volt. It is just a 480 winding with one end grounded. There is not a neutral but rather a grounded conductor. Many utilities prefer to use a 240/480 arrangement with a grounded center tap to avoid having 480 to ground. I suspect the 480 to ground system helps with fault clearing on the very long runs typically found in street lighting.
What is unusual about it is that it is being used for something other than street lighting. The OP will have 1 ungrounded and 1 grounded conductor going to his transformer. As I said in my previous post, he'll just have to use 2 pole equipment with solid neutral hardware and just abandon 1 pole.

 

[jap]

Not meaning to be harsh here and intended to be gentle but some are making this out to be much more complicated than it is. This is a very common arrangement for street lighting with FPL and many other utilities. It is no different than an old fashion 120 volt 2 wire service to a home except that it is 480 volt. It is just a 480 winding with one end grounded. There is not a neutral but rather a grounded conductor. Many utilities prefer to use a 240/480 arrangement with a grounded center tap to avoid having 480 to ground. I suspect the 480 to ground system helps with fault clearing on the very long runs typically found in street lighting.
What is unusual about it is that it is being used for something other than street lighting. The OP will have 1 ungrounded and 1 grounded conductor going to his transformer. As I said in my previous post, he'll just have to use 2 pole equipment with solid neutral hardware and just abandon 1 pole.

You the man texie.... you da man.

I must have misread the OP's intent on bringing only the Ungrounded Conductor to the xfmr to feed both H1 and H4 in his original post.


JAP>

 

[woodduder]

Tell your guy in the field he's not alone.
It freaks me out also.

Where is the difference in potential if your using a single leg of 480 jumpered between H1 and H4 to be able to produce the secondary you need?


JAP>

The 480 volt single line is not jumping to both terminals. The one 480 leg would be on either H1 or H4 and the neutral would be on the other. I think it would work but after a phone call with Square D today, they say it won't work, but I think because they do not want the liability.

POCO came out and explained to us today that they have no issue with it but in order for the electronic meter to work we would need to install a jumper between the neutral and the 2nd (normally hot leg) line terminal of the meter so it would receive power.

Since Square D has decided to say no to us connecting this, we opted to also say no to protect ourselves from liability as well.

GC will now be paying POCO to install a 240/480 pad mount transformer immediately adjacent to the 480 single line transformer. This way we can just have them connect what we have and move on from this mess.