can I run 120/208 3 phase 400 amp service overhead? and 120/208 in 120/240 rated panels

[Cartoon1]

Currently I have a small campus that is being fed to a 300amp exterior panel 120/240 single phase overhead service. I need 400amp 3 phase main service

-is there a limitation of how high an amperage service can come in from overhead?
-should I go with 120/240 3 phase or 120/208 3 phase since this panel will refeed all existing buildings and all existing panels are rated at 120/240 single.

sorry for the multiple questions. no need to answer all questions

 

[Dsg319]

Currently I have a small campus that is being fed to a 300amp exterior panel 120/240 single phase overhead service. I need 400amp 3 phase main service

-is there a limitation of how high an amperage service can come in from overhead?
-should I go with 120/240 3 phase or 120/208 3 phase since this panel will refeed all existing buildings and all existing panels are rated at 120/240 single.

sorry for the multiple questions. no need to answer all questions

Should be no problem to get the overhead service drop but check the local power company specs.

I would also say go with 208y/120volt rather than the 240volt delta high leg unless you have a lot of motor circuits.

 

[electrofelon]

Probably should talk to the POCO first. Many consider 120/240 three phase "non standard" and will not provide new or upgrades at this configuration. In addition, many people don't like high leg deltas, but I actually like them because of the higher voltage.

POCOs also have limitations on how large they will serve overhead. You will need to talk to them.

So in summary, did I mention talk to the POCO?

P.S. you will also want to check metering configuration, some will allow a self-contained class 320 socket others will require a CT cabinet for above 200A.

 

[tom baker]

Probably should talk to the POCO first. Many consider 120/240 three phase "non standard" and will not provide new or upgrades at this configuration. In addition, many people don't like high leg deltas, but I actually like them because of the higher voltage.

POCOs also have limitations on how large they will serve overhead. You will need to talk to them.

So in summary, did I mention talk to the POCO?

P.S. you will also want to check metering configuration, some will allow a self-contained class 320 socket others will require a CT cabinet for above 200A.

Right my POCO no longer offers 120/240. And it seems like on the POCO side that the primary is open delta and to have 120/208 requires an additional wire. Perhaps a someone can explain this better.

 

[texie]

As others have said, talk to your POCO. I'm thinking this is FPL so unless they have all 3 primaries available and you can show something like 150 KW of demand there is no way they will give you 208Y. 150 KW of actual demand is a pretty fair amount of power. They love 240/120 3 phase 4 wire due to capital cost. I've seen them do 400 amp overhead routinely.
Download their service handbook for starters as I recall theirs is pretty good.

 

[kwired]

Currently I have a small campus that is being fed to a 300amp exterior panel 120/240 single phase overhead service. I need 400amp 3 phase main service

-is there a limitation of how high an amperage service can come in from overhead?
-should I go with 120/240 3 phase or 120/208 3 phase since this panel will refeed all existing buildings and all existing panels are rated at 120/240 single.

sorry for the multiple questions. no need to answer all questions

Maybe clarify just what your load is. 300 amp 240 volt single phase is capable of delivering 72kVA.

you said you need 400 amp three phase, but undecided if should go 208/120 wye or 120/240 delta. If you have no three phase loads then the high leg is nearly useless unless you have some significant 240 single phase you can connect it to, so outside of that would still leave you putting all the load across what is essentially 120/240 single phase.

If you did have 208/120 wye then @ 400 amps you potentially could supply up to about 144kVA.

If majority of load is 120 volts, and there is no three phase loads at all, you may be best off with sticking with single phase supply.

If you have say higher capacity HVAC but no other three phase loads, maybe high leg delta with larger transformer on the 120/240 side to cover the remainder of the load and a "stinger" transformer to supply whatever the HVAC needs for the third phase- need to work that out with POCO if going that way.

So what you have for loads to supply can be somewhat a big factor in what may be best for you.

 

[Cartoon1]

Maybe clarify just what your load is. 300 amp 240 volt single phase is capable of delivering 72kVA.

you said you need 400 amp three phase, but undecided if should go 208/120 wye or 120/240 delta. If you have no three phase loads then the high leg is nearly useless unless you have some significant 240 single phase you can connect it to, so outside of that would still leave you putting all the load across what is essentially 120/240 single phase.

If you did have 208/120 wye then @ 400 amps you potentially could supply up to about 144kVA.

If majority of load is 120 volts, and there is no three phase loads at all, you may be best off with sticking with single phase supply.

If you have say higher capacity HVAC but no other three phase loads, maybe high leg delta with larger transformer on the 120/240 side to cover the remainder of the load and a "stinger" transformer to supply whatever the HVAC needs for the third phase- need to work that out with POCO if going that way.

So what you have for loads to supply can be somewhat a big factor in what may be best for you.

Probably should talk to the POCO first. Many consider 120/240 three phase "non standard" and will not provide new or upgrades at this configuration. In addition, many people don't like high leg deltas, but I actually like them because of the higher voltage.

POCOs also have limitations on how large they will serve overhead. You will need to talk to them.

So in summary, did I mention talk to the POCO?

P.S. you will also want to check metering configuration, some will allow a self-contained class 320 socket others will require a CT cabinet for above 200A.

I was just thinking about that. Most of the new load to the facility is going to be new AC units. Unfortunately the feeder for the 300 amp is rated for 285amp. The panel is rated 400, I'm thinking that if I upsize the feeders I can get away with running single phase. I'm not sure though if I need to still contact POCO since the feeder to the weatherhead is going to be rated for 400a

 

[Cartoon1]

Probably should talk to the POCO first. Many consider 120/240 three phase "non standard" and will not provide new or upgrades at this configuration. In addition, many people don't like high leg deltas, but I actually like them because of the higher voltage.

POCOs also have limitations on how large they will serve overhead. You will need to talk to them.

So in summary, did I mention talk to the POCO?

P.S. you will also want to check metering configuration, some will allow a self-contained class 320 socket others will require a CT cabinet for above 200A.

I'm think I'm going to stick to 1 phase and upsize feeders to 400amps since panel is rated for 400amps. As far as I know here, we involve ct cabinet if service is more than 400amps

 

[kwired]

I'm not sure though if I need to still contact POCO since the feeder to the weatherhead is going to be rated for 400a

I think you should probably at least inform them of increase in load, they can decide if they want to up transformer size or service drop cable. Also depending on rate/demand structures in effect additional load could impact billing beyond just simple more kWH being used. Yes you will likely use more energy, but depending on how they set up rates might cost owner less to set up some new contract based on the new expected usage, or owner possibly ends up paying more because of overage penalties on the old arrangement, in such cases the monthly minimum will likely go up so that needs consideration as well.

 

[garbo]

Should be no problem to get the overhead service drop but check the local power company specs.

I would also say go with 208y/120volt rather than the 240volt delta high leg unless you have a lot of motor circuits.

In my area I have ran overhead 600 & 800 amp services that passed inspection every time. Best to double check with the local power supplier. What agvrevated me is how the electric company can get away with supplying a 800 amp service with 4/0 aluminum wire that is only rated for 200 amps. Do understand that they do not come under the NEC so get away with it. Once did a 300 amp service that the end box was feed by 75 year old frayed rubber covered 60 amp wire. They told me that being wire is underground the ground keeps it from over heating . Yea right.

 

[synchro]

Currently I have a small campus that is being fed to a 300amp exterior panel 120/240 single phase overhead service. I need 400amp 3 phase main service ...

-should I go with 120/240 3 phase or 120/208 3 phase since this panel will refeed all existing buildings and all existing panels are rated at 120/240 single.

I'm think I'm going to stick to 1 phase and upsize feeders to 400amps since panel is rated for 400amps. As far as I know here, we involve ct cabinet if service is more than 400amps

Since the system now is 240/120V, it's possible there are grounded conductors in existing feeders that were reduced in size compared to the ungrounded conductors. That could be an issue if you went with 120/208V, and if so it would be another reason to stay with 240/120V single phase.

 

[kwired]

In my area I have ran overhead 600 & 800 amp services that passed inspection every time. Best to double check with the local power supplier. What agvrevated me is how the electric company can get away with supplying a 800 amp service with 4/0 aluminum wire that is only rated for 200 amps. Do understand that they do not come under the NEC so get away with it. Once did a 300 amp service that the end box was feed by 75 year old frayed rubber covered 60 amp wire. They told me that being wire is underground the ground keeps it from over heating . Yea right.

Well it can help, but probably not that much for 300 amps on what is otherwise 60 amp conductor.

You will seldom see anyone do a 'positive ampacity adjustment' for an underground conductor but it generally will be in a low enough ambient that is able to be done.