I have a couple of questions about ungrounded 480v. I need to feed a building with 480v for some motor loads, at present I have 480v from the secondary side of the POCO x-formers. I would like to set a 480v delta/ 480/277 wye tranformer but don't see one listed in supply catalog, is there one? Second question, this run will be aprox 100' would it be a better design to hit this transformer right away or wait until it is closer to the building.
transformer
- Thread starter eds
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I would confirm that the POCO supply is 480 delta and not 480Y.
If your supply is delta you can use that as your service either as an "ungrounded" system or a corner grounded system. Unless you need the 277 volt, there is no need to go to the expense of developing a neutral.
If you go grounded delta please note 240.22, 430.36 & 37.
If you go ungrounded please note 250.21(B)
If your supply is delta you can use that as your service either as an "ungrounded" system or a corner grounded system. Unless you need the 277 volt, there is no need to go to the expense of developing a neutral.
If you go grounded delta please note 240.22, 430.36 & 37.
If you go ungrounded please note 250.21(B)
I have found what I believe is a 480 corner grounded system from the POCO, a call will be made tomorrow to verify. I would like a little better understanding of when I can bring a ungrounded system to the building. I need to supply motor loads and don't think that this would fall in the 250.21(A) guidelines.
tyha
Senior Member
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so there are no lights in this building?
I stand to be corrected, but I've not know of POCO to "provide" a corner grounded system in that they ground one phase. Normally they ground the center tap (neutral) when the system has such.
If their transformer is a 480 3 wire output, then the decision to ground one phase is yours.
The advantage of an ungrounded system is the ability to "troubleshoot" phase to ground problems without having a fault take equipment out of service.
If POCO doesn't have the neutral available, you will most likely need to install a transformer to supply you 120 volt and lighting loads.
If their transformer is a 480 3 wire output, then the decision to ground one phase is yours.
The advantage of an ungrounded system is the ability to "troubleshoot" phase to ground problems without having a fault take equipment out of service.
If POCO doesn't have the neutral available, you will most likely need to install a transformer to supply you 120 volt and lighting loads.
Cold Fusion
Senior Member
- Location
- way north
Gus -
One of us is having a senior monemt:roll:
480 corner grounded is not uncommon. 480 center-tap grounded delta is sufficiently uncommon that I never seen one or heard of one - heard thay do exist though.
But, I'm thinking you already knew all of this
cf
One of us is having a senior monemt:roll:
480 corner grounded is not uncommon. 480 center-tap grounded delta is sufficiently uncommon that I never seen one or heard of one - heard thay do exist though.
Usually that is either mandated by the poco, negotiated with the poco, or if speced by the customer then it will be paid for by the customer. Once installed, if the poco corner grounded, then it's corner grounded - not selectable by customer.
Gus - It's a 480 service. There is no 120V.
But, I'm thinking you already knew all of this
cf
I am still a little bit confused on when I could bring a 480v ungrounded system into a building. The system I am dealing with is actually a corner grounded system, but I am looking to learn something on the ungrounded system. Short of a few items listed in 250.21(A) I don't see how I could bring a ungrounded system in for motor loads?
cf,
Definitely subject to senior moments.
My point, based on POCO in this area, is that they don't corner ground any of their delta services. If you request and they agree to supply a delta 3 wire supply, then you can elect to corner ground or leave it ungrounded at your service equipment.
OP stated POCO supplied him with a corner grounded system. May be true, but would not happen with any of the POCOs in my inspection area.
I agree, of course, if POCO grounds anything, that's what you get.
I mentioned the transformer as, in all probabilty, he will need 120 volt power for something, and 210.6(D) would seem to prohibit most 480v lighting.
As I recall, this started with the OP trying to obtain 277v and as of yet, he might not need to
eds, If the system is already corner grounded prior to it's reaching your service, that's what you will have to live with. The 3 phase motors care less (grounded or ungrounded) as long as they receive their rated voltage.
Definitely subject to senior moments.
My point, based on POCO in this area, is that they don't corner ground any of their delta services. If you request and they agree to supply a delta 3 wire supply, then you can elect to corner ground or leave it ungrounded at your service equipment.
OP stated POCO supplied him with a corner grounded system. May be true, but would not happen with any of the POCOs in my inspection area.
I agree, of course, if POCO grounds anything, that's what you get.
I mentioned the transformer as, in all probabilty, he will need 120 volt power for something, and 210.6(D) would seem to prohibit most 480v lighting.
As I recall, this started with the OP trying to obtain 277v and as of yet, he might not need to
eds, If the system is already corner grounded prior to it's reaching your service, that's what you will have to live with. The 3 phase motors care less (grounded or ungrounded) as long as they receive their rated voltage.
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