3 Phase 3 Wire Electrical Service (No Neutral)

Status
Not open for further replies.
L

L'uomo Universale

Member
Location
Plano, Tx, USA
Is it acceptable to have an 480V 3ph, 3w electrical service for an office building? I have only designed 3ph 4w systems so I am wondering if anyone has any knowlege of such a service or can direct me to a reference. I am assuming since it is before the service disconnect that it will be covered by the NESC rather than the NEC.
 
480, 3 phase ungrounded systems are permissible by the NEC. Some utilities are not real prone to provide the service and there are some negative aspects (you can perform a search on the Forum and read some details). Such service are more common in industrial applications than offices as 277 is a often used voltage for office lighting. IMO, there would be more of a disadvantage than an advantage to such a system for an office.
 
It is fine with the code, but that would be very unusual for an office. Also take a look at 250.21(B).
 
There is also corner grounded delta systems which may be a little more likely to be utility supplied then ungrounded systems.

It still is only useful for HVAC/mechanical loads of the building but most everything else will need transformed to run on 208, 240 or 120 volts.
 
Around here I have never seen a utility supplied 480 volt corner grounded system. I have seen number of utility supplied 240 volt corner grounded systems and a number of 480 volt ungrounded systems.
 
Acceptable to the NEC, yes, but your poco will have the final say. The poco in my area would not let that remain for that usage, it would have to be converted to a wye service.
 
don_resqcapt19 said:
Around here I have never seen a utility supplied 480 volt corner grounded system. I have seen number of utility supplied 240 volt corner grounded systems and a number of 480 volt ungrounded systems.
Click to expand...

If you go out to remote single/limited load applications you might run into more service supplied 480 volt corner ground. Like irrigation wells, oil wells, remote pumping stations. It is more likely if supplied by pole mounted transformers that have been networked into a three phase bank as well, otherwise a single core transformer is probably less cost to get a 480/277 wye connected unit as those are the common ones.
 
augie47 said:
480, 3 phase ungrounded systems are permissible by the NEC. Some utilities are not real prone to provide the service and there are some negative aspects (you can perform a search on the Forum and read some details). Such service are more common in industrial applications than offices as 277 is a often used voltage for office lighting. IMO, there would be more of a disadvantage than an advantage to such a system for an office.
Click to expand...
Not sure where you'd derive the 277V?
 
Besoeker said:
Not sure where you'd derive the 277V?
Click to expand...
That was Gus's point, an ungrounded Delta limits the service to phase to phase voltages whereas a grounded Wye allows 277V for lighting (and possibly a few other things) which is pretty much the norm for most commercial buildings that I deal with.

Roger
 
roger said:
a grounded Wye allows 277V for lighting (and possibly a few other things) which is pretty much the norm for most commercial buildings that I deal with.

Roger
Click to expand...
But that would require the neutral to be grounded and the OP says there is no neutral.
 
iwire said:
Yes and that was the point Gus was making. A straight three phase service to an office building would be unusual as an office building will have 277 loads.
Click to expand...
Yes. I stated my previous point badly. The 277V would be phase to neutral whether the neutral is grounded or not. But, if there is no neutral, my point remains. So where would you get the 277V?

I'm not trying to be argumentative. Just trying to understand the point about the 277V.
 
Besoeker said:
Yes. I stated my previous point badly. The 277V would be phase to neutral whether the neutral is grounded or not. But, if there is no neutral, my point remains. So where would you get the 277V?

I'm not trying to be argumentative. Just trying to understand the point about the 277V.
Click to expand...

The point was that a three phase, three wire service to an office building while allowed, is unusual.
 
Besoeker said:
... my point remains. So where would you get the 277V?
...
Click to expand...
Well there are ways... such as a 480V Delta Primary to 480/277V Wye Secondary. However, I cannot see an office building being supplied with a 480V ungrounded or corner grounded service if it needs 277V for some loads. And if that was POCO dictated, that be one messed up POCO if you ask me.
 
Besoeker said:
Yes. I stated my previous point badly. The 277V would be phase to neutral whether the neutral is grounded or not. But, if there is no neutral, my point remains. So where would you get the 277V?

I'm not trying to be argumentative. Just trying to understand the point about the 277V.
Click to expand...

Under the NEC you would not have an ungrounded neutral so you would not have an ungrounded 480Y/277V system and Gus was pointing out that this is the more common system.

Roger
 
roger said:
Under the NEC you would not have an ungrounded neutral so you would not have an ungrounded 480Y/277V system and Gus was pointing out that this is the more common system.

Roger
Click to expand...
But the OP states that there is no neutral, grounded or otherwise.
 
Besoeker said:
Yes, but as far as I can tell, it won't directly give you 277V. That was my point.
Click to expand...

No one claimed it would directly provide 277 volt, that is why it would be unusual to use that type of system to supply an office building or any non-industrial building really.
 
Status
Not open for further replies.
Top