Commercial Voltages

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mefalk55

Member
Hello, Soon I will be changing jobs and must get myself familiar with these new transformer and voltage configurations. In the past I have worked mainly with Industrial WYE voltages from general lighting 120V, 220V single phase, and 480V three phase. Commercial lighting transformers and voltages will be quite different. I NEED HELP! Delta systems and wiring. Can you please tell me where to get the right Commercial Transformers and wiring techniques Information that can Help me to adjust SAFELY?
Thanks for any info. you can give
mefalk55
 

iwire

Moderator
Staff member
Location
Massachusetts
Where I am almost all commercial services are Wyes.

480Y/277 or 208Y/120, outside of industrial I run into very few delta systems.
 

mefalk55

Member
Commercial Voltages

iwire, Thanks for the reply, I feel better already..... BUT.... The facility I will be working at is a new building. I guess I should not be concerned with to many changes, huh? The "high leg" orange marked, is that used only in Delta configs.? Is three phase, four wire typical? mefalk55
 

mefalk55

Member
Commercial Voltages

iwire, thanks for the reply. I feel better already.. This facility is 1 year old. So, I guess the old Delta systems are not a concern, huh? mefalk55
 

peter d

Senior Member
Location
New England
Delta was once the norm when there was major manufacturing around here....most of those services are gone now, though a few remain. I don't think the poco will even provide delta anymore without special permission.
 

Energy-Miser

Senior Member
Location
Maryland
iwire said:
Where I am almost all commercial services are Wyes.

480Y/277 or 208Y/120, outside of industrial I run into very few delta systems.
Iwire, one of my guys came back from a commercial field service today and told me that in a sub panel he measured 120 and 277 coexisting. How is that? e/m
 

iwire

Moderator
Staff member
Location
Massachusetts
Energy-Miser said:
Iwire, one of my guys came back from a commercial field service today and told me that in a sub panel he measured 120 and 277 coexisting. How is that? e/m

Only two ways I can think of.

Someone may have interconnected branch circuits somewhere. This has gotten me before, I shut off the 480 volt feed to a lighting panel only to get hit with 120 from the load side connection of a breaker that was off.

The other way is control circuits, shunt trips, monitoring circuits etc.
 

peter d

Senior Member
Location
New England
iwire said:
Someone may have interconnected branch circuits somewhere. This has gotten me before, I shut off the 480 volt feed to a lighting panel only to get hit with 120 from the load side connection of a breaker that was off.

The 120 volt backfeed to this 480 volt panel would have to be on the same phase, or else it would go boom, would it not?
 

iwire

Moderator
Staff member
Location
Massachusetts
peter d said:
The 120 volt backfeed to this 480 volt panel would have to be on the same phase, or else it would go boom, would it not?

It would have gone boom anyway. :smile:

It had never been turned on, the building was in the end stage of construction. Months earlier someone had tied a 277 volt home run into a receptacle circuit. Eventually the receptacle circuit was live and in use, but that lighting circuit was supposed to be waiting in the ceiling for sofit lights yet to arrive.

I think you have been there, RT 146 Lincoln RI
 

peter d

Senior Member
Location
New England
iwire said:
It would have gone boom anyway. :smile:

It had never been turned on, the building was in the end stage of construction. Months earlier someone had tied a 277 volt home run into a receptacle circuit. Eventually the receptacle circuit was live and in use, but that lighting circuit was supposed to be waiting in the ceiling for sofit lights yet to arrive.

I think you have been there, RT 146 Lincoln RI

Ahhh....ok, that makes sense, I couldn't comprehend how that would work electrically without a fireball. ;)

I haven't actually been to that store...didn't do much "stoplight" work.
 

wirenut1980

Senior Member
Location
Plainfield, IN
mefalk55 said:
iwire, thanks for the reply. I feel better already.. This facility is 1 year old. So, I guess the old Delta systems are not a concern, huh? mefalk55

You'll have a few different types of delta systems in use. In industrial settings you might come across an ungrounded delta, 480 V used only for phase to phase loads, no phase to ground loads without a transformer.

In commercial settings there are still many 240/120 V delta secondaries in existence. The center tap of one transformer winding is grounded and handles the majority of the single phase current. This is where you see the wild leg measuring 208 V to ground. This configuration is usually only found on older installations, and are not installed new. New installations in commercial are almost always wye.

Three phase 4 wire can mean either wye or delta.
 

peter d

Senior Member
Location
New England
iwire said:
If it's delta where did the 4th wire come from?

The only thing I can think of is center tapped delta (high leg.) But that's not the first thing that comes to mind when I hear "3 phase, 4 wire."
 

Smart $

Esteemed Member
Location
Ohio
peter d said:
The only thing I can think of is center tapped delta (high leg.) But that's not the first thing that comes to mind when I hear "3 phase, 4 wire."
Yes, a 240/120 3? Delta is a 4-wire system.
 
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