Voltage issue

john2016

Member
Location
California
Occupation
Electrical Engineer
Bottom line is that I messed up on a design. I designed two new 480/277V, 3ph, 4W panels to two seperate existing 480V, 3ph, 3w distribution panels. See attached one line diagram for reference. What would be the best way to correct this mistake? The 480/277V, 3 ph, 4W panels are already installed and the feeders have been pulled. The electrical contractor just brought this to my attention. Thank you.
 
Last edited:

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
Bottom line is that I messed up on a design. I designed two new 480/277V, 3ph, 4W panels to two seperate existing 480V, 3ph, 3w distribution panels. See attached one line diagram for reference. What would be the best way to correct this mistake? The 480/277V, 3 ph, 4W panels are already installed and the feeders have been pulled. The electrical contractor just brought this to my attention. Thank you.
The panel labeling probably says it must be installed on a system that does not exceed 277V L-G. It likely does not require that a neutral conductor actually be run to panel.
 

dkidd

Senior Member
Location
here
Occupation
e
Do panels 1ERCH1 and 1ERSH1 have any line-to-neutral loads? If so, the only solution I see are 480-480Y/277 transformers.
 

john2016

Member
Location
California
Occupation
Electrical Engineer
One of the panel has lighting loads at 277V. I was thinking 480-480Y/277 transformers as well but wanted to see if anyone had any other ideas. Thanks.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Is the problem that there is no neutral? Can one be added?
Might be harder than we think. There is a neutral from the utility to the MDP. We don't know if it was also carried to MDPA. But both of them are 3W, so I don't know where the neutral would be landed. If the neutral is available at the two MDPs, you would have to bring it through the ATSs and to the downstream panels EDP and ECDP (which are also 3W), and from there to the new panels.

But I see a far more significant issue. Gen 1 is called a "Separately Derived System," and Gen 2 is called a "Non-Separately Derived System." Someone please check me on this. I don't believe that can happen (i.e., one of each type) at the same facility. An SDS would require the generator's neutral to be bonded to its case, and would require downstream ATSs to switch the neutral (i.e., 4 pole). The Non-SDS would require the generator's neutral to not be bonded to its case, and would require downstream ATSs not to switch the neutral (i.e. 3 pole). The PDF does not show us the complete wiring downstream of the two generators, and it does not say whether the ATSs are 3-pole or 4-pole. So I can't tell if this system was set up correctly.
 

john2016

Member
Location
California
Occupation
Electrical Engineer
Unfortunately there is no neutral between the two MDP's. Hopefully you can read the one line diagram below. I couldn't get the PDF to attached since it was over 2MB.
 
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hillbilly1

Senior Member
Location
Atlanta,Ga
Another issue may be its a corner grounded delta service instead of a wye, so there would be no 277 tap, so a 480 to 480/277 volt transformer may be the only solution.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Unfortunately there is no neutral between the two MDP's. Hopefully you can read the one line diagram below. I couldn't get the PDF to attached since it was over 2MB.
Sent you a PM

Depending on the load there is hope- I'd imagine the lights and other items typically on 277 are on 120.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Might be harder than we think. There is a neutral from the utility to the MDP. We don't know if it was also carried to MDPA. But both of them are 3W, so I don't know where the neutral would be landed. If the neutral is available at the two MDPs, you would have to bring it through the ATSs and to the downstream panels EDP and ECDP (which are also 3W), and from there to the new panels.

But I see a far more significant issue. Gen 1 is called a "Separately Derived System," and Gen 2 is called a "Non-Separately Derived System." Someone please check me on this. I don't believe that can happen (i.e., one of each type) at the same facility. An SDS would require the generator's neutral to be bonded to its case, and would require downstream ATSs to switch the neutral (i.e., 4 pole). The Non-SDS would require the generator's neutral to not be bonded to its case, and would require downstream ATSs not to switch the neutral (i.e. 3 pole). The PDF does not show us the complete wiring downstream of the two generators, and it does not say whether the ATSs are 3-pole or 4-pole. So I can't tell if this system was set up correctly.
In addition, with just a brief glance at the drawing I don't see how you can have a non-SDS genset connected to 3 wire gear.
 
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