750KVA transformer manufactured as step-down, submitted as step-up: accept or revise/resubmit

I have a job that requires a 750KVA 208:480/277V step-up. The contractor submittal is for the same transformer configured as a step-down. When I returned the submittal to "revise and resubmit," the contractor said they'd just wire it in reverse. I denied that strategy as it isn't my design. The contractor is pushing back hard (causing me to suspect they already released the order).

As an Engineer of Record, would you accept this, understanding the near certain litigation and potential liability if the contractor improperly reconfigured the grounding for the derived service moving from the low voltage side to the high voltage side, or improperly sized the over current protection? Are there other significant factors I may be overlooking?

Thanks all.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I have a job that requires a 750KVA 208:480/277V step-up. The contractor submittal is for the same transformer configured as a step-down. When I returned the submittal to "revise and resubmit," the contractor said they'd just wire it in reverse. I denied that strategy as it isn't my design. The contractor is pushing back hard (causing me to suspect they already released the order).

As an Engineer of Record, would you accept this, understanding the near certain litigation and potential liability if the contractor improperly reconfigured the grounding for the derived service moving from the low voltage side to the high voltage side, or improperly sized the over current protection? Are there other significant factors I may be overlooking?

Thanks all.
There is no way to get 480Y/277V from a standard design transformer 'wired in reverse'.
 

tom baker

First Chief Moderator
Staff member
If the submitted transformer was a delta wye, when reverse wired its a wye delta, and then you have the issue of grounding the secondary IE corner ground, or ungrounded with detectors. Plus the transformer would need to me marked it can be reverse wired, see 450.11 (B).
I know transformers are frequently reverse wired, but its a bad idea and may be a code violation
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I have a job that requires a 750KVA 208:480/277V step-up. The contractor submittal is for the same transformer configured as a step-down. When I returned the submittal to "revise and resubmit," the contractor said they'd just wire it in reverse. I denied that strategy as it isn't my design. The contractor is pushing back hard (causing me to suspect they already released the order).

As an Engineer of Record, would you accept this, understanding the near certain litigation and potential liability if the contractor improperly reconfigured the grounding for the derived service moving from the low voltage side to the high voltage side, or improperly sized the over current protection? Are there other significant factors I may be overlooking?

Thanks all.
As mentioned, you won't have 277 available. Even if 277 was not needed this would be a very poor idea as it presents all kinds of other issues that would have to be dealt with. The contractor should be supplying a proper 208 delta primary with a 480/277 Y secondary. That are readily available.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The original poster indicated 480-277 so that would imply it was wye on the 480 side.

Most transformers can be reverse wired these days. I would just want to get a statement from the manufacturer about it.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
The original poster indicated 480-277 so that would imply it was wye on the 480 side.

Most transformers can be reverse wired these days. I would just want to get a statement from the manufacturer about it.
It is unlikely the OP has a transformer with a 480Y/277V primary and a 208V secondary. Wye-wye transformers are not commonly applied below 1000V. Some manufacturers offer standard design wye primary transformers for drive isolation purposes, but typically not in the 750kVA range.

Regardless, as the engineer of record, the OP has the right to reject products that do not meet the project specifications.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I think we do not know what the contractor actually procured. If he can get 480/277 out of it with a 208 V input as he is claiming, and the transformer manufacturer supports that, I just don't see the problem.

I agree it would not be a standard design, but we don't know what the contractor actually bought, or wants to buy.
 

d0nut

Senior Member
Location
Omaha, NE
At the same time, the owner bought a specific design through the contracting of the project. The owner shouldn't have to settle for a lower quality or more complicated system because a contractor thinks he can make something work. The costs to purchase and install the correct equipment may end up being minor over the life of the installation. The owner should be getting what was in the contract, and should be getting a credit or added value in the installation from any deviation from the contract.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
...but we don't know what the contractor actually bought, or wants to buy.
At least three times in the past 5 years, I have been involved in installations where the contractor provided documentation from a manufacturer saying their transformer could be 'wired in reverse'. The problems all, occurred because none of the manufacturers were told the output of the transformer needed to be an actual wye output. They provided an answer without knowing the full situation.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
IMHO the nit-pickyness is slight.

You designed with a delta:wye transformer.

IMHO you should be willing to accept any transformer than has the same characteristics, in particular:
taps on the side used as primary _or_ taps on the secondary and primary able to accept any normal input voltage
neutral on the secondary that can be used for solid grounding and for 277V loads
acceptable inrush current on the side used as primary.

The simplest way to provide the expected characteristics is a delta:wye transformer. But if the contractor has something that provides the required characteristics I see no reason to reject it. But the onus is on the contractor to meet the required characteristics.

-Jon
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
It’s not like the transformer specification wasn’t in the specs. It is up to the contractor to submit any change for approval, and not expect that change to be granted without any reasonable documentation that it is similar.
 

DB444

New User
Location
australia
Occupation
eng
As the specifier you should have stipulated which was the winding arrangement on the HV and LV as well as if the neutral point is to be earthed.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
It’s not like the transformer specification wasn’t in the specs. It is up to the contractor to submit any change for approval, and not expect that change to be granted without any reasonable documentation that it is similar.
I agree, but we don't know exactly what the contractor wants to use versus what was spec'd. It is not unusual for specs to be written in an unintentionally ambiguous way.

IMO, as long as it can be made workable, I would accept it.
 
As the specifier you should have stipulated which was the winding arrangement on the HV and LV as well as if the neutral point is to be earthed.
Dunno, 750KVA 208:480/277V step-up seems fairly unambiguous (since most transformers are connected delta->wye, it's reasonable to assume that unless otherwise stated). If it was confusing to the contractor- that's why we have RFIs.
 
Dunno, 750KVA 208:480/277V step-up seems fairly unambiguous (since most transformers are connected delta->wye, it's reasonable to assume that unless otherwise stated). If it was confusing to the contractor- that's why we have RFIs.
Yeah I agree. In this forum we get into all sort of weird hypothetical scenarios, but 99.9% of the time that would be a 208 Delta to 480/277 wye and anyone beyond a first year apprentice should know that.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The OP says this.

I have a job that requires a 750KVA 208:480/277V step-up. The contractor submittal is for the same transformer configured as a step-down.
I am not entirely sure what he means by that. If the contractor has a transformer with a 208 V secondary and a 480/277 V primary, I don't see why that would be inappropriate to use back wired, assuming the manufacturer approves back wiring it.

if the 480 side is delta, than obviously it is not usable.
 
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