240V 3ph Delta High Leg Service Upgrade to 208V Wye

[32Lateralus]

As the title says, doing some additions and POCO says existing transformers need to be upgraded. We are adding some 208V 3ph specific loads so it would be best to change the utility secondary from the existing 240V 3ph delta center-tap high leg, to a 208V 3ph Wye system.

There is an existing Service Entrance listed at 240V 3ph 4W delta. If we change the utility transformers out, do we need to change anything physically about this service entrance? Does it need to be relisted by manufacturer and provided with new labels?

We already confirmed motors etc. downstream nameplates list both 208V and 240V. Any other considerations?

Thank you for the help!

 

[augie47]

Since they are changing the supply you might want to ask about any change in available fault current.

 

[32Lateralus]

Since they are changing the supply you might want to ask about any change in available fault current.

Ah, definitely, good point!

 

[synchro]

Are all of the line conductors of the existing service the same size? Sometimes a high leg conductor is reduced in size.

 

[winnie]

I would expect most if not all equipment rated for 240V high leg delta to also be rated/listed for 208V wye.

But as others have noted there is more than just the voltage rating of the equipment in play.

 

[kwired]

Re adjustment of motor overloads is something to look into. Motor will draw more on 208 than it will on 240 when delivering same output.

Some cases the minimum required motor conductor ampacity is high enough that you need a larger conductor for 208 than for 240 as well.

 

[hillbilly1]

Load balancing may be an issue, unless the majority of the loads are three phase. Usually those type services have one or more single phase panels using the other two legs. With utility transformers, they usually oversized one transformer to cover that. With the wye, all three will be the same size.

 

[kwired]

Load balancing may be an issue, unless the majority of the loads are three phase. Usually those type services have one or more single phase panels using the other two legs. With utility transformers, they usually oversized one transformer to cover that. With the wye, all three will be the same size.

Kind of is no different than converting an existing single phase service to three phase though. You probably will want to try to assure you balance some the major loads at very least.

I've done that in two different school facilities in the past. HVAC additions were the main reason to convert to three phase and was the majority of the load when all was done. That portion of load was fairly balanced, but deciding which feeders to put on what lines maybe took some thought to try to achieve the best balance of remaining load. Certain feeders did get converted to three phase as well during the upgrade.