Connecting a Delta - Wye transformer to a corner grounded service

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canote100

Member
Location
San Diego, CA
Occupation
Electrical Engineer and C10 Contractor
I have a customer that has a Well pump for an avocado farm irrigation system that is being powered by a dedicated 480V corner grounded service (Phase B grounded). He wants to use that service to provide power to a house that he is planning to build for the farm. For that I will need to install a 480V Delta-Wye 120/208V transformer.

Corner grounded systems are not common nowadays and I am not very familiar with them, so I need help on clarifying the following.

1) Will there be any issue with the new Delta- Wye transformer being corner grounded as well since Phase B of the service is already grounded?

2) On the Delta-Wye transformer's nameplate, the Delta diagram shows H1 being the one they identify to be grounded (see image below). Should I connect H1 to Phase B instead of Phase A, or just connect H2 to Phase B and make H2 the grounded corner? is this indifferent to the transformer internally? My understanding is that for corner grounded Delta systems usually phase B is the one grounded.

3) Should I have a dedicated GEC for the secondary of the Delta-Wye transformer, separate from the GEC of the service? (The GEC of the Service and the transformer location would be very close to each other)

Thanks for the clarification here.

s-l1600.webp
 
Welcome to the forum.

The delta primary won't care which line is grounded; it's merely a delta load.

The wye secondary should have the neutral grounded, as with any wye SDS.

One electrode system should be used for both the service and the wye system.
 
No issues with connecting a delta transformer primary to a corner grounded system.
The secondary Wye side will be a separatly derived system because it is isolated from the primary.
 
Thank you, guys. So, a separate GEC should be installed then for the secondary. And yes, Xo and ground need to be bonded. Thanks again.
 
canote100 said:
2) On the Delta-Wye transformer's nameplate, the Delta diagram shows H1 being the one they identify to be grounded (see image below).
Click to expand...

If you are referring to the dashed line from H1 on the Delta "triangle", that is not a grounding indicator.

Rather, it's a phasing symbol, which along with the same dashed line at X0 (on the wye secondary), is showing the 30 degree phase shift from the primary to secondary inherent in a delta to wye transformer.

At least that's what I was always taught.
 
canote100 said:
Thank you, guys. So, a separate GEC should be installed then for the secondary. And yes, Xo and ground need to be bonded. Thanks again.
Click to expand...
A separate GEC but connected to your existing grounding electrode system.
I know of no reason you can't use the existing grounding electrode system for your secondary.

In fact, if it were a building, 250.30 requires you to connect to the building GES.
 
LarryFine said:
Other than (possibly) better load balance, not really.

Most appliances can be had in 208, but not cheaply.

But it would be kinda cool to have a 3-phase service.
Click to expand...
Really can’t think of any appliances that wouldn’t run on 208 single phase, and would have to be special ordered. Dryers use 120 volt drum motors, the heating elements will work on 208 or 240, same with ovens. Most A/C’s are dual voltage.
 
LarryFine said:
True, although at 75% heating power.
Click to expand...
Most users would never notice the difference.

Maybe would notice difference with glass top cooktops, they don't heat very well even at 240 volts compared to old fashioned cooktop elements. I hate cooking on them, but wife wants this kind of top as it is easier to keep clean. I use a countertop electric skillet more than the range top as it heats faster and is easier to maintain a temperature than the range top does.
 
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