480 wye to delta; neutral or not?

Status
Not open for further replies.

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
I've not thought much about delta, wye and neutral since EE 443 w/Prof Klingshirn, or even longer ago, installing 3ph transformers and starters.

But I'm now looking at some plans from an electrician.

Q1) If you're fed with 480/277 wye, and run it 1000 ft to a 480 delta:208/120 wye stepdown transformer; are you required to carry a neutral along with those three legs?

(I've always thought it was "no"....)

Q2) What, if anything, changes when you add 480v 3ph motors upstream of the transformer?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I've not thought much about delta, wye and neutral since EE 443 w/Prof Klingshirn, or even longer ago, installing 3ph transformers and starters.

But I'm now looking at some plans from an electrician.

Q1) If you're fed with 480/277 wye, and run it 1000 ft to a 480 delta:208/120 wye stepdown transformer; are you required to carry a neutral along with those three legs?

(I've always thought it was "no"....)?

You thought correct. If you have no need for the neutral, it can be omitted. In most cases, a EGC will be required.
Q2) What, if anything, changes when you add 480v 3ph motors upstream of the transformer?
Nothing same answer
 

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
I've read enough here over the past few days that I suspect the correct answer is "buy Mike's book on grounded vs. grounding" but I'll blunder in anyhow.....

Grounding the various motors is not an issue. What to, may be.

What size ground will be needed between the utility xfmr/meter/switchboard; and the 480 panel/xfmr? The run is about 1000 ft and the electrician has called for 350MCM for the phases. [That's why I asked re: neutral. If it was 10 feet, no issue.]

A further question: he's said the ground would be in the duct, & insulated. Why is that? I would have thought that a 1000 foot of bare ground in the ditch would improve the system ground resistance considerably. He's also spec'ing Ufer grounding on the house.

[I'd thought the 400' well casings would help lower the ground R, until I found out they make them out of PVC now...]
 
Status
Not open for further replies.
Top