Looking at utility poles

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teufelhounden91

teufelhounden91

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Austin, TX, USA
Can you tell by looking up at a 3ph utility pole whether it is delta or wye and whether it is corner or center tapped? I came across an unlabeled service and subpanel today and read 217v line to line and 120v line to neutral. Trying to hook up motors and I'm assuming that is just a high 208v reading but it could also be a terribly low 230v reading. (Either way my calcs will be under the 208v column in 430.250 because it's lower than 220v - but damn it's right in he middle)

I still know I have 120v line to neutral and no high leg so it's not delta period. So it has to be 208v wye. However hypothetically...if I didn't have access to the panel can I look up and see somehow what I have?


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ActionDave said:
Yes, you can tell. A wye system will have three taps all tied to ground.
Click to expand...

That makes so much sense that I feel stupid now for even asking lol - does a center tapped delta just have a ground coming out of one can for center tap, and corner tap have two pots tied together with ground then?


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teufelhounden91 said:
Can you tell by looking up at a 3ph utility pole whether it is delta or wye and whether it is corner or center tapped?
Click to expand...

When the transformers are on the pole, yes. The first times you try it, take some time and draw the circuit of the transformer primaries and secondaries. Pay attention to the ground wire running down the pole and into the ground.

distribution_transformer.jpg
 
teufelhounden91 said:
does a center tapped delta just have a ground coming out of one can for center tap, and corner tap have two pots tied together with ground then?
Click to expand...

A centertapped delta usually has only two transformers, and is called an "open delta". One transformer is much larger than the other and looks like a standard 120/240 Volt single phase hookup.

OpenYOpenDelta.jpg


This transformer bank is actually three phase. It has two primary 13.8 kV phases from the PoCo, connected as an open Wye, and then an open Delta secondary that delivers three phase 120/240 four wire.
 
teufelhounden91 said:
That makes so much sense that I feel stupid now for even asking lol - does a center tapped delta just have a ground coming out of one can for center tap,
Click to expand...
Yes
and corner tap have two pots tied together with ground then?
Click to expand...
Corner ground is a rare bird, at least where I live. I have only seen one.

Open delta is one other. Al posted about it.
 
Is it realy 120V

Is it realy 120V

teufelhounden91 said:
Can you tell by looking up at a 3ph utility pole whether it is delta or wye and whether it is corner or center tapped? I came across an unlabeled service and subpanel today and read 217v line to line and 120v line to neutral. Trying to hook up motors and I'm assuming that is just a high 208v reading but it could also be a terribly low 230v reading. (Either way my calcs will be under the 208v column in 430.250 because it's lower than 220v - but damn it's right in he middle)

I still know I have 120v line to neutral and no high leg so it's not delta period. So it has to be 208v wye. However hypothetically...if I didn't have access to the panel can I look up and see somehow what I have?


Sent from my iPhone using Tapatalk
Click to expand...

If you have 217v phase to phase you are 4.1% high. This should make your 120v end 125volts

Odd ratio should be there
 
teufelhounden91 said:
Can you tell by looking up at a 3ph utility pole whether it is delta or wye and whether it is corner or center tapped? I came across an unlabeled service and subpanel today and read 217v line to line and 120v line to neutral. Trying to hook up motors and I'm assuming that is just a high 208v reading but it could also be a terribly low 230v reading. (Either way my calcs will be under the 208v column in 430.250 because it's lower than 220v - but damn it's right in he middle)

I still know I have 120v line to neutral and no high leg so it's not delta period. So it has to be 208v wye. However hypothetically...if I didn't have access to the panel can I look up and see somehow what I have?


Sent from my iPhone using Tapatalk
Click to expand...

You are unlikely to see 230V services anymore. Old school.
 
meternerd said:
You are unlikely to see 230V services anymore. Old school.
Click to expand...
That's true for new transformer banks for new customers, but there's that installed base of old "high leg deltas" that are still in service to thriving occupancies that we have to provide support for.
 
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