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Newb needing guidance on 3-phase service.

tinrat

Nov 21, 2021
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I have what I understand to be a 3-phase service from my provider. It has three legs: A) 120v. B) 208v. C) 120v. A and C are individually used for all 120 electronics and A with C for all 240 single phase connections. A, B, and C run 3-phase motors and welders. How can this be? I just can’t comprehend how I get the 180 degrees wave on 240 single phase motors yet 120 degrees on the 3-phase outputs. This has been set up this way and ran for years. Is this wired wrong or am I not seeing something? I am lost on the understanding and any explanation would be greatly appreciated.
 

ivak245

Jun 11, 2021
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Have you actually measured the line voltages with respect to neutral? Unbalanced 3 phase voltages would end in damage to equipment, or loss of "smoke".
 

tinrat

Nov 21, 2021
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“As we post”… so to speak. What must I do to make A and C @ 180 degrees to one another?
 

Minder

Apr 24, 2015
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Where are you located,?
If you had 3ph service there would be 120deg between each phase.
Also the voltages do not sound right, if 3ph.
if this was 3ph and single phase to a star neutral, it would be multiply by square root 3
 

tinrat

Nov 21, 2021
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I’m attached to Commonwealth Edison service. All three legs measure approximately 250v between any given pair.
 

Minder

Apr 24, 2015
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I’m attached to Commonwealth Edison service. All three legs measure approximately 250v between any given pair.
So where does the 120v come in.
The residential service in N.A. is a secondary of a 1ph centre tapped transformer 120v-0-120v ??
Is this an industrial installation or residential?
 

Bluejets

Oct 5, 2014
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I have what I understand to be a 3-phase service from my provider. It has three legs: A) 120v. B) 208v. C) 120v. A and C are individually used for all 120 electronics and A with C for all 240 single phase connections. A, B, and C run 3-phase motors and welders. How can this be? I just can’t comprehend how I get the 180 degrees wave on 240 single phase motors yet 120 degrees on the 3-phase outputs. This has been set up this way and ran for years. Is this wired wrong or am I not seeing something? I am lost on the understanding and any explanation would be greatly appreciated.

You have 2 phase and neutral, not 3 phases.

A) 120v. B) 208v. C) 120v.

Star 120.jpg
 

tinrat

Nov 21, 2021
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So where does the 120v come in.
The residential service in N.A. is a secondary of a 1ph centre tapped transformer 120v-0-120v ??
Is this an industrial installation or residential?
It’s a commercial account.
 

Minder

Apr 24, 2015
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If you have the set up per Blue jets post, I would expect you to have all 3 phases available ?
These transformers were often supplied in industrial applications to share the 120v loads across 3 phases for banks of lighting fixtures.
 

Minder

Apr 24, 2015
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I have only come across those in an industrial installations
Never seen residential 120v done that way?
 

JWHassler

Dec 22, 2014
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It's a 3phase 240v delta service, with the center of one phase taken as neutral for 120 volt loads. The 208 v measured to neutral is(was) called the "stinger leg."
 

Bluejets

Oct 5, 2014
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Never seen a secondary as a delta arrangement.

As the neutral in a star system is for the imbalance, or for a standard single phase arrangement, where is the neutral supposed to originate in a delta output.?
Can you show a typical supply authority example.?

Your claims don't add up, especially when 3 phase is standard 120 degrees electrical.
 

Kiwi

Jan 28, 2013
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Would this be what he has?
Four Wire Delta Circuits - Continental Control Systems, LLC (ctlsys.com)

A four-wire delta (4WD) electrical service is a three-phase delta service with a center-tap on one of the transformer windings to create a neutral for single-phase loads. Motors loads are commonly connected to phases A, B, and C, while single-phase loads are connected to either phase A or C and to neutral. Phase B, the “high” leg, is not used for single phase loads.

This type of service, which is also known as a “high-leg”, “wild-leg”, “stinger leg”, or “wild phase” service, is common in older manufacturing facilities with mostly three-phase motor loads and some 120 volt single-phase lighting and plug loads.

120/208/240 Volt Service
 

tinrat

Nov 21, 2021
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FIRST! I would like to thank everyone for there comments. Everyone has helped me to better understand the three phase phenomenon I didn’t quite understand. Fortunately I never got smoked as I see that there are portions of this where I need extra precautions and safeties. I realize that I have not studied or had enough comprehension as to how my service was/is set up. Kiwi has pointed out the service that I have. This explains and answers many of the questions I have been perplexed with. Thank you ALL again.

So as I understand it, I AM going to need some form if transformer to offset or shift the 120 legs back to 180 degrees of one another?
 

tinrat

Nov 21, 2021
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I had wondered why an air compressor (240 1ph)that is in use, sometimes as the pressure reached close to its peak, seemed to “run out of steam”. I also have an on demand water heater that never quite worked real well. Perhaps these are because they were not actually in designed alignment. Anyway, I would like to have the ability to use my service AND be able to run single phase motors on the system. So I am again asking for support.
 

JWHassler

Dec 22, 2014
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“As we post”… so to speak. What must I do to make A and C @ 180 degrees to one another?
You cannot. The transformer would need to be changed.
Also: I'm not convinced you need to.
What are you trying to power?
 

tinrat

Nov 21, 2021
17
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Nov 21, 2021
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Everything three phase runs fine. I have an antique air compressor that runs off 240 single phase using L1 (120v) and L3 (120v). It kind of runs at a slower speed when the pressure is up. I worry it will burn up or mess something up. If I don’t keep an eye on it, it’ll run for a very long time at this lower speed. I have contemplated exchanging motor w/ 3ph but of course running new wire further to three phase box; etc;etc. I haven’t gone that route yet. Just shut air off when not in use. Other possible prob was an on demand water heater (240-1ph). It never seemed to work right. Com Ed interests don’t seem to go past the fact of whether your bill is paid or not. Supposedly an engineer is going to call me but his recall was last week. I’m still waiting…
 
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