Voltages at a service

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GG

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Ft.Worth, T.X.
This is a post from another forum. Has anyone seen this type of service the writer descibes? He is stating that on a 3 phase service he reads 208V to ground on 1 leg and 120V to ground on the other 2 legs, and 208V between any 2 legs. Read for yourself. " one leg reads 208 to neutral, the other two reads 118 to 120 to neutral as well as ground, one of the city electricans told me that along time ago when this was put in they wired it some sort of delta something, the stinger leg was wired to one of the sides of the delta not the corner, it was done because of something with the transformer made then, between the hot leg and any other leg reads 208, and the two 120 circuits reads 208 between them,
city hall downtown has major power problems during peak load it can drop below 160 volts on line readings,
the new city hall lost all four compressors on their recip cillers, seems york supplied an discounted unit left over from soem other job, but it was 230 volts only, and when the machine started seeing 16 volts they didnt last,
however part of that was the city's fault as they slashed the budget and cut out controls, left out chill water bypass valve, and other controlss dur to budget restrains, this came back to haunt them, badly,"
 
This sounds like a 3 phase, 4 wire Delta system except that the voltage between any two phases would be 240 volts not 208. Otherwise I can't think of a configuration that would provide the voltages that you've described.
 
It's not uncommon for people to get confused. I met a guy a while back who insisted that the voltage on a midpoint-grounded delta system was 208 volts line-to-line, and 213 volts hi-leg to ground.

People remember things funny.

Chances are, the guy was working on a 120/240V midpoint-grounded delta and got confused, IMO.

The 160V could be from any number of bad, bad things. :)
 
I have been following the other thread. They are saying the system is an open wye. What are the voltages phase to phase and phase to ground on an open wye? TY
 
I'm no expert on transformers, but I believe the voltage is the same on an open wye or open delta configuration.

The kVA rating of the system must be reduced (because two transformers are being used to do the work of three), but the voltage remains the same.

Source:
http://www.federalpacific.com/university/transbasics/chapter3.html
 
It is a Delta, it can be open or closed but it is center grounded.

From Ed MacLarren

ED's4Wdelta2.JPG


Roger
 
Oh Oh! I missed this part pf the OP. "and 208V between any 2 legs" Never mind my post.

Roger
 
infinity said:
0101bx.gif



I found this info on an open Wye.
I was looking like crazy tonight and coming up short.

One odd detail of the picture you posted: I don't think the statement "VPO = VL / 2 " is correct.

Wouldn't it be the same as a regular wye, with VL being 1.73 times the voltage from line to the center point?

(Although I have a sneaking suspicion some crow is in the microwave for me... :) )

Edit for correcting question
 
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The formulas for Vl-l and Vl-n are the same for any wye system regardless if it is open or closed. This is no different than the Vl-l and Vl-n (for center taps) in delta systems.

208/120 1PH3W circuits are common in individual apartments that are fed from an overall 208Y/120 3PH4W service.
 
georgestolz said:
I'm no expert on transformers, but I believe the voltage is the same on an open wye or open delta configuration.

The kVA rating of the system must be reduced (because two transformers are being used to do the work of three), but the voltage remains the same.

Yes, the voltages will be the same, but you are correct on reduction in the KVA rating. If memory serves me correct, I think the transformer can only be loaded to 57% of the normal rating when using the 3 transformers.
 
georgestolz said:
I was looking like crazy tonight and coming up short.

One odd detail of the picture you posted: I don't think the statement "VPO = VL / 2 " is correct.

Wouldn't it be the same as a regular wye, with VL being 1.73 times the voltage from line to the center point?

(Although I have a sneaking suspicion some crow is in the microwave for me... :) )

Edit for correcting question


I agree. I noticed that after I posted the thing.
 
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