# Voltage lag



## readydave8 (Sep 20, 2009)

199-201 from POCO transformer? Or customer owned?


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## readydave8 (Sep 20, 2009)

By the way I don't understand why low voltage is being called "lag"


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## Helmut (May 7, 2014)

208V plus/minus 5% is all the utility will probably supply.


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## woodlandeer (Aug 17, 2018)

The voltage lag, as I call it, is within the NEC standards. But not within the sensitive equipment standards. It reads low voltage on the lcd screen.

I believe the main PG&E service is probably 480/277 transformed to 208/120 "Y" typical.


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## Helmut (May 7, 2014)

I doubt the motor cares if it's low, so it must be the electronics that fuzz out.

Sounds like a control transformer issue


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## MDShunk (Jan 7, 2007)

woodlandeer said:


> Question: What is the best way to increase the "Y" 3 phase voltage up 8+ more volts.


Ask the utility to change the tap. It might be within their tolerances, but if you ask them to bump it up one, they will.


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## woodlandeer (Aug 17, 2018)

I wondered about asking PG&E about that. Hum.
I had read somewhere that ferroresonant transformers, or Magnetic synthesizers may do the trick. Never installed one.


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## gpop (May 14, 2018)

Have you done a voltage drop calculation on the wire. At low voltage any additional problems will just add to the problem


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## MDShunk (Jan 7, 2007)

woodlandeer said:


> The voltage lag, as I call it, ...


At the risk of being a terminology nazi, you call it the wrong thing. Voltage lag is a specific term that means something completely different than what you have measured and observed. What you are observing would be more properly called "low voltage".


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## woodlandeer (Aug 17, 2018)

It is consistent low voltage from nominal 208/120 service. Ok low voltage works for me.


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## glen1971 (Oct 10, 2012)

woodlandeer said:


> The voltage lag, as I call it, is within the NEC standards. But not within the sensitive equipment standards. It reads low voltage on the lcd screen.
> 
> *I believe the main PG&E service is probably 480/277 transformed to 208/120 "Y" typical.*


You believe? I've always known the supply voltage when I'm doing troubleshooting...
Is it low at your 480 volt main? What voltage are you seeing there? Changing the tap on the main may not be the issue, but rather on the 208 volt transformer..


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## gnuuser (Jan 13, 2013)

voltage "Lag" 

the only place i've heard that term is in generator theory!
now voltage drop and voltage loss are the better terms.
I agree with the others this sounds more like a control voltage issue!
in any event the use of buck and boost transformers can correct minor issues with voltage but be aware that changing values on a transformer will affect the current as well.


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## brian john (Mar 11, 2007)

woodlandeer said:


> A new air compressor was installed, and it requires no less than 208 "Y" 3 phase volt.
> The main service was tested at 199 to 201 "Y" 3 phase. just that lag in voltage is causing problems with the air compressor.
> 
> Question: What is the best way to increase the "Y" 3 phase voltage up 8+ more volts.
> ...


First I DOUBT your compressor needs a Wye service unless it has some weird control setup.

2nd What issues are you having at 199? 199 is about 4.5% low and generally in the acceptable range.

What is the voltage at the service without the compressor running?
What is the voltage at the service with the compressor running?

Same questions with readings taken at the compressor.

Many utilities do not have taps on their transformers as a cost-saving measure, as noted above use a buck-boost.


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## 460 Delta (May 9, 2018)

Please give us more details, such as the problem you are having and the size and type of compressor. As always, pics are very helpful. If you have a 200 volt motor, you'll be fine, the controls, such as the starter coil may not like 200 volts if it is a 230 volt setup.


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## frenchelectrican (Mar 15, 2007)

woodlandeer said:


> The voltage lag, as I call it, is within the NEC standards. But not within the sensitive equipment standards. It reads low voltage on the lcd screen.
> 
> I believe the main PG&E service is probably 480/277 transformed to 208/120 "Y" typical.


There is few missing information you posted here .,,

A. Did you ever check the voltage on 480 volts side ? if before the downstep transformer ? 

B. did you look the control panel or contractor to make sure you using correct coil voltage ? 

C. how far is from the source to the compressor and conductor size and how many HP it is ?

D. most case the customer owned downstep useally have a taps to change the voltage ( on 30KVA or larger ) 

E. where the sam hill you read the voltage at ?? 

the more info you posted the easier for us to find the curpit.

Yes most 208 volt motors can run just fine on 200 volts that is common. but just beaware of starting perfomace that all .


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## MDShunk (Jan 7, 2007)

brian john said:


> 2nd What issues are you having at 199? 199 is about 4.5% low and generally in the acceptable range.


I was wondering the same thing. He said "low voltage" comes up on the digital alarm display. That could be purely a function of a voltage sensing/phase monitor relay that could stand a little adjustment of the dial for the low voltage alarm trip point.


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## MTW (Aug 28, 2013)

"Voltage lag"? That would be called capacitance.


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## woodlandeer (Aug 17, 2018)

Thanks for all your replies.

A little about the building being served. It is part of a complex of commercial units occupied by product manufactures, retail/wholesale sales supplies etc.

Each unit has from one to five 120/208V 200A elec panels, the feeders are 3/0 copper.

The unit I'm referring to is less than 100 ft away from the switchgear (PG&E Main) and is supplied by a 200A 3 phase "Y" CB. Didn't think that a voltage drop on the lines could be a problem, because the voltage is within NEC specs, but I could be wrong.

I also didn't think that three buck/boost transformers were the right solution for the compressor, hoping for a different approach to boost the voltage up just 8 or so volts.

The compressor sits about 30 ft away from the elec panel and is supplied by 3 #10 THHN conductors and one #10 grounding conductor in a fuseable disconnect, fused at 50A CL.

Compressor requirements are: 208V 28.8A and the control transformer is on the 208V tap, of the several taps that are available, inside the unit.

The measurements I took were from the: CB, the load side of the disconnect and the contractor block (inside the unit). everything had the same voltage (199-201 volts line to line, 118-121 volts line to ground) Amps were from about 21A to 27A running load. I had my (true RMS) meter on high/low record for a few minutes on each test.

Again sorry about the terminology "voltage lag" I'll refer to voltage drop from now on.


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## woodlandeer (Aug 17, 2018)

Just a note. 
I will be gone for a few days playing Old-Time music at a campout. 
But please still post your suggestions, and I will respond when I return.
Again thank you,
Brian


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## readydave8 (Sep 20, 2009)

woodlandeer said:


> Just a note.
> I will be gone for a few days playing Old-Time music at a campout.
> But please still post your suggestions, and I will respond when I return.
> Again thank you,
> Brian


suggestion:
don't play "Wildwood Flower":wink:


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## woodlandeer (Aug 17, 2018)

Thanks Dave, I'll keep that in mind :biggrin:


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## woodlandeer (Aug 17, 2018)

Back from a campout, played a lot of tunes.

Anyway thanks again for all your replies, any other suggestions will be greatly appreciated.

Thinking to go with the easy and safest way.

Brian


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