voltage problem on single phase circuit

[unytko]

Problem:
NYC old Hotel/Residence-
HVAC company is claiming that dropped voltage is causing compressor problems that is lading to poor performance of the unit and sometimes dead of the compressor. I checked on that and on single phase 20 Amp rated circuit I am getting 197V and unit requires 230V

What would be the quickest solution to fix this problem. -without replacing the feeders in the building ...This is Landmark building so even changing of the A/C units is impossible .. Would installation of voltage booster transformer work ?? Did any of you have similar problem ? and how did you fix it.
Thank You All

 

[mcclary's electrical]

Problem:
NYC old Hotel/Residence-
HVAC company is claiming that dropped voltage is causing compressor problems that is lading to poor performance of the unit and sometimes dead of the compressor. I checked on that and on single phase 20 Amp rated circuit I am getting 197V and unit requires 230V

What would be the quickest solution to fix this problem. -without replacing the feeders in the building ...This is Landmark building so even changing of the A/C units is impossible .. Would installation of voltage booster transformer work ?? Did any of you have similar problem ? and how did you fix it.
Thank You All

That would be a dangerous fix and I would not recommend that. How long is this branch circuit?

 

[nakulak]

I am I understanding correctly that you have a 230v unit on a 208v supply ? If that is the case, and the unit won't run properly on 208, then it sounds like you need a buck boost or a unit that will run on 208 (wrong motor or wrong unit ?)

 

[mcclary's electrical]

I am I understanding correctly that you have a 230v unit on a 208v supply ? If that is the case, and the unit won't run properly on 208, then it sounds like you need a buck boost or a unit that will run on 208 (wrong motor or wrong unit ?)

Maybe, but I thought he meant single phase service.

If he does mean he's running a 230 volt unit on a 208 volt service, then yes a buck boost would do fine, but I thought he was questioning fixing a VD problem with a buck boost

 

[unytko]

Not sure, but the closest CBP is approx 60-80 feet away from this room. I think that the problem is not between CBP and receptacle but with the feeder for this apartment or the service in this building. I will do more investigation when they allow access this week.... ("high profile" people) last time I had only enough time to stick my tester in to receptacle to confirm the voltage reading to what HVAC guy reported. And he was right instead 220V+ we getting only 197V (between hot legs) ...I will be able to tell more in few days...
thank you

 

[LarryFine]

How many hot legs are there at the service, and (if three) do they all measue the same voltage to the neutral?

 

[poeboy]

what is the voltage at the source BEFORE it goes down to 197?? How far from the source is the appliance???

If you have bad wiring a buck boost will be nothing more than a band aid to a cut that requires stitches. First you need to determine if the drop is reasonable or not, then after that decision is made find the fix.

Its very common to boost up 208 to 230 or so in order to get HVAC related stuff to work right. But if your starting with 240 and losing 40+ volts going a relatively short distance, the only real way to resolve the problem is to replace the wiring.

 

[LarryFine]

Remember, too, that using a transformer or auto-transformer to boost voltage increases the primary current, which increases the voltage drop even more, requiring greater boost, adding to the primary current, etc.

When boosting is inevitable, it's better to boost the voltage at the source, rather than at the load. In fact, you might be better off using two transformers, boosting the voltage on the feeder, and back down at the load.

Plus, when the load is lessened, and the drop decreases, you can end up with an over-voltage to any equipment that is remaining on the line. That's one reason it's best done on a single load's branch circuit, not a feeder.

 

[unytko]

Update:
Apartment is on 14th floor Service is 3Ph At the panel between each ungrounded wire and neutral is 115V and between two ungrounded wires ( at the time when tested) 202V-103V at the receptacle 198V-200V First time I checked it was 197V. The problem is not only with the VD but the politics in the building. They (HVAC contractor) don't want to fix it because they will loose lots of $$$ I don't know for how long by now, but they changing compressors (through the wall units) every 2-3 years in residential and hotel part of the building. So I was told to leave it alone and that the building will not upgrade power distribution ....
What can I do???

 

[augie47]

Certainly sounds to me like the HVAC guy has installed 230v units in a building supplied with a 208 volt service.
Sounds like he might be in the market for a load of buc-n-boost transformers.

 

[mcclary's electrical]

Update:
Apartment is on 14th floor Service is 3Ph At the panel between each ungrounded wire and neutral is 115V and between two ungrounded wires ( at the time when tested) 202V-103V at the receptacle 198V-200V First time I checked it was 197V. The problem is not only with the VD but the politics in the building. They (HVAC contractor) don't want to fix it because they will loose lots of $$$ I don't know for how long by now, but they changing compressors (through the wall units) every 2-3 years in residential and hotel part of the building. So I was told to leave it alone and that the building will not upgrade power distribution ....
What can I do???

This guys probably PRAYING you don't figure this out. He's been ripping the owners off for years. Intentionally, or from stupidity, he's been installing a compressor rated for 230, on a 208 volt service. IMO, he should refund about 75% of the money they've spent over the years replacing these things, and then install the correct machines in their place

 

[unytko]

Re:

Re:

He (HVAC contractor) is claiming that the new compressors are rated 208/230V. And now, that units are physically to small (landmark building and he can not change the sleeves) to keep up with the low temperature demand and that VD is only small part of the problem. -yea.. but they keep changing them on and on...
Anyway finale question is:
Would installation of back-boost transformer help in this case.? would it work even if there are waves of VD in range of 197V-202V ? on different time of the day .
Thank You all for your input.
Lets close this thread....

 

[mcclary's electrical]

He (HVAC contractor) is claiming that the new compressors are rated 208/230V. And now, that units are physically to small (landmark building and he can not change the sleeves) to keep up with the low temperature demand and that VD is only small part of the problem. -yea.. but they keep changing them on and on...
Anyway finale question is:
Would installation of back-boost transformer help in this case.? would it work even if there are waves of VD in range of 197V-202V ? on different time of the day .
Thank You all for your input.
Lets close this thread....

Yes, if he insist on 230 volt machines (they are not dual rated, he's lying)

then you'll need buck boost at each machine

 

[Electric-Light]

230v motors are meant for 240v nominal
200v motors are meant for 208v

208-230 motors don't like to be on the low end of allowable voltage for 208v service (197v). Many units are though, rated 208-230.

197v seems like its just shy of -5% (the limit of utility voltage regulation for many parts). I was getting 127v from my outlet once, which exceeds the utility's own quality standard. Called and bi*ched, and they changed taps at the green box (transformer) and fixed the problem. You may be able to convince the utility to change taps, so you're getting closer to 208v + a percent or two.

Calling and complaining at the utility is a bit easier than adding a boost auto-transformer. Also keep in mind that these transformers hum, uses some power at idle and it is less than 100% efficient and the cost of install + power lost in transformer is yours to pay.

If it's a hotel or an apartment, you most likely have 208Y/120v with each unit served two of the phases and a neutral. It wasn't unheard of to drop voltage at a tap as an intentionally planned power savings and it works with regular light bulbs and magnetic fluorescent ballasts, but backfires with motors and electronic ballasts, because they draw more current to compensate.

If the transformer is owned by the building, then change taps, so the voltage is slightly above nominal

 

[hurk27]

for the most part using a buck boost for voltage drop will not really work, sure after the compressor is running you might be able to get the voltage close to 230 volts but remember if you have a voltage drop problem its because of the resistance in the feed conductors, and resistance is current limiting so when the compressor is starting up, the condition is much worse, try measuring the voltage when this compressor starts, you will be lucky if you even have 150 volts, and there is no fix for that with a buck boost as Larry has pointed out, up sizing the conductors is the only real fix, installing power boost capacitors can also help to get over the start up current, but as was said buck boost will only cause the voltage to fluctuate even more and any other loads on the compressor or after the buck boost will be over voltage when the heaver loads is turned off.

What wiring methods are used to feed this compressor? if a raceway maybe larger conductors can be used, I agree with others if the nominal voltage is 208 then a 200 volt compressor should have been used and the AC person is passing the buck, even if a compressor is rated 208-230 volts I have found that on 208 any voltage drop will cause problems and it doesnt leave much room for voltage drop as your already supplying it with 208, and at 197 the motor is slipping out of sync causing it to even pull more current then it should.

 

[unytko]

Thanks

Thanks

Thank You all for the help. I submitted letter to the client with explanations and recommendation to complain to the building management.
After researching details about the "back boost" transformer I agree with you 100%.
Thanks again.

 

[Electric-Light]

for the most part using a buck boost for voltage drop will not really work, sure after the compressor is running you might be able to get the voltage close to 230 volts but remember if you have a voltage drop problem its because of the resistance in the feed conductors, and resistance is current limiting so when the compressor is starting up, the condition is much worse, try measuring the voltage when this compressor starts, you will be lucky if you even have 150 volts, and there is no fix for that with a buck boost as Larry has pointed out, up sizing the conductors is the only real fix, installing power boost capacitors can also help to get over the start up current, but as was said buck boost will only cause the voltage to fluctuate even more and any other loads on the compressor or after the buck boost will be over voltage when the heaver loads is turned off.

What wiring methods are used to feed this compressor? if a raceway maybe larger conductors can be used, I agree with others if the nominal voltage is 208 then a 200 volt compressor should have been used and the AC person is passing the buck, even if a compressor is rated 208-230 volts I have found that on 208 any voltage drop will cause problems and it doesnt leave much room for voltage drop as your already supplying it with 208, and at 197 the motor is slipping out of sync causing it to even pull more current then it should.

197.6v to 218.4 would be considered acceptable voltage range for a 208Y/120v service, which most apartment complexes, dormitories and hotels have. I think that original poster is expecting 240v from 208v service and complaining that voltage is 43v too low. Anything in the aforementioned range at panel is within range, so you'll have to ask the utility really nicely to get it to about 211v. If you get too close to the upper limit, it will severely reduce the life of incandescent lamps. At 126v(upper limit), a 120v light bulb's life is halved. At 114v, it's doubled. The power consumption of simple ballast HIDs will increase substantially as well. Even though the brightness will increase, the gain is unnecessary and leads to an increased bill for the management.


For single phase power, 240v is the most common at houses(120-N-120) and 208v(208 phase-to-phase, 120 phase to neutral) in commercial and multi-unit buildings where there are a lot of 120v plug-in loads. It's an inevitable consequence of working around 120v. Since they're both so common, manufacturers don't make apartment version vs house version and it is true that many units are designed for 208 and 240v service, except for PTACs that they sell almost exclusively to hotels and apartments.

I think the only 200v rated ones you'll find are Japanese models, which are rated 200v 50/60Hz.