Voltages on HVAC specs

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Grouch1980

Grouch1980

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New York, NY
Hi all,
I haven't been on here in some time!

Kind of a basic question: usually when I see the mechanical / HVAC schedules on a set of mechanical drawings, I'll see an AC unit (for example) with a voltage rating of 208 / 230 volts. I understand it is saying the AC unit is compatible with both voltages. However, the 230 volt rating... is it really a 240 volt rating, and they show 230 volts to take into account voltage drop? If that's the case, how come they don't show something less than 208 volts? If 230 volts is shown to account for voltage drop from a 240 volt system, why not show 200 volts to account for voltage drop as well in a 208 volt system? It's as if voltage drop is accounted for in one system, but not the other. Unless I'm interpreting this wrong.

Thanks!
 
The unit's rating is technically 208v to 230v, but is designed for supplies from (usually) 200v to 240v.

Most HVAC equipment comes marked with an acceptable voltage range, often greater than the above.
 
LarryFine said:
The unit's rating is technically 208v to 230v, but is designed for supplies from (usually) 200v to 240v.

Most HVAC equipment comes marked with an acceptable voltage range, often greater than the above.
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I’m gonna have to disagree…
the 208/230 rating is 208 minimum voltage.

230 volts +- 10%
 
Officially, there are “distribution” voltage levels, and “utilization” voltage levels. Distribution is what the utility delivers to your service entrance. Utilization is what the end use equipment is designed to work on and yes, it is purposely lower to account for expected voltage drop. so 230V is the utilization voltage for a 240V distribution, and yes, 200V is the utilization voltage for a 208V distribution.

The 208/230V thing is an industry standard “compromise” design on the motor windings. You can kind of think of it as taking a 220V design but instead of being +-10%, it is +-15%. So 220+15% makes it good up to 253V, which is the same as 230+10%, and 220-15% makes it good down to 187, which is the same as 208-10%. The motor has to be made that way, but most OEM motors are.
 
So the 208 / 230V rating on the specs doesn't mean the typical voltage systems of 208 volts or 240 volts (or 230 with voltage drop). It is actually instead saying the unit can work anywhere from 187 volts to 253 volts?

In other words, the 230 volts is not based on a 240 volt system minus voltage drop, but rather the 230 volts was chosen so that 230 + 10% is equal to the 220 + 15% value?
 
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Grouch1980 said:
Shouldn't nominal volts though be marked at 208/240? It's a 240 system, not 230. That's where I'm confused.
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See what J said in post #4. And this is far from the first discussion about it.

Also, "nominal" voltages used to be lower. Back when I was a helper, we had 110/220 and a 190v high leg.
 
ok, I think I follow now. I have to read things several times sometimes to understand it. So the 'compromise' that Jraef mentioned made the 230 volts as a nominal value. So the two nominal values are 208 / 230. 240 volts is not considered to be the nominal value in these cases, since the compromise brought it down to 230. Do i have it right?
 
HVAC is a specialty ... The manufacturers base their minimum ampacity and maximum overcurrent device on the fact that the refrigerant suction return cools the compressor, that's why it is hard to figure out.
 
Grouch1980 said:
So the two nominal values are 208 / 230. 240 volts is not considered to be the nominal value in these cases, since the compromise brought it down to 230. Do i have it right?
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Kinda-sorta. In no particular order:

240v is a nominal source voltage, and 230v is a nominal load voltage. I think the reason they use 208 instead of 200 as the lower nominal number is to get us to worry about voltage drop more.

A motor, which attempts to be a constant-power load, draws current inversely to its applied voltage, which is why the current at 208v is always higher than the 230v current.

Think of 208v to 230v as being a voltage range (within a greater voltage range), rather than two distinct voltages. As you reach the extremes of this range in either direction, the motor runs hotter.
 
LarryFine said:
Kinda-sorta. In no particular order:

240v is a nominal source voltage, and 230v is a nominal load voltage. I think the reason they use 208 instead of 200 as the lower nominal number is to get us to worry about voltage drop more.

A motor, which attempts to be a constant-power load, draws current inversely to its applied voltage, which is why the current at 208v is always higher than the 230v current.

Think of 208v to 230v as being a voltage range (within a greater voltage range), rather than two distinct voltages. As you reach the extremes of this range in either direction, the motor runs hotter.
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Sorry..🥴
Answered a tad quick…you are correct..

Some manufacturers will build to a 220V base to cover them selves on 220+- 10%.
242V-200V as you stated.. As utilities like us keep voltages a little high (we are 216V on a 208 system and 248V on 240) the motor can be used on both systems.

Once you get below 200V (as in 208 - 10%) your outside the range of a 208/230 motor.
A motor for a 208 system with low utility voltage or long lines should be a 200V motor.
 
LarryFine said:
See what J said in post #4. And this is far from the first discussion about it.

Also, "nominal" voltages used to be lower. Back when I was a helper, we had 110/220 and a 190v high leg.
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But marking it 208/230 is in a way a mix of both nominal and utilization voltages in the same specification.

208 is a nominal voltage, 230 is a utilization voltage. That 208/230 should really be marked 200/230 if they intend to list utilization voltage or 208/240 if they intent to list nominal voltage.

But in picture in post 6 at least they did put a min 197 and max 253 on the nameplate as well, that kind of overrides the 208/230 and how you might read into it.
 
I agree that the actual voltage range listing clarifies any confusion.

IMHO the reason that the label apparently mixes a nominal voltage and a utilization voltage is the normal tolerance on those voltages.

That motor is good for +-10% at 230V, but doesn't have the - tolerance for a 200V utilization voltage, and thus is not marked for it.

Jon
 
A compressor rated at 208/230 that has a supply voltage of 253v will not last long, it will overheat, draw to many amps, heat wire up, trip breakers. A compressor rated at 240v can easily handle the 253v supply
 
kennymayo said:
A compressor rated at 208/230 that has a supply voltage of 253v will not last long, it will overheat, draw to many amps, heat wire up, trip breakers. A compressor rated at 240v can easily handle the 253v supply
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I disagree. A compressor with a nominal 230V rating is intended for a nominal 240V supply. 230V is the normal 'utilization voltage' for a 240V system. A compressor for a 240V system should be able to tolerate the normal ANSI tolerances for a 240V supply.

The _nameplate_ of this particular HVAC system makes this explicitly clear. The unit has a nominal rating of 208/230V, and has a specified supply voltage tolerance range of 197-253V. This unit supplied at 253V exactly is in its rated supply range, but at the extreme end. I'd expect that it would work for a 'normal' life, although it will probably age faster than if it was supplied right in the middle of its allowed operating range.

-Jon
 
A compressor rated at 208/230 that has a supply voltage of 253v will not last long, it will overheat, draw to many amps, heat wire up, trip breakers. A compressor rated at 240v can easily handle the 253v
winnie said:
I disagree. A compressor with a nominal 230V rating is intended for a nominal 240V supply. 230V is the normal 'utilization voltage' for a 240V system. A compressor for a 240V system should be able to tolerate the normal ANSI tolerances for a 240V supply.

The _nameplate_ of this particular HVAC system makes this explicitly clear. The unit has a nominal rating of 208/230V, and has a specified supply voltage tolerance range of 197-253V. This unit supplied at 253V exactly is in its rated supply range, but at the extreme end. I'd expect that it would work for a 'normal' life, although it will probably age faster than if it was supplied right in the middle of its allowed operating range.

-Jon
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winnie said:
I disagree. A compressor with a nominal 230V rating is intended for a nominal 240V supply. 230V is the normal 'utilization voltage' for a 240V system. A compressor for a 240V system should be able to tolerate the normal ANSI tolerances for a 240V supply.

The _nameplate_ of this particular HVAC system makes this explicitly clear. The unit has a nominal rating of 208/230V, and has a specified supply voltage tolerance range of 197-253V. This unit supplied at 253V exactly is in its rated supply range, but at the extreme end. I'd expect that it would work for a 'normal' life, although it will probably age faster than if it was supplied right in the middle of its allowed operating range.

-Jon
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I will notified the power company 250v and up, I've seen what constant high voltage can do in the feild. It can handle spikes here and there but constant 253v it wouldn't last 6 months, my way of looking at it is this, we can get equipment rated at 208, 208/230, or 240 plus/minus 10% so if the voltage runs constantly higher than 245v I make sure to use equipment rated at 240v. When I look at equipment with 208/230 I see 219v plus/minus 10%
 
kennymayo said:
A compressor rated at 208/230 that has a supply voltage of 253v will not last long, it will overheat, draw to many amps, heat wire up, trip breakers. A compressor rated at 240v can easily handle the 253v


I will notified the power company 250v and up, I've seen what constant high voltage can do in the feild. It can handle spikes here and there but constant 253v it wouldn't last 6 months, my way of looking at it is this, we can get equipment rated at 208, 208/230, or 240 plus/minus 10% so if the voltage runs constantly higher than 245v I make sure to use equipment rated at 240v. When I look at equipment with 208/230 I see 219v plus/minus 10%
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As a former engineer at a compressor manufacturer, I agree with Winnie.
 
A compressor rated at 208/230 that has a supply voltage of 253v will not last long, it will overheat, draw to many amps, heat wire up, trip breakers. A compressor rated at 240v can easily handle the 253v
winnie said:
I disagree. A compressor with a nominal 230V rating is intended for a nominal 240V supply. 230V is the normal 'utilization voltage' for a 240V system. A compressor for a 240V system should be able to tolerate the normal ANSI tolerances for a 240V supply.

The _nameplate_ of this particular HVAC system makes this explicitly clear. The unit has a nominal rating of 208/230V, and has a specified supply voltage tolerance range of 197-253V. This unit supplied at 253V exactly is in its rated supply range, but at the extreme end. I'd expect that it would work for a 'normal' life, although it will probably age faster than if it was supplied right in the middle of its allowed operating range.

-Jon
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winnie said:
I disagree. A compressor with a nominal 230V rating is intended for a nominal 240V supply. 230V is the normal 'utilization voltage' for a 240V system. A compressor for a 240V system should be able to tolerate the normal ANSI tolerances for a 240V supply.

The _nameplate_ of this particular HVAC system makes this explicitly clear. The unit has a nominal rating of 208/230V, and has a specified supply voltage tolerance range of 197-253V. This unit supplied at 253V exactly is in its rated supply range, but at the extreme end. I'd expect that it would work for a 'normal' life, although it will probably age faster than if it was supplied right in the middle of its allowed operating range.

-Jon
Click to expand...
I will notified the power company 250v and up, I've seen what constant high voltage can do in the feild. It can handle spikes here and there but constant 253v it wouldn't last 6 months, my way of looking at it is this, we can get equipment rated at 208, 208/230, or 240 plus/minus 10% so ifbi low the voltage runs constantly higher than 245v I make sure to use equipment rated at 240v. When I look at equipment with 208/230 I see 219v plus/minus 10
retirede said:
As a former engineer at a compressor manufacturer, I agree with
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retirede said:
As a former engineer at a compressor manufacturer, I agree
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retirede said:
As a former engineer at a compressor manufacturer, I agree with Winnie.
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This is very interesting to me would like to learn more, I just had a call yesterday to a residental home with 251v between L1And L2 coming from the power company, last year same place I had 242 everything working great, now have a bad compressor, partially going to ground the home is experiencing all kinds of electrical issues lights blowing hot switches, hot outlets, I read 129v in a 120v outlet
 
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