Minimum operating voltage rating

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manuel bonilla

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What is the minimum operating voltage that an HVAC unit should operate with if it is built for a 208V system?

On a recent installation I found an equipment that says Min Voltage is 198V (4.8% under 208!!).

In this case, distribution voltage in the area is not very stable and tends to lower to 205V at the pad mounted transformer terminals (this an apartment building with a 120/208V Tx). Under this circumstances, considering 5% voltage drop to HVAC equipment terminals, voltage at that point would drop to 194V and it in fact triggers the HVAC protection.

Is not it true that the standard min. voltage for an equipment should be 10% under rated voltage?
 
manuel bonilla said:
What is the minimum operating voltage that an HVAC unit should operate with if it is built for a 208V system?

On a recent installation I found an equipment that says Min Voltage is 198V (4.8% under 208!!).

In this case, distribution voltage in the area is not very stable and tends to lower to 205V at the pad mounted transformer terminals (this an apartment building with a 120/208V Tx). Under this circumstances, considering 5% voltage drop to HVAC equipment terminals, voltage at that point would drop to 194V and it in fact triggers the HVAC protection.

Is not it true that the standard min. voltage for an equipment should be 10% under rated voltage?
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Air conditioning equipment is acutely designed to tolerate more voltage drop.

That is why they give you the min allowable voltage on the tag.
 
manuel bonilla said:
Min Voltage is 198V
. . . voltage at that point would drop to 194V and it in fact triggers the HVAC protection.
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Sounds like it's doing exactly what should be expected.
 
I agree with that. I guess my question is, would this equipment low voltage threshold be considered "standard"?

I want to add that is installed outside the US, and my concern is if this is an equipment that would be considered "sub standard".
 
manuel bonilla said:
I agree with that. I guess my question is, would this equipment low voltage threshold be considered "standard"?

I want to add that is installed outside the US, and my concern is if this is an equipment that would be considered "sub standard".
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It all depends on the place where the equipment is to be installed. An example here in the Philippines, voltage from the POCO is 230V plus/minus 10%. Equipment should then be able to tolerate the POCO standards, otherwise problems concerning equipment operation will arise.

equipment buyers are advised by the POCO here to check their equipment ratings before buying them
 
Check the transformer and see if it has taps. You may be able to get the utility change them and get the voltage reading a little higher.
 
The big clue is the "minimum voltage rating" being 198V. What they did, as many OEMs do, is to design the system voltage to be 220V, that way it covers everything from 200 to 240V and they only need to purchase and support one motor. So by using 220V wound motors, they would be good for +-10%, and 220 x .9 = (drum roll please...) 198V! What they fail to tell you directly is that it is not good for 208 - 10% of course, but they indirectly let you know by showing that "Min Voltage" rating.
 
I think this is exactly the point.

Now, by checking the equipoment box, it says "not suitable for sale in the United States".

I guess this reinforces my suspicion that this equipment is not suitable per US standards. Now, I still have not been able to confirm if there is a standard (i.e. Nema...) that would require an equipment to be suitable for "rated voltage-10%"
 
manuel bonilla said:
I think this is exactly the point...
Now, I still have not been able to confirm if there is a standard (i.e. Nema...) that would require an equipment to be suitable for "rated voltage-10%"
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I can't (at this moment) tell you where NEMA or the NEC defines voltage ranges
but I do remember years ago seeing it on some GE made equipment I was working on. Their range for supply voltages (from my memory):
208 (nominal) ~ 197-219
240 (nominal) ~ 228-247. (FWIW)
 
BryanMD said:
I can't (at this moment) tell you where NEMA or the NEC defines voltage ranges
but I do remember years ago seeing it on some GE made equipment I was working on. Their range for supply voltages (from my memory):
208 (nominal) ~ 197-219
240 (nominal) ~ 228-247. (FWIW)
Click to expand...

Voltage ranges are defined in ANSI(American National Standards Institute) Standards.
 
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