Voltages on HVAC specs

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kennymayo said:
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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129 to an outlet tells me you have a neutral issue, or a runaway regulator down the line. If neighbors on the same transformer or same phase dont have problems, look at the service neutral
 
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 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





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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The utility standard is nominal +-5%. A 240V system is within tolerance at 252V. Call the utility and they’ll tell you to pound sand.
I agree with the previous post. If you have 129 L-N and 251 L-L, there is a neutral issue.
 
High horsepower 3ph motors are made in dedicated 200v and 230v specs for optimized performance at the specified service voltage. 208-230 rated motors are a compromise and can not be expected to provide the identical efficiency throughout the usable load range.

A lot of regulatory politics are involved in HVAC system design. The compressor doesn't slip a whole lot, but the fan slips considerably. Ordinary HVAC fan motor speed is set by varying the voltage with coil taps, thus changing the slip (difference in actual RPM vs synchronous RPM). If you look in the detailed spec sheets for single phase PSC air handlers, the CFM is actually different for 208 vs 230 service. The CFM difference affects the performance/efficiency as well as the efficiency curve difference of the compressor.

A certain system could pass the rebate qualification threshold when it is tested under standardized laboratory conditions which includes making avail exact voltage as prescribed in test protocol and qualifying for rebate is pivotal to equipment sales, because the rebate is tied to how the system performs in the lab. So equipment are often designed to look good to the prescribed lab test standards.

That same piece of equipment though could very well not pass the SEER rating at alternate voltage input and could affect real world efficiency.
 
aks20000 said:
For load calculation, which voltage do you use - 230V or 240V ?
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For Art 220 calculations? If so those are all in VA anyway.

That said 240 volts is a nominal system voltage. 230 is an equipment voltage rating, ideally it should draw nameplate amps if operating at nameplate load and input volts is 230. If voltage varies a little then the amps will vary a little as well, still going to get very near the same VA out of it though.
 
I'd just like to add that I've found it somewhat common to have 125V L-N and 250V L-L on split-phase residential services and often 2*teens* on 208V systems. Quite a few household lamps are rated at 125V. Much like the older nominal values of 110V & 220V got bumped up to 120 and 240, utilities have nudged up their service voltages to keep up with increased load demand.
 
Electromatic said:
I'd just like to add that I've found it somewhat common to have 125V L-N and 250V L-L on split-phase residential services and often 2*teens* on 208V systems. Quite a few household lamps are rated at 125V. Much like the older nominal values of 110V & 220V got bumped up to 120 and 240, utilities have nudged up their service voltages to keep up with increased load demand.
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The concept there is usually that as you load the system there will be some voltage drop, the values you mention are quite common around here as well when there is either minimal or no load on the system.
 
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