Minimum voltages?

[skintdigit]

Hi gang...what should my voltage range be for residential single phase 3-wire service? I replaced a pool pump motor for a next door neighbor today and noticed 198 volts across lines 1 and 2 at the pool timer subpanel. Came back to my place, shut the 200amp main breaker off at my panel, and checked line voltage at the feeds from the meter can...203 volts. Shouldn't we be within a few percentage points of 220 volts at the service entrance? As I recall, motors(a/c compressors, fridge compressors, pool motors, etc.) run a lot hotter when the supplied voltage is low. Is this correct? Don't know if I should call the service supplier or if voltage numbers like this are normal on a hot afternoon in Texas when everyone's running air conditioners full blast.

[Snoonyb]

Its actually, 240 & 120V and when considering the efficiency of motors, remember, they are generaly operating equip. with fixed loads and at a rated RPM.

[HayZee518]

The voltages also depend where you are on the "crib line." This is the service entrance conductors that come off the transformer secondary on the pole. If you are at the end of a high voltage run, you may be below the rated voltage. Middle of the run is also different. If I were you I'd call the utility and have them check for any voltage drops along your run. A motor rated at 230-240 operating at 198 or 203 will run hotter and will burn up eventually causing you headaches. Normally 120 loads operate in a span of 113 to 127 volts.

[skintdigit]

Thanks, guys. We'll call the electric supplier. Do I understand that being near the end of the high voltage crib line can cause lower voltages past the transformer that supplies us because of the loads imposed along the hi-vo run? If so, I s'pose a high-load period (hot weather, kids home from school during the day) might cause temporary voltage drops that fall below the normally acceptable range. A good reason to run the pool filter at night, perhaps.

[skintdigit]

Snoonyb, your reply brings up another question...written documentation on motor specs, etc. always specify 120/240 for voltages, but I've never read any metered voltages close to those numbers. Always closer to 110/220. What accounts for the difference?

[Snoonyb]

"always specify 120/240"

So much for chit-chat.

In a perfect world, the "quoted" voltages are as HayZee alluded to, and while the high voltage transmission voltages are fairly stable, as they are steped down through transformer and distributuin stations, fluctuations can occur, yet seldom affect equip. performance.
The last leg of the distribution process, the lowley transformer on the pole adjacent to your house,also has optimum operating limits, and unlike "regulated power supplies" acts pretty much like a repeater.

[SSN596]

In my area, the supplied voltage is always pretty close to 120/240. 110/115/120 would all be considered "normal". 198 seems pretty low. Some large motors are spec'd at 208/240 but I think you have to wire them specifically for the voltage you have.

[HayZee518]

if you wanted to be real technical with motor running loads you could incorporate buck-boost transformers, but if the load goes up or down the transformers would also go up or down with their voltages