Motor Ckt. 230 rated 208 feed

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shockingthemonkey

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I'm tring to wire a motor for a spa blower for a Hotel.

It's rated at 110/230V 17.8/8.9A 2HP
I wired it for 230V, but I got 208V 1PH from a 3PH panel. It's about 20' from the panel to the timeclock and then about 150' to the motor (via a 2pole toggle switch for disconnect)

Now check at the disconnect, which is 5' from the motor I check voltage. Without the motor running I have 208V, I turn on the disconnect, and as the motor is starting up, the voltage goes to 190V and when the motor is running it's at 200V.

The motor runs for about 5 to 10 minutes then the thermal protection in the motor shuts off, until the motor cools down.

I ran the ckt in #12 wire. mc for about 100 feet then goes in jbox and switches over to PVC and THHN.

Now I was gonna change the wire to #10 for voltage drop.

But my Question is should I also wire it for 110V since I have 120V or should a motor rated at 230V work fine with 208V??????????
 
Re: Motor Ckt. 230 rated 208 feed

I calculated the VD and came up with about the same as your measurement(6 volts). Installing #10 won't help much. VD using #10 was 4 volts. You need to measure the voltage at the breaker so we can know the total VD. You may want to consider a 6% or 10% boost autotransformer. Wiring at 120 volts yields a VD of 12 volts with #12 and 7+ with #10.

[ April 09, 2005, 03:13 PM: Message edited by: bob ]
 
Re: Motor Ckt. 230 rated 208 feed

If the motor is rated at 230v it will draw more current at 208 therby over heating. Either get a 208V motor or boost the voltage to 240V.
 
Re: Motor Ckt. 230 rated 208 feed

Based on some basic calculations, and using the values provided by your post, the single-phase motor rated at 230V and operating on 208V will draw more current about 9.8A vs 8.9A. using this value, at 340 ft round trip the VD is about 6.5 volts with No. 12 cu conductors. 208 - 6.5 - 201.5V at the motor. By increasing the conductors to No. 10 Cu, the VD is about 4V. 208 - 4 = 204V, which is about 2 percent drop. Operating a motor at 110 percent of its rated current will shorten the life span of the motor. You will have to increase the value of the overload devices to match the new full load amperes due to the reduced voltage. The above are approximate values.
 
Re: Motor Ckt. 230 rated 208 feed

Besides the fact the motor won't work well as pointed out above, its a violation of 110.3 (B)
A 230 volt motor is designed with a +/- 10% voltage tolerance. 230-23V = 207, but if the 208 secondary is low, then the motor will be have low voltage.
 
Re: Motor Ckt. 230 rated 208 feed

A 1 kva boost buck will do the job very nicely as I have done this dozens of times with propane pump motors in the same conditions. Remeber with a bost buck you only need a transformer lage enuf to carry the boosted current so 1 kva will work just fine for this motor . An Acme T-1-81050 will work just fine. Wired in an autotransformer configuration you will get your voltage up to about 223 wich will falls within the 10% +- of nema rating. As I say I have used this dozenz and dozens of time with very good results. Never had any problem. Eliminates that hassle of trying to find a 115-208/230 motor etc.

[ April 26, 2005, 07:07 PM: Message edited by: stew ]
 
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