TECO FM50 2hp wire size question

B

bkcorwin

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I am working on setting up a couple of VFDs around my shop to drive machines I am in the process of acquiring and am trying to figure out my wiring plans.I am in the process of acquiring a logan lathe and a bridgeport series 1 j head. Both of these have motors under 1.5 hp and are setup for 220 3 phase. I am planning to run two teco fm50 202-x vfds rated for 2hp. The manual states that a 202 series vvd requires a molded case circuit breaker of 20 amps and recommends 14 awg wire. I was going to up this to 12 awg wire to agree with my understanding of residential electric. Seem ok?The next question is what awg wire do I need to run from the vfd to the motor? The specs say the output current is 7.5 amps. This says to me that I should be plenty safe running a 4 conductor 14 awg vfd cable. Does this seem ok or should I upsize this cable?Thanks muchBrian
 
If you're not planning to run both machines off the same branch simultaneously, I think you're on the right track. If the branch feed is a short distance from the breaker, 12 ga is fine. 14 ga from the VFD to the unit is also fine assuming the distances are about 10 to 15 feet.


Ray
 
Why the concern about the distance, honestly curious? 10-15 feet isn't much and the voltage drop in an AC systems is low compared to DC. My rough calculations would show that pushing 7.5 amps even over 30 feet at 220v single phase would only be a drop of about 0.55% or ~1 volt?
 
The lines radiate a whole lot of high frequency noise. The longer the run the more it radiates and interferes with TVs, Radios etc...

If you have those issues (I did) get some copper braided shielding, run the wires through it and ground one end of the braid.


Ray
 
I see. I was aware of that issue on the vfd to motor connection and I meant "vfd cable" specifically such that is typically double shielded.

https://www.platt.com/platt-electric-supply/Tray-Cable-Shielded-with-Ground/Multiple/08611404/product.aspx?zpid=634841

http://www.alliedelec.com/search/productdetail.aspx?sku=70004268

I have also read that in the case of vfd motor drives one should ground both ends of the shielding not just one end as is done with control shielding. See the belden termination guide at

http://www.newark.com/pdfs/techarticles/belden/VariableFrequencyDriveCableTerminationGuide.pdf

There are also some other discussions about grounding around on the web with the same conclusion

Brian
 
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