Adding a new 230V single-phase outlet

[jmarkwolf]

When I built my detached garage shop I had the foresight to include a 230V 20A single phase duplex, for my mill and lathe.

Now i need an additional 230V 20A outlet because I'm changing the motors on some other power tools to 3-phase with a VFD.

Is it Kosher to simply add a box below the existing duplex box and run a short length of 20A romex between 'em, vs swapping plugs as needed? No more than one 230V tool is running at any one time.

Wall covering is T1-11 so I'd have to cut a hole and use one of those boxes designed for after thoughts like this.

Thoughts?

 

[pattenp]

That is okay.

 

[mark flucke]

hope you are using motors rated for a vfd

 

[jmarkwolf]

Actually, rethinking this, it may make better sense to just enlarge the hole in the T1-11, fish the old box out, and make it a double duplex with one of those "cut-in" boxes.

 

[wyliesdiesels]

hope you are using motors rated for a vfd

Yes many people dont pay attention to this.

Actually, rethinking this, it may make better sense to just enlarge the hole in the T1-11, fish the old box out, and make it a double duplex with one of those "cut-in" boxes.

The boxes are called ‘old work’ boxes

 

[jmarkwolf]

It is my understanding that the prohibitions against using non-inverter rated motors with VFD's have to do with operating RPM and length of power cable between the VFD and the motor. Motors can overheat if run too slow, and length of power cable aggravates motor induced electrical noise if the cables are VERY long (over 100ft).

My motor will be run at rated speed, and my power cable length between the VFD and the motor will be 2ft.

Although I can imagine inverter rated motors are better for use with VFD's, I've run 50 year old motors on Bridgeport milling machines from VFD's without issue.

Can you guys advise of other issues?

 

[outdoorspace]

VFDs generate transient voltages which can break down the stator winding insulation if it's not designed for it. These stresses weaken the insulation over time.

Also these transients can cause current to flow through the bearings causing pitting and premature failure. This can be mitigated with a shaft brush.