For those of you with 3 Phase wiring in your shop ...

[Tom Bain]

Construction of my new shop is finally underway, and I plan to upgrade a few pieces of machinery (planer, drum sander) which will have 3-phase motors. The largest would probably be a 7.5HP motor. I plan to implement a rotary converter (or phase perfect if budget allows) and then hang a 3-phase panel off that, with a dedicated branch circuit for each 3-phase machine to/from the panel. I am in a residential setting (the workshop is essentially a 2-story barn) and I realize that in a commercial environment the 3-phase wiring would most likely be THHN wire run in EMT conduit. I am experienced and comfortable with residential electrical wiring having wired up my previous 2 shops, but have zero conduit experience. Soooo, my question is ... are there any major issues utilizing the appropriate gauge NM-B (i.e., Romex) wiring for 3-phase?? I'm thinking that 10/3 Romex would be much easier for me to install for the branch circuits to each machine rather than trying to master conduit bending, fitting, and pulling . I should note that the shop has an accessible basement so the wiring will be run from there (not buried in the walls) and then stubbed up to the main shop floor, so I can move/change circuits as needed.

Any insights from the 3 phase crowd are appreciated!

Thanks,
Tom

[Rod Sheridan]

Hi, there would be nothing wrong with Romex for your application providing that local codes allow you to mark the white conductor as a phase conductor by colour coding.

As you're looking at Romex I presume that your 3 phase system is a 208 or 240 volt system?

Where I live you can't have distribution in excess of 150 volts to ground in a residence............Rod.

[Tom Bain]

Yes, a 240 Volt system and I was planning on coloring the white ("neutral") wire to blue since I won't need a neutral for 3 phase. That's interesting about the 150V limitation ... do you not have electric ovens or dryers than run on 240V??

[Malcolm McLeod]

I just added electrical to my new (old) garage shop, using THHN - but alas, all 'single' phase (I have to save the 3-ph stuff for the real job). I also have zero conduit bending experience, so ran it in PVC conduit and surface mounted it. Simple.

As I recall, during planning stages I looked at NM and found it to be more expensive to do what I wanted (5ea. dedicated 240V circuits; 5ea. 120V circuits; 1ea. switched 120V). I never considered not using surface mounted conduit as I didn't want to strip and reinstall all the drywall.


Hope this helps.

[Mike Henderson]

Yes, a 240 Volt system and I was planning on coloring the white ("neutral") wire to blue since I won't need a neutral for 3 phase. That's interesting about the 150V limitation ... do you not have electric ovens or dryers than run on 240V??

In the US - and I assume in Canada - the 240 volts coming into your home is center tapped and the center tap is grounded. So each side of 240 volts is 120 volts to ground.

Mike

[Tom Bain]

In the US - and I assume in Canada - the 240 volts coming into your home is center tapped and the center tap is grounded. So each side of 240 volts is 120 volts to ground.

Mike

Ahhh, now I understand ... although how would a 3-phase system violate the distribution limitation? Isn't it also 120 Volts to ground on each leg, but with 3 phases. My 3-phase knowledge is admittedly fairly rudimentary.

[Mike Henderson]

Ahhh, now I understand ... although how would a 3-phase system violate the distribution limitation? Isn't it also 120 Volts to ground on each leg, but with 3 phases. My 3-phase knowledge is admittedly fairly rudimentary.

I wasn't paying attention to how you have your 3 phase set up, but if you set up as a Y with the center grounded, you could certainly stay below 150 volts. This is a generalization but most voltage calculations in 3 phase are related to the square root of 3.

Remember that the 3 phase grounding has to occur after you generate the 3 phase. Your 3 phase will be isolated from your distribution supply.

Mike

[Tom Bain]

Malcom -- I hadn't thought about using PVC conduit, but that's an idea as I have worked with that before ... sparingly. Did you glue the conduit and fittings, or just friction fit? I figure I'll be saving a ton of money by doing the wiring myself rather than hiring it out, so not as concerned about the cost differential between Romex and THHN.

[Jim Becker]

Tom, I used the schedule PVC conduit when I did the wiring for my CNC machine and my MiniSplit. It was a pleasure to work with for sure and I'd use it over EMT any day as long as code permits it. (yes for here)

[Rod Sheridan]

Ahhh, now I understand ... although how would a 3-phase system violate the distribution limitation? Isn't it also 120 Volts to ground on each leg, but with 3 phases. My 3-phase knowledge is admittedly fairly rudimentary.

That's true Tom, however only on 208 volt systems.

The line to line voltage is the the square root of three multiplied by the line to neutral voltage.

In the USA 277/480 is common for low voltage systems, in Canada we have 120/208 and 347/600..........Regards, Rod.

[Malcolm McLeod]

Malcom -- I hadn't thought about using PVC conduit, but that's an idea as I have worked with that before ... sparingly. Did you glue the conduit and fittings, or just friction fit? I figure I'll be saving a ton of money by doing the wiring myself rather than hiring it out, so not as concerned about the cost differential between Romex and THHN.

I used glue almost everywhere. My main run is 1"dia, mounted on the wall ~1" below the ceiling. At the various LL/LR/T fittings, I drop a 3/4" conduit down to the receptacle boxes. The drop is mechanically held into the fitting, so I didn't glue the drops into the LL/LR/T's (...it's not my 'forever' shop and if the next buyer is nervous about add-ons, I can strip it out in 15-20 minutes).

[Arthur Fleming]

2 points- I believe the NEC states the wire gauge has to be #6 or larger to repurpose with colored tape. We used to do it for years, and the electricity certainly has no idea what color the wire is, but I believe they changed the code, if this makes a difference to you. If your shop is not heated/cooled to a fairly consistent temperature, PVC WILL contract and expand somewhat noticeably. They do make expansion couplings if you have any long runs, and want to protect. I have seen meter sockets torn from houses due to this.

[Jon Snider]

I’m building a shop and putting in single and 3 phase wiring and boxes as we speak After reading this I called the Electrical inspector at Regional Building who said 10/3 Romex was fine for my 30 amp 3 Phase connections, and that it was ok to add colored tape to the neutral. This is in Colorado Springs.

Jon

[Jeff Bartley]

Here in VA it's ok to use tape to re-color wires.

I just built a shop and ran a 3-phase system using romex. Just use the proper guage for your circuits and blue tape.

And do yourself a favor and keep the black/red/blue consistent on all your breakers, outlets, and plugs!

The nice thing about 3-phase is that amp loads are lower so you can use a lighter gauge (less expensive) wire. I think my 5hp Oliver saw only pulls 12.3 amps!

Good luck with your shop Tom.

[Bill Dufour]

I like to color the wire with a sharpie and slip heat shrink tube over it as well. Heat shrink comes in many colors including blue and red. NEC says hot wires are any color other then white, green, or bare naked.
Bill D.