3-Phase Electrical Service

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Forum topic by MJCD posted 04-20-2018 10:39 PM 808 views 0 times favorited 7 replies Add to Favorites Watch
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603 posts in 3150 days

04-20-2018 10:39 PM


This is a narrow subject; and, I’ll try to ask the question clearly…

I’m upgrading to Felder equipment, and need to provide 3-Phase electric to the machines. I will do this via a Phase Perfect PT-355. For the sake of clarity, the Source of the 3-phase is not that important… and, I’m trying to avoid debating Digital vs. Analog; and one brand versus another.

My single phase is being delivered to the Phase Perfect, which outputs 3-phase… Do I need to run the output to a 3-phase panel box – that would support several independent 3-phase circuits, or can I run the output directly to the machines via a sufficiently sized wire (probably handling 50 amps)?

Thanks for the consideration.


7 replies so far

View Loren's profile


10477 posts in 4426 days

#1 posted 04-20-2018 11:29 PM

You’ll want to get the panel box. Your phase
converter probably just has 4 outputs, 3 hots
and a ground. All that thick wire is stiff and
uncooperative and it’s hard to stick it into small
boxes anyway. The panel gives you room to
have it hooked up in a way that you can open
the door and see exactly what’s going on in there.

In industrial situations they hook up a second
breaker/cutoff switch at the hardwired machine
for maintenance.

View Firewood's profile


1224 posts in 2412 days

#2 posted 04-21-2018 12:01 AM

I agree with Loren. A 3 phase panel will make a much cleaner solution I’M HOME.

-- Mike - Waukesha, WI

View Richard Lee's profile

Richard Lee

298 posts in 1553 days

#3 posted 04-21-2018 12:24 AM

I used a panel also , but I added a plug from the panel for an extension cord for my jointer.

View CaptainKlutz's profile


3209 posts in 2273 days

#4 posted 04-21-2018 12:45 AM

You can run directly between with converter and tool, assuming they have sufficient space for the wiring connections in existing junction boxes, and proper strain relief for wire/conduit.

The details vary depending on interconnect method:

-Temporary power connection between independent source and tool can be accomplished with most an suitable 50A plug/receptacle and portable cable rated wire, as long as wire junctions are inside a rated box. Since you have control of a remote 3 phase source, and tool connection: You can get away with using most any 250VAC 50A plug that has 4+ poles to support tool, such as regular NEMA 14-50P, providing you label it 3 phase. There are very few NEMA rated 50A plugs, so many options used in industrial applications are custom and costly. I suggest using a locking version like this one to help avoid any confusion between household oven circuit and your 3 phase system?

- Permanent power installation requires that any wiring junctions be inside a rated junction box. So need a box at/on converter which holds conduit feeding machine and a box at/on machine when power terminates into machine. You may or may not be able to use existing junction boxes, it depends on style and size. If tool is not bolted to floor, the conduit from a fixed junction box to machine must be flexible version.
As Loren stated, it is common for industrial sites to use a breaker or disconnect junction box near machine for lock out during maintenance. This industrial protection lock out disconnect is added even if machine has junction box mounted directly on it due differences in “line of site” requirements for power disconnects, as most machine junction boxes are too low for line of sight across a room.

If you want to connect more than one tool at time to 3 phase power for a permanent installation, then you will need to install a separate 3 phase panel board with breakers to protect individual 3 phase circuits. If is not allowed to have more than 1 device on a 3 phase circuit. Remember breakers protect wire in circuit, not tool.

IMHO – If you do not need portable power via temporary connection, it is usually cheaper to run wire run inside conduit between junction boxes.
Cost for 50A plug/receptacle, plus 6AWG flexible cord is significant (50A locking plugs cost $125+ pair, while junction box cost $20 each?). Another benefit of using conduit is allows use of higher 75 degree temperature rating for THWN/THHN wire, which means only need 8 AWG for 50A permanent install instead of 6AWG for temporary wire. Four conductors of THHN cost about $1.50 foot, while 6AWG SOOW/SEOOW portable wire costs $2.50+/foot.

Hope this helps.
Enjoy your new tool.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

View MJCD's profile


603 posts in 3150 days

#5 posted 04-21-2018 01:55 AM

Excellent, Excellent Answers. Thank you, ALL for helping me evaluate this – I’ll have a certified electrician do the install – I’m just trying to decide what to have him do.


View MJCD's profile


603 posts in 3150 days

#6 posted 05-06-2018 10:38 PM

I want to provide some closure on this… as a thanks for your comments and consideration…

I’ve added a 100A service to my workshop, to support a living-space expansion upstairs. Within two years, I’ll have all 220-V machines on 3-phase – this will be my dust collector & bandsaw; and the J/P and sliding TS that I have on-order, now. The new sub-panel will feed a Phase Perfect PT-355 (already arrived); which outputs 65A of 3-phase power.The PT-355, with a surge protector between the single & three-phase systems, will output to a 100A 3-phase sub-panel.

For the next two years, there will not be concurrent loads on the 3-phase panel (only one of the J/P & Slider machines will be on, at a time). With the addition of the DC and BS, it’s likely that two or more machines will be on concurrently – if I’m ripping on the BS, I often clean the cut-edge on the joiner; plus the DC will be on, as well.

In summary, I’m taking the sage advice, and outputing to a 3-phase sub-panel; eventhough, I could probably just daisy-chain a 30A circuit in the short-term.

Thanks, again.

View TheFridge's profile


10859 posts in 2264 days

#7 posted 05-06-2018 11:12 PM

You need a panel.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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