Wire my shop

I just got the 200 amp electric line to the new shop. Now for the wiring. The shop has a 20 hp. bed mill and a 20 hp. lathe. Both machines have 100 amp 220 volt three phase mains. The shop will also have an EDM, surface grinder, tubing bender,welders, and etc.

My understanding is that electrical code requires a safety switch disconnect by each machine. I'd like to be able to run both the mill and lathe at the same time. I made a line diagram below of how I'm thinking of wiring all this up.

If anyone can make sense of my ASCII art, is this how you'd do it? Do you see any code violations to watch for?

200 amp line | | | [J box]---------[1 phase 200 amp load center] | | | {lights, plugs,etc.} | [200 amp switch] | | | [phase converter] | | [J box 3 phase] ------[100 amp switch] | | | [J box 3 phase] -----[100 amp switch] | | | | [100 amp switch]----[20 amp switch] | | [30 amp switch] etc.

SWITCH is an enclosed safety switch with the indicated fuses J box is a junction box for connecting wires load center is a standard household type circuit breaker panel

----- wires | | wires

An apple a day keeps the doctor away. Two apples a day gets the doctor's OK. Five apples a day makes you a fruit grower, like me.

Karl Townsend in beautiful Dassel,MN

Reply to
Karl Townsend
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What is the full load amperage of the mill and lathe and at what voltage? What kind of phase converter are you using and how much is it going to draw powering the equipment at full load? Keep in mind amps at 208 three phase are multiplied by 360 to get VA, by 240 if single phase, so you will have reduced amperage available at three phase.

Reply to

I can see your point here. Maybe I should look for a used three phase breaker panel as my first option.

I'd like to know how the code reads here if someone is familar. The machines already have a main switch right on the back of the machine, and if I put in a breaker panel with a circuit breaker disconnect for each machine. Is another fused disconnect right before the machine required??? Seems WAY to redundant to me. BTW, everything is in the same room and close together.


Reply to
Karl Townsend

No, the purpose of the switch is to kill power to the machine so it can be serviced, redundant switching is not required.

Only issue there is to make sure that there is some wayy to kill power in the event that something is going to hell in a hand basket around one of the pachines precluding your reaching around it to kill power. The breaker panel should be at some remove, and UNOBSTRUCTED.

Reply to
Bradford Chaucer


The shop has a 20 hp. bed mill and a 20 hp. lathe. Both machines have 100 amp

220 volt three phase mains.

First - I read your message and after that the 4 replies. My first & second questions remain the same. How come you ran single phase and why just 200 amps? You are at the least just over the edge of the 200 amps and probably should be at least 400 amps or at least enough wire size to do 400 amps and then connect

200 amp panels as needed for your loads. And all this 3 phase.

Three phase panels are on Ebay. Usually inexpensive. Be sure to invest in all the same brand and model.

What is the source for the power? Perhaps even 440 volts 3 phase. For sure it needs to be three phase. And yes each load will need a disconnect. I usually think that most posters can do their wiring if the desire is there but do yourself a favor and find an electrician qualified to look this over. Do you have a permit for this work? I would be surprised if it would be approved to do things this way. And finally unless the 20HP machines will sit idle all the time it will be cost effective for you to go three phase. It is a lot simpler for what you have. Take care Bob AZ

Reply to

I only have one phase 200 amp service on my place. Upgrading the service to larger and/or 3 phase would be WAY to expensive.

I started looking on Ebay for disconnects and 3 phase panels. MUCH cheaper than Grainger.


Reply to
Karl Townsend

A 30hp rotary converter should easily run two 20 hp machines, I would think.

I run some heater / contactors at the converter idler feed so if it overloads it will shutdown the entire buss, and it also disconnects the static converter except during startup.

This is a 30 hp rotary that runs three Fadal cnc and also Fanuc 6mb machine W/ 7-1/2 hp spindle..........

The hydraulics on the fanuc machine drew too much inrush current so a second

20 hp idler was added--it only runs the hydraulic pump and so is not fed into a breaker panel but instead is hard wired to the hydraulic contactor in the control cabinet--I suppose I should add a separate disconnect for this, but it is only ~ 3 feet from the converter and breaker panels so.........

The single phase feeder breaker for the 30 hp unit is a 100 amp while the

20hp feeds from a 70 amp.

We are a bit slow so if anyone would like me to post ammmeter readings under no load conditions I could likely do that sometime this week........

Reply to

I'm not certain about current codes, but I think that a plug in counts as a disconnect.

Yes, depending upon the voltage and the HP of the load.

Otherwise, a disconnect is required.

Reply to
Peter H.

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