New CNC machine wiring help, please!

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Forum topic by Polynomial posted 05-16-2016 02:31 PM 706 views 0 times favorited 5 replies Add to Favorites Watch
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1 post in 162 days

05-16-2016 02:31 PM

I’m new to the group. We just received our first CNC machine last week. It’s used but I saw it run at the sellers location and then had it shipped to the manufacturer where we did training on it.

The three phase power in our shop is a high leg delta system. This means leg 2 is 208 volts to the ground. Legs 1 and 2 are 120 volts to ground. leg to leg is 240 volts.

We wired the machine as the manufacturer told us, knowing we had this type of power. The K1 breaker inside the control panel that runs the computer trips when we turn the control panel switch on.

Any ideas? I’m worried we fried the machine. Fingers crossed that didn’t happen it was a huge investment for our small business.


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5 replies so far

View bonesbr549's profile


1137 posts in 2487 days

#1 posted 05-16-2016 03:03 PM

do yo u have any documentation? Could be that yours is 220 three phase.

-- Sooner or later Liberals run out of other people's money.

View MadMark's profile


966 posts in 873 days

#2 posted 05-16-2016 04:36 PM

You need to be working with tech support and a good licensed electrician. This is a major safety issue. I’ve not heard of ‘high leg delta’ and am having a hard time envisioning the wiring.


-- Madmark -

View Mainiac Matt 's profile

Mainiac Matt

5955 posts in 1749 days

#3 posted 05-16-2016 05:45 PM

High leg delta (also called orange leg delta) is very common (the “wild” leg should have orange wire)

Are you sure that you are actually getting 120 vac at the computer breaker and not 240 vac?

If the breaker is tripping, it should be protecting you, so I wouldn’t think you fried anything, but I’d give the mfg. a call and pick their brain.

-- Pine is fine, but Oak's no joke!

View MadMark's profile


966 posts in 873 days

#4 posted 05-16-2016 08:42 PM

Where is the third leg coming from? Normal house is 240v single phase center tapped into two inverse phase 120v lines. You are showing a three phase input, I’ll bet he only has two phase power. That will cause this symptom. What is the plug on this or is it panel wired? What does your electrician say? Is your phase order right? Is there a schematic or wiring diagram? What is the draw required? How big is the motor?


-- Madmark -

View REO's profile


883 posts in 1494 days

#5 posted 05-17-2016 01:58 AM

there is more than likely a power transformer for 110 or a power supply down to 24v dc it may have been wired for 480 when demoed and they forgot to rewire the transformer for the lower voltage. check the input voltage of each part. the computer part is more than likely single phase either 220 or 110. I haven’t seen a breaker blow with to low a voltage usually the devise will fault with a code for low input voltage. try switching two of the legs.

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