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Old 05-14-2016, 07:44 PM   #1
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Default CNC machine power wiring. High leg delta system - HELP PLEASE!

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.

Thanks!!
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Old 05-14-2016, 07:57 PM   #2
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I like your username.

You're not giving enough info about the conditions of the fault/problem.
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Old 05-14-2016, 08:00 PM   #3
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Sometimes the drive just doesn't like a hi leg.
If it's breaker fed, move the breaker up one position in the panel. If that doesn't work, move the breaker down one space from the original spot.

If it's a disconnect, move phase A to B, B to C and C to A.

The idea is that if they are bootlegging a control circuit to ground, it will a one point roll past it.
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Old 05-14-2016, 08:05 PM   #4
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And make sure the supply rotation is correct due some drive system will not run in reversed supply..


( note : normal is ABC the reversed is CBA )
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Old 05-14-2016, 11:14 PM   #5
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And see if there is a UV relay in the controls.
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Old 05-15-2016, 12:46 AM   #6
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If there's a VFD involved, most likely the MOVs in the front end saw the high leg as a surge and clamped it to ground.

Nothing is wrecked, most VFDs can operate on a high leg system but you'll need to disconnect the MOVs.

What brand of VFD (if there is one)?
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