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Discussion Starter · #1 ·
CNC is 220V 3ph. Manufacturer: Miyano. Specifications state 30KVA. Called CNC technical rep who said the machine draws 70 amps. CNC manual does not specify a feeder size.
CNC is located in Canada.
From previous experience, I would feed this with an 80 amp line #4AWG.
Current draw on a CNC is always varying with the job, but usually does not reach anywhere near the rated amperage.
So the question is: Whats the correct sizing according the code book,
(CEC or NEC). I don't believe that sizing according to the CEC section on motors is applicable as it would result in unrealistic wire sizes and cost for the measured load.
 

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I don't believe that sizing according to the CEC section on motors is applicable as it would result in unrealistic wire sizes and cost for the measured load.
I don't believe either code cares about cost of installation.

What circuit size would you like to feed it with?
 

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Have you done the math with the given 30kva rating? It's not 70 amps.
 

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Discussion Starter · #4 ·
Have you done the math with the given 30kva rating? It's not 70 amps.
That’s one of the problems. The literature may say one thing and when the machine arrives, the nameplate says something else. I find it better to ask the CNC tech, who knows the machine, what the exact load is. In this case 70 amps.
 

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That’s one of the problems. The literature may say one thing and when the machine arrives, the nameplate says something else. I find it better to ask the CNC tech, who knows the machine, what the exact load is. In this case 70 amps.
Usually the techs have a good handle on what is needed. Large machines with servos need to have a "stiff" supply for voltage drop during a very small time frame. All of the axises accelerating from stop to rapid feed at the same time and/or a heavy spindle load can add up to a large draw. Similar to multiple large induction motors all starting at the same time.
 

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Discussion Starter · #8 ·
Follow-up
Machines installed.
Just before I started the install, I went over to the machinery supplier and pulled out the manuals. Found in the manual the required wire size-25mmsq (3AWG) so thats what I installed.
The job on this cnc is at maximum capacity, so I put my fluke clampmeter on the input to see maximum current input. CNC has a load meter that was going into the red for this job. My clampmeter showed 82.5A for a few seconds only.
Machine Nameplate said 70 amps. 30KVA

bullmike-Production machine stays on minimum of 8hrs a day
 
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