Sizing Conductos for CNC

[Logan35]

I am trying to figure out how to size conductors for a CNC machine. I have done a lot of research and I keep coming back to theses questions.

Does a CNC fall under Article 670 of the NEC (industrial machinery)

The size of the supply conductor shall be such as to have an ampacity not less than 125 percent of the full-load current rating of all resistance heating loads plus 125 percent of the full-load current rating of the highest rated motor plus the sum of the full-load current ratings of all other connected motors and apparatus, based on their duty cycle, that may be in operation at the same time.

If so which do I add considering there is no heaters

Is it considered a continuous load?

This is an example of one CNC Name plate I choose this one due to the largest motor being at 96amps
220/480v 3PH 60HZ
Rated capacity 30.5KVA
FLC 80.1/36.7
Largest motor is 96amps the name plate does not specify what voltage this is at.
interrupt Cap 25/7.5

 

[charlie b]

What is a CNC? :?

 

[petersonra]

What is a CNC? :?

I am trying to figure out how to size conductors for a CNC machine. I have done a lot of research and I keep coming back to theses questions.

Does a CNC fall under Article 670 of the NEC (industrial machinery)

almost certainly.

The size of the supply conductor shall be such as to have an ampacity not less than 125 percent of the full-load current rating of all resistance heating loads plus 125 percent of the full-load current rating of the highest rated motor plus the sum of the full-load current ratings of all other connected motors and apparatus, based on their duty cycle, that may be in operation at the same time.

If so which do I add considering there is no heaters

add zero, since that is the number.

Is it considered a continuous load?

why does it matter?

This is an example of one CNC Name plate I choose this one due to the largest motor being at 96amps
220/480v 3PH 60HZ
Rated capacity 30.5KVA
FLC 80.1/36.7
Largest motor is 96amps the name plate does not specify what voltage this is at.
interrupt Cap 25/7.5

how can the entire machine be 80 FLA with the largest motor at 96A?

There is a reason for the nameplate. they already did the hard work. Take the FLC from the machine nameplate and add 25% of the FLC of the largest motor. That is the required ampacity.

 

[petersonra]

What is a CNC? :?

CNC = computer numeric control.

A way of automating things like lathes and grinders to do repetitive but varying tasks.

 

[gar]

140220-1417 EST

CNC is Computer Numeric Controlled. I can not answer the question on the wiring. I would suggest contacting the manufacturer.

We just received a new HAAS VF-2. The advertized spindle motor is 40 HP, there is a small coolant pump, and control electronics. This is being supplied by a 240 V high leg delta, and the breaker installed is a QO 80 A. I don't know what wire size was used, it was sized per HAAS specifications, but it is probably less than 30 ft of wire from a 100 A subpanel. This machine is unlikely to ever be loaded to 40 HP. Usual load is probably 5 HP.

Most low volume CNCs are not a continuous high load. High volume production machines may be a continuous load, and in some cases near maximum spindle capability.

.

 

[Logan35]

96amps?

96amps?

how can the entire machine be 80 FLA with the largest motor at 96A?

There is a reason for the nameplate. they already did the hard work. Take the FLC from the machine nameplate and add 25% of the FLC of the largest motor. That is the required ampacity.

This is a question I can not answer this is what is on the name plate.

 

[Logan35]

This is the actual name plate.

 

[petersonra]

that is really odd.

I think I would run some #6 wires on a 60A Cb and not worry all that much about it. Probably a mistake on the nameplate.

 

[Logan35]

Name plate

Name plate

that is really odd.

I think I would run some #6 wires on a 60A Cb and not worry all that much about it. Probably a mistake on the nameplate.

That is the problem there is a couple that have the motor rating larger than the FLC.
Another reads
220/480v
3ph
60hz
38KVA
FLC 99.8/45.8
Largest motor rating 219A
Short circuit rating 30/10 KA

 

[GoldDigger]

Possibly they are giving the Locked Rotor Amps of the largest motor (needed for some design decisions) rather than the FLA/FLC of that motor?

Tapatalk!

 

[Logan35]

is this correct

is this correct

how can the entire machine be 80 FLA with the largest motor at 96A?

There is a reason for the nameplate. they already did the hard work. Take the FLC from the machine nameplate and add 25% of the FLC of the largest motor. That is the required ampacity.

96A*.25=24
24+80=104A
or
Because it requires in 670.4 to add 125% is it this
96A*1.25=120
120A+80A=200A
Please explain why you only add 25% of the FLC and not at 1.25%

 

[mike1061]

96A*.25=24
24+80=104A
or
Because it requires in 670.4 to add 125% is it this
96A*1.25=120
120A+80A=200A
Please explain why you only add 25% of the FLC and not at 1.25%

Somethings wrong there. Unless I'm missing something (which happens way more than I want to admidt too). What you do is take the right number and add 25%, which means multiply by 125%.
IMO you would use the FLC number. I would say they put it there for a reason. There my be control circuits, a display screen or some other loads above the motor load.
Thanks
Mike

 

[Logan35]

I will break down numbers

I will break down numbers

Somethings wrong there. Unless I'm missing something (which happens way more than I want to admidt too). What you do is take the right number and add 25%, which means multiply by 125%.
IMO you would use the FLC number. I would say they put it there for a reason. There my be control circuits, a display screen or some other loads above the motor load.
Thanks
Mike

96amp is largest motor 80amp is FLC so it would be this
96*25%= 24
24+80=104amp

I need to size overcurrent and wire to the next standard size to accommodate 104amps
This is from A670.4(a) industrial machines
Please let me know is I am correct
Thank you for all the help everyone it has been fun

 

[petersonra]

I don't think we know what is correct.

We do not have enough information to make a determination.

It appears that the information on the machine nameplate does not correspond to the information one traditionally expects to see on a US made machine.

You may have to do some digging to figure out what the real numbers are.

Or you can oversize the wires. Those are your two choices.