CNC Equipment Install

[MatthewM]

Hello Electrical Gurus,

Bottom Line Up Front:
I am installing equipment and am concerned that the calculated service requirements far exceed the manufacturers recommended install requirements.


History:
I am the maintenance supervisor for a manufacturing facility. I have worked here for eight months and before coming here had very little experience in the electrical industry. I am currently assigned to a project in which I am working on the installation of several pieces of CNC equipment. Specifically my guys are installing several HAAS CNC machining centers. We have an electrician at the facility; however, he is not a licensed electrical contractor (there are no certifications for electricians in the state of Arizona outside of a contractor's license).
My degree is in mechanical engineering, but through research and study I have developed an extremely rudimentary understanding of the code and electrical systems. I did my best at calculating the requirements for our equipment and what I calculated far exceeds the manufacturers recommended installation instructions. I am here to seek counsel from experienced electricians. I would like to know if I made incorrect assumptions in my calculations, and if not why the code differs so much from what the manufacturer recommends.

The System:
The machines run on 240V, 3 pahse power. Each machine will have its own run of conduit with 3 current carrying wires and a ground wire. Runs are no longer than 50 ft total. Busway switches are rated at 75 deg C.

Machine Type 1 - HAAS VF1
Feed: 3 Phase Power at 240V off of a bus bar (Bus bar is fed from a 175kVA transformer)
Peak Load: 20 kVA
Continuous Load: 14 kVA

Manufacturers recommended wire size @ 240V: #8 AWG
My calculated wire size @240V:#3 AWG


Machine Type 2 - HAAS TL-2
Feed: 3 Phase Power at 240V off of a bus bar (Bus bar is fed from a 175kVA transformer).
Peak Load: 14 kVA
Continuous Load: 20 kVA

Manufacturers recommended wire size @ 240V:#8 AWG
My calculated wire size @ 240V:#6 AWG

Machine Type 3 - HAAS ST-20SS
Feed: 3 Phase Power at 480V to individual transformer.
Peak Load:40 kVA
Continuous Load:28 kVA

Manufacturers recommended High Voltage wire size @ 480V: 8 AWG
Manufacturers recommended Low Voltage wire size @ 240V: 4 AWG
My calculated wire size (primary side of transformer): #3 AWG
My calculated wire size (secondary side of transformer): 3/0 AWG

I have included a basic spreadsheet with the results of my calculations. I used the following website to calculate wire size because it seemed to be the most thorough, taking into account temperature ratings of terminals and number of conductors in a raceway in its calculations:

http://www.electrician2.com/calculators/wireocpd_ver_1.html

Please check my work and provide any insight you may have on this matter.

Machine	Voltage	Continuous (KVA)	Peak (KVA)	Continuous Current (Amps)	Peak Current (Amps)	Conductor Size	Ground Wire Size
VF1	240	14	20	34	48	#3 AWG THHN	#8 AWG THHN
TL-2	240	9	14	22	34	#6 AWG THHN	#8 AWG THHN
ST-20SS (Primary)	480	28	40	34	48	#3 AWG THHN	#8 AWG THHN
ST-20SS (Secondary)	240	28	40	67	96	3/0 AWG	#6 AWG THHN

Thanks,
Matt

 

[MatthewM]

I believe I have made a mistake in using the calculator. Based on the NEC code the wires must be sized according to the Continuous Load and the Non-Continuous load. What I have entered into the calculator is the continuous load and the PEAK load, which I believe are different. To get the Non-Continuous load I must subtract the Peak load from the continuous load (i.e. NonContinuous=Peak-Continuous).

Am I correct?

 

[MatthewM]

Please forgive me, in addition the transformer that will supply the three smaller machines is 75kVA not 175kVA.

Matt

 

[maghazadeh]

I believe I have made a mistake in using the calculator. Based on the NEC code the wires must be sized according to the Continuous Load and the Non-Continuous load. What I have entered into the calculator is the continuous load and the PEAK load, which I believe are different. To get the Non-Continuous load I must subtract the Peak load from the continuous load (i.e. NonContinuous=Peak-Continuous).

Am I correct?

No, the noncontinuous load + 25% of noncontinuous load is = continuous load.
The best way is to tell us the total HP of each equipment or the total rating shown on the name plates of the equipments and the duty cycle. My undrestanding is that machine # 3 is a 75 Kva transformer, if so then,
75 KVA / 480 x 1.73 = 90.25 Amp the primary current @ 480V
75 KVA / 240 x 1.73 = 180.6 Amp the secondary current @ 240V.

 

[MatthewM]

Let me make this a bit more simple because I think i've only made it more complicated. Please show me how to determine the size conductor for the following piece of equipment:

HAAS VF-1 Vertical Milling Center
240 Volt 3-Phase Supply with 75 Deg C Terminals
Continuous:14 kVA (34A)
Peak: 20 kVA (48A)

My confusion comes from the distinction and use of Continuous, Non-Continuous, and Peak Loads. I understand that continuous load is one that occurs for longer than three hours, by default, non-continuous is anything less than three hours.

How does the manufacturers given "Peak" load factor into the calculation?

Thanks,
Matt

 

[maghazadeh]

Please forgive me, in addition the transformer that will supply the three smaller machines is 75kVA not 175kVA.

Matt

MatthewM, I think I misundrestood you. You have 3 machines that all 3 will be power through the 75 KVA transformer and the Xmer feeding the busbar. If I got it right 1 machine is doule voltage rated mostlikely for 460/230V rather than 480/240V and the other 2 machines are single voltage rated 230V but not 240V. In other word the supply power 480V and 240 V, but the machines are 460/230V and 230V. Correct?

 

[maghazadeh]

Let me make this a bit more simple because I think i've only made it more complicated. Please show me how to determine the size conductor for the following piece of equipment:

HAAS VF-1 Vertical Milling Center
240 Volt 3-Phase Supply with 75 Deg C Terminals
Continuous:14 kVA (34A)
Peak: 20 kVA (48A)

My confusion comes from the distinction and use of Continuous, Non-Continuous, and Peak Loads. I understand that continuous load is one that occurs for longer than three hours, by default, non-continuous is anything less than three hours.

How does the manufacturers given "Peak" load factor into the calculation?

Thanks,
Matt

Where did you get the peak load from? If machines have nameplates on them I would trust the data and size accordingly. So if peak load means maximum load or fully loaded machine, then a # 8 AWG cu is good for the 48A for the distance to busbar as you mentioned, but I would use # 6 AWG cu.

 

[MatthewM]

MatthewM, I think I misundrestood you. You have 3 machines that all 3 will be power through the 75 KVA transformer and the Xmer feeding the busbar. If I got it right 1 machine is doule voltage rated mostlikely for 460/230V rather than 480/240V and the other 2 machines are single voltage rated 230V but not 240V. In other word the supply power 480V and 240 V, but the machines are 460/230V and 230V. Correct?

I have 5 machines total, they all run off of 240V power(none are dual voltage):

3 Smaller machines will run on 240V bus bar powered from 75 kVA transformer:
2 each 14 continuous kVA/20 peak kVA
1 each 9 continuous kVA/14 peak kVA

2 Larger Machines will run on 480V bus bar and will each use a seperate transformer:
2 each 28 continuous kVA/40 peak kVA

I am going to rate these as continuous load machines, but do I size the conductor based on the manufacturers continuous or peak load rating?

Thanks for the help and for your valuable time.

 

[maghazadeh]

I have 5 machines total, they all run off of 240V power(none are dual voltage):

3 Smaller machines will run on 240V bus bar powered from 75 kVA transformer:
2 each 14 continuous kVA/20 peak kVA
1 each 9 continuous kVA/14 peak kVA

2 Larger Machines will run on 480V bus bar and will each use a seperate transformer:
2 each 28 continuous kVA/40 peak kVA

I am going to rate these as continuous load machines, but do I size the conductor based on the manufacturers continuous or peak load rating?

Thanks for the help and for your valuable time.

I still do not know where you got the peak value and what it mean in relating to CNC machines. Normally for equipements/machines with motor loads, dealing will be with duty cycle.
If you can please post the exact data on the name plates.

 

[bob]

Size = 125%continuous + non-continuous. Your post is some what confusing and needs clearing up.
you said you have 2 machines. Do these have both continuous and non-continuous duty?
It sounds like you have(each mtr) 14 kva continuous + 6 kva non-continuous for a total of 20 kva.
1 mtr has 9 kva cont and 5 kva non-cont for a total of 14 kva.
2 mtr has(ea) 28 kva cont and 12 kva non-cont for a total of 40 kva.
Is this correc?

 

[MatthewM]

I do not believe that a non continuous load rating is required, as the machine will consistently run for longer than 3 hours.

The manufacturer lists two power ratings for each machine, continuous and peak. I believe the continuous is the load machine consistently runs at when it is performing regular operations. I believe the peak is the highest possible load the machine could produce. I would like to know which to use when sizing the conductor (it appears the manufacturer has recommended a conductor sized for the continuous load). I have included an image from the HAAS' manual.

For the model shown in the image the manufacturer recommends #8 wire.

I am guessing they did the following:

(14kVA(this is the continuous load value for the VF1) x 1000)/(1.73 x 240)=34 Amps

34 x 1.25 = 42.5

Based on NEC 2005 table 310.16 for 75 deg C connenctors #8 AWG will support up to 50 Amps, so they recommend #8.

Am I on the right track here?

 

[bob]

Lets say your machine runs at a continuous load of 14kva for 8 hours but for some reason in the process it jumps up to 20 kva for an hour. That's and additional 6 kva non-continuous load. It seems to me that
the load should be 1.25 x 14 kva + 6 kva for the circuit ampacity. Am I correct in saying that the load does increase from 14 to 20 kva during the process, or will the jump to 20 kva never happen?

 

[gar]

111222-1900 EST

What kind of material and parts are you going to machine? Is this a heavy continuous production shop, a job shop, tool room, or a die shop?

Aside from that information I would use the HAAS recommendations. Have you watched any machine run your type of product? Where does the spindle meter average? Some of the machines you mentioned have 20 HP advertized on the machine. But this is 150% rating.

Highly unlikely you will run all machines at 100% for very long. I suppose if you were roughing a big pocket in a large die you might run at 100% for a long time, meaning several hours. But I would not load one of those machines to a continuous 100%. Too hard on it. A lot of typical part jobs have quite a variety of tools, therefore loads, and a lot of in between table or tool changer motions.

I doubt that our machines when running average over 10% of their 100% rating. These are basically VF-2, and VF-3s. For 5 machines during running hours (50 per week), the average load is less than 10 kW which includes lights, computers, air compressors, and air conditioning.

Without going to the shop and looking I believe the wires are #8 or #6 copper. HAAS has taps on their input transformer in order to provide the correct DC bus voltage that I believe is 325 V DC.

The HAAS machines, after about 96 or 98, use a common DC bus for both the spindle and servos.

.

 

[MatthewM]

I think gar hit the nail on the head. These machines are specifically being used in a tool shop, they will very likely never be loaded to the peak load rating.

I am going to install them as per the manufacterers reccomendations. I just wanted to cross reference against what the code reccomends to ensure we are safe and in compliance. Thanks for the help as well Bob, I appreciate all of the input I have recieved here.

Matt