Service main sizing

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Tyler1931

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Controls Technician
Hello all,

My company is looking at renting out a space in a larger building. They currently have a 200A 3 phase service which we would have to upgrade to support our manufacturing.

To account for just our equipment, can someone help point me in the right direction for what size we would need? (Remove lighting, hvac, 110, etc from this scenario).

We would be installing 7 machines that have 125A breakers (they were sized by highest motor FLA *1.25 + branch circuits on the machines).

In use, each machine will always pull <20A and typically stay around 10A. the 125 is more of worst case scenario.

How would I go about figuring out the proper main sizing for this?

Thanks for any help.
 
Many areas would require an engineering plan, if not then Larry, as mentioned above, would be a great person to talk with about this issue.
 
Tyler1931 said:
Buck,

We're about 4 hours away from Richmond.

I'm not real familiar with panel sizing for this kind of situation. Is there a formula or rule of thumb or code that specifies this?


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In order to get the service size you need a lot more info. What size motors, 3 phase equipment and single phase. Heating /and or a/c , water heaters etc. Sq. footage helps, number of receptacles, etc.
 
Dennis Alwon said:
In order to get the service size you need a lot more info. What size motors, 3 phase equipment and single phase. Heating /and or a/c , water heaters etc. Sq. footage helps, number of receptacles, etc.
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Hi Dennis thanks for the reply,

The main motor on each machine is a 50hp 480 3phase 1800rpm. 60A fla. We are planning for ~7 of these machines. They have some 24vdc IOs/controls, 2 20A 3phase 480v drives controlling 4 480v Servi motors rated at 6.5A each.

The other things you mentioned would be ignored for now. I'm being asked to look into just what our equipment would require.

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Tyler1931 said:
Hello all,

My company is looking at renting out a space in a larger building. They currently have a 200A 3 phase service which we would have to upgrade to support our manufacturing.

To account for just our equipment, can someone help point me in the right direction for what size we would need? (Remove lighting, hvac, 110, etc from this scenario).

We would be installing 7 machines that have 125A breakers (they were sized by highest motor FLA *1.25 + branch circuits on the machines).

In use, each machine will always pull <20A and typically stay around 10A. the 125 is more of worst case scenario.

How would I go about figuring out the proper main sizing for this?

Thanks for any help.
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Essentially this sounds like an unfortunate situation where the worthless NEC load calcs will provide, as typical, an absurdly oversized service. What you end up having to install will probably depend on how picky your AHJ is about load calcs. Perhaps if you can get some utility data from your existing location per 220.87 that would help a ton. There is also a provision for non- coincident loads that possibly could be applied to some of the machines.
 
electrofelon said:
Essentially this sounds like an unfortunate situation where the worthless NEC load calcs will provide, as typical, an absurdly oversized service. What you end up having to install will probably depend on how picky your AHJ is about load calcs. Perhaps if you can get some utility data from your existing location per 220.87 that would help a ton. There is also a provision for non- coincident loads that possibly could be applied to some of the machines.
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Hi Electrofelon,

I agree. In our current facility we are grossly oversizing what's needed for the machines to meet code IMO. 125A breakers, 2awg wires, etc then we pull 10-20A at our heaviest load on each machine. I understand the need for the oversizing, but just seems silly.

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Tyler1931 said:
Hi Electrofelon,

I agree. In our current facility we are grossly oversizing what's needed for the machines to meet code IMO. 125A breakers, 2awg wires, etc then we pull 10-20A at our heaviest load on each machine. I understand the need for the oversizing, but just seems silly.

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Are you moving same operation to a different location? As in load conditions will be very similar after move?

If so get demand history from POCO where you are currently at, that will tell you absolute minimum you will be needing. Possibly still good idea to build in some extra capacity, especially if you are expecting additional load eventually.
 
Tyler1931 said:
Hi Electrofelon,

I agree. In our current facility we are grossly oversizing what's needed for the machines to meet code IMO. 125A breakers, 2awg wires, etc then we pull 10-20A at our heaviest load on each machine. I understand the need for the oversizing, but just seems silly.

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To get a ballpark idea of what the NEC would require, you would use the FLC charts in article 430 with the largest motor at 125,%. That is 65 amps so 6(65) + (1.25*65)= 471 amps at 480 three phase. I doubt in real life you would see a quarter of that.
 
You are probably looking at a 600 A service, where you will probably never see sustained loads in excess of 200 A.

I see no provision in the code to allow you to use the data from another location to size the service.
 
petersonra said:
You are probably looking at a 600 A service, where you will probably never see sustained loads in excess of 200 A.

I see no provision in the code to allow you to use the data from another location to size the service.
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One would think a "reasonable" AHJ would allow data from another location that is being moved and possibly tweaking and extrapolating from that data....but reasoning often goes out the window when government bureaucrats get involved. Here you have a facility where the people who work with these machines every day and know how they are used, along with the assistance of an experienced electrical contractor, yet the government thinks they know best.... End rant, sorry.
 
electrofelon said:
One would think a "reasonable" AHJ would allow data from another location that is being moved and possibly tweaking and extrapolating from that data....but reasoning often goes out the window when government bureaucrats get involved. Here you have a facility where the people who work with these machines every day and know how they are used, along with the assistance of an experienced electrical contractor, yet the government thinks they know best.... End rant, sorry.
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There are provisions for asking the AHJ for "special permission", but there are likely no AHJs that allow an inspector to grant special permission, although they often do so on an informal basis.
 
Tyler1931 said:
Hi Electrofelon,

I agree. In our current facility we are grossly oversizing what's needed for the machines to meet code IMO. 125A breakers, 2awg wires, etc then we pull 10-20A at our heaviest load on each machine. I understand the need for the oversizing, but just seems silly.

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I don't get this.. You said 50 hp 3 phase a 60 amps then you say the motors will only pull between 10-20 amps
 
Dennis Alwon said:
I don't get this.. You said 50 hp 3 phase a 60 amps then you say the motors will only pull between 10-20 amps
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Sorry, the motor FLA is 60A.

We require a high torque that the larger hp motor provides, but use nearly no amperage. When running at our "heaviest" process, I've personally seen 12A continuous as the highest, however I haven't measure a peak in rush upon start up.
 
There are tiles when engineering services are well worth the investment :)

Barring that, I would agree with post #11,.
 
electrofelon said:
I worked as a CNC operator for a year, and have realized that many of these machines run at practically no load. I'm not sure what no load draw would be on a 60 FLC motor. Would it be as low as 1/3 to 1/4?
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You might be surprised. When lightly loaded, a typical induction motor can have a higher current than you might think, although because the actual power being used is fairly low, the current is at a lower power factor.

Most CNC machines use drives of some sort so the input current to the machine is close to unity power factor.
 
petersonra said:
You might be surprised. When lightly loaded, a typical induction motor can have a higher current than you might think, although because the actual power being used is fairly low, the current is at a lower power factor.

Most CNC machines use drives of some sort so the input current to the machine is close to unity power factor.
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Yeah it's kinda like clamping an unloaded transformer. Current seems "very high" but super low power factor. I metered an unloaded 15 KVA recently and IIRC the power factor was about .1.
 
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