Wonder if anyone would mind helping me size this service. I'm going to have to tell the owner that there's going to be a drastic change in his plans of machinery if my calculations are right. A lot of the machinery he has will have to be changed to 480 volts in order for the existing 120/240 service to handle just a portion of the machines he has. What I have is an existing 120/208 service, which I may have to have the power company to retap to make it 120/240, since his name plates specify 230/460 volts.
I have a 200 amp. 42 cir. 3 phase main breaker panel, with a main lug sub panel fed out of the side of it.(someone else done the existing wiring) There is a 100 amp. breaker ahead of the sub panel.( This is a Seimans "plug in type" ) I have a total of 7 pieces of machinery, with a total of 115 amps.including the 125% for the largest motor My supplier has informed me that the 100amp. breaker is the biggest 3 phase "plug in type" that I can get. The only way I can see that this will work, is that the "authority having jurisdiction" ok it, because some of the motors may not be used at the same time. Is my figuring right so far??
Next the total load on the building consist of: "industrial" application
11,700 sq. ft. X 2 wts./ sq. ft. = 23,400 v/a
Since this is an industrial establishment, according to table 220-11, there is no demand factor that can be applied. It is taken at 100%
I have about (35) 120 volt outlets. If I figure these at 180 v/a I get 6,300 v/a
Since there is no demand factor that can be given to the lighting circuit, I must take these at 100% also.
I have:
(1) 10 hp motor at 230 volts = 28 amps
(1) motor with ? HP = 18.2 amps
(1) more motor with = 18.2 amps
(1) machine with 2 motors
2 hp each (6.8amps/motor) = 13.6 amps
(1) more with the same as above= 13.6 amps
(1) 5 hp motor at 230 volts 15.2 amps
(1) 5 hp motor (same as above) 15.2 amps
Note: all above motors are 3 phase
(1) 3 hp single phase 230volt =17 amps
I have:
2 window a/c and heat units (230 volt
single phase )18.8 x 2 = 37.6 amps
(1) 1.6 hp 115v gas heater motor = 4.4 amps
I get a total of 74848 va / 360 = 207.9 amps
Wonder if this anywhere right, if you care to help? Thanks ..Steve
This is not counting at least 94 amps of other 3 phase machinery he wants to put on this same service. Thanks again for the help. It's been a while since I've had to do these calculations, so I've probably missed something somewhere.
