Calulating Machines For a Busduct

[alchemist562]

Hi :bye:

So here's what I'm up against. I have a 1200 amp bus duct with a 1000 ton injection molding machine (600 amps FLA) a 800 ton Injection molding machine (400 amps) another 800 injection molding machine (400 amps). Now the amperage of machines is not what they draw, it's just what they are feed with because of nameplate rating. they each have heats and motors to run hydraulic pumps. the 1000 ton and one of the 800 tons have VFDs. Now my question is do I have to pick apart the whole machine for a load calc or would I size the bus duct off the machine nameplate???? I'm at a loss with this!

 

[steve66]

I would normally use the nameplate. Actually, I'd probably use the nameplate and leave some spare capacity.

Some factories change things and add things a lot.

 

[alchemist562]

Thanks Steve66. That's what i figured but i had a maintenance manager (unlicensed) tell me i could double the rateing.....:slaphead:

 

[steve66]

If the nameplates are accurate, they should list a "Minimum Circuit Ampacity" or MCA that basically includes an extra 25% of the largest motor load on each piece of equipment.

To do a total load calculation to find your total MCA, you would only have to include an extra 25% of the largest motor out of all 3 pieces of equipment. So in theory, if each piece of equipment was one large motor, you could shave 80 amps off the load of each 400 amp piece of equipment. (This is the best case scenario for reducing the load - if each piece of equipment is several smaller motors or other loads, you won't get that much reduction.)

So in theory, the 1400 amp total load might only be 1240 amps. That still doesn't quite get you below 1200 amps.

So again, I would just count each piece at its nameplate.

 

[petersonra]

Hi :bye:

So here's what I'm up against. I have a 1200 amp bus duct with a 1000 ton injection molding machine (600 amps FLA) a 800 ton Injection molding machine (400 amps) another 800 injection molding machine (400 amps). Now the amperage of machines is not what they draw, it's just what they are feed with because of nameplate rating. they each have heats and motors to run hydraulic pumps. the 1000 ton and one of the 800 tons have VFDs. Now my question is do I have to pick apart the whole machine for a load calc or would I size the bus duct off the machine nameplate???? I'm at a loss with this!

I don't see how they can be exactly 600 FLA, 400 FLA, and 400 FLA. That sounds more like the rating of the main on the machine.

Usually industrial machine nameplates will tell you the FLA plus the largest motor size so you can size the conductors appropriately.