# Thread: Bridge Crane power requirements

1. Member
Join Date
Jul 2004
Location
MN
Posts
49

## Bridge Crane power requirements

Does anyone know how I can come up with load requirements for Cranes with the following sizes: 10ton, 20ton, 50ton, and 80ton. I'm working on a budget so it doesn't need to be exact...just in the ballpark.

2. Moderator
Join Date
Feb 2003
Location
Portage, Indiana NEC: 2008
Posts
9,507
With the bridge, trolley, and hoist that can all work in unison, your going to have to know the HP of each motor and voltage they will be run on, before you can calculate the feeders and disconnect for each.

But for a ruff estimate, I would say at 480 3 phase:

10 ton = 30amp disco (not because it would require it but in industrial it would be the smallest I would install)
20 ton = 30 amp

50 ton = 60 amp

80 ton = 100 amp

240/208 volt 3 phase

10 ton = 30 amp

20 ton = 60 amp

50 ton = 100-125 amp

80 ton = 150- 200 amp

again these are just ruff, with out knowing stuff like voltage, HP, DC/AC motors, wound rotors, it would be impossible to narrow it down.

If someone who works more with DC cranes would chime in maybe get a little closer for you? most of the ones I have worked on were 100 ton + although we did have some smaller ones in the plant.
Last edited by hurk27; 07-02-09 at 06:37 PM.

3. Junior Member
Join Date
Dec 2009
Posts
5
To calculate the max amps for an overhead crane take 100% nameplate FLA from the largest motor on the crane plus 50% nameplate FLA of the next largest motor, and add 25% to that total for max working amps.

If there are multiple motors that run together (bridge motors, for example), the nameplate FLA for those motors are added together and treated as one motor.

Example using 480 VAC:

A single hoist motor at 25 FLA
A single trolley motor at 3.5 FLA
Two bridge motors at 3.0 FLA each = 6.0 FLA

25 + (6 / 2) = 28 x 1.25 = 35A

Calculate your load requirements to be able to supply not less than 93% of the nominal system voltage to the runway conductors at the farthest from the supply taps.

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