Power supply for 20 Ton Bridge Crane

[alphabraxon]

Im doing a load calc for a commercial client. Has office block inside pre-fab building with open floor mechanics workshop. He has intention of installing 20 ton Overhead Bridge Crane. Looked on internet but cant find any info on power supply [Amps] needed. Unfortunately client hasnt bought crane yet, but i need to allow for it in the main distribution panel. Crane will probably be 480/3/60. Any recomendations? Also, they will probably be welding, running air comps, etc. Anything to look out for in the operation of the offices. Will welders etc affect computers or flour lights etc? Thanks for any help.

 

[jdsmith]

Im doing a load calc for a commercial client. Has office block inside pre-fab building with open floor mechanics workshop. He has intention of installing 20 ton Overhead Bridge Crane. Looked on internet but cant find any info on power supply [Amps] needed. Unfortunately client hasnt bought crane yet, but i need to allow for it in the main distribution panel. Crane will probably be 480/3/60. Any recomendations? Also, they will probably be welding, running air comps, etc. Anything to look out for in the operation of the offices. Will welders etc affect computers or flour lights etc? Thanks for any help.

A 30 ton overhead crane I used to use was also 480v 3 ph. It was on a 60A disconnect, so it was in the 30A - 60A range. I'm sure 60A is a safe assumption for a somewhat smaller crane. I'm assuming the offices are fed through a 480/208 transformer? As long as everything is grounded/bonded per code you shouldn't have problems. There are some potential issues in how you lay out the 480V panelboards if you have 277 lighting and depending on how many other compressors, machines, welders, etc are connected in the shop.

 

[mdshunk]

You can make some guesses, but the horsepower of the hoist motor will be directly related to the feet per minute of the hoist. I've seen 20 ton bridge cranes with 10HP motors and I've seen them with 50hp motors. The trolley and endtruck motors will normally only be 1 horse each for the 20 or so ton bridge cranes. I'd plug in 60 to the calc if I was guessing as a middle ground without manufacturer's data.