With all the diversity and wisdom of ARFCOM I know someone can help me out so if any of you guys out there are an electrician that knows stuff about wireing large motors I have a few questions.

I have a piece of equipment I need to get hooked up in my shop that has one 20 hp motor (two speed if it matters), one 15hp motor and three 7 hp motors and all the associated contactors and motor starters all 440v . I only have 208Y in the shop and I need to purchase a transformer. I had an electrician come in and give me a price of $7000 to set a transformer and wire up the machine. I know its a little work but $7000? tThe machine is only about 15 feet from the panel. and I know the panel has room, I have a new 400 amp service on this wall with only one 20A breaker in it for a few lights ( I have another 400A panel and two 200A panels elsewhere in the shop)

I have been shopping around online to find some deals and I found a bunch of new transformers, I would like to buy one that would handle this machine and save a few hundred bucks. A couple of the auctions are over tomarrow afternoon and are within 60 miles so I could go pic them up. I just need to know if they are big enough. Is 25KVA enough?

I already have a few disconect switches laying around that I found on ebay ranging from 20A 3ph to 200A 3ph. If I could get the transformer and some of the stuff here in the shop, my uncle said he would come in townd and wire it up for me. BTW he is an Electrician and works on large grain elevators and this would be easy for him. Yes I could ask him but he is somewhere on the east coast in an RV and I haven't been able to get ahold of him this week.

Thanks for reading this

Are the motors Single Phase or Three Phase? If they are Three Phase then you are screwed because then you will need a whole new service run and it might not be available in your location.

for 7000 it sounds like you'll get a three phase drop, new panels, etc

still sounds high

Your going to need what is called a 'Buck-Boost' transformer.

Buck-Boost


To calculate three phase KVA  --  Volts x amps x 1.73 divided by 1000





                                                                                 
                                                                   

Quoted: Are the motors Single Phase or Three Phase? If they are Three Phase then you are screwed because then you will need a whole new service run and it might not be available in your location.

If he has 208Y then it a three phase service.  Almost all motors are wound so that they can be hooked up with either 208V or 480V.  Do the motors have nine leads in the peckerhead?

edit:  you have a total of 50 HP worth of motors.  Each HP at 100% efficiency uses 746 watts.  You should probably figure about 1000VA per HP x 50 hp = 50kVA.  So no, a 25kVA will not do the job.

If you look inside the peckerhead (the little box attached to the side of the motor), you will see t-marked leads, usually marked 1-9.   If there are 9 leads, they are probably dual-voltage motors and can be hooked up to 208V.

Thanks for the replies.  

lu380, only the 7hp motors are dual wound and the 7hp and the 15 hp motors are kind of a specialized motor, only used in this machine and they are 8000 rpm. The 20 Hp motor does have a bunch of leads, I don't know how many there are but I do know it cannot be wired for 240 as none have been made for this machine that could. IT is a two speed motor I believe 1800 and 3600 rpm. I looked into having the motors rewound for 208 but the cost was high, almost as high as the $7000 price quote. I still don't know why it was so high. A year ago I had seven 3 ph machines hooked with a new 600 amp service brought in one end of my building( its split up between one 400 amp panel and one of the 200 amp panels) and was still under seven grand.

I've called five electricians, one flat said he didn't know that much about hooking up transformers. WTF? is it really that specialized?

One guy came out and looked at the machine and said: " Whoa! Dude, thats alot of wires! Nice pretty colors too!" When I asked him for an estimate he just said "I don't know man, THats alot of wires! I lost all confidence in him, however cheap he is.


The third guy came out and never called me back, I guess he wasn't interested.

The fourth guy, a friend of mine, wanted to do it but his wife just had a baby and he's only working about 20 hours a week right now. He has a maintenence contract with a local business that has him tied up right now.

THe fifth guy gave me the $7000 estimate. He didn't have a new panel or service listed on the estimate.


If a 50kva transformer will work, I'll look around for one. I called an electrical supply house that I have an account with and they suggested 47kva and quoted a price of $970 plus freight. So I'm guessing around $1200 for the transformer. What I would like to do is get all the stuff here and get my uncle to come in and hook it all up. He wants to come here and tinker in the shop anyway.

I'm not an electrician, but I did stay at a Holiday Inn Express last night...