Between the disconnect and the incoming line

Discussion in 'General Electronics Chat' started by Chipperi, Apr 9, 2015.

  1. Chipperi

    Thread Starter New Member

    Apr 9, 2015
    I am finishing up my AAS in Electromechanical Technology. I have a pretty good grasp on how 3 phase power works. But all of my classes so far only concentrate to installing or repairing a machine and hooking it up to a disconnect.

    What is between the disconnect and the line into the building? When I used to work at a big printing plant there were 3 large transformers, supplied by the power Company. I am certain these supplied the 3 legs of power into the building, just inside where the lines came in was a Huge circuit breaker, I have since learned was a "Switch Gear.

    Now what is between that switch gear and the disconnects that the equipment was hooked to?

    I also noticed that around that particular plant you would see floor mounted transformers, I am assuming these were to step down 480 to voltages needed for 208, 240, 120 etc.
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    the answer is:
    It depends on the company. Where I currently work the switch gear panel has a large number of square steel channels to convey the power lines to machines. Disconnects at the machines receive the power cables.
    In some cases, there are floor standing trsnsformers AFTER the disconnect and more circuit breakers on the power lines coming from the transformer secondaries.
    We have many three phase 480 Volt driven machines, several smaller 240 volt pieces of equipment, and thousands of 120 volt standard power outlets. circuit breakers are present near all of the 240 and 120 volt power distribution points. What country do you live in?
    This can make a large difference in how protection and disconnects are arranged.
  3. Chipperi

    Thread Starter New Member

    Apr 9, 2015
    I'm in the US Tennessee
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    here we have 12 kv coming into the buildingsw with indoor substations to drop the voltage and distributi ti around. most of our machines run on 480 3 phase, and ther are transformers fot dropping the 480 to 120 for offices and such. we use 208 for lighting, also 3 phase. usually between the 480 and machines are motor control centers or fused buss plugs before the disconnect for the machine,. the machine disconnect is required to be near each machine, for safety. the overhead 480 buss is enclosed and has boxes plugged in to power the machines, the boxes have disconnects and fuses inside. seems to be overly complicated, but makes it safer.
  5. MaxHeadRoom


    Jul 18, 2013
    Back in the 80's a large plant I was employed at used 4kv into the plant and this was transformed down to 580-600v three phase for general distribution using individual breaker panels for each section of plant machinery.
  6. gerty

    AAC Fanatic!

    Aug 30, 2007
    As Kermit2 said it depends on several things. In a factory setting you would/could have buss duct. these are long grey overhead troughs that carry power from one end of the building to the other, at least in areas where the 480 might be needed. Smaller businesses or those without a bunch of large machinery may have motor control stations where several machines get their power from a central location. Or you could just have a power distribution panel, fed from the main service. These would have individual 3 pole/phase circuit breakers for the individual machines.
    I worked in a plant that had another option, we had 13,200 volts coming into the building . The building was nearly 1,000,000 square feet in size. We had 9 substations that transformed the 13,200 down to 480 volts, which fed buss ducts all over the building.

    Edit: I was interrupted for over an hour while answering this and now Max and Alfacliff beat me to it :)
    Last edited: Apr 9, 2015