hello, i want to run 480/3ph to a 50hp motor and i have a 3phase 208 panelboard available. if i get a 208/480 transformer and run that between the panelboard and motor, do i only need to protect the primary side with a breaker in the panelboard and i would then run the secondary wires to a fused disconnect and then from there to the motor. does this sound correct? thanks Randy
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- Thread starter randypape
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- Wisconsin
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- PE (Retired) - Power Systems
randypape said:
Are you planning to use a 480-208Y/120 transformer in reverse, or something else, like a 208-480Y/277 step up transformer?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
480sparky said:
There are many options and each has its own set of application issues. That is why I asked what was going to be used. One advantage of a 480Y/277 secondary is the simplicity of dealing with the grounding issues.
reply to my project ?
reply to my project ?
hello guy's , this is a school project and that is why he's having us go from a 208/120 panelboard to supply power to my 208/480 xfmr, then supply 480 to a motor. what i've found in the NEC,i would use a 70kva xfmr and then 125% of current for the primary,i would have to use 250 kcmil and 250A fuses for this protection. i then have to run conductor to a disconnect 285 ft. away and then into the 50hp motor. from what i was told is i would want to keep the xfmr close to the panelboard and adjust the conductor size on the secondary side for the voltage drop. does this sound correct.
we were never told anything about wether the panelboard could accomodate such a breaker, i guess we're assuming for this case it can.
how else would you guy's do this with the things we have? i'm an apprentice and still learning about all this stuff and hopefully we'll go over this in class tomorrow.
thanks randy
reply to my project ?
hello guy's , this is a school project and that is why he's having us go from a 208/120 panelboard to supply power to my 208/480 xfmr, then supply 480 to a motor. what i've found in the NEC,i would use a 70kva xfmr and then 125% of current for the primary,i would have to use 250 kcmil and 250A fuses for this protection. i then have to run conductor to a disconnect 285 ft. away and then into the 50hp motor. from what i was told is i would want to keep the xfmr close to the panelboard and adjust the conductor size on the secondary side for the voltage drop. does this sound correct.
we were never told anything about wether the panelboard could accomodate such a breaker, i guess we're assuming for this case it can.
how else would you guy's do this with the things we have? i'm an apprentice and still learning about all this stuff and hopefully we'll go over this in class tomorrow.
thanks randy
- Location
- Illinois
- Occupation
- retired electrician
Randy,
Unless the transformer is a delta/delta, you will have to protect the secondary conductors per the rules in 240.21(C). In most cases this will require an OCPD (overcurrent protective device) within 25' wire feet of the transformer secondary terminals.
Unless the transformer is a delta/delta, you will have to protect the secondary conductors per the rules in 240.21(C). In most cases this will require an OCPD (overcurrent protective device) within 25' wire feet of the transformer secondary terminals.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
For controlling voltage drop, it is usually best to have the highest voltage run the longest distance. I got confused when you said to keep the transformer near the panelboard.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
I think that's a good point. The starting current for a 50HP motor at 208V plus the transformer losses is going to be a big hit on the 208V system. If you have a 200A panel, you may not be able to feed it at all. You will need at least a 250A circuit breaker to feed it.VinceS said:
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