3 phase tap - motor involved

[Telaid]

The equipment i normally design includes both 3- phase and 120v single phase loads. There are instances where I only have access to the 3 phase supply. Im having trouble intrepreting the code when it comes to tapping feeders for motors. the single phase devices are only lights and ac/dc converters for PLCs so there isnt enough load to spread evenly across all three phases. The 3 phase supply I use to power motors. Can i tap off of one leg of the three phase to supply my single phase loads if i size the wiring correctly and install breakers to protect the motors and sngle phase loads? Or will unbalanced loading be an issue?

Thanks

 

[augie47]

tap

tap

If you have only the three phase supply available, it would seem you would need a transformer to obtain a 120 source. If you are concerned about balancing, a three phase transformer (3 ph/208Y120) would allow you to balance your load.
If the load is comparitively small, and the neutral is available, taps should not be a problem, if as you say, you properly size the wire and over-current devices. (Depending on your 3 phase system, you should be able to tap from at least two of the phases and not put the entire 120v load on 1 phase)

 

[kingpb]

it doesn't have to do with Code requirements, but putting single phase loads on panels with motors, could give you some voltage flucuation problems when the motors are started. If these motors are switching on and off frequently, or are very large in size, then it could be even more of a concern. in this case, put in a small step down transformer to derive a cleaner source of 120V, and check/use the transformer taps to give you a stiffer line voltage.