Same power source, two feeds, common connection

[hrc]

OK...picture this.

Two 3phase 208Y w/neutral into a box, from the same load center. Picking off a phase and neutral from each to get 120VAC.

Open frame AC/DC power supply, powered from the 120VAC.

Typically both power cables are active, so just picking one of them to provide power to the DC unit is fine, but in the case where the chosen source does go down, I don't want the supply to also go down. '

So, any problems with putting BOTH 120VAC sources on the supply? If they are both off the same phase, there shouldnt be any side effects, other than the possible feeding back from one phase to the other.

 

[VEBill]

All you need are "AC diodes (*)" ;-) to prevent trying to run half the factory via the little wires that run into your little power supply.

(*You might be able to rig up some relays to perform this function...)

 

[VEBill]

Further to previous, just use the first AC source to hold up a relay to the first power source. If the first source fails, then the relays fall back to the second source. If the second is also out, then who cares...

Or, get two DC power supplies and use diodes to combine the outputs.

 

[hrc]

Two supplies is a choice, but not so cost effective. Relays are an option, hate to add a mechanical point of failure but its probably the most cost effective.

Thanks for the input.