Is the insulation level for a delta wire configuration the same as a grounded-Y voltage?

Question

Considering that both delta and grounded wye have the same line to line voltage, would the insulation level be the same for both delta and grounded wye to protect from ground faults?

Answer 1

No, the delta wiring configuration requires insulation rated for the phase-to-phase voltage. A grounded-wye voltage requires insulation rated for the phase-to-ground voltage.

Wye: 277/480 volt, 3-phase, 4-wire needs 300 volt insulation.
Delta: 480 volt, 3-phase, 3-wire needs 600 volt insulation on the cables.

If your question is related to a high voltage distribution system, a 3-wire delta system requires a higher BIL level than a comparable 4-wire wye system. For example:

- A 34.5 kV 3-wire system is designed with a 200 kV BIL.
- A 19.9/34.5 kV 4-wire system uses 150 kV BIL equipment.

Answer 2

i did no longer desire to dig it up however the configuration you're searching for is as Dan defined an "Open Delta configuration". i think Dan had the voltages incorrect. You do have a "wild leg" . All 3 stages could be 120V to floor, yet between the two directly linked stages the voltage could be 208. yet around the open end of the Delta the voltage could be 240 volt. application companies used to apply this configuration for residential centers because of the fact it basically calls for 2 windings.