UK 480v Split Phase, new workshop, VFD's required

[Lucien Nunes]

a live from each side. A neutral plus earth

No neutral - the two lines of the split-phase supply are a 460V single-phase supply as far as the VFD is concerned. Obviously they must both be fused and switched as lines, rather than a line and a neutral.

 

[robertl]

No neutral - the two lines of the split-phase supply are a 460V single-phase supply as far as the VFD is concerned. Obviously they must both be fused and switched as lines, rather than a line and a neutral.

Understood, can probably just take a line from each 240v consumer unit then. Don't you need a neutral with these vfds then?

 

[Lucien Nunes]

can probably just take a line from each 240v consumer unit then

Nope, that could backfeed one CU from the other when switched off, a very dangerous situation. Any switches / MCBs anywhere on the 460V circuit from suppliers' meter to VFD must be linked double pole devices. IIRC not all 3-phase boards are officially rated for 460V, worth checking.

 

[robertl]

Nope, that could backfeed one CU from the other when switched off, a very dangerous situation. Any switches / MCBs anywhere on the 460V circuit from suppliers' meter to VFD must be linked double pole devices. IIRC not all 3-phase boards are officially rated for 460V, worth checking.

Maybe a stand alone double pole switch mounted in an enclosure would be the way to go, what about the neutral though? Not required?

 

[Lucien Nunes]

Not for the VFD power itself. If the machine had any auxiliary devices, lights etc. they might need the neutral (or need feeding separately from a 230V circuit).