Is "very rough" 2 phase supply usable?

[treez]

Hi,
Supposing we were desperate for a 2 phase mains supply in UK.
We can’t wait to order one, and can’t afford one.

We then find that 2 mains wall sockets 3 metres apart in our (commercial) office actually are from two different phases…….they share the same neutral and obviously the same earth.

Now, we have a 15kW power supply (VDC output = 50 to 800VDC and Iout = 0 to 30A).
This power supply can take a 2 phase mains input.

What might be the problems of connecting up this somewhat “contrived” 2 phase input to this power supply?
Would you suppose that the sheer area of the noise current loop bounded by the 2 phase wires (from the two different mains wall sockets) would be so big that the noise would stop the power supply from working?

(We were thinking that we can add a common mode filter comprising a common mode choke to which the two phases would be connected. Also, we can add Y caps to Earth from each phase. Also, we can add diff mode caps between the 2 phases.)

 

[betwixt]

Sounds like your building has a three phase supply and the sockets are on two of them. Expect ~120 degrees phase shift between them. In a three phase system, if equal currents are drawn for each phase and the loads have the same V/I phase, the neutral current is zero. However if you load two phases with a common neutral, you introduce complex currents into the neutral wire. What you propose will probably work but if the electricity company find out they may have you taken out and shot. Your call...

Brian.

 

[treez]

Thanks, i take it that the actual building mains junction box will have electronic mains sensors to sense if this kind of thing is going on, and then it would trip out the breakers for these two phases?
The building is a engineering factory downstairs, and offices upstairs.
We werent actually intending to connect the neutral to the equipment...just the two phases and Earth. We would choose this way because it would make the common mode choke we intend to put on it more simple....as youve guessed, we're not "spenders" at the moment....we're a bit hard up.

 

[Easy peasy]

If you go across 2 phases ( 400V ) there is no neutral current, 2 phase operation is just single phase at a higher voltage ... - unless you have a split phase 2 phase system which is 3 wires, e.g. -120Vac, 0, + 120Vac there is no phase displacement between them as they are still all the same phase ...

 

[FvM]

Very unclear, please clarify the "two phase" power supply specification (voltage, current). Is it 400V/37.5A, as guessed by Easy peasy?

 

[treez]

thanks, it measures 415VAC on the DMM, when we probe from one socket's live to the other socket's live...as such, as you know, they must be 120 degrees apart.,
I am not sure what current its rated for...its just a UK office mains supply.

 

[betwixt]

If it is a standard UK socket on a ring main and wired to present day standards it will have a 32A circuit breaker in line with each 'live' pin on the to sockets. Note that if one breaker operates it will leave your PSU still connected to the other 'live' line.

Again, depending on wiring you might have problems with residual current breakers if they check for equal live and neutral currents.

Brian.

 

[FvM]

It sounds still unlikely that a 15 kW power supply is designed for 400V single phase input. What's the manufacturer and type? I presume you realized that the EA-PSB 91500-30 discussed in your parallel thread requires 230/400V three phase supply.

 

[zepus169]

STOP!
What you try to do is highly dangerous!
While in theory the system is correct and these 2 phases comes from the same tree-phase circuit, should be easy to suply a two-phase consummer.
But these circuits are for wall sockets, with maybe 2,5mm2 cabling and fuses of 16Amps (hoping so), which made for a power of about 3kW each. Now, two of them will be able to deliver 6 to max. 7 kW, but planning for more than double, which will burn the wiring and start a fire, if the fuses are not working.
Better check out where is the distribution panel, see for 2x 40Amps fuses and connect a cable with 3x6mm2 (2 for phases and one for earth) if less than 10 m lenght or 3x10mm2 if 50 meters lenght.
Good luck!