3 phase to single phase conversion

[arkin]

Been asked to do a conversion of 3 phase 4 wire supply to a single phase . Swap 3ph mcb for appropriate single , identify two of the cores as brown and blue at both ends make the other two earth. Re calc volt drop for 230 . Any objections?

 

[Plonker 3]

Cant think of any, but why would you want to do this?

 

[arkin]

Cant think of any, but why would you want to do this?

Never been asked to do this before. It's for change of control unit for a roller shutter door from 3ph to single.

 

[Plonker 3]

Why not leave the 3 phase supply intact and just connect to one phase and neutral in the isolator?

 

[Darkwood]

The load will have been balanced over the phases it is to be assumed and the original 4core sized to suit... you now are loading it all onto 1phase and this may compromise the ccc of the cable.

You need to calculate the load and do a calculation as if you were supplying a new cable and see if you require a bigger supply or not.. you could always have 2ph/2N with the 4 cores use the swa as earth and add additional earthing as you have effectively doubled the core size but not increased the csa of the armour. Run an earth equal to or larger than the new Phase size (2x XXmm cores) and if you are extending the equipotential zone through this submains then this will have to be added to the earth size.

 

[arkin]

I was always taught to make any spare cores into cpc. And besides that running separate earth is out of the question, far to difficult and quite long run. I originally though like billb, just take a phase and n from isolator. But the vd has to be treated differently as really this is now a 230v circuit. Maybe I'm reading too much into it.

 

[arkin]

And the new demand on the supply is less than the original design

 

[i=p/u]

Do the calcs then..

 

[arkin]

Do the calcs then..

Well I will then

 

[i=p/u]

I installed roller shutters few weeks ago inn car wAsh , very small motor

 

[arkin]

This shutter is pretty big, some other company replacing the control gear. I just sortin the supply.

 

[Darkwood]

The roller shutter could be industrial sized but still tend to be small motors ... im surprised the roller shutter wasn't spec'd for the existing 3ph supply seems a cock up on their part either way you ned the motor rating to know if the existing is ok, as we lack info here about the existing we can't advice much.

 

[arkin]

Not really looking for advice on sizing cables or protective devices, that's not a problem. Just wasn't sure if I was going too far, and maybe should just take a ph and n at isolator.