3Phase To Single Phase

[boltonsparky]

Hi all. My understanding of 3phase with a neutral was that the neutral conductor carried any imbalance in load between the 3 phases.

So would I be correct in thinking that with a device like this (32a 3phase input and 3x 32a single phase outputs)



with a 32a 3 phase input you can safely pull 32 amps off each of the 32a single phase plugs without over loading the neutral conductor to the 32a 3 phase socket that this device is being fed from.

the actual loading will be L1 5kW L2 5kW L3 2.5kW which by my reckoning makes the neutral conductors load 11a.

Or with a device like this will it be sending 55a (total load of all 3 phases) down the neutral conductor? (calculations are rounded up so not exact)

 

[ProDave]

Your first assumption was correct, the neutral only carried the imbalance.

In days gone by, it was normal to use a smaller conductor for the neutral because of this, but we no longer do that.

DO check before using an adaptor like that, that you do have a neutral.  Some 3 phase sockets are wired without a neutral (but they should only be a 4 pin socket if wired like that).  you would get a nasty surprise (and probably some dead single phase kit) if you don't have a neutral.

 

[Andy™]

Hi all. My understanding of 3phase with a neutral was that the neutral conductor carried any imbalance in load between the 3 phases.

So would I be correct in thinking that with a device like this (32a 3phase input and 3x 32a single phase outputs)



with a 32a 3 phase input you can safely pull 32 amps off each of the 32a single phase plugs without over loading the neutral conductor to the 32a 3 phase socket that this device is being fed from.

the actual loading will be L1 5kW L2 5kW L3 2.5kW which by my reckoning makes the neutral conductors load 11a.

Or with a device like this will it be sending 55a (total load of all 3 phases) down the neutral conductor? (calculations are rounded up so not exact)

yes, the neutral carries the imbalance, but if you have all of those running at the same per phase then there is no imbalance.

if 2 are running at 32a, that doesnt mean there is 64a imbalance either

 

[Sidewinder]

Be wary of the types of load though...

 

[boltonsparky]

Thanks for the help, wanted to double check I wasn't going to cook the neutral.

Sidewinder the 2 5k loads are 5k tungsten lamps and the 2.5k load on the third phase are 30 fluorescent tubes with individual ballast controls, are the ballasts likely to cause an upset in the balance being non linear? I should have said what the loads were in the OP.

 

[Sidewinder]

It is mainly harmonics that you need to think about, but generally non-linear loads yes must be considered, along with the power factor really, ie the phasing of the N currents, if they are sufficiently out of phase they can sum, like harmonics.

These such connection arrangements are quite common though,