Split Phase / 3 Phase Queries

[soapstar]

Hi Guys,

 

This area of electrics has always confused me and I have just taken it for granted.

 

We are looking to determine our current power supply for our business. From what I believe we have a 100Kva transformer on a split phase supply. Our board has 3 x 100amp fuses to which only 2 seem to be utilised - I assume this is the split (or dual) phase? With the other 100amp not used is for a 3 phase setup

 

I also assume that we have 100amp per phase?

 

I can provide photos to clarify. Sorry my knowledge of electrics is very limited so be kind to me ?

 

[markc]

Yes you are right, Split phase gives you double the capacity and allows lighting etc to be on different phases to prevent total outages and strobe effect on lighting.

If you are going to be using any serious machinery you need the 3rd phase

[soapstar]

Hello @markc thanks for confirming. So given the fact that the transformer is deemed at 100KVa does this mean we have scope for a larger output if the fuses for the split phases we increased? Or does it not quite work like that?

 

I guess the main question are we currently running at full capacity with the current setup?

[TonyT]

 Deleted

Edited March 15, 2021 by TonyT

[markc]

1 hour ago, soapstar said:

Hello @markc thanks for confirming. So given the fact that the transformer is deemed at 100KVa does this mean we have scope for a larger output if the fuses for the split phases we increased? Or does it not quite work like that?

 

I guess the main question are we currently running at full capacity with the current setup?

You would only get more capacity using the 3rd phase ... extra 100 amps. Although the transformer is rated higher its unlikely the cable will allow an increase of amps/phase plus the incomer fuses and switch would also need uprating

[TonyT]

There may only be 2 phases, 2 phase supply is a common rural thing

[ProDave]

Please show a photo of the transformer, that is presumably up a pole or more likely a pair of poles.

 

[soapstar]

Thanks. The transformer has 2 wires opposed to 3 which I assume means 2 phase? I notice some lines have 3 lines.

 

What determines the fuse rating for each phase? ie why are they both 100amps - Is it as simple as saying if several appliances were being used which totalled over 100amps of current this would trip the fuse?

 

Yes my knowledge of electrics truly is shocking ?

[soapstar]

17 hours ago, soapstar said:

Thanks. The transformer has 2 wires opposed to 3 which I assume means 2 phase? I notice some lines have 3 lines.

 

What determines the fuse rating for each phase? ie why are they both 100amps - Is it as simple as saying if several appliances were being used which totalled over 100amps of current this would trip the fuse?

 

Yes my knowledge of electrics truly is shocking ?

 

One other question I had is given we have a 100kVA transformer how does this effect the power available at each phase? If this was a 50kVA transformer for example what different would this make to the available power at each phase?

[TonyT]

The power output is depended on what is available at your location, condition of the infrastructure etc . not what the size of transformer may be.

 

for example 100 amp fuse carriers are standard but may be fitted with 60 amp fuses, or 80. Depends what’s available and what you want to pay for/mixture of both

[ProDave]

A normal house supply is typically rated at 18kVA which translates to 80Amps at 230 Volts.

 

Your 100kVA transformer will comfortably supply 6 or more houses, usually a lot more when you allow for diversity.  We currently have 8 houses sharing a 100kVA transformer here.

 

If you really have bi phase, then you could get up to a total of 44KVA from that, but bi phase is not common in the UK.  What is your business doing that you think it is going to need anything like that much?