Combing two incoming municipal electricity supplies

[davesparks]

What you might refer to as a consumer unit or CU in the UK is termed a DB in South Africa. You can have other distribution boards fed from the main DB, these would be 'sub DB's but they would be isolated via the main circuit breaker in the DB which is referred to as the 'point of control' in the SA regs.

The OP is referring to a scenario that would have two separate electrical supplies which would have two points of control within the same premises. This is not legal. I understand why he's thinking about this because there would be costs involved to have the supply authority upgrade the supply at his original DB which he thinks he could avoid by such an arrangement.

We call them DBs too, it would only be a CU usually if its in a house.
We tend to refer to all DBs just as DBs rather than making the distinction between main and sub DBs hence my confusion.

It is permissable in the UK to have multiple incoming supplies to a building.
Most of the theatres I work in have at least two, sometimes more, incoming supplies, one for the domestic installation and one for the stage lighting/production power.

 

[Theo.vogel]

I am pretty sure both incoming supplies are on the same phase as the the minisub 20 meters down the road where both originate only seen to have three cables. How would I confirm that both are the same phase?

 

[davesparks]

I am pretty sure both incoming supplies are on the same phase as the the minisub 20 meters down the road where both originate only seen to have three cables. How would I confirm that both are the same phase?

Even if they are on the same phase you cannot just join the two together to create a bigger supply, this will create a dangerous situation.

If there are three cables coming in to a substation then it is almost certainly three phase as the incoming HV will be 3 phase delta.

If you need a larger supply capacity then your only option is to contact the supply company and get the correct size supply installed.