3 phase supply

[tintin1]

Hello Ladies and Gents,

I am just in the middle of my sparks apprenticeship and just wanted some advice so i did not look to dim at work.

Basically there is a house being converted into three flats with a 3p supply with an additional fuse for the landlord. Each one of the flats will be having a sub-main. My question is how is the sub-main connected to the supply. Would it be each sub-main to three separate swichfuses and then tails to a tp&n board/isolator. if so then 1 flat and landlords on brown phase and the other flats on the other phases.

Any info would be greatly appreciated,

 

[Wontdothatagain]

What the DNO will do is fit a 3 phase service head. Each fuse has 2 entry ports, so they will loop another tail from one of the phases to a 4th seperate fuse holder. They will then fit a Henly block for the Neutrals, 2 will come from the service head, 2 will come from the block. The Neutral setup may vary depending on each particular DNO

 

[Adam_151]

Easyist way would be a metal clad switchfuse for each flat and swa submain straight into a metal clad board, neutrals can be jointed in a henley block, as can the phase which needs to be taped off for the landlands board which assuming its in the switchroom can just be tails, but further away, it'll be switchfuse and submain again

Seen it done with a TPN board containing MCBS before, but don't like seeing that as it normally doesn't descriminate very well... allthough if you were talking a much larger building of flats then you might well use a panel board with an MCCB feeding each flat

 

[tintin1]

Thanks for the responses just to make sure i have it straight.

Swa submain from flat to switchfuse then tails from each switchfuse for connection to supply. Do you have to use swa not say 16mm t+e

Thanks again i am used to single phase but just wanted some clarification on 3 phase.

 

[Adam_151]

Swa submain from flat to switchfuse then tails from each switchfuse for connection to supply. Do you have to use swa not say 16mm t+e

I don't like the undersized cpc that it gives you on a submain (could run a 6491x G/Y in parralall though), if you installed just using the 6mm internal earth, you'd have to make sure you considered:

- Sizing of the cpc against I²t; the adiabatic
- Whether the core needs to be sized as a bonding conductor as well as a CPC
- Increased touch voltage (which on a 0.4 sec circuit isn't considered a vast problem as far as BS7671 is concerned (but good design tries to keep it as low as possible) , but if the subboard feeds a circuit which only acheives and requires 5 sec [unlikely as we normally use mcbs which disconnect in 0.1 sec], then you have to be aware that this will be putting a touch volatage on the ECPs connected to other circuits, and this needs to be kept to below 50v

 

[tintin1]

Many Thanks,

Any flats that i have worked on before i have always run a 10mm g/y as well. This time i am doing the meter room for the first time. Many thanks for that info

 

[Monkeh]

I'm no electrician, but I'd run SWA. It's not much more expensive, and it avoids the requirement for RCD protection at the source, without having to get silly with chasing the cable in.