Correct cabling for flat consumer unit supplies

[James McDonough]

I'm after some advice please guys..

I've got a job where the builder is converting a shop and flat above into 3 separate flats. There is currently just a 100a single phase supply into the shop on the ground floor.

I have requested a new three phase supply to be installed, which will be located on the ground floor and will eventually be the hallway for the 3 new flats.

So in the hallway will be a three phase supply and three meters (one for each flat). I then need to run a cable from the meter to the consumer unit in each flat and trying to work out the best way to do this.

Has anyone done this before as has any good suggestions?
The supply cable for each flat will ideally have to be inside the wall and floor at some point so if I use t&e it will require a 30mA RCD. Which will then cause issues because it may trip before the consumer unit RCD. Also thought about using a time delayed RCD but I can't seem to find a 30mA version out there.

Thanks in advance!

James

 

[Deleted member 26818]

Of course, if the Gas and Water are supplied in plastic, there would be no need for a separate Earth conductor.

 

[Leesparkykent]

This will come under what's called a Building network operator installation. The DNO will give you guidance on what they want but a single point of isolation for the building will be needed and a ryefield board or similar so it can be sealed. Normal layout is head, fused switch or isolator depending on the distance, ryefield, Meter, switch fuse or isolator them armoured cable to the flat. You have to get it all in place leaving the connection ready for the DNO to connect in to the head and have the tails in place from the ryefield to the meter and from the meter to the switch fuse/isolator ready for the meter operator to connect.

 

[Leesparkykent]

Of course, if the Gas and Water are supplied in plastic, there would be no need for a separate Earth conductor.

you can't run plastic gas pipes in a building as it would be catastrophic in a fire. If the gas is run in plastic externaly it has to change to be being metallic before it enters the building. The yellow plastic pipe feeding external gas meters is not allowed to be exposed so again needs to change to be being metallic before it comes out of the ground.....in other words it's pretty hard to get away with not bonding gas.

 

[dinger809]

This will come under what's called a Building network operator installation. The DNO will give you guidance on what they want but a single point of isolation for the building will be needed and a ryefield board or similar so it can be sealed. Normal layout is head, fused switch or isolator depending on the distance, ryefield, Meter, switch fuse or isolator them armoured cable to the flat. You have to get it all in place leaving the connection ready for the DNO to connect in to the head and have the tails in place from the ryefield to the meter and from the meter to the switch fuse/isolator ready for the meter operator to connect.

I wish I’d taken a bit more time in my reply, but that is exactly what I did! Thank you for the perfect explanation

 

[Ian1981]

This will come under what's called a Building network operator installation. The DNO will give you guidance on what they want but a single point of isolation for the building will be needed and a ryefield board or similar so it can be sealed. Normal layout is head, fused switch or isolator depending on the distance, ryefield, Meter, switch fuse or isolator them armoured cable to the flat. You have to get it all in place leaving the connection ready for the DNO to connect in to the head and have the tails in place from the ryefield to the meter and from the meter to the switch fuse/isolator ready for the meter operator to connect.

Would you need a switch fuse after the BEMCO or ryefield as you call it? or just from the BEMCO via meter and double pole isolator as you would have potential say 2 60 amp fuses in series and it’s a different set up to say a house where the tails are greater than 3 meters and is the origin of the supply?

 

[Deleted member 26818]

you can't run plastic gas pipes in a building as it would be catastrophic in a fire. If the gas is run in plastic externaly it has to change to be being metallic before it enters the building. The yellow plastic pipe feeding external gas meters is not allowed to be exposed so again needs to change to be being metallic before it comes out of the ground.....in other words it's pretty hard to get away with not bonding gas.

Hmm, seen quite a few yellow plastic pipes connected to internal meters. Have even seen them bonded.
Yes the internal pipework has to be metal for gas, that is if there is gas.
The internal pipework for Water can be either metal, plastic or a mixture of both.

 

[Ian1981]

Do you mean were they connect to the meter externally?
Because where the gas enters the building is always in copper as it has to be , at least that’s what I’ve always experienced
I suppose the question is that the pipework entering the property, is it extraneous?

 

[Deleted member 26818]

Doesn’t have to be copper where it enters a building.

 

[Ian1981]

Doesn’t have to be copper where it enters a building.

Like I say I’m not a gas engineer but I’ve never seen plastic gas pipes enter a building from the outside

 

[Leesparkykent]

Would you need a switch fuse after the BEMCO or ryefield as you call it or just from that via meter and double pole isolator as you would have potential say 2 60 amp fuses in series and it’s a different set up to say a house where the tails are greater than 3 meters?

Tell you the truth Ian we just install switch fuses but reading the info the DNO supply you with, you could use a DP switch as you have the fuse in the Ryefield/BEMCO board. 9/10 times the flats we do a 60A supply is adequate so 100A fuses in Ryefield and 60A fuses in the switch fuses. Using the rule of thumb of x 1.6 for discrimination between upstream and downstream fuses of the same type then discrimination is just about achieved. I prefer it this way if it's possible so if there was a fault, the fuse in the switch fuse goes and an electrician can replace it rather than entering a sealed Ryefield which is frowned upon by whoever sealed it.

 

[Deleted member 26818]

I have seen yellow plastic gas pipes in cellars, have seen them enter buildings above head height (though outside on the external wall, the plastic pipe was inside metal tube.

 

[Ian1981]

Tell you the truth Ian we just install switch fuses but reading the info the DNO supply you with, you could use a DP switch as you have the fuse in the Ryefield/BEMCO board. 9/10 times the flats we do a 60A supply is adequate so 100A fuses in Ryefield and 60A fuses in the switch fuses. Using the rule of thumb of x 1.6 for discrimination between upstream and downstream fuses of the same type the discrimination is just about achieved. I prefer it this way if it's possible so if there was a fault, the fuse in the switch fuse goes and an electrician can replace it rather than entering a sealed Ryefield.

That’s a good way of looking at it lee.
Just we’ve done a few buildings/flats with BEMCOs and then double pole switches to flats as we consulted the DNO and they saw no problem with it and the BEMCO boards were fed from fused isolators anyway and via a single source of isolation.
We only had 63 amp fuses in the BEMCOs as the supply to the 1 bedroom flats were only 16mm swa so we saw no point in having 2x 63 amp fuses in series.

 

[Leesparkykent]

Plastic pipe for gas is not allowed to be used within a building at all...The options are copper, barrel or tracpipe. Externally plastic pipe is allowed to be used but not exposed so it has to change to one of the pipes mentioned above or be covered so it's not exposed.