Suuply main switch 50m from CU

[acsparks]

I'm rewiring a bungalow and currently the supply is a TT system and the meter and distributors switch is in a garage about 50 m from the bungalow.The supply up to the bungalow is currently wired in 10 mm SWA via a fused isolating switch.The owner is getting this system swapped to PME.If i wire from the meter to the isolating switch with 25mm tails,approx 1m,then away from the isolating switch in SWA up to the bungalow.Does the swa need to be RCD protected?It currently isn't.

 

[Spudnik]

No it doesnt as it has its own mechanical protection.

You will need to check your VD.

 

[beaver74]

i make it to need a 16mm swa for a 60A supply over that distance

 

[Guest123]

Hi.

Just for clarification...do you intend installing a new SWA???

Dont forget, technically you will be exporting the PME form the garage to the bungalow, so theres that to think about.

As a rough calc I get a minimum of 25mm SWA as the max VD will be 3% (6.9V) due to the lighting circuits.

 

[acsparks]

Yes i intend to install new SWA.Ialso calculated that 25mm would be needed due to the volt drop over that distance.My preference would be for the customer to get the distributor to move the meter and main fuse up to the house.I think he contacted them and for what they charge compared to the cost of the SWA and time for me to do it there was not a lot in it.

 

[Guest123]

I agree, moving the meter to the bungalow is a better move, and if there isn't a lot in it then it's probably the way to go.

Maybe you could re-use the old 10mm SWA as a supply down to the garage, couple of sockets and a light for him.

 

[Spudnik]

Dont forget, technically you will be exporting the PME form the garage to the bungalow, so theres that to think about.

But will he?

Its a TT.

However, if there are no other services in the garage then i dont see it as being an equipotential zone.

But, if using 3 core 25mm submain to the house then the cpc will be adequate for the house and if there are services, main bonding could be done at the supply.

Am i right or am i right?

 

[Guest123]

I dont know. you've just confused me.

Personally I dont see the point in doing anything other than upgrading the size of the SWA.

Leave it as TT...it works doesn't it.

 

[peteludman]

i would use 35mm 2core or 25mm 3core i think i would use the 35 mm for size of cable

 

[Spudnik]

I dont know. you've just confused me.

I know.

I typed the reply and then read it back, found it was TT being swapped to PME.



Anyhow, in answer to the OP, no it doesnt need RCD protection.

 

[beaver74]

Hi.

As a rough calc I get a minimum of 25mm SWA as the max VD will be 3% (6.9V) due to the lighting circuits.

would you not do calcs on the fact it is feeding a db then recalc for lighting circuits on a circuit by circuit basis as most db have a lighting cicuit and doing your way would rule out 5%
i may be missing something

 

[Guest123]

VD is calculated from the origin of an installation in this case the garage so you must include the sub-main as part of it.


Quote from ECA...

Answer by the ECA: The overall voltage drop limit is 3% (6.9V) single-phase, if the sub-main is feeding lighting circuits.

 

[acsparks]

Thanks for all the replies very helpful.

However if the supply is swapped to PME, and due to the distance of the origin from the property,do you foresee this causing problems in reaching ZS,ZE readings?