Long Long Cable Run

[OxiaUK]

Hi,

Just moved in to a new house that has a large out building about 80m away from the house. I was told by the last owner that the supply was good for about 63a in the out building but after closer inspection I now doubt that!

There is a 16mm cable coming from the house via a 63a MCB then travels underground to a plastic control panel 40m from the house. In here the supply is split in two (one cable supplies some garden lights from a 6a MCB and 50a MCB for the out building)

Another 16mm cable then goes back underground for another 40m run to the outbuilding where it terminates in to a consumer unit (TT earth at out building)

Is this good for 50-60a or does it all now need looking at? I will be wanting to run some hand wash units, lights, water pumps, sockets etc and want it to be able to cope

Any advice would be great!

Thanks

 

[xr4x4]

What cable is it, type and number of cores.

 

[OxiaUK]

What cable is it, type and number of cores.

16mm twin and earth in 4inch ducting from house to control panel (40m) then 16mm 2 core SWA from control panel to out building (40m or so )

 

[Steve]

What cable is it, type and number of cores.

16mm twin and earth in 4inch ducting from house to control panel (40m)

This is WRONG for a start.

And how exactly are you measuring 16mm? You don't, perchance, have a ruler across the width of it do you?

 

[OxiaUK]

What cable is it, type and number of cores.

16mm twin and earth in 4inch ducting from house to control panel (40m)

This is WRONG for a start.

And how exactly are you measuring 16mm? You don't, perchance, have a ruler across the width of it do you?

its printed on the cable.... when you say wrong what do you mean?

 

[mfarrow]

T&E should not be in permanent contact with water. There's a certain risk of that when running it underground.

 

[RF Lighting]

Also it's prohibited by regs to run cable under ground which is not surrounded by earthed metal.

You would need a 35mm² cable to supply 50A over that sort of distance, so the current cable in all reality is completely unsuitable.

 

[mfarrow]

Also it's prohibited by regs to run cable under ground which is not surrounded by earthed metal.

"Except where installed in a conduit or duct which provides equivalent protection against mechanical damage..."

But as RF points out, the volt drop may be prohibitive for 50A full load, unless you're starting out with a voltage higher than 230V (which is this country, to be honest, is relatively likely) and/or equipment/lighting which can operate to a lower voltage than 218.5V/223.1V.

Loop impedance you should be OK with, but difficult to tell without a loop impedance tester.

 

[EFLImpudence]

What rating are the OPDs in the outbuilding CU.

It is unlikely you will be using 50A there (some houses only have a 60A supply) so volt drop could be calculated on the actual load.

 

[OxiaUK]

our supply voltage is between 242-247v and we also have access to 3 phase. What are my options? Im having an even soon and we are hiring some toilets and showers (showers are gas powered) but both these need a 32A supply.

When using the tool at the TLC site it says the cable is good for 50A if all 2 core PVC SWA:


http://www.tlc-direct.co.uk/Technic...240&length=80&submit=Calculate+Min+Cable+Size

 

[DaftPunk]

The tlc calculator shows that your volts drop is too high. You're only allowed a 3% volt drop between your incommer and the furthest light in your out building.

 

[OxiaUK]

The tlc calculator shows that your volts drop is too high. You're only allowed a 3% volt drop between your incommer and the furthest light in your out building.

so what is the max current with the existing cable I can use?

 

[EFLImpudence]

The tlc calculator shows that your volts drop is too high. You're only allowed a 3% volt drop between your incommer and the furthest light in your out building.

Don't forget that there's more (or should that be less) to it than a straight 3% blanket coverage.

If the lighting is not affected by volt drop then it doesn't matter.

 

[mfarrow]

our supply voltage is between 242-247v and we also have access to 3 phase.

The volt drop on your cable will be about 11.2V at 50A, that's bringing the voltage down to 230.8V min, which would be absolutely fine, being as that is the nominal voltage anyway!

What are my options? Im having an even soon and we are hiring some toilets and showers (showers are gas powered) but both these need a 32A supply.

As long as the diversified load of everything you're plugging in down there is below 50A, that will be OK. Remember that's load, not the size of any protective device required for discrimination, or size of socket on the end of the cable, therefore please please clarify this with the equipment suppliers if things don't add up, and ask what the 32A is made up of if they say it's load. You should not need anywhere near 32A if you've gas hot water.

 

[OxiaUK]

our supply voltage is between 242-247v and we also have access to 3 phase.

The volt drop on your cable will be about 11.2V at 50A, that's bringing the voltage down to 230.8V min, which would be absolutely fine, being as that is the nominal voltage anyway!

What are my options? Im having an even soon and we are hiring some toilets and showers (showers are gas powered) but both these need a 32A supply.

As long as the diversified load of everything you're plugging in down there is below 50A, that will be OK. Remember that's load, not the size of any protective device required for discrimination, or size of socket on the end of the cable, therefore please please clarify this with the equipment suppliers if things don't add up, and ask what the 32A is made up of if they say it's load. You should not need anywhere near 32A if you've gas hot water.

Thanks for your reply. I have seen pictures of the units we are to hire and had specs... they are connected via a 240v 32a plug to the electric supply and there are lights, water pumps for showers etc and for waste. There are also what looks like water heaters above the sinks powered by fused spurs (look like hand wash units) possibly dryers too but cant be sure.

We have two units coming, one toilet block and one shower block.

Now I cant see them all been used at once or at full capacity so that may help.