Long extension between meter and consumer unit

[Manfred Jarvis]

I am planning to go semi off grid with a victron and battery system. The system will be installed in an out building about 20 meters away from where my consumer unit and meter currently is.
I need to run the grid power from my meter to the out building to the victron inverter, but then also need to run the power back to the consumer unit.
Here's my question:
What size swa cable should I use? My main incoming fuse is 60 amp so I think 16mm conductors should be ok, or should I use 25mm?
Also could I use a 4 core swa cable to do this "send and return" job, or should I use two individual 2 core cables?

 

[pc1966]

This is not a DIY sort of job!

You would need at least 25mm due to voltage drop as much as anything, as well as steps to make sure you can disconnect on a fault in under 5s, etc. Due to the safety implications of an internal cable fault crossing what you might have thought was isolated circuits at the out building, you really should be looking at two cables.

The disconnection time aspect, as well as the potential bonding implications if your mains supply is TN-C-S, might require you to use 3C SWA for the mains side (assuming CPCs are common at the house end), or to have a separate CPC run along side. If on TT earthing (or too high a Ze on TN-S) you are looking at an up-front delayed RCD.

I would suggest you look at putting in something like 115mm twinwall duct to run the power cables through, and another small duct for any data cables for monitoring things and have them in sand or fine gravel to avoid damage. Then get in a professional to design and install the cables. Duct allows for future changes or repairs (unlikely for armoured cable that is not crushed in stony ground) with a lot less trouble

 

[Manfred Jarvis]

I totally understand its not a diy job for a novice but if I were to pre lay the cable, then I can same time and money by getting an electrician to only connect it up and mot spend hours laying the cable.
In my situation, I live in an old house where the meter and consumer unit are above the front door, and my out building is at the rear, joind to the house via an inter linked building, so the plan would be to run the cables along the under side of the roof (of the interlinked building) to the out building. And inside the house, to run the cable through the ceiling of the ground floor as this is already in line with the meter location.. so the cables will not be at any point on or below ground level. So would 2 runs of 25mm 2 core swa cable be ok? I would run a separate 10mm cpc as well as earth the armour of the swa.

 

[westward10]

Your electrician will be signing this off so they need to be involved in the design and installation. Whether they allow you to get involved with this is their decision so it is them you need to consult.

 

[davesparks]

I totally understand its not a diy job for a novice but if I were to pre lay the cable, then I can same time and money by getting an electrician to only connect it up and mot spend hours laying the cable.

You could also waste time and money by doing all that to then have the electrician tell you you need to remove it and start again because you have not done it correctly.

So would 2 runs of 25mm 2 core swa cable be ok?

Maybe, you need to do cable size calculations to work this out. Also note that is some relatively heavy and awkward cable to work with, if you don't actually need the protection of cable armour you could consider alternative cable.

I would run a separate 10mm cpc as well as earth the armour of the swa.

You need to work out the design of the earthing arrangements before deciding this, you need to consider how the supply from the inverter is going to be earthed and how that needs to integrate with the earthing of the DNO supply.
You can't use a DNO supplied earth as a means of earthing for a private supply.

 

[Manfred Jarvis]

Thanks for the advice, so if I'm able to run the cable through the house under first floor and under out building roof (which is at the same level as house first floor) what 25mm cable could you suggest which is easier to work with, as I totally agree swa cable is horrible, especially around bends. Rest assured I have appointed an electrician to call to me this week, I just want to be armed with information I could use as suggestions when we talk together about the proposal.

 

[Cbelectrics]

You could also waste time and money by doing all that to then have the electrician tell you you need to remove it and start again because you have not done it correctly.


Maybe, you need to do cable size calculations to work this out. Also note that is some relatively heavy and awkward cable to work with, if you don't actually need the protection of cable armour you could consider alternative cable.


You need to work out the design of the earthing arrangements before deciding this, you need to consider how the supply from the inverter is going to be earthed and how that needs to integrate with the earthing of the DNO supply.
You can't use a DNO supplied earth as a means of earthing for a private supply.

Ahhh beat me to it with the separate earthing arrangement.

 

[HandySparks]

Is the Victron inverter going to be supplying the house in parallel with the mains supply or will there be a changeover switch and, if so, where will it be located?

In any case there will need to be some overcurrent/fault protection for the cable to the outbuilding irrespective of the supplier's fuse.