Hi,

I need some guidance.

The wire for our house's outbuilding, a separate standing garage, was run under ground without conduit. I don't know how many owners ago this was, but this cable was damaged in the past and when it rain enough (happens every winter in CPT), then that causes the earth leakage to trip. Then I have to turn off the outbuilding breaker and can get the whole house back online.

So my plan is to re-run a new cable. This time I won't run it through the garden (underground run of at least 90m) along the property line etc (silly IMHO), but instead run it through the roof like all the other wiring, and then use the shortest route underground between the 2 buildings which will only be 3m underground and inside conduit.

I will run the wire myself then get an electrician to connect over to the new wire in both DBs in each building. The reason for this, I will be running some other networking cables too myself so may as well get the cable there ready. I also already have new empty conduits between the 2 buildings.

The breaker in main house for outbuilding is 20A.
The DB in outbuilding has a main-switch of 20A, a plugs breaker of 20A and a lights breaker of 10A. Very simplistic.

What I need to know, what is the correct wire size I need to buy for this, so that it is legal. Should I go with 2.5mm or 4mm?

Many thanks in advance!
 

Edited August 23, 20223 yr by Tinuva

9 minutes ago, Tinuva said:

Hi,

I need some guidance.

The wire for our house's outbuilding, a separate standing garage, was run under ground without conduit. I don't know how many owners ago this was, but this cable was damaged in the past and when it rain enough (happens every winter in CPT), then that causes the earth leakage to trip. Then I have to turn off the outbuilding breaker and can get the whole house back online.

So my plan is to re-run a new cable. This time I won't run it through the garden (underground run of at least 90m) along the property line etc (silly IMHO), but instead run it through the roof like all the other wiring, and then use the shortest route underground between the 2 buildings which will only be 3m underground and inside conduit.

I will run the wire myself then get an electrician to connect over to the new wire in both DBs in each building. The reason for this, I will be running some other networking cables too myself so may as well get the cable there ready. I also already have new empty conduits between the 2 buildings.

The breaker in main house for outbuilding is 20A.
The DB in outbuilding has a main-switch of 20A, a plugs breaker of 20A and a lights breaker of 10A. Very simplistic.

What I need to know, what is the correct wire size I need to buy for this, so that it is legal. Should I go with 2.5mm or 4mm?

Many thanks in advance!
 

I don't know what is the Sans specifications but using 2,5 mm2 over 90 meters is going to give you an approximately  +_ 8 V voltage drop based on that distance I would go for 8 mm2 I could be wrong

Run a wire 90meters and a 20 Amp load you will need 10mm2 cable. This will ensure you have a voltage drop less than 5%(3.38%)

Few things to ponder:

Normally a cable supply from one to another DB is SWA (Armoured cable).  Don't know what the legalities are about running wiring in conduits. Electrician should be able to give you answers.

Current carrying capacity should not be a problem.  2.5 I think can carry 20A.  Voltage drop as mentioned above would be an issue and requires a thicker cable as mentioned.

Fault currents to be kept in mind. Cascading of breakers. Get an expert to check.

If your earth leakage trip then the breaker is most likely in the wrong position in the board. Get someone in the know to check.

Maybe it is an option to install a lights and plugs breaker in the main house DB and run twin and earth in conduit for each to the flat bypassing the DB in the flat.  Someone in the know can comment.

Edited August 23, 20223 yr by Pietpower

2 minutes ago, Pietpower said:

Few things to ponder:

Normally a cable supply from one to another DB is SWA (Armoured cable).  Don't know what the legalities are about running wiring in conduits. Electrician should be able to give you answers.

Current carrying capacity should not be a problem.  2.5 I think can carry 20A.  Voltage drop as mentioned above would be an issue and requires a thicker cable as mentioned.

Fault currents to be kept in mind. Cascading of breakers. Get an expert to check.

If your earth leakage trip then the breaker is most likely in the wrong position in the board. Get someone in the know to check.

Maybe it is an option to install a lights and plugs breaker in the main house DB and run twin and earth to the flat bypassing the DB in the flat.  Someone in the know can comment.

Unsure about this. The earth leakage trip when it should almost always. It is only when it rains, I have to bypass the outbuilding, which tells me, there is a problem there, however most of the time, there is almost nothing turned on there, only the garage motor. I've looked it over and over, and it has to be this wire underground that is the issue, only place I can see any water getting to something it should not.

2 hours ago, Tinuva said:

Unsure about this. The earth leakage trip when it should almost always. It is only when it rains, I have to bypass the outbuilding, which tells me, there is a problem there, however most of the time, there is almost nothing turned on there, only the garage motor. I've looked it over and over, and it has to be this wire underground that is the issue, only place I can see any water getting to something it should not.

Under correction but I think the breaker for your secondary board should not be connected via the earth leakage.  You should have another earth leakage device in the secondary board for the plug circuit.

Thanks everyone. It looks like I should go with 10mm2 cable.

As for the EL switch, I will do a CoC from a reputable company and find out what gets signed off. 

I would suggest you run the network cable in a separate conduit. Otherwise the power will influence your network speed/traffic.

On 2022/08/24 at 6:46 PM, p_i said:

I would suggest you run the network cable in a separate conduit. Otherwise the power will influence your network speed/traffic.

I am running fibre for the network, because the distance is long enough that copper wouldn't work anyway or just give too much issues.
I have no intention of mixing things, which is why I run more than one conduit underground. I really want quality network connectivity