Can I connect an outdoor socket to a junction box which feeds my garage?

[banksey88]

Hi,

I’m looking at adding an external socket on my house. I have a external junction box which is fed from the main consumer unit, in the junction box is a connector block which feeds a SWA cable which goes under my patio to my garage. In the garage is a smaller consumer unit which has a socket circuit, and a lighting circuit.

My question is, can I connect an outdoor socket to the external junction box directly? So the MCB in the main consumer unit will be feeding my garage consumer unit, as well as an outdoor socket.

Thanks for your help.

 

[banksey88]

I’ll assume the SWA is earthed properly at the garage end. (Banjo with flylead to earth bar)

Not a problem adding an exterior socket to this circuit from the joint box.

First time I’ve been inside the garage consumer unit since in moved in and the banjo is not connected to the earth bar! Thanks for pointing that out, I will be addressing that before I do anything else.

 

[littlespark]

The reason to make sure the armour of the cable is earthed is basically safety… even though one core within the cable is used as an earth.

imagine going through the cable with a spade (accidents happen)
The spade cuts through the armour, then into the live… the spade and armour goes live, causing a short to earth, and then causing the mcb to trip. Goes with quite a bang, but it does trip.

without an earth, both the armour and spade become live and STAY live.

 

[brianmoooore]

Garage CU is metal, which is connected electrically to the earth bar, so, assuming paint doesn't provide an insulating layer, the SWA gland, and hence the SWA is earthed at the garage end. It's good practice, though, to earth the SWA at the source end, and preferably at both ends, so the banjo in the adaptable box should be connected to the earth wire.
Why would anyone fit a banjo, and then connect nothing to it??

 

[banksey88]

The reason to make sure the armour of the cable is earthed is basically safety… even though one core within the cable is used as an earth.

imagine going through the cable with a spade (accidents happen)
The spade cuts through the armour, then into the live… the spade and armour goes live, causing a short to earth, and then causing the mcb to trip. Goes with quite a bang, but it does trip.

without an earth, both the armour and spade become live and STAY live.

Makes perfect sense and very important. The gland is touching the metal box so should have contact to earth, but most probably not earthed well enough as the metal casing is painted.

 

[banksey88]

Garage CU is metal, which is connected electrically to the earth bar, so, assuming paint doesn't provide an insulating layer, the SWA gland, and hence the SWA is earthed at the garage end. It's good practice, though, to earth the SWA at the source end, and preferably at both ends, so the banjo in the adaptable box should be connected to the earth wire.
Why would anyone fit a banjo, and then connect nothing to it??

Exactly what I thought, why add the banjo if it’s not being used! The house is 8 years old, but I’m not sure if this was part of the original installation or if it was an added extra. by the previous owner.

 

[banksey88]

My next question is… how many sockets can I add? My plan is to only add the one at the moment, but may add more in future in a radial?

Would I need a switched connection unit if I was to add more sockets? The main MCB is currently rated at 16A and is also powering the garage.

 

[littlespark]

You can have what you like as everything is protected by the 16A.
Depending of course that the cable used to supply the sockets can carry more.

 

[pc1966]

If the supply MCB is 16A than any power cable (1.5mm or larger) is fine if not heavily insulated or hot zone and no realistic limit to number of sockets.

But...you are obviously limited to 16A total! Also some larger loads with motors like chop saws, etc, might take enough of a start-up surge to trip a 16A B-curve MCB. Going for a 16A C-curve might be an option but really then you need to do a bit more design and testing.

Ultimately your cable run and loads are limited by one or more of the following:

• Current carrying capacity of the cable (mostly conductor size, but also thermal insulation of its route / installation method)
• Voltage drop (should be less than 5% at max load)
• Fault impedance to disconnect fast enough (usually met if VD met)

For guidance, a 16A circuit on 1.5mm T&E should be limited to 27m (or 15m if C-curve depending on supply Ze, typical TN-S limit). If it is in 2.5mm (more likely as safe for greater range of installation methods) then 45m (or 24m C-curve).

 

[banksey88]

If the supply MCB is 16A than any power cable (1.5mm or larger) is fine if not heavily insulated or hot zone and no realistic limit to number of sockets.

But...you are obviously limited to 16A total! Also some larger loads with motors like chop saws, etc, might take enough of a start-up surge to trip a 16A B-curve MCB. Going for a 16A C-curve might be an option but really then you need to do a bit more design and testing.

Ultimately your cable run and loads are limited by one or more of the following:

• Current carrying capacity of the cable (mostly conductor size, but also thermal insulation of its route / installation method)
• Voltage drop (should be less than 5% at max load)
• Fault impedance to disconnect fast enough (usually met if VD met)

For guidance, a 16A circuit on 1.5mm T&E should be limited to 27m (or 15m if C-curve depending on supply Ze, typical TN-S limit). If it is in 2.5mm (more likely as safe for greater range of installation methods) then 45m (or 24m C-curve).

Thank you. If I run in more than 1 socket, do I have to run the next socket off the previous one like a radial? Or can I run 1 socket 1 way from the junction box, and one socket the opposite way from the junction box (wago connected inside).

 

[pc1966]

Thank you. If I run in more than 1 socket, do I have to run the next socket off the previous one like a radial? Or can I run 1 socket 1 way from the junction box, and one socket the opposite way from the junction box (wago connected inside).

You can do ether, but obviously have to have the appropriate number of terminal holes to do so (5-way Wago as they don't make 4-way).

However you do it, make sure it is obvious and/or suitably labled to allow future fault-finding. It might be someone else who knows nothing about your reasons, or you if a few years time when you forget!