SWA cable for an LED garden light

[robbieee]

The stairs at the bottom of my garden are really dark. So my plan is to run SWA from my house to the bottom to light up the area.

However, i have a few questions:

1. Should it be 3 core or 2 core? I assume 2 core as the outer shielding will be connected to earth at both sides?
2. For the light end should i connect straight to the light or go via a waterproof junction box? This is the light I have bought:

http://www.screwfix.com/p/lap-bulkhead-led-wall-lamp-with-pir-6w-black/86524

3. How deep should the trench be? I will just have to dig up a trench in my grass.
I have calculated that 1.5mm SWA is enough its only one light I will be powering.

Rob from Scotland

 

[PrenticeBoyofDerry]

However, i have a few questions:

1. Should it be 3 core or 2 core? I assume 2 core as the outer shielding will be connected to earth at both sides?

Three core

2. For the light end should i connect straight to the light or go via a waterproof junction box? This is the light I have bought:

http://www.screwfix.com/p/lap-bulkhead-led-wall-lamp-with-pir-6w-black/86524

Ideally straight to the lamp, but it could well be that the SWA does fix too good at the entry point and then adaptable box may be best used, this can be mounted quite close to the light, then form that box use a cable/flex suitable for the environment or you use T&E in conduit.

3. How deep should the trench be? I will just have to dig up a trench in my grass.

600mm.

I have calculated that 1.5mm SWA is enough its only one light I will be powering.

.
1.5mm2 SWA will deal with 6W load, very comfortable on a 6A circuit.

 

[robbieee]

However, i have a few questions:

1. Should it be 3 core or 2 core? I assume 2 core as the outer shielding will be connected to earth at both sides?

Three core

2. For the light end should i connect straight to the light or go via a waterproof junction box? This is the light I have bought:

http://www.screwfix.com/p/lap-bulkhead-led-wall-lamp-with-pir-6w-black/86524

Ideally straight to the lamp, but it could well be that the SWA does fix too good at the entry point and then adaptable box may be best used, this can be mounted quite close to the light, then form that box use a cable/flex suitable for the environment or you use T&E in conduit.

3. How deep should the trench be? I will just have to dig up a trench in my grass.

600mm.

I have calculated that 1.5mm SWA is enough its only one light I will be powering.

.
1.5mm2 SWA will deal with 6W load, very comfortable on a 6A circuit.

I assumed 2 core? Surely with 3 core you would have earth loops with the earth wire and stealth both being the same earth?

Thanks for your responses, much appreciated.

 

[Gutterball]

just use 2 core, but make sure you gland the armour correctly, and use a fly lead to earth.

 

[JohnW2]

I assumed 2 core? Surely with 3 core you would have earth loops with the earth wire and stealth both being the same earth?

As you are discovering, views about this issue are very polarised. Some will say that to use 3-core is unnecessary, others would always advise 3-core. FWIW, I personally tend towards the latter view.

If you do use 3-core, there are not really 'earth loops' per se, since the armour and earth core are in parallel - so I wouldn't letthat put you off.

Kind Regards, John

 

[mfarrow]

View media item 67014
Regulations guidelines document, though recommends 500mm minimum:

A depth of less than 0.5m is usually inadvisable as shallow laid cables may be inadvertently damaged by general gardening etc. Cables that cannot be buried at a reasonable depth should be specifically protected, e.g. by ducts encased in concrete, or installed along an alternative route.

 

[bernardgreen]

Using 2 core with the "earth" dependent on the sheath is OK in the short term but the armour is steel and will rust if there is any damage to the outer sheath and moisture can reach the armour.

Since the "earth" from the supply ( unless TT ) is invariably not at ground potential any rusting of the armour will be accelerated by electrolysis.

Damage can be from a fork and will go un-noticed as the lamp will still work.