Concreting Swa & earth fly leads???

[ppelec100]

So I have a job of installing an old cast iron lampost which will need to be buried into the ground about 600mm deep due to its weight. I am planning on drilling a hole at an angle from the patio area (next to the hole) into the hole to pass the 1.5mm swa into. Once the cable is in, I’m planning on concreting over the cable so that the cable is in the middle of the concrete foundation and the lampost will sit over the foundation and so that the cable doesn’t get damaged when putting the lampost in the hole. Question is, do I need to put the 1.5mm swa through some duct/copex before concreting or can I concrete over it bare? There is no chance of replacing the cable in the future if needed anyway unless the lampost gets dug out again.

Also I am going to terminate the swa gland into a plastic enclosure which will house a quinetic receiver (supply side). When using the piranha earthing nut, what size cable should I use for the fly lead from the piranha nut to the connector block with the other CPC’s? Could someone also tell me where they got the cable size of the earth fly lead from please. I feel like if I use a 1.5mm I am downgrading the resistance of the armouring...

If I was using a bigger armoured how would I know what size earth fly lead to use. Also for metal containment... would like to know for future use.

Thanks for any help I receive

 

[telectrix]

2 core or 3 core SWA?

 

[ppelec100]

2 core or 3 core SWA?

1.5mm 3 core swa L / N / E

 

[telectrix]

i would duct it throught the concrete to protect from damage when concreting and fixing lamp post. then it'sreplaceable. as for flylead/s i would use 4mm.

 

[ppelec100]

i would duct it throught the concrete to protect from damage when concreting and fixing lamp post. then it'sreplaceable. as for flylead/s i would use 4mm.

Okay thanks I’ll put some ducting in!
For the fly leading, I was thinking to use 4mm earth fly lead but where does the idea of the cable size come from? Just want to know for any future jobs/design/planning.

 

[davesparks]

I would duct the SWA to be sure, and use a 1.5mm fly lead.

The fly lead should be, as a minimum, the size required for a CPC for the circuit. So either calculate the required size using the adiabatic, or select it from the table.

 

[ppelec100]

I would duct the SWA to be sure, and use a 1.5mm fly lead.

The fly lead should be, as a minimum, the size required for a CPC for the circuit. So either calculate the required size using the adiabatic, or select it from the table.

Okay thanks mate, this makes more sense. What about when it comes to metal trunking/conduit/tray? How do I know what size to use then?

 

[telectrix]

Okay thanks I’ll put some ducting in!
For the fly leading, I was thinking to use 4mm earth fly lead but where does the idea of the cable size come from? Just want to know for any future jobs/design/planning.

generally you fit flylead same size as cable cpc, you can go up a size or even 2 sizes. as for conduit/trunking etc., you could calculate resistances and work out equivalent copper csa,but generally it's guess a figure and add a bit.

bigger is better as the actress said to the bishop.

 

[davesparks]

Okay thanks mate, this makes more sense. What about when it comes to metal trunking/conduit/tray? How do I know what size to use then?

Trunking and conduit will often be earthed by the connection of the cpc of every circuit throughout the installation if it is a complete system using seperate cpc's pulled in. If the trunking/conduit is being used as the CPC then you need to work out what size CPC is used bearing in mind the regulations covering CPCs which are shared between circuits.
A good rule of thumb would be to use, as a minimum, an earth the same size as the largest CPC that is required for a circuit inside the trunking/conduit.

With a properly constructed trunking/conduit you should always have a good metal to metal contact with the DB and all metal accessories so it will pick up good earth connections through these points.


Tray is a whole other debate that a lot of people just can't agree on. Generally speaking tray doesn't normally need earthing, but it could need bonding.

 

[James]

Just to throw a spanner in the works,

the fly lead is not required at the lamp post at all.
providing the following is true

armour is correctly earthed at the supply end of the cable
one of the cores of the cable is being used as a cpc and correctly identified at both ends.

 

[ppelec100]

Just to throw a spanner in the works,

the fly lead is not required at the lamp post at all.
providing the following is true

armour is correctly earthed at the supply end of the cable
one of the cores of the cable is being used as a cpc and correctly identified at both ends.

Okay that’s fair enough.

The armour does not get glanded into the lamppost, it will be glanded into a wiska box and I’m going to use some of that ho7rn cable to go into a BC lamp holder which will sit in the top of the lamppost. So I will need to earth the lamppost, can I do this by using the Cpc core from the ho7rn cable to crimp, nut and bolt to the lamppost somewhere?

 

[pc1966]

So I will need to earth the lamppost, can I do this by using the Cpc core from the ho7rn cable to crimp, nut and bolt to the lamppost somewhere?

Yes, so long as it is reliably able to clear any fault. If you are using the came CSA for the flex as for the SWA, and overall the system meets the disconnection time it should be fine.