SWA to shed

The armour must be earthed - it kind of defeats much of the purpose of using SWA in the first place if its not.

Personally I would earth the armour at the origin, feed to the socket, and continue to the outbuilding.

You could isolate that earth at the destination, and use a local earth rod for just the outbuilding. However since the source end is TT anyway, there is nothing stopping you from having the local TT earth joined to the shed earth rod as well via the submain. It will just lower Ze for both ends (unless the shed is so close that the resistance area of the rods overlap - in which case it won't make much difference).

Well much the same here, but what you said seems fine to me!

Only other thing to keep in mind is that the presence of the socket mid way means the submain will need 30mA trip RCD protection at the origin, and that means no discrimination for earth faults at the shed end. You could work round that with a RCD protected socket midway, or with emergency lights in the shed if deemed appropriate. (although keep in mind the hot tub feed will need a RCD as well)

I thought 2 separate locations for earthing rods and joining them up was frowned upon?

Hence I would isolate the armour from any circuit at the outbuilding.

I would have RCDs at the outlets, so RCD protection is co-located at the outbuilding, and a separate RCD for the hot tub.

Having a single RCD at the source/house may require many treks between the house and outbuilding to find a leakage path. It may be good exercise but.................

Are you sure that inside the ?plastic Wiska box he hasn't joined the tag on the armour nut to the earth that goes back to your consumer unit ?.

That was the intention.

However since the source end is TT anyway,

I have done that before, and achieved exactly what you said - lower Ze all round. The shed is about ten metres from the house.

It does have 30mA RCD protection at the origin. If the earth was isolated at the shed end, and was just connected to the local earth, wouldn't that get over the dicrimination problem?

You

The hot-tub has been installed for some time, on a separate circuit, and is fed via an RCD protected circuit.

Many thanks for your helpful reply.

I get no continuity reading between the armour and the earth connection.

No. The imbalance in the live and neutral (which is what the RCD detects) will be the same at the origin and the shed end.

Yes of course, thank you.

If the supply was TN-S, then yup - there is a risk of a different earth potential between them. But on TT or TN-C-S you can add additional rods and they don't need to be in the same place.

That does not help if there is one on the submain feed already - either or both could trip.

Unless its a Type S (time delayed) then you may still have to walk anyway.

No, because any leakage to earth from the circuit will also be seen as an imbalance in the head end RCD as well.

Sorry, go the impression it was the same circuit for some reason.

I was assuming there wasn't a RCD on the feed. Otherwise there is less need for SWA cable.

As it seems you are stuck with the 30mA RCD at the head end then just earth up the SWAs armouring (need only be at one end if you feel lazy) and stick in an other earth rod if you want to (personally I do not think you would gain anything by doing so).