6mm SWA into CU for hot tub

[jimuthy2]

You could export the "earth" from the house to the ground around the hot tub using the SWA armour and/or a conductor in the SWA cable. This would create a potential gradient in the ground surrounding the earth rod.

The ground rod and the soil in contact with it will be at the potential of the "earth" exported from the house.
The soil a few feet from the earth rod will be at natural ground potential.

Where there is no fault these two potentials will be very close. If there is a fault ( or significant unbalance between phases in the local network ) then the "earth" potential in the house could be many tens of volts different from the natural potential of the soil thus creating potential gradient. People standing in bare feet in the area of the potential gradient may feel an electric shock from foot to foot.

So a earth mat / rod near the hot tub (connecting to the tub, SWA armour and CPC, and no earth connection at the CU?

 

[bernardgreen]

This is how I would set it up.

The armour of the SWA should be earthed at the consumer unit in the house and fed via an RCD. This will disconnect power if the SWA cable is damaged

The armour of the SWA should not be connected at the far end. The SWA would feed a small consumer unit. The "earth" for this consumer unit would be from ground rods as close as possible to the hot tub ( or preferably an earth mat under the tub ) The consumer unit would have two RCBOs ( combined RCD and MCB ) One for the hot tub and the second for lights. If the hot tub trips the power off at night it would be sensible to still have some lights still working,

Given that 30 mA through the human body can be fatal I would consider using an RCBO with a 10mA trip rating

 

[jimuthy2]

This is how I would set it up.

The armour of the SWA should be earthed at the consumer unit in the house and fed via an RCD. This will disconnect power if the SWA cable is damaged

The armour of the SWA should not be connected at the far end. The SWA would feed a small consumer unit. The "earth" for this consumer unit would be from ground rods as close as possible to the hot tub ( or preferably an earth mat under the tub ) The consumer unit would have two RCBOs ( combined RCD and MCB ) One for the hot tub and the second for lights. If the hot tub trips the power off at night it would be sensible to still have some lights still working

Thanks bernardgreen, I see the logic of this - much appreciated. This is definitely one for a spark, but I want to understand the issues for peace of mind.

I take it the CPC of the SWA would only be earthed at the new consumer unit end, to avoid the export issue you explained? Would you put a rotary switch between the new CU and the supply cable to the tub?

A mat under the tub sounds a good idea, especially as a base will need digging out anyway.