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to stop you getting a shock if you lose the neutral,Why’s that
Discuss Hot tub supply in the UK Electrical Forum area at ElectriciansForums.net
to stop you getting a shock if you lose the neutral,Why’s that
Also as a couple of threads have reported tingling feet when getting out due to potential difference of real earth and PME earth.Why’s that
It is a dedicated supply to the hot tub so RCD selectivity is not important but I agree 100% that having two in series for no single point of failure is a good idea. Just take the supply off the usual RCD or RCBO in the house CU, but have a 2nd double-pole RCD out at the tub and a local rod.I'd be breaking the earth on a PME and rodding down adjacent to the tub. 8 foot coupled rod. Small non-conductive four way external IP rated board with a 10mA and a 100mA s-type RCD in line. Rotary isolator mounted adjacent to the board. Take off a non-RCD way at the supply DB.
Due to the sensitivity of a 10mA RCD that's why I suggested having it seperate to other RCDs in the installation and dedicated only for the hot tub. The 100mA s-type will delay tripping in the event of a failure of the primary and although it would never meet regulated disconnection times it would serve as a last line of defence only. You would still need to have a primary RCD to meet the requirements of discrimination.It is a dedicated supply to the hot tub so RCD selectivity is not important but I agree 100% that having two in series for no single point of failure is a good idea. Just take the supply off the usual RCD or RCBO in the house CU, but have a 2nd double-pole RCD out at the tub and a local rod.
The only way you can guarantee the seasonal stability of a rod is with depth. 4' rods are next to useless for providing stable earth fault paths. Resistance is ultimately a moot point. 200 ohms is a recommendedation only. What matters is that the value won't fluctuate. A 4' rod in the wrong soil type and a dry season can easily see 1667 ohms exceeded.Depending on the soil you probably don't need an 8' rod, if the usual 4' style is measuring below 200 ohms then it is fine. Often you can extend the rod by another 4' using the threaded coupled if it turns out to need it. Just take care/inquire about any buried services before hammering one in!
I recommended non-conductive for a reason. The more you limit simultaneously accessible exposed conductive parts on an installation like this the better. Also, it leaves no chance for a path to present itself between the supply earth and the sub circuit earth. Personally I wouldn't be using SWA as it's unnecessary. I'd likely be using HO7.You can use a metal IP rated mini-CU such as this:
You don't need to use the matching RCD, though that is convenient, as you are using it as a DIN enclosure so no specific busbar alignment to worry about. The enclosure body would be on the local TT earth, so any SWA entering it should have a plastic IP68 style of gland for support/weatherproofing to keep it electrically isolated from the supply PME earth on the armour.
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