I am hoping the wonderful experts on this forum can answer some questions about a hot tub feed. I have purchased a hot tub for my home and the supplier has said it must have a TT earthing system as there is a risk of if neutral is lost on the house PME system with a fault on the hot tub the water could be live (not sure I have explained that well, I am a simple mechanical engineer). The hot tub suppliers view is that all hard wired hot tubs should have a TT earth.

My electrician has looked at the exact location of the hot tub and has said that there is a metal outside light, an outside socket and an air source heat pump close to the hot tub all protected by the house PME  he has a concern that under an extreme set of cirumstances / faults it could be that the PME and TT would not protect you, hsi strong preference is to stick with PME for all devices/sockets/lights/air source heat pump with the same earth type. The socket and light are not less than 2 metres from the hot tub per regulations. He also commented that the TT earth is only there to protect in a extremely unlikely circumstance, that is, the neutral source to the house is lost, the live remains to the house and there is a fault in the hot tub. Is there a right or wrong answer to earthing to a hot tub or a single solution that presents the least risk?

My registered electrician has also commented that the regulations call for an impedance less than 20 ohms for a TT earth and that this is extremely difficult to achive with a single 1200m earth rod. He believes we would need multiple earth rods to get the impedance below 20 ohms. What is the experience of the forum on getting TT systems below 20 ohms?

This is a live 'difference of opinion' between the electrician and the hot tub supplier so I would appreciate your expertise quickly. Thanks!