Another Hot Tub Thread Part 2

Midwest · Aug 22, 2020

Following on from the last two more technically debated threads:

32A supply for Hot Tub of a PME supply
Another Hot Tub install

I posted a question, in the last one, but didn't get a reply, so starting another one. Hope the Mods don't mind.

So posting my question again, slightly edited.

I’ve been reading lots of threads, about hot tubs & the like, using a PME supply.

I’m thinking of buying one of those inflatable hot tubs Lazy Spa, primarily as a glorified paddling pool for my grandson. I was quite happy to plug into my outdoor socket on my composite (plastic) decking; I have a PME supply.

But since then, I've been reading all sorts things about extending pme (to an outside environment), and I've been contemplating whether to risk it. Manufacturer recommends connecting to equipotential bonding terminal

My options I know, are to either TT just the supply to the tub socket, use my pme supply and try and supplement that with a rod of <20. My sub soil is littered with rocks. Or just use the pme supply without a rod, and don't worry cause its on my plastic decking.

Or just forget it, and keep filling the paddling pool!

Your thoughts?

partplonker · Aug 25, 2020

Midwest said:
The manuals I’ve read online, refer to attaching to grounding point etc. No mention of what Class electrical appliance they are? It suggest the pump is 12v.

I'll be honest, I started out thinking this thread was a bit daft, but you're right. I'm not sure where I got the class 2 from because I've just looked and I can't find a double insulated logo on the unit or any mention of device class in the manual. It does state that the filter/pump is 12V and the heater/jets are mains voltage and their peak demand but that's about it.

The manual states "This appliance must be connected to a grounded mains supply socket and a supply cord fitting with a plug and PRCD equipped with a tripping current of 10mA. The appliance with earthing must only be plugged directly into an earthed socket-outlet of the fixed wiring."

Ok, so far so good.

It then says "A qualified electrician shall wire the spa control unit to the household equipotential terminal using a minimum 1.5mm2 solid copper conductor".

I wonder if this is really aimed at other countries where sockets without an earth are still a possibility?

I can't really see your average consumer buying one of these and being expected to crack open the tub electrics, whip out some singles and lugs and start bonding things, so I have no idea what they're on about.

Interesting that they state a minimum CSA for the earth conductor though. I'm pretty sure there are still older installations around that used 2.5mm2 T+E with a 1mm2 earth.

Thankfully, I have a TN-S supply so I'll not give it any further thought and enjoy my hot tub!

Midwest · Aug 25, 2020

partplonker said:
I'll be honest, I started out thinking this thread was a bit daft, but you're right. I'm not sure where I got the class 2 from because I've just looked and I can't find a double insulated logo on the unit or any mention of device class in the manual. It does state that the filter/pump is 12V and the heater/jets are mains voltage and their peak demand but that's about it.

The manual states "This appliance must be connected to a grounded mains supply socket and a supply cord fitting with a plug and PRCD equipped with a tripping current of 10mA. The appliance with earthing must only be plugged directly into an earthed socket-outlet of the fixed wiring."

Ok, so far so good.

It then says "A qualified electrician shall wire the spa control unit to the household equipotential terminal using a minimum 1.5mm2 solid copper conductor".

I wonder if this is really aimed at other countries where sockets without an earth are still a possibility?

I can't really see your average consumer buying one of these and being expected to crack open the tub electrics, whip out some singles and lugs and start bonding things, so I have no idea what they're on about.

Interesting that they state a minimum CSA for the earth conductor though. I'm pretty sure there are still older installations around that used 2.5mm2 T+E with a 1mm2 earth.

Thankfully, I have a TN-S supply so I'll not give it any further thought and enjoy my hot tub!

Bear in mind these products were originally designed for US market, so they would be adapted for European markets accordingly. The manuals are probably just a cut paste from the US ones, with certain bits changed, like the voltage etc. Thats why I think, words like grounding are used. The Lay-z-Spa instructions, suggest a 2.5mm solid conductor.

On your last point, you may wish to reconsider your TN-S supply. From what I heard and read, most TN-S supplies would of had repairs carried out on the DNO cables, at some point. Any such repairs would convert it to TN-C-S. If you have what you think is TN-S, you should treat as TN-C-S.

telectrix · Aug 25, 2020

with these modern hot tubs, you are more in danger of being clouted round yer 'ed with a frozen turd dropped from a 747 @ 37,000ft.

partplonker · Aug 25, 2020

Midwest said:
On your last point, you may wish to reconsider your TN-S supply. From what I heard and read, most TN-S supplies would of had repairs carried out on the DNO cables, at some point. Any such repairs would convert it to TN-C-S. If you have what you think is TN-S, you should treat as TN-C-S.

I heard about that and I think that happened in the previous house I lived, where the supply was a 1960s lead sheathed cable.

I currently live in a flat in a converted former hospital/mental asylum/country house. We have our own 11kV transformer and all the feeds to our flats or communal areas are mostly in MICC with some SWA for later additions. Earth is separate from neutral all the way back to the transformer. It's quite an interesting setup because the DNO are only responsible for the transformer. All the LV switchgear and cabling is our responsibility (the tenants) to maintain. But I digress ...