Hi guys if you have a TNS system or TNCs is it mandatory to TT a outdoor hot tub ? Say TNS up to the rotary switch then earth rod from that point ? Thanks guys
Nothing in BS7671, the issue will be if there is any bonding required, as there are minimum sizes for a bonding conductor especially for TNCS. If your cpc is going to double up as a bonding conductor then the cpc will need meet the requirements for bonding conductor.
However there is the issue with an open neutral on the suppliers side, if you search the old forum you will find a few posts on exporting PME/TNCS
If the installation is such that the installation could be seen as similar to an outdoor swimming pool, then the regs would recommend either a grid beneath, or TT.
Section 702 Swimming Pools AND OTHER BASINS may well apply here. 30mA R.C.D.s are a requirement for many applications and essential for equipment in zone 2. (702.410.3.4.3 (iii)).
Above ground level basins are illustrated in Fig. 702.2. It looks like a hot tub.
The hot tube makers will no doubt insist of 30mA R.C.D. protection for their hot tub as it will contain 240 Volt heating elements, and possibly pumps, that could under fault conditions make the water live in relation to Earth.
I personally prefer to use a TT earthing arrangement for outside hot tubs with a dedicated earth electrode. I also have a personal preference for two 30 mA R.C.D.s in series to ensure that if one becomes faulty or sticky the other will trip off reliably under fault conditions. Perhaps one indoors and the other near to the hot tub outdoors.
Although a supply may look like a TN-S supply, in many cases it may be in reality a TN-C-S supply these days.
