Hot tub electric shock

[LastManOnline]

But wouldn't this voltage go once the power is removed from the tub?

Correct. Once power is removed you should no longer feel any voltage. Is your rcd double or single pole?

 

[Samhhh]

Correct. Once power is removed you should no longer feel any voltage. Is your rcd double or single pole?

Double pole mate

 

[LastManOnline]

Double pole mate

Based on that then it can only be the supply earth that's causing the issue. I agree with your brother. Disconnect the supply earth and see if "tingle" disappears.That will confirm it.

 

[Samhhh]

Based on that then it can only be the supply earth that's causing the issue. I agree with your brother. Disconnect the supply earth and see if "tingle" disappears.That will confirm it.

I think for this one I will just stick with the multimeter results rather than doing the finger test ? thankyou for the help is much appreciated

 

[brianmoooore]

I would never install a hot tub on TNC-S. My own are on a genuine TNS system, and use the DNO earth, but if it were TNC-S, the tubs, and the buildings by them, would be TT.

 

[pc1966]

I would never install a hot tub on TNC-S. My own are on a genuine TNS system, and use the DNO earth, but if it were TNC-S, the tubs, and the buildings by them, would be TT.

More and more I am thinking all hot tubs should be on a TT supply, as even if your supply appears to be TN-S there is a chance that elsewhere repairs or cable replacement has essentially converted your supply to TN-C-S (just a rather long 'S' there).

 

[LastManOnline]

I would never install a hot tub on TNC-S. My own are on a genuine TNS system,

And now we come to the nub of the problem. An unsatisfactory supply system. TNS was and is the only proper supply system. Ironically I thought that a combination of outside metalwork like heat pumps, electric gates, electric vehicles etc would highlight the frailties of TNC-S. But I now wonder if it may be hot tubs that eventually highlight the issues!!

 

[brianmoooore]

By "genuine TNS" I mean that I can see all the earthing rods, and every inch of the supply cables, all the way from the 11kV - 230-0-230 Tx, to all three DNO service heads

 

[pc1966]

By "genuine TNS" I mean that I can see all the earthing rods, and every inch of the supply cables, all the way from the 11kV - 230-0-230 Tx, to all three DNO service heads

You are very lucky then!

 

[LastManOnline]

By "genuine TNS" I mean that I can see all the earthing rods, and every inch of the supply cables, all the way from the 11kV - 230-0-230 Tx, to all three DNO service heads

Then as pc1966 states you have truly a unique situation. Can I enquire about the earth rods? TNS is the one supply's system I have never worked on. What is the earth electrode arrangement?

 

[timhoward]

Excuse quick diversion, then back to interesting TNS question!

More and more I am thinking all hot tubs should be on a TT supply, as even if your supply appears to be TN-S there is a chance that elsewhere repairs or cable replacement has essentially converted your supply to TN-C-S (just a rather long 'S' there).

In addition, one could argue that:
-GN7 says hot tubs outside should have section 702 applied.
-702.140.3.4.3 (ii) NOTE says:
"Where a PME earthing facility is used as the means of earthing [.....] it is recommended that an earth mat [...] of suitably low resistance e.g. 20 ohms or less , be installed and connected to the supplementary bonding."

Ok, I accept that's a recommendation based on a guidance note but had it been followed the (likely) problem in this thread wouldn't have happened.

 

[brianmoooore]

Changed from TNC-S about ten years ago, when the single service head (at the time) was relocated, and the 3 separate overhead service wires (Ph, Ph, and N+E) were deemed to contravene some regulation, and was replaced by what looks like 4 wires loosely twisted together, but are actually joined, and reinstated as TNS.
There are three earth electrodes. One, on the Tx pole, earths the TX metalwork and the neutral, a second on the Tx pole is for the supply, and there is third at the base of the service pole.

 

[LastManOnline]

Changed from TNC-S about ten years ago, when the single service head (at the time) was relocated, and the 3 separate overhead service wires (Ph, Ph, and N+E) were deemed to contravene some regulation, and was replaced by what looks like 4 wires loosely twisted together, but are actually joined, and reinstated as TNS.
There are three earth electrodes. One, on the Tx pole, earths the TX metalwork and the neutral, a second on the Tx pole is for the supply, and there is third at the base of the service pole.

That's almost historical. A TNC-S supply being converted to a TNS
supply. I suspect the earth rods are a leftover from the original TNC-S.Which is a bonus. I think if I was selling up I would advertise "house with genuine TNS". It looks like there could be a growing market for such dwellings (especially if you like "tingle" free hot tubs)

 

[LastManOnline]

Ok, I accept that's a recommendation based on a guidance note but had it been followed the (likely) problem in this thread wouldn't have happened.

No question. Body resistance would be virtually shorted out.

 

[pc1966]

That is a fairly specialised form of advertising!

 

[LastManOnline]

That is a fairly specialised form of advertising!

Agreed. But by the time I, m finished with moaning about the shortcomings of TNC-S on this forum (which I do religiously) I, m hoping it all becomes a, bit more "mainstream"

 

[brianmoooore]

That's almost historical. A TNC-S supply being converted to a TNS
supply. I suspect the earth rods are a leftover from the original TNC-S.Which is a bonus. I think if I was selling up I would advertise "house with genuine TNS". It looks like there could be a growing market for such dwellings (especially if you like "tingle" free hot tubs)

Nothing extra was added at the Tx pole when the change was made, but the service pole and its earth rod were new. Old service pole (now a bird table) did not feature an earth rod.

 

[marcuswareham]

I've just removed my main fuse at the cut out and ran all my usual tests, 246v 0.22ze so it's good coming in. Like you say I think it's has to be potential difference especially if the hot tub is still recieving a voltage when the isolater is switched off. Could this voltage increase and be dangerous or will it always stay the same dependant on conditions, i.e if the ground is dry I do not feel it but if the ground is wet I do, will it still only be 0.2volts or could it get worse/be life threatening thankyou

If your supply Neutral breaks in it in the future from some ground works or something like that then the voltage in the tub could be life threatening,

The joys of money saving PME

 

[timhoward]

If your supply Neutral breaks in it in the future from some ground works or something like that then the voltage in the tub could be life threatening,

The joys of money saving PME

I genuinely don't know how to quantify this one. It comes up fairly often on here and I've raised it before too. If it happens, it's certainly a nightmare scenario.
But stats seem to suggest we are taking around 500 occurrences in about 25 million properties in a year. So chances of any given property having this issue are mathematically miniscule. As new builds are almost all PME and more supplies are converted the number of incidents are bound to marginally increase as there are simply more out there.
Thing is, we don't tell people they might die crossing the road to go and buy the beer to have in the hot tub even though it is far more likely. Thoughts welcome!

 

[Samhhh]

More and more I am thinking all hot tubs should be on a TT supply, as even if your supply appears to be TN-S there is a chance that elsewhere repairs or cable replacement has essentially converted your supply to TN-C-S (just a rather long 'S' there).

There arent many true TN-S systems anymore. As I jointer everytime we drop a section of cable in especially within our area the cable is always PME'd in the joint. Everytime a new substation is installed or a board change is done the legs in the substation out of the new board are pme even if they are being jointed onto a split supply.