Spa shock issue and competence to install

[TrevorM]

Hi all

I have an issue with a spa installation we had a few months ago.
Just as a bit of background info, I am a TV engineer and run a TV engineers forum, I have also completed many of my own electrical installations at home before things got a tricky without the relevant qualifications etc.

The install consisted of splitting the tails, installing a new metal clad fuse box with appropriate fuse and RCD and running the larger of the applicable sizes of armoured cable around the house to a 32a rotary isolator, then there is a length of armoured cable into the spa.
This was completed by a qualified electrician prior to the spa arriving.

The was fitted and has been OK.

Last night I decided to check the chemicals in the spa before getting in, this is highly unusual for me, checks are usually performed earlier.
I was barefoot on an outside block paved patio, I dipped the test meter in the water and got a good tingle through a few days old cut in one finger.

Put a non injured finger in and you feel nothing, put my shoes on and put the cut finger in and you feel nothing.

I have read through any posts referencing spa shocks on this forum but the solution isn't entirely clear to me. As I recall the armoured cable was three core and I can't remember what the electrician said or did about the earth conductor and the armoured outer, are they joined together????

Anyway, I have contacted the spa installer and they are coming out tomorrow.
I asked the following question, which probably didn't go down well.

Can you tell me what qualifications your installer has please?

The answer was "years of experience, knows hot tubs inside out etc etc" & "was approved as competent by the NICEIC"

It seems strange that a qualified electrician must install everything but someone with proof of nothing can be left to make the final connections to the spa given the current legislation as I understand it.

Can anyone tell me what the situation is regarding who can or can't make the final connections and should any tests have been completed on the installation before or after the installation of the spa. Should a record of installation have been left for us?

Considering the longish run of armoured cable around the house was there a more appropriate method to install it, I read a lot about rods being driven in the ground near spa's in the other threads.

Thanks for any advice offered. This is a little different to what my forum members normally deal with.

regards
Trevor

 

[Leesparkykent]

You probably have a tncs/pme earthing arrangement and the tingle you are feeling is the potential difference between true earth and the earth of the electrical installation. An earth electrode connected to the MET with a very low impedance could be used negate the potential difference.

 

[uksparks]

Hi TrevorM,

i cover Rushden so if you would like me to take a look and assess what needs to be done to resolve the situation let me know.

 

[Leesparkykent]

The installation could well be compliant/safe and you could still experience the tingle when barefoot so don't go in all guns blazing even though its defiantly worth having it looked at/checked

 

[TrevorM]

Hi
Many thanks for the quick reply, I was hoping that's what the issue was. It was suggested by a member on my forum as well.

So that connection must be to the MET and not at the spa end where it would be easier to to get deep into the clay soil.

Is there a requirement regarding the maximum length of cable from the rod to the MET and gauge of wire to be used?

And I assume that doing that work would require a part P qualified person rather than a competent person?

Thanks again.

Don't know how you guys on here cope, I have read the rule books and they seem wide open to be interpreted differently each time I read them.......

 

[Leesparkykent]

Out of interest TrevorM did you receive an electrical installation certificate for the new circuit? If you did, under the section of supply characteristics it should have a tick next to what earthing arrangement you have.

 

[Octopus]

Why don't you call the installer of the circuit back and get him to retest the circuit and compare the results with the certificate he gave you?

 

[Dave OCD]

To the OP- Are you absolutely certain the 'tingle' wasn't the cut on your finger reacting to the chemicals in the water ?

 

[uksparks]

Lee, what's your preference when it comes to hot tubs? I have connected a few, not many, and I normally connect it back to the supply earth as it's going to be better than any rod, however these were all sitting on decking limiting the risk. I know sticking rods in would be nice and cut off the supply earth but it's never going to compete.

however, I suppose you could always put a rod in local to the tub and connect it back to the met, gives you redundancy in the event of fault.

 

[TrevorM]

Thanks for the replies guys.

Yes, after researching this issue tonight and the help from this forum, I suspect all is OK and the potential difference is the issue.
Unfortunately I seem particularly sensitive to 50Hz and any AC voltages.

As I frequently work on live equipment I am especially careful and was probably a bit unfair to the spa installer over the phone.
Of course this on mostly isolated supplies but a hefty wallop can still be administered.
I shall grovel a little bit tomorrow and offer tea and cake :icon12:

And thanks for the offer.

regards
Trevor

 

[uksparks]

To the OP- Are you absolutely certain the 'tingle' wasn't the cut on your finger reacting to the chemicals in the water ?

I did wonder that, I know my finger would have tingled.

 

[uksparks]

Why don't you call the installer of the circuit back and get him to retest the circuit and compare the results with the certificate he gave you?

Thats not a bad idea, I know if someone called me to say that about my install I'd be round there like a shot as I would hate for something bad to happen and get the blame!

 

[TrevorM]

Hi
The electrician is customer of mine and did the work for me one weekend so I do not have a certificate.
I am going to call him for a chat but only got the answer phone tonight.

Yes, I am absolutely sure it is a shock, the cut provides a lower resistance to the rest of the skin.
I even popped my Fluke probes in the water and onto my skin and get a 2-3 VAC depending on pump speed.
And it doesn't happen with shoes on.

It might be interesting to try the same thing with bare feet and the metal kitchen sink.

 

[TrevorM]

So you wouldn't expect the spa fitter to have a Fluke or Kewtech to make certain everything was OK before making the connections?

regards
Trevor

 

[Darkwood]

Lee, what's your preference when it comes to hot tubs? I have connected a few, not many, and I normally connect it back to the supply earth as it's going to be better than any rod, however these were all sitting on decking limiting the risk. I know sticking rods in would be nice and cut off the supply earth but it's never going to compete.

however, I suppose you could always put a rod in local to the tub and connect it back to the met, gives you redundancy in the event of fault.

Have you ever considered extending the equipotential zone as well as rodding, this would give the best of both worlds, excellent low earth resistance with local equalised true earth to provided earth.