Hot tub - 2 core or not 2 core

[Brownerg]

Hi there,

Im installing the cabling for a hot tub outside. I have already started and installed 10mm, 2 core armored cable through the garden. However, I have a feeling 3 core is required for most hot tubs.

The hot hub has not been selected yet but does the cabling require 3 cores? If so I'm digging up concrete! .

Can anyone help?

 

[pete50]

Select your hot tub and look at the wiring on that. I would be very very surprised if any hot tub didn't come with an earth wire and if it didn't have an earth wire then I, for one, wouldn't buy it. I would lay 3 core anyway. Having said that I am no expert.

 

[winston1]

This is notifiable work. Had you engaged an electrician, as you should have and will have to, this mistake would not have happened. Enjoy digging up your concrete!

EDIT. Maybe you could TT it. Your electrician, when you get one, could advise.

 

[Brownerg]

So I thought the armouring is used for earthing? Is that not correct?

 

[davelx]

So I thought the armouring is used for earthing? Is that not correct?

Depends on a number of things - sometimes it can be, other times it can't. Measurements and calculation are involved, which an electrician will need to be on site to do.

 

[Taylortwocities]

The steel armour is not a conductive as copper. As a result, using the armour is not always appropriate.
You should have installed 3-core.

For once, I am in agreement with Winston. You need some proper advice, on site.
I wouldn't want to jump into electrified water unless the job has been designed, installed and tested properly.

 

[Brownerg]

Thanks for your help davelx, I don't think Winston1 read my description properly. As I understand the armouring is required to be used as the CPC in any case.

 

[Taylortwocities]

The armour is required to be earthed, that is as a protection for the inner live cores.
The matter of whether the armour may be used as the earth for the appliance needs to be calculated using what is known as an adiabatic equation.

This will confirm if the armour will (or will not) carry a fault current sufficient to operate the CPD.

Want to know more? Here's your easy guide. CLICK

 

[Brownerg]

I came here to look for advice before I pay hundreds for a jack hammer, or pay hundreds for a sparky. I have seen many discussions on the correct use of armouring used as an earth, in fact 522.8.10 as I understand requires it. I have yet to see why it cannot be used, or should not.

I will of course get someone to check things out so i appreciate you need to say this, but I wanted to get some immediate advice to try and guage what or who I need to speak to first.

Shame I'm no clearer.

 

[bernardgreen]

For once, I am in agreement with Winston. You need some proper advice, on site.

I second that,

Expert advice is needed about the earthing method.

Exporting the Earth from house is one option but may not be the best option TT ( ground rod ) earthing of the water in the tub is another option.

RCD protection of the supply to the tub is essential

As I understand the armouring is required to be used as the CPC in any case

That is to provide protection to the cable should it be damaged. Where the earth cannot be exported to the remote location ( in this case the hot tub ) the armouring should be connected to the Earth at the supply end ( house ) and NOT connected to the CPC ( Earth cabling ) of the remote installation. This is the case where the remote location has TT ( ground rod ) earthing.

Why is TT earthing of the hot tub preferable.

The Earth in the house may be true ground ( when the house has a ground rod ) or the Earth may be derived from the Neutral supply to the house ( a PME system ). With PME Earthing the Earth is not at true ground potential but it is at the same potential as the supply Neutral

The Neutral potential in a PME is normally never more than a few volts different from true ground potential. Hence if the PME Earth is exported to the hot tub and its water then between water in tub and wet ground there may normally be a potential difference of a few volts. This voltage difference may be noticable as a tingle when getting in or out of the water. The hazard with exporting a PME Earth to a hot tub is that a fault or load inbalance on the supply network might raise the supply Neutral many volts above true ground and this would make getting in and out of the tub hazardous to health.

.

 

[Taylortwocities]

I was not implying water is electrified. Normally it will not be. My point was that Under fault conditions it can be. That's when adequate earths (and other safety measures) come into play.

In any event, this NEW CIRCUIT is notifiable work. Have you/will you be raising a case with LABC?

 

[Brownerg]

Electrified water comment retracted. Didn't know I sent it, apologies just some people here get on high horse alot of the time and appreciate detail on adiabatic equation.

You will be able to sleep tonight knowing the this NEW circuit will be registered when necessary to do so

 

[Brownerg]

Bernard green really helpful thanks

 

[EFLImpudence]

You will be able to sleep tonight knowing the this NEW circuit will be registered when necessary to do so

As it is necessary, the law says you must do it before you start - or employ a registered electrician.



Whilst everything that has been said may be correct, surely if the armour is adequate for ADS and protection of the cable then it is adequate for ADS to protect the hot tub and occupants.
An electrode certainly will not be - without the RCD - but may be required for other reasons.

Doesn't the problem of the armour being of insufficient size regarding conductance relative to copper only relate to bonding if it is required? - the usual reason for fitting an electrode.

 

[winston1]

I don't think Winston1 read my description properly.

I most certainly did. I even noticed you spelt armouring as a Yank would, but declined to comment on it as there were more important issues.