Hot tub - 2 core or not 2 core

[bernardgreen]

That's why larger csa is needed for Bonding Conductors.

The real reason for large CSA in bonding conductors is that they are part of a circuit that has no fuse or MCB to limit fault current in that circuit.

Bonding the Main Earth Terminal (MET) of a house with PME ( Earth connected to Neutral ) to a low impedance ground such as a metallic supply pipe allows a portion of the Neutral load current to flow through the bonding top ground and hence to the Neutral of the substation on parallel to the Neutral conductor to the sub station..

When there is a lost network Neutral ( metal theft etc ) bonding conductors in houses may be called on to carry the full local area Neutral current to ground. In most cases the impedance to the ground will limit the current to a value that the bond conductor can safely carry. There have been several incidents reported in the media where a bond wire has over heated and caused damage to property.

 

[bernardgreen]

Hot Tub Electrical Safety

We are digressing from the main theme. The theme was safety of people using the hot tub and which earthing system carries the least risk of injury from electric shock.

People have varying sensitivity to small electrical potentials applied to their body.

A voltage that is a pleasant tingle to one person can be a muscle twitching painfull shock to another person.

The potential on the CPC in a PME installation can be a few volts different to the true Ground potential. With one foot in the CPC "earthed" water and the other on wet ground those few volts might produce in person A a mild tingle but for person B they create muscle twitches which may result in a fall and subsequent injury. The falll may also increas the area of body in contact with the voltage and hence the shock effect through the body increases

 

[JohnW2]

We are digressing from the main theme. The theme was safety of people using the hot tub and which earthing system carries the least risk of injury from electric shock.

Whilst I don't disagree with anything you say here, even what you write here is "digressing from the main theme" (i.e. the question in the OP).

The original question clearly assumed that the house's earth was being 'exported' (and we don't know what earthing system the house has) and merely asked whether it was acceptable to use the SWA, rather than a core of the SWA, as the CPC to do that exporting.

Kind Regards, John

 

[John D v2.0]

"Lost TN-C-S neutrals" are rare enough in the first place, and the chances of anyone touching a tap or shed light switch whilst standing with bare feet on the ground, at the very right moment, are ..... !!

We have all heard of situations eg "every time I touch X I get a shock". The neutral could have an intermittent problem for a while before it goes completely. Our lights were flickering since we moved in, then after 6 months it got worse so we called the supplier, turned out there was a broken cable under the road.
The other solution that hasn't been mentioned is to mesh under the hot tub.

 

[JohnW2]

We have all heard of situations eg "every time I touch X I get a shock". The neutral could have an intermittent problem for a while before it goes completely.

I think you're probably thinking of a 'partial fault', rather than an intermittent (but 'full blown') one.eutral faul

A neutral fault 'complete enough' to result in a dangerous N-E (true earth) potential (whether permanent or intermittent) would result in sufficient reduction in L-N potential that a lot of equipment/appliances would malfunction (or not function), so I imagien would fairly rapidly be detected, reported and rectified.

The other solution that hasn't been mentioned is to mesh under the hot tub.

Do you mean using just the mesh (i.e. TTing, which has been extensively 'mentioned'), or connecting the mesh to an exported earth? If the latter then, particularly with TN-C-S, one would then have the problem of needing an adequate bonding conductor - and the armour and/or a core of SWA may well not be adequate for that.

Kind Regards, John

 

[John D v2.0]

True, the mesh is just a way to reduce the step potentials rather then relying on the tncs earth being close to local earth, so it would have to be bonded using adequate.
The ideal equipotential zone wouldn't need any bonding, but in this case it would help as you can't get rid of the extraneous ground as easily. Another alternative would be decking though.

 

[JohnW2]

True, the mesh is just a way to reduce the step potentials rather then relying on the tncs earth being close to local earth, so it would have to be bonded using adequate.

Indeed - but, as has been discussed, an alternative is to NOT use the TN-C-S earth, but to just TT the hot tub, using a local rod, mesh or whatever. You would then, of course, be reliant of an RCD for ADS.

The ideal equipotential zone wouldn't need any bonding, but in this case it would help as you can't get rid of the extraneous ground as easily.

Well, yes, but the whole problem is in getting the earthed parts of the tub's electrics equipotential with the surrounding ground.

Another alternative would be decking though.

I'm not sure that I would want to rely on potentially soaking wet wood to insulate me from the ground - but it could be used as a 'belts and braces' measure.

Kind Regards, John

 

[deadshort]

Indeed - but, as has been discussed, an alternative is to NOT use the TN-C-S earth, but to just TT the hot tub, using a local rod, mesh or whatever. You would then, of course, be reliant of an RCD for ADS.
Well, yes, but the whole problem is in getting the earthed parts of the tub's electrics equipotential with the surrounding ground.
I'm not sure that I would want to rely on potentially soaking wet wood to insulate me from the ground - but it could be used as a 'belts and braces' measure.

Kind Regards, John

DS

 

[bernardgreen]

The original question clearly assumed that the house's earth was being 'exported'

Implied that the house's earth was being exported.
Hence my explanation of why exporting the house's earth to the hot tub could present a serious hazard to the safety of people in the hot tub. Exporting a house Earth to the frame of an electric garden lawn mower is not allowed ( or strongly not recommended ) due to the risk of the difference in Earth and Ground potentials becoming a shock hazard

 

[JohnW2]

Exporting a house Earth to the frame of an electric garden lawn mower is not allowed ( or strongly not recommended ) due to the risk of the difference in Earth and Ground potentials becoming a shock hazard

I'm not sure what 'disallows' it, but I can understand the concerns, hence that many may feel that it is 'not recommended'. One is then, of course, stuck with Class II equipment, since one cannot TT a moving object!

I would imagine that Class I equipment intended for use outdoors has not been produced for a long time, but I presume that it once was.

Kind Regards, John

 

[EFLImpudence]

There is, of course, a difference between 'not allowed' and 'not recommended' as with 'compulsory' and 'recommended'

It is unlikely that a hot tub has a metal outer casing.

Surely these hot tubs come with instructions and there are standard arrangements.
I have only found an American one which says it must be 'bonded' to nearby metal fixtures and the concrete pad.

How would this be achieved?

 

[JohnW2]

I have only found an American one which says it must be 'bonded' to nearby metal fixtures and the concrete pad. How would this be achieved?

Goodness knows. Am I also not right in recalling that all properties in the US have to be locally TTd (in addition to supplier-provided earth) - which presumably reduces/minimises the possible PDs between the installation's earth and true earth which so much concerns bernard?

Kind Regards, John

 

[bernardgreen]

Am I also not right in recalling that all properties in the US have to be locally TTd (in addition to supplier-provided earth)

The American local distribution system is often three phase HV ( 11Kv or more ) feed on poles along the street with tin can transformers hung from the poles. Each tin can provides providing an LV (110 v) to one or two houses. There is seldom an Earth ( or grounded ) conductor along the pole route and if there was it would be related to the HV supply and thus not suitable for providing Earth ( or Ground ) for the LV supplies to the houses.

 

[JohnW2]

The American local distribution system is often three phase HV ( 11Kv or more ) feed on poles along the street with tin can transformers hung from the poles. Each tin can provides providing an LV (110 v) to one or two houses. There is seldom an Earth ( or grounded ) conductor along the pole route and if there was it would be related to the HV supply and thus not suitable for providing Earth ( or Ground ) for the LV supplies to the houses.

Are you saying that nearly all the properties are individually TTd? If so, then the sort of concerns you express in relation to the UK presumably would not be applicable over there?

However, in terms of my comment, I thought that there was a requirement for an individual earth electrode at each property, even if there were a distributor-supplied 'earth' of some sort - but I might be wrong about that.

Kind Regards, John

 

[ban-all-sheds]

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

Shouldn't you, as designer and installer, know that?