Hot tub installation !

[SPARTYKUS]

Its not just about a fault on the tub, you should TT a hot tub, its all about the potential difference between true earth and the MET (PME)

Its the failure of the PME thats the worry here,

Why? because 1 in ten million have temporarily lost the neutral that is subsequently fixed pronto?

Plus class 1 fittings in and around the tub could be a problem.

personally i would TT a hot tub

So you prefer to rely on a device thats proven to be unreliable and subject to high failure rates (the RCD) for disconnection! Theres a lot more chance (probably several orders higher) of the RCD failing than the PME neutral being lost.


Don't get me wrong I am not a fan of PME (TNS all the way) but .... the logic puzzles me. Loss of neutral is unheard of. And fixed quickly the miniscule few times it happens. RCD failure is rife and often never checked, fixed or found. Especially when they're fitted by a "friend" that has 'acquired' the board and RCD and has no registration, invoice, and more importantly, test equipment. Changed a few things for a mate who had the board changed 8 years ago, as above, RCD was kaputt. Probably never worked. How would we know? It was never tested.

 

[Chr!s]

So you prefer to rely on a device thats proven to be unreliable and subject to high failure rates (the RCD) for disconnection! Theres a lot more chance (probably several orders higher) of the RCD failing than the PME neutral being lost.


Don't get me wrong I am not a fan of PME (TNS all the way) but .... the logic puzzles me. Loss of neutral is unheard of. And fixed quickly the miniscule few times it happens. RCD failure is rife and often never checked, fixed or found. Especially when they're fitted by a "friend" that has 'acquired' the board and RCD and has no registration, invoice, and more importantly, test equipment. Changed a few things for a mate who had the board changed 8 years ago, as above, RCD was kaputt. Probably never worked. How would we know? It was never tested.

How would you know if the Earth was lost on a TN-S? That's one advantage of PME, the DNO are alerted to it.

Each system come's with risk, non are infallible.

Broken PEN'S, it hapens, quite rare

RCD'S failing, it happens, more down to not testing the RCD quarterly or the system to which it connects to than the RCD itself.

TN-S loss of Earth, it happens, though very little TN-S in most area's now, certainly Domestic anyhow.

 

[SPARTYKUS]

Hi Chr!s

good point re loss of earth on TNS. Not sure. Assume most losses would be because cable is severed or damaged, isn't the outer usually the earth on TNS?

I'm just a cynic and suspect they dropped the idea of having 3 hard lines back to the sub station as it is (clearly) cheaper to have 2 instead.... all about money.

I agree, nothing is infallible.

Not sure about the quarterly testing. I have come across a few that operate satisfactorily on the test button, but do not operate when tested (ramp, x1, etc) and have been replaced). So as mentioned, nothing is infallible including the test button!

TNS a dying breed.

Don't know much about the construction, etc between a house and substation of a TNS cable. Would love to though!

 

[Knobhead]

Don't know much about the construction, etc between a house and substation of a TNS cable. Would love to though!

Here you go!
View attachment 14514
1/ Outer sheath (PVC)
2/ Armouring
3/ Bedding
4/ Sheath (lead or lead alloy)
5/ Fabric tape
6/ Worming (filler)
8/ Insulation
10/ Conductor
The picture is of a MV cable so I've missed some bits out that aren't used for LV

 

[electric will]

That's interesting, so it's not the armour used for the earth conductor, it's a lead sheath which is actually deeper inside the cable

 

[SPARTYKUS]

So, are there two conductors inside Tony?

 

[electric will]

It looks to me that the picture is of a 3 core cable, with a lead sheath then a swa outer for mechanical protection

 

[SPARTYKUS]

Yes me too Will.