Another Hot tub install

[Gazthesparky]

I have my tin hat on because I know this has been done to death and have read through a lot of the old posts.

I just wanted to run my proposal past a few of you and see if there is anything I have missed as its always good to get someone else's view.

Customer is needing a 32amp supply and hot tub company has said they require a 6mm supply with an isolator and flex left for them to connect.

My plan is to run a 10mm 3 core swa to a 40amp isolator from a new 2 way consumer unit Henley blocked from the tails. There is a Isolator on the current tails so will keep this and it will mean that there is one form of complete isolation. I have done the calculations and a 6mm will suffice with a volt drop of 11.2v so its on the borderline so hence going a larger size cable. It also allows for future proofing.

Now this is where it gets a bit messy. The supply to the property is PME. I intend to use the PME for the hot tub supply supplying it from a 32amp RCBO in the house. I am also intending to install an earth rod am I right in thinking that this gets installed at the hot tub end of the SWA? the idea is that should there be a PEN failure there is an earth path and the potential between the floating PEN earth and true earth is reduced as far as possible.

am I right in thinking that the rod does go at the hot tub end and not by the intake position of the property?

I am going to mount the isolator onto some uni strut installed into the ground. There is a fence panel 1 meter from the hot tub so too close to the tub. Also the fence doesn't seem too safe so I want to install my own support.

Finally they have also asked for a double socket by the tub again, I'm going to keep this 2 meters away from the tub. I am thinking of running a separate cable back to the house so this can be isolated as the customer is wanting to plug fairy lights in so the customer can switch them from the house. Im just wondering if i'm over complicating it though and should I just spur off the hot tub supply and install a fused spur and double socket

Thanks to any replys

 

[Ian1981]

If you are installing an electrode to supplement the existing PME then the electrode can be anywhere outside but to save on running cable, I’d install it as close to the point of entry (Where you drill the cable out) to the building as you can, so the run is short.
Obviously be weary of underground services like drainage etc.

 

[buzzlightyear]

This would come Andy for you professional electrician a guide for hot tubes NIC EIC
Summer 2020.

 

[stevethesparks]

Unless you get a really low Ra on your rods, you may just increase the step potential around the rod in the unlikely event of a lost neutral.
Why not just TT the hot tub and use the same earth system for the socket outlet as it will be in fairly close proximity? I would also opt for a DP RCD/RCBO personally.

I take it you are not commissioning the hot tub? What I have done in the past is supplied both pme and TT at the isolator, not connected the two together, and have marked each as such.
Put the ball in the court of the commissioning/installing company they can choose one or the other or choose to connect both together.

 

[telectrix]

and locate the socket outlet at least 3m from tub. if numpty wants to plug in an extension, not your problem.

 

[Gazthesparky]

Unless you get a really low Ra on your rods, you may just increase the step potential around the rod in the unlikely event of a lost neutral.
Why not just TT the hot tub and use the same earth system for the socket outlet as it will be in fairly close proximity? I would also opt for a DP RCD/RCBO personally.

I take it you are not commissioning the hot tub? What I have done in the past is supplied both pme and TT at the isolator, not connected the two together, and have marked each as such.
Put the ball in the court of the commissioning/installing company they can choose one or the other or choose to connect both together.

that is a good idea providing both types of earthing but the written paperwork that has been provided to me by the customer from the hot tub company states that they do not provide any wiring and they require 5meters of flex left connected to the isolater. They just connect up the flex and if it’s not as requested then they charge for a return visit. So I get the feeling they are not interested what they have just as long as it looks like they normally have.

with regards to the DP RCBO I am going to go down that route but the customer is wanting another DB installing so they can fit a hob in the future as there current one is full so I was going to install a second consumer unit and use RCBOs.
I’m just not sure how these DP RCBOs fit do they need a separate enclosure or could I fit a consumer unit and cut the bus bar back and fit the DP RCBO at the end with a link from the neutral bar ?

The isolator will be at least 2 meters away from the tub and the socket 3 meters away.

I am still thinking of going down the supplementary rod road just incase the loss of a PEN conductor

 

[pc1966]

I’m just not sure how these DP RCBOs fit do they need a separate enclosure or could I fit a consumer unit and cut the bus bar back and fit the DP RCBO at the end with a link from the neutral bar ?

A few of the normal CU single-wide RCBO are DP-switching, but only have the over-current trip on the phase side. I know the Wylex/Crabtree ones are like this and it helps for testing, etc, and someone mentioned that Fusebox ones might be.

Other full DP RCBO (i.e. they have over-current on both poles) might be OK as the end-of-busbar device, as you suggest, where the 2nd pole is then fed from a neutral wire link.
[automerge]1597649829[/automerge]
Just checked, the Fusebox RCBO are not DP switching so would be unsuitable for a TT style of supply isolation for an open PEN risk.
[automerge]1597650022[/automerge]
Also checked and it is the Crabtree 'Starbreaker' miniature that is DP switched, not the 'Loadstar' ones.

 

[Gazthesparky]

A few of the normal CU single-wide RCBO are DP-switching, but only have the over-current trip on the phase side. I know the Wylex/Crabtree ones are like this and it helps for testing, etc, and someone mentioned that Fusebox ones might be.

Other full DP RCBO (i.e. they have over-current on both poles) might be OK as the end-of-busbar device, as you suggest, where the 2nd pole is then fed from a neutral wire link.
[automerge]1597649829[/automerge]
Just checked, the Fusebox RCBO are not DP switching so would be unsuitable for a TT style of supply isolation for an open PEN risk.
[automerge]1597650022[/automerge]
Also checked and it is the Crabtree 'Starbreaker' miniature that is DP switched, not the 'Loadstar' ones.

Thanks for this

So basically its a double pole switching RCBO that I am requiring, has anyone got any other suggestions as to how install a DP RCBO whilst installing a new consumer unit for the customer to have a spare ways to future proof it

Also found this
32A Double Pole 2 Module C Curve 10kA 30mA Type AC RCBO - https://www.cef.co.uk/catalogue/products/921330
it says it is double pole switching so it switches the neutral.


Did also find this one From Fusebox single module and it appears that it is double pole switching maybe install a consumer unit with main switch and this rcbo leaving a few spare ways for other RCBOs
FuseBox RTAMB32 Miniature RCBO 32amp Double Pole A Type - https://www.gil-lec.co.uk/fusebox-rtamb32-mini-rcbo-32amp-a-type

cheers

 

[pc1966]

Did also find this one From Fusebox single module and it appears that it is double pole switching maybe install a consumer unit with main switch and this rcbo leaving a few spare ways for other RCBOs

OK, so it looks like there are two types of Fusebox RCBOs as well! That one is DP switching, but this one (which I found earlier) is not:

FuseBox RTA063230B 32A RCBO Type A

FuseBox RCBO 32A A Type

www.gil-lec.co.uk

[automerge]1597656760[/automerge]
I have never had one of the Fusebox CUs, etc, to play with but a few folk on here like them as the budget choice-to-go. They do reasonably priced CU with SPD as standard and, as it appears now, they have DP-switching RCBOs are a good price as well.

If you are happy with them just go for a Fusebox 2nd CU for the hot-tub with that DP RCBO and a few spare slots for anything else they need in the future.

 

[Gazthesparky]

OK, so it looks like there are two types of Fusebox RCBOs as well! That one is DP switching, but this one (which I found earlier) is not:

FuseBox RTA063230B 32A RCBO Type A

FuseBox RCBO 32A A Type

www.gil-lec.co.uk

[automerge]1597656760[/automerge]
I have never had one of the Fusebox CUs, etc, to play with but a few folk on here like them as the budget choice-to-go. They do reasonably priced CU with SPD as standard and, as it appears now, they have DP-switching RCBOs are a good price as well.

If you are happy with them just go for a Fusebox 2nd CU for the hot-tub with that DP RCBO and a few spare slots for anything else they need in the future.

thanks PC1966 I wasn't having a pop regards the fusebox RCBO its just good to share knowledge of new products.

i'm probably going to go for the fusebox with an spd and the double pole switched RCBO

 

[marcuswareham]

I am still thinking of going down the supplementary rod road just incase the loss of a PEN conductor

Would TT not be safer than a rod attached to the PME earth, as with TT there is no risk from open PEN conductor. And for the suplimentery rod to be of any use it would need to be around the 2 ohm mark (depending on the fault) which could be hard to achieve

 

[Gazthesparky]

Would TT not be safer than a rod attached to the PME earth, as with TT there is no risk from open PEN conductor. And for the suplimentery rod to be of any use it would need to be around the 2 ohm mark (depending on the fault) which could be hard to achieve

I get that but it seems silly to go to the effort of isolating the extremely efficient and low resistance PME earth path and solely relying on the fluctuating and higher earth rod path.

I know this is the big debate and can see both sides. If only we had something like a regulations book to give definitive answer lol

Failing that I scrap the rod idea and just use the PME and hope that there is never a PEN Failure.

My gut is telling me that although I need to achieve the 2 ohm mark on the rod to be successful it is better being there and providing some sort of earth path than not being

Im also going to install a DP RCBO so this will disconnect both live conductors should a fault occur.

 

[littlespark]

I never understand this instruction from a hot tub installer.... “leave an isolator and 5m of flex“

so they want you to leave a connected flex, with bare ends, and the only protection is hoping no one turns on the isolator.
even padlocking it and leaving the key in the hands of a normal person (the customer) is questionable.

 

[Gazthesparky]

I never understand this instruction from a hot tub installer.... “leave an isolator and 5m of flex“

so they want you to leave a connected flex, with bare ends, and the only protection is hoping no one turns on the isolator.
even padlocking it and leaving the key in the hands of a normal person (the customer) is questionable.

I know right I am planning to connect the flex up in an adaptable box and leaving the isolator switched off. That way I know the cable is terminated safely. My only concern is the hot tub company not liking it and trying to charge the customer for a return visit as they just want to see a coiled flex ready to go.



This is the paperwork they provided to the customer even there so called example of the supply rough no glands on the isolator the SWA swooping and cable tied to a couple of brackets and the fact that they have left a coil of cable potentially live. this is how they are wanting the install to be left

 

[Mike Johnson]

These are double pole switching: Electrical Wholesaler - Hager RCBO 2P(1P+N) 6kA B-40A 30mA A Class AD940J - https://www.electricalwholesaler.ie/products/switchgearfuses/switchgeardistribution/rcboresidualcurrentbreakers/hagerrcdrccb2p40a30maaclassad940j. All the double pole switching units that are definitely double pole are two module wide, all those that say they are and are only one module wide on investigation are not.

 

[stevethesparks]

These are double pole switching: Electrical Wholesaler - Hager RCBO 2P(1P+N) 6kA B-40A 30mA A Class AD940J - https://www.electricalwholesaler.ie/products/switchgearfuses/switchgeardistribution/rcboresidualcurrentbreakers/hagerrcdrccb2p40a30maaclassad940j. All the double pole switching units that are definitely double pole are two module wide, all those that say they are and are only one module wide on investigation are not.

What about the Wylex NHX miniature rcbo's, it's a switched neutral.

 

[SJD]

Just checked, the Fusebox RCBO are not DP switching so would be unsuitable for a TT style of supply isolation for an open PEN risk.

The older Fusebox RCBOs are not DP, but the new compact ones are DP, for example RTAMB32.

 

[pc1966]

The older Fusebox RCBOs are not DP, but the new compact ones are DP, for example RTAMB32.

I found that later, once the OP linked to the newer model!

 

[Mike Johnson]

I am surprised that Wylex have been able to produce a switched neutral RCBO in a single module, what surprise's me mostly is that if and I emphasise the if they are able to achieve a 3mm air gap (unverified) on both the phase and neutral in that space I would like to see how they do it, because that is what is required under EU specifications.

 

[nicebutdim]

I am surprised that Wylex have been able to produce a switched neutral RCBO in a single module, what surprise's me mostly is that if and I emphasise the if they are able to achieve a 3mm air gap (unverified) on both the phase and neutral in that space I would like to see how they do it, because that is what is required under EU specifications.

Can't find a single module DP RCBO tear down, but here's one of the Crabtree/Wylex single module RCBO/AFDD which crams even more into the same space.

View: https://www.youtube.com/watch?v=gdVntVfP6Q8