Hot Tub Wiring

[mk1rob]

Hi,

I'm going to be putting a supply in for a hot tub. Something I haven't done before. I planned on putting a 6mm twin and earth from the consumer unit to an external rotary isolator, connecting the cpc straight through to a SY flex which will run to the hot tub. However, the company fitting the hot tub have said the Earth needs to be separate on an earth rod. So the cpc of the twin and earth terminates in the back of the isolator enclosure and the cpc of the SY flex connects to the earth of the rod. Is this correct? I've looked in the regs book but cant find anything on it.

Any help would be much appreciated.

 

[Andy™]

whats the earthing type in the house?

 

[mk1rob]

It is TNCS. Thanks

 

[Andy™]

then it should be TT'd since you shouldnt be exporting the earth... hope you have RCD's on it

 

[mk1rob]

Ok thanks for the help. The consumer unit is 17th ed. so has two RCDs if that what you mean? Is the hot tub likely have a built in RCD do you think if its going to be TT'd?

 

[steptoe]

Ok thanks for the help. The consumer unit is 17th ed. so has two RCDs if that what you mean? Is the hot tub likely have a built in RCD do you think if its going to be TT'd?

There is no such thing as a 17th edition consumer unit.

Depends where you put the rod as to how you connect it to the CPC,

Regardless of whether the hot tub has an RCD or not, you still have to protect the cable. 

 

[mk1rob]

The rod will be within a meter of the rotary isolator, and that will protect the SY flex. I ask about the hot tub having its own RCD as the RCD in the consumer unit wont provide protection for the hot tub if the CPC isn't connected through. 

 

[Andy™]

er... maybe look up how an RCD works? your earth even if 'connected through' still isnt connected to the RCD anyway

 

[steptoe]

:coat

 

[mk1rob]

Ok i'll do that thanks. When you say I shouldn't 'connect through' as shouldn't be 'exporting the earth', why is that?

 

[Tony S]

You seriously think a single rod is sufficient for something so inherently dangerous as a hot tub?

 

[mk1rob]

As said its not something I have done before so trying to find out the best way of going about installing it.

 

[apprentice87]

Ok i'll do that thanks. When you say I shouldn't 'connect through' as shouldn't be 'exporting the earth', why is that?

Have a think about what TNCS is and how and why it is different to TNS and what might happen??

john

 

[steptoe]

As said its not something I have done before so trying to find out the best way of going about installing it.

Do you know how to measure Ra,?

and do you have a meter that can measure it,?

 

[Doc Hudson]

The rod will be within a meter of the rotary isolator, and that will protect the SY flex. I ask about the hot tub having its own RCD as the RCD in the consumer unit wont provide protection for the hot tub if the CPC isn't connected through. 

Stop and have a quick think about how an external RCD'd 13A socket can protect a person using a double insulated electric hedge trimmer and they accidentally cut the flex then go and touch the live exposed wires. try and draw a sketch of the earth fault path, remembering that the supply flex is two core with no integral CPC. So if we have no CPC connected from the flex via the plug back to the earth terminal in the socket, does an RCD need a CPC through to the load for it to provide shock protection?

Doc H.

 

[Bruspark]

Agree with Doc

Earth leakage circuit breakers - check your local museum -  needed a fault return path to 'system earth'.  

RCD and RCBO's are best thought of as detecting missing current - i.e.  an amount > xx  mA that went out but didn't come back.  They don't care where it went, just that it went

However driving all but 100mm of a 2m earth rod through the floor of the Hot Tub should cover all the issues  :B

 

[Andy™]

slightly related, no idea what happened though

http://www.bbc.co.uk/news/world-europe-40388161

 

[phil d]

slightly related, no idea what happened though

http://www.bbc.co.uk/news/world-europe-40388161

Probably some of their dodgy wiring, I saw a picture recently of a joint box next to a pool with no cover on it, I'm sure we've all seen similar things, unfortunately in a lot of these foreign countries it seems to be a case of "well it works doesn't it" . We're already seeing this over here as migrants start tackling their home electrics.

Remember the one I had a few months back? Spanish bloke replacing light fittings, every joint twisted and covered in masking tape. When I pointed out it wasn't the right way to do it the reply was "why, that's how we'd do it back home".