Hot Tub

[DaveVector]

Hi Folks,
have been asked to remedy problems created by an 'electrician' who left his spurs and saddlebag in the understairs cupboard...
:cowboy:
Here is what there is:
Its a TT system
At the CU end is a 40A 30mA RCD, 4mm SWA run of approx 8 meters to outbuilding.
In the outbuilding a 63A 30mA RCD 2x 20A and 1x 6A mcbs.
One of the 20A mcb's feeds a 13A fused spur which has a length of 2.5mm flex intended for the hot tub connection.
The other is for sockets and the 6A is for lights.

My plan is to replace the 40A RCD with a 63A. Replace the 4mm SWA with 6mm (as per manufacturers info)
Put a 63A 100mA RCD in the outbuilding.
Replace the 20A mcb with a 32A and ditch the fused spur for a 32A rotary isolator.

Now my question is, do I need a separate earth for the outbuilding as the house is already TT? The earth spike is in the garden about 5 meters from the outbuilding and about 2 meters from the tub.

 

[Richard Burns]

what is the rating of the hot tub?

 

[DaveVector]

Info says 16A and 32A mcb type C required

 

[JD6400]

So are you leaving a 30mA RCD in the house but replacing the one out in the shed for a 100mA RCD ?

 

[DaveVector]

Intended to change house 40A /30mA for 63A/30mA and put 63A/100mA in outbuilding

 

[JD6400]

Why would you want a 100mA on the hot tub , and have you thought about discrimination ? Not trying to be smart , just trying to understand why you have gone this route .

 

[Des 56]

Intended to change house 40A /30mA for 63A/30mA and put 63A/100mA in outbuilding

I can not follow why you are intending doing so,please explain your reasons


Forum is freezing me out again,annoyed,is it only me that is now getting these probs ?

 

[Richard Burns]

There seem to be a lot of things wrong with both the initial install and your proposed changes.

I cannot understand why the hot tub requires both a 16A and a 32A type C breaker so I am misunderstanding something there.

The likely design current for the whole installation is likely to be less than 30A (unless the hot tub is actually a 7kW hot tub), therefore the supply cable should be OK.
The installation of 2 RCDs in series is pointless, but an RCD is required at the start of the circuit, so changing the 40A 30mA RCD for the 63A 30mA RCD would be fine, however the far end should just have a switch in that case.
If you want to install a 100mA time delayed RCD then this would be required at the upstream end not the downstream and the 30mA should be at this end.
A rotary isolator would be OK for the hot tub, though a cooker switch may be neater if it is inside.
You could put an additional earth rod in near the tub as a further aid to maintaining a consistent earth.
2.5mm flex seems small for a 32A load but OK for a 16A.

that is all I can think of.

 

[DaveVector]

aah. Ok. Was trying to achieve some discrimination at the load end. But the existing TT system has sidetracked me.
Please advise on the best way to install this system

 

[JD6400]

Mate I have the feeling the electrical gestapo are on the way as I type , Richard has pointed you in the right direction so with that I am off !:willy_nilly:

 

[Richard Burns]

The design of the system has to come from you and it has to comply with the regulations, as you will be the one notifying building control and signing the EIC.
I have given some pointers but you need to be able to justify your decisions and you also know the system and the appliances in detail whereas we are on the outskirts and could get things wrong.

 

[DaveVector]

Many thanks Richard, I had initially thought of just an RCD at the supply end, but was then trying to protect the cable separate to the outbuilding, before I asked myself the 'do I need another spike' question. Maybe I need to stop and start thinking again tomorrow.

 

[DaveVector]

Thanks JD640 for the input. Will reboot my brian tomorrow and rethink....

 

[JD6400]

No worries . Now best keep quite before they notice the thread !:30:

 

[tanna]

Check ze at out building , if it's under tt max ze then no u don't need another earth rod, two rcds is pointless, one at either end just make sure the swa mechanical protection is earthed