advise please!

[ChrisRogers]

I am about to install a hot tub and other electrical items in my garden, so i will have a CU out in the garden fed by 16mm SWA. I am putting the CU in a large grey IP56 box. The lenght of te SWA to the CU is about 15m. I have it fed by a 50amp breaker in the CU.
My question is if i have a RCD in the CU feeding the cable, will i need one in the CU in the garden? Although its fed with a 50amp breaker, I'm putting it in a dedicated CU for all outdoor power. I am using a dedicated CU for all the outdoor power as it seperates it nicely, I have no room in my 21 module MK CU and it is plastic, so terminating 4 SWA cables into it would be a challenge. So I have a metal clad based CU on order. so my set up should look like this:

main incomming cable from REC
|
henly block----CU for house
|
CU for outdoor power (with 30ma RCD)-----assorted power
|
16mm 3 core SWA
|
CU in IP56 box for hottub and garden lighting

Thanks for your help

trust my explaination is clear enough

Chris Rogers

 

[plugwash]

seems fine to me

putting multiple rcds of the same rating one after the other is pointless and will make testing the install difficult

haveing the rcd in the first CU is fine just means you might have a bit of a walk if you trip it

finally
1: don't try to do this live
2: the main switches in all CUs should be off before pulling the service fuse(should eleminate risk of arcing)

 

[masona]

Out of interest why is the 16mm SWA is being use for ChrisRogers hot tub + garden lighting when my electrician fitted a 4mm SWA for my hot tub + garden lighting ?

Is it to do with the length of cable ? or is it because my hot tub only run on 13 amp ?

ChrisRogers, I buying the hot tub from the same company as you, does your hot tub run on 13 amp ? if not, perhaps that's why you need a bigger cable ?

Just trying to understand the difference !

 

[securespark]

You should use one rcd in the house (100mA) to protect the cable feeding the outside circuits, and another outside to protect the circuits themselves (30mA).

 

[ChrisRogers]

Out of interest why is the 16mm SWA is being use for ChrisRogers hot tub + garden lighting when my electrician fitted a 4mm SWA for my hot tub + garden lighting ?

Is it to do with the length of cable ? or is it because my hot tub only run on 13 amp ?

ChrisRogers, I buying the hot tub from the same company as you, does your hot tub run on 13 amp ? if not, perhaps that's why you need a bigger cable ?

Just trying to understand the difference !

We are using 16mm for a few reasons

1. We had some lying around
2. The hot tub is 20a
3. I thought i should put in the biggest supply possible, avoiding digging up the patio in a few months time.
4. It might be used to supply some power to a shed or garage at a later date so i was trying to think ahead!

 

[ban-all-sheds]

That's some thinking ahead!

16mm SWA is rated at 110A.....

 

[Big_Spark]

I concur with Securspark on this.

The cable should be protected by a 63A 100mA RCD mounted in the house.

The Consumer unit could have a similar rated RCD as the main switch, however this should have a 30mA rating NOT 100mA.

Chris, an alternative setup to this, which may make it easier to fault find if there is a problem would be this.

Mains at house....63A 100mA RCD for cable protection.

CU in Garden. Main switch 63A Double Pole Isolator

Then each circuit on it's own suitable rated 30mA RCBO. This would increase cost, but a fault on one circuit would not mean the loss of all of them, and would make it instantly easier to idendify which circuit had the fault on..should one ever occur.

Just a thought.

 

[ivyelec]

seems fine to me

putting multiple rcds of the same rating one after the other is pointless and will make testing the install difficult

haveing the rcd in the first CU is fine just means you might have a bit of a walk if you trip it

ATLEAST THIS WAY YOU WONT BE TEMPTED TO RESET AN RCD ON THE GARDEN CU IN THE RAIN!!!!!!!
finally
1: don't try to do this live
2: the main switches in all CUs should be off before pulling the service fuse(should eleminate risk of arcing)