changing from SWA cable to twin flat in junction box.

[4xpaws]

I'm looking into wiring an outdoor hot tub.

2.5mm SWA cable going to an IP56 junction box mounted externally, changing to 2.5mm flat twin for internal wiring going to an isolator switch before going on to a 32 amp RCBO in the consumer unit.

I'm looking for info on how to do the change over of cable types in external mounted junction box. The SWA will be side entry. Can I then run the the flat twin & earth out the back of the box to get it indoors, or has it got to go side entry too through a glands before going inside. If it can go out the back how do I maintain the IP integrity of the box. Do I fit the same type of glands I used for the SWA and channel out a hole big enough to accomodate the glands?

The same applies too the isalotor, which will be mounted externally. I want the twin flat earth to enter and leave via the back of the box. Again what sort of glands do I need?

 

[Taylortwocities]

If you are going out of the back of the box with T&E then your best gland to use will be silicoln.

Just as an aside, as i am a nosey bstrd, what is the KW rating of your hot tub and what is the length of the cable run from the consumer unit to the tub?

 

[CallEdsFirst]

Yes! I thought 2.5 sounded a bit small too!

 

[Cremeegg]

Part P anyone?

 

[CallEdsFirst]

To be fair, Part P is not an excuse not to give advice! He may be well aware of the requirements to notify before starting work and fully prepared to pay LABC to inspect after.

Having said that, it might be worth explaining that if you dont know that you shouldnt put T&E into a BW20s gland, you might not know about part P and might be risking your life and a fine.

I like the idea of a recessed gland in a large conical hole behind the adaptable box though!

 

[4xpaws]

The tub needs a 6m cable run from the CU to the tub.
The heater's 3 KW bu then there's the pumps as well to include.
The tub's 20 amps (its a 3 seater).
So its either 4mm or 6mm SWA with a 32 amp RCBO?

Does the tub isolator need to be sited externally (at least 1.5m away from tub) or can it be located inside the house?

 

[plugwash]

unless you have got a good reason not too I stronly reccomend bringing the SWA into the house, external joints are just a source of potential problems. If you must join externally remember to use a CW gland for the SWA and put a drain hole in the bottom of the box (you don't want to create a situation where once water gets in it never gets out).

If you need to connect SWA to a normal plastic CU I reccomend screwing the gland into a through galv conduit box and then taking the inner part of the SWA throug the box and into the CU.

Remember armour must be earthed even if there is a seperate earth core.

 

[Lectrician]

Gewiss 4 x 4 x 2

 

[4xpaws]

Thanks for the advice to date!

-Does the isolator need to be sited externally? and in sight of the tub?

An alternative, rather than dig a direct tench for the SWA from where it leaves the house to the tub, is to run the SWA the long way round, above ground, fixed to the outside wall of the house to where the tub is closest to the house (just 0.3 metres away)

-How far above ground on the wall should the SWA be fixed?

-Also, running the SWA the 0.3m between the tub and the building. What are the alternatives to digging a trench? The ground there is paving slabbed (footing for the tub).

 

[ukants]

2.5mm SWA cable going to an IP56 junction box mounted externally, changing to 2.5mm flat twin for internal wiring going to an isolator switch before going on to a 32 amp RCBO in the consumer unit.

Check the current-carrying capacities of the aforementioned cables. 2.5mm T&E cannot be protected with a 32A rcbo (I'm assuming it's a radial). Also, don't assume the same sized SWA and T&E have the same CCC; they don't.

 

[Lectrician]

We generally spec 32amp for tubs - even if it has a lighter loading. The tubs we have commisioned are the same inside, but have jumpers on the PCB that moved around to prevent the heter and pumps operating together, and also to remove elements from the heating side to reduce loading.

There have been times when customers have complained of pool cooling, and the dealer has then recommended altering the jumpers on the PCB, which increases the current - hence we fit 32 as standard.

Depends hugely on installation, if tub is near the wall, I would be very tempted to use 6mm split concentric from DB directly out wall, cleated or clipped around to an isolator (two TRS glands in bottom of isolator), and then onto the tub. Duct the short length between building and tub. Isolator must be atleast 2m from tub edge to comply to swim pool regs which are the only regs that can really be considered suitable until the new edition comes out.

It is also very common to run SWA (again 4mm or larger), and take this through an IP rated rotary isolator - get one that is a decent size and allows loop in/out with SWA. The banjos can share a single hole for the nut/bolt then. I would use a gewiss 4 x 4 x 2 to change from SWA to T+E, and would prefer to see a gland used, but often drill a hole out the rear of the box, low down in the box. Seal this with either non-setting compound from BiCast, Perrelli or BICC, or use some silcon. Keep your through crimps/terminal blocks high up in the enclosure, and drill a small drain hole at the bottom. Always try to gland out the bottom of an enclosure, not the side.

RCBO in the CU is best.

Isolator does not need to go at "light switch" height. Fit it at the height you clip the cable around the wall - 300mm or so from ground. No need for it to be flying high - it just looks stupid seeing cables cleated up and back down!

Isolator should be outside - most tub maintenance companies (if you pay maintenance) need to be able to gain access to your tub and isolator when you are at work.