Power Shower Feed, external run legal??

miloharrisson · Feb 25, 2023

Hello, hello, long time listner, first time caller...

So, I have an issue in a house I'm trying to get ready to rent. The plumber has installed a power shower despite my asking him to install a mixer type. He's not gonna come back and fix it, and I havent paid for shower.

The issue I have is getting power to the thing. I've literally just had it carpeted so really dont want to be ripping them up, and dont want to have to retile the bathroom. Then someone suggested running power around the outside. The house is an end terrace, and the consumer unit is on an outside wall. I'm wondering if there is anything in the regs that would prevent me running a high csa flex around the outside and drilling thru the wall at each end??

Around 14m run and 8.5kw, I make it 6mm2 flex

All help gratefully recieved

Regards

Milo

MJPD29 · Feb 25, 2023

Running outside with cable is fine. Wouldn't use flex though, swa more suitable.

miloharrisson · Feb 25, 2023

Hey, thanks for your reply! I didn't think swa would be required as it'd start a 2m above ground, and run straight up to 3.5 odd?

LewisM · Feb 26, 2023

Can't really use flex as a supply cable, use NYYJ as it's UV stable has relatively decent mechanical protection and it's easily available by the meter.

6mm² 3 Core NYY-J Cable Black - 100Mtr Drum

davesparks · Feb 26, 2023

LewisM said:
Can't really use flex as a supply cable, use NYYJ as it's UV stable has relatively decent mechanical protection and it's easily available by the meter.

6mm² 3 Core NYY-J Cable Black - 100Mtr Drum

Why can't you use flex?

pc1966 · Feb 26, 2023

H07RN-F flex with ferrules on the ends would be acceptable if it is adequately supported and not at risk of damage as it is outdoor/UV resistant. NYY-J is stiffer and tends to sit better, and no need for ferrules.

One thing about going out through a wall and along is to take care of the cable's minimum bend radius. Typically that is 6-8 times the cable diameter and for 6mm 3C it ends up about 10cm, i.e. think of wrapping around a 20cm / 8" diameter pipe. It is big by wall exit standards!

Using some 25mm PVC conduit outside and 6mm T&E might be better as it can bend tighter in the "flat direction" if done with care to line up that way. The conduit would protect against UV light and looks nice and straight (assuming well installed with support saddles at sensible intervals). Something like these at the two ends so the cable can exit through the centre it to the wall's hole:

25mm PVC Conduit Terminal Box Black (Sold in 1's)

Provision for brass earth terminal

www.cef.co.uk

LewisM · Feb 26, 2023

davesparks said:
Why can't you use flex?

Just seems rough to me but you are correct

Regulation 521.9.1 permits the use of ﬂexible cables for ﬁxed wiring if they’re of the heavy duty type or the risk of damage is low or protection against mechanical protection is provided.

littlespark · Feb 26, 2023

You wanted a mixer, so why can’t another plumber supply and install a mixer?

It might be a simpler solution than external wiring.

The circuit would require rcd protection and need to go through an isolator at the bathroom before the shower. Plus working at height outside…

Taylortwocities · Feb 26, 2023

miloharrisson said:
The plumber has installed a power shower despite my asking him to install a mixer type.

I assume that your DHW is heated with a gas boiler? If so, remember that electricity is more than 3 times the cost of gas, so you'll be paying £££ for the plumber's mistake every time you have a shower.

I totally agree with Littlespark.

littlespark said:
You wanted a mixer, so why can’t another plumber supply and install a mixer?

It might be a simpler solution than external wiring.

brianmoooore · Feb 26, 2023

We've had this on here before - the OP says 'power shower'. That's a conventional mixer shower using a pump to increase the flow rate, NOT a shower that uses large amounts of electricity to heat cold water.
The OP might have meant 'electric shower' of course, but that can't be assumed.

littlespark · Feb 26, 2023

brianmoooore said:
We've had this on here before - the OP says 'power shower'. That's a conventional mixer shower using a pump to increase the flow rate, NOT a shower that uses large amounts of electricity to heat cold water.
The OP might have meant 'electric shower' of course, but that can't be assumed.

The OP also said 8.5kW... so large amounts of electricity

brianmoooore · Feb 26, 2023

So it's not a 'power shower' then. Anything but. The flow rate from a 8.5kW shower is likely to be pathetic, even when compared to a tank fed mixer shower installed in a bungalow.

pc1966 · Feb 26, 2023

LewisM said:
Regulation 521.9.1 permits the use of flexible cables for ﬁxed wiring if they’re of the heavy duty type or the risk of damage is low or protection against mechanical protection is provided.

Indeed, helpfully referencing BS EN 50565-1 which I'm sure we have all bought?

OK, stop laughing at the back!

This page has some hints as to what would be considered acceptable here:

BS EN 50525 Cable | Eland Cables

View Eland Cables' range of flexible cables manufactured in accordance with BS EN 50525. Technical support, fast quote and same day despatch available.

www.elandcables.com

For flexes it seems the heavy duty ones all start 'H7' (so 450/750V max rating) so our old friend H07RN-F is indeed acceptable here, even if not the ideal choice.

nicebutdim · Feb 26, 2023

While the use of flexible cable may be permitted, I'm not sure it's something that should be recommended without detailed knowledge of the installation.

HO7 may be perfectly acceptable for a short external run to a light, but may be entirely unsuitable for a 14m 37A shower supply that runs through fabric of building and upwards externally from a height of just 2m. It's certainly not something I'd be comfortable with in my own home.

HO7 may be farily durable where general wear and tear is concerned, but its cut resistance is minimal. Suitable containment would resolve any issues, but would also push costs far beyond that of SWA.

Perhaps it is impossible to route this cable internally (unlikely), but I can't imagine installing this externally in exposed HO7 and thinking it was a job well done. In line with early suggestions, I'd be inclined to think NYY-J at a minimum (or SWA) and not expect overall cost to be any higher than if flex was lashed in.

This thread seems to be another example of technicality triumphing over practicality and suitability, while little consideration is given to actual advice offered to a trainee.

pc1966 · Feb 26, 2023

nicebutdim said:
Perhaps it is impossible to route this cable internally (unlikely), but I can't imagine installing this externally in exposed HO7 and thinking it was a job well done. In line with early suggestions, I'd be inclined to think NYY-J at a minimum (or SWA) and not expect overall cost to be any higher than if flex was lashed in.

Very true. My point was not that H07RN-F is a good choice, just it is a perfectly acceptable choice in terms of regulations.

As I mentioned before, the bend radius is a serious practical issue if you just drill out and then want the cable going 90deg from that path. All 6mm 3C round cables, SWA, NYY-J, or H07RN-F are roughly the same diameter and have roughly similar bend radius. True it is far easier to bend H07RN-F sharply, but that does not mean you should!

Going inside is a far better option, but if outside I still think T&E in some plastic conduit is going to be easier to run without unacceptably sharp bends, or having to cut some fancy slot/curve in the wall to allow a sane radius (probably a poor idea anyway from a physical strength point of view).

nicebutdim · Feb 26, 2023

pc1966 said:
Very true. My point was not that H07RN-F is a good choice, just it is a perfectly acceptable choice in terms of regulations.

As I mentioned before, the bend radius is a serious practical issue if you just drill out and then want the cable going 90deg from that path. All 6mm 3C round cables, SWA, NYY-J, or H07RN-F are roughly the same diameter and have roughly similar bend radius. True it is far easier to bend H07RN-F sharply, but that does not mean you should!

Going inside is a far better option, but if outside I still think T&E in some plastic conduit is going to be easier to run without unacceptably sharp bends, or having to cut some fancy slot/curve in the wall to allow a sane radius (probably a poor idea anyway from a physical strength point of view).

I wasn't aiming criticism at you or any specific person.

Every point made in this thread has raised valid points, but in such discussions the overall response to a trainee or DIYer can be less than ideal.