shower plumbing & electrics

[Fred]

Hi,

My mother would like her electric shower replaced. The hot water header tank is in the airing cupboard, not the loft, so I think the shower is higher than the tank meaning negative head, which may make a pumped shower expensive. Unless anyone knows better?

It may also confuse her having to wait for a tank of hot water rather than shower as and when she likes, so for both reasons we may stick with what she knows and do a like for like swap.

I haven't looked at the cable yet. Hopefully the CSA will be stamped on the side. I had a feeling it was quite meaty but the MCB is only

32A, which limits us to a 7.5kW shower. Is there a reason an electrician would fit 40A capable cable but fit a 32A MCB?

I haven't looked at the old shower to see its rating but it is very, very old. Perhaps it is

[Roger Mills]

If you're doing a like for like replacement, why is there any plumbing to do? Can't you use the existing pipework?

[Fred]

The existing pipe goes up into the loft into the most inaccessible corner (behind a chimney) and it has recently frozen, which is what had prompted the decision to upgrade everything. Since the basin is next to the shower cubicle, I could run a new pipe from that and there would be no danger of anything freezing and not having to crawl through the loft. Really it was the pipe that needs changing but I thought I may as well change the medieval shower it is fitted to at the same time.

[Adam Wadsworth]

You will be lucky to have the CSA stamped on the cable. You will probably have to measure the cable.

With 4mm cable you are stuck with the 7.5kW shower.

As for the plumbing, then anyway you want it. Through the wall or buried are both fine.

[Windmill]

He was discussing the idea of either keeping an electric shower of some kind, or of fitting an ordinary shower instead. Though maybe his post wasn't quite as clear as he could have made it.

[andrew]

There are a couple of other shower options than electric or pumped. Venturi showers can successfully use the cold water pressure to draw hot water up out of the tank -

don't know if that model is still available, but others are.

Alternatively,

either of those are sensible solutions depends on the layout of the existing setup.

A

[Fred]

I suggest you re-read the original post.

I said that the existing electric shower was fed from a pipe in the loft. A pipe. I never said that this was fed from a header tank. FYI whoever fitted the shower decided it was easier to take the rising main into the loft and across the ceiling and down into the bathroom, hence there is a pipe in the loft and it is fed from the mains.

I knew someone would suggest that the electric shower be replaced with a power shower, and I quite agree that the latter is much better, but the header tank is lower than the shower (i.e. negative head) and this is why I talked about header tanks elsewhere in the post.

[Fred]

Thanks. I thought I had seen T&E with 1.5 or 2.5 printed on the sides but perhaps I have imagined that or perhaps I have just been lucky with the brands I have seen. Before Harry chips in, of course I would not dream of using such small cables for an electric shower!

I've been and had a look at the cable to the shower and as you expected, the grey insulation (where it enters the isolation pull switch) has nothing printed on it. Is there a foolproof way to tell

4mm^2 and 6mm^2 apart? Stick a vernier caliper across the conductor with the power OFF?

The CU is in the room beneath the bathroom so the cable run is quite short (so possibly could be changed without too much hassle) but all the cables run up the wall in some sort of trunking and then under the floorboards together so I guess I need to check about grouping derating too.

Thanks.

[Adam Wadsworth]

gives a good guide for the external diameter of the outer PVC sheath.

Adam

[Fred]

[Fred]

Thanks. I'm reading using agent and whenever anyone posts a link to the faq, I always see a "3D" after the equals sign. Have I got a setting wrong somewhere?

I think in my earlier posts I was worrying whether it was 6mm^2 or

10mm^2. It seems more likely that the choice is now between 4mm^2 or 6mm^2. If it is 4mm^2 then that would explain the 32A MCB because isn't that the limit for 4mm^2?

I've never seen 4mm^2 T&E. From what I have read here, people don't like it because the cpc is too small. Perhaps that will be another clue to help identify it?

Are 7.5kW showers worth bothering with? Most seem to start at 8.5kW, with 9.5kW being a common option. I worry that putting in another

7.5kW model might be disappointing. I think it might be best to change the cable. The CU is "squared D". I see their mcbs are available from toolstation. Who are square D; are they a good make?

I would think if you are fitting an electric shower it is best to go for the most power-hungry one you can find? A 10kW model could be ruin at 8kW but an 8kW model could never be turned up to 10kW. That's my reasoning; is it flawed?

TIA

[Mike Humphrey]

This allows special characters to be posted by encoding them as a sequence beginning with "=". This then requires an actual "=" to be encoded (so it's not mistaken for the start of an encoded character), and an encoded "=" is "=". Possibly Agent doesn't understand quoted-printable encoding and shows you the encoded version.

Mike

[ARWadsworth]

If the CU is a new one and match Toolstations MCBs (an slightly older CU may have different MCBs) then that is fine.

Yes, get the highest powered one that you can that is suitable for your cable.

The difference between 4mm and 6mm cable is easy to check if you have a bit of 2.5 T&E knocking about. The cpc(earth) of 4mm T&E is 1.5^2 the same as the cpc of the 2.5 T&E. The cpc of 6mm T&E is 2.5^2 - the same size as the

2.5 oddly enough:-)

Cheers

[Andy Wade]

Assuming you're familiar with 2.5 T&E, or have got a bit to hand, look at the earth conductor in the 4 or 6 mm^2 cable. Then:

- if it's 6 mm^2 the earth will be the same size as the L & N conductors in the 2.5 sample;

- if it's 4 mm^2 the earth will be the same size as the earth conductor in the 2.5 sample.

[Fred]

That was my worry, that they may have changed the design. I can't remember when the house was rewired but it is definitely in red and black, so how long ago is that? 2006? I think it must have been rewired in the early 2000s but that's 10 years ago. Will they have changed in that time?

If so, can you buy "old" mcbs or do you have to look on ebay?

Thanks. That's clever.

I have a horrible feeling it will be 4mm^2, otherwise why use a 32A mcb?

I know fat T&E is expensive but I'd only need what, 5 metres ?, at most so if I had to put 6mm^2 in, it wouldn't be the end of the world. I suppose you'll say that if I am changing the wire to go to 10mm^2?

Re. the other reply about venturis. They are a good idea, thanks, but the URL you gave said they need a 30cm head. I think the header tank is more or less at shower height; in fact the shower is probably higher than the bottom of the tank, so this rules out venturis. I think it rules out power showers because all the neg. head pumps I have seen are in the region of £400

The wall is hollow, so that's some good news but with my luck, I'll want to drill through a stud. Assuming it's got some studs. I have a zircon detector but IME it is useless.

Thanks again.

[dennis]

If its along length of cable they could use 6 mm^2 to avoid voltage drop. You would still fuse it at 32A if that's what the fitting instructions said.

Probably, its hard to make cable too big, it just gets harder to fit in the terminals and to bend. ;-)

.

[Fred]

Thanks. I'll have to measure the conductors to see. Let's hope I am lucky and they rewired in 6mm^2 but used a 32A MCB because that was all that was needed by the (presumably) 7kW shower.

Since the wall is hollow, could I thread plastic pipe inside it or would it need supporting at regular intervals? I don't want it falling off and flooding the place!

Thanks

[dennis]

You can get coils of plastic pipe so there wouldn't be anything to fall off inside the wall. I have had plastic pipe in my system for 30 years and nothing bad has happened yet. I do know of copper pipe that has failed in less time (but there is a lot of copper pipe that old and not much plastic that old).

[PeterC]

That's what I did, 30 years ago when 7kW was the norm., then fitted a 40A MCB for the 8.5kW unit - both on 6mm² cable.

[ARWadsworth]

I am:-) And for only a few pennies more.

Not my link mate.

Of course there will be studs in just the wrnong place! Measure the existing cable first and satart from there