time for a new electric shower?

[Harry Bloomfield]

Assuming the 30/32amp MCB is the correct one, then it certainly ought to be 6mm.

[ARWadsworth]

4mm T&E is fine for 36A if clipped direct. The biggest problem is if Stuart is using a BS1361 semi enclosed fuse such as as this is not allowed to power a 4mm cable due to the 0.725 derating factor applied to the cable when using these fuses.

[stuart noble]

I suppose I'll just have to take the shower front off and have a look :-)

[ARWadsworth]

^^^^^^^ meant BS3036 (I have a hangover)

[stuart noble]

It's a Wylex NB30 type 2. From the consumer unit the cable goes into plastic trunking then AFAIK runs with the joists (so presumably lying on the ground floor plasterboard ceiling) for 4 metres. I will check the exact size, but I don't imagine they would have fitted 6mm for a shower

25 years ago somehow.

[John Rumm]

If you have a combi, then you will probably find a mixer shower running from the combi will dwarf the performance of even the best electric. (even the most asthmatic combi can usually deliver HW at a 20kW heating rate). No need for pumps since the combi output will be mains pressure.

[robgraham]

Give me to the end of this week and I'll tell you - I've what I think is a daft customer doing just that. I've to replace one Mira with another because she thinks the efficiency has fallen off - and in Edinburgh we're soft water so it is unlikely to be furring up.

[John Rumm]

Nominal rating clipped direct 47A actually. Even buried in an insulated wall its still 35A.

See table here:

[ARWadsworth]

touching the inner wall surface.

The rating is 23.5A if the cable is not touching the inner wall surface.

[John Rumm]

Which installation method did you have in mind here? (note we are talking about 6mm^2 here).

Having said that, the important point obviously is the cable rating is heavily influenced by the circumstances.

[ARWadsworth]

See

[John Rumm]

in contact with the plasterboard (so basically not far off being buried in insulation all round!). The 32 Harry quoted is for similar but with the cable also in conduit. Neither of which sound appropriate for the OPs installation, which sounds more like combination of clipped direct, in free space, and possibly in conduit in contact with PB etc.

[stuart noble]

I did give that some thought. The output is 10L per min at 35 degC. I assume the hot water automatically has priority over the heating when both are running?

[John Rumm]

Compare that with the 3.5L per min you will get from a 8.5kW shower for the same rise...

With the vast majority of combis, yup - a diversion valve routes all of the primary flow through the DHW plate heat exchanger. Not usually a problem unless you have a number of teenagers who are going to effectively embargo the heating for hours at a time! ;-)

[stuart noble]

A no brainer then. It would of course escalate into a total gutting of the bathroom, but that's probably overdue anyway. Summer job.....

[stephen.hull]

On our other house we fitted an 8kw Gainsborough shower that was direct mains fed and it was fantastic, we had excellent water pressure so the delivery was high, so when we moved house seven years later we purchased an alternative 8kw Gainsborough shower hoping the output would be the same but is was disappointing.

We live in the same area and still have very high water pressure so we thought the new shower should have the same output, but it had very poor delivery, this is also mains fed, we got so fed up with the poor performance we changed it for a 9kw shower after a couple of years but find this also to be very poor.

My conclusion is the newer showers seem to be restricted perhaps to save water consumption, also at work we had new like for like taps fitted but the water flow from the new taps is extremely poor compared to the old taps, perhaps again these are also restricted to save water flow.

Stephen.

[John Rumm]

A simple bar mixer is relatively easy to retrofit without too much disruption ;-)

[John Rumm]

Water consumption is really a non issue with electric showers, since they are naturally limited by how fast they can heat the water. Remember that fine control of water temperature is achieved not by varying the power input but by regulating the water flow rate.

Even a 10.5kW shower can only deliver 10500 x 60 / 4200 / 35 = 4.3 lpm with a 35 degree rise. In the winter with the cold supply coming in at 5 degrees that means that or less at a usable shower temperature.

Some taps are fitted with aerators to reduce the water use and make it fell nice for hand washing. However a common cause of poor flow is fitting taps designed for mains pressure (i.e. the majority) on traditional british style gravity fed water systems.

[stephen.hull]

I fitted a ball lever valve to the inlet pipe hoping to alter the flow rate but it made no difference at all.

Using the same water flow at the same temperature during the summer made no difference either, you have to turn the shower to almost cold in order to get a decent flow from the shower head.

I don't think the taps at work are fed from the mains, there are too many of them, although the new taps recently fitted do have these aerators.

Stephen.

[John Rumm]

Which suggests the limitation is heating power...

Depending on how deep in the ground your water main is, you may find relatively little variation in supply temperature over the year.

If you measure (bucket and stopwatch) what you consider a "decent flow" you will probably find its at least double what you could hope to heat with 10kW of input.