Putting in a second electric shower?

SwordofLight

Hi Everyone,

I'm just wondering if anyone might know if I can add an electric shower, not sure if fusebox will take the load of an extra MCB spcially for it.

At the moment, the top row of the fusebox is protected by a 63A RCD, and carries five 20A fuses. The bottom has the Mains 63A, four 10A fuses, one 40A fuse supplying a small kitchen extension with its own fusebox, and another 40A for an electric shower.

The little kitchen extension has three double sockets, a cooker, and a light. Maybe they could be spread out on the other ones and put the new electric shower on that one.

Any ideas?

Dayo93

We have 2 electric showers, we have a priority switch fitted so only one shower can be usedat anytime

adgib

Recently got a second shower, electrician put in a second fusebox,and as above, only one shower can be used

Sleeper12

You can have as many electric showers as you like in your home. As already stated above you can only run one at a time. A priority switch is around €150 at the moment on top of the cost of a new shower installation. You are well over the thousand euro mark all told

SwordofLight

@Sleeper12 that is crazy to install an electric shower. Sometimes I am in total shock as to how people in this country can afford things like that.

The only thing is, if you can't use both at the same time then why would you have the two of them? I am guessing when someone is in one bathroom taking a long time to do their nose powdering...

Currently I have one shower on the immersion tank, maybe I should keep it that way by the sounds of it, the only problem is people leaving the damned thing on with the cost of electricity :(

Sleeper12

I agree it's a lot of money. Plumber, electrician, shower, pipe fittings, electric cable, RCBO, isolation switch. It all adds up.

I've seen 3 & 4 electric showers in the same home. I was in a house yesterday with 6 bedrooms, all with their own onsuite and then the main bathroom. 7 showers in a 6 bed house. In the average house I'd suggest one electric & one power shower. Best of both worlds.

An immersion booster switch is an excellent invention. I have one myself with a timer for the last 15 years or so. Using the boost function turns on the immersion for 30, 60 and 120 minutes. It makes it impossible to leave the immersion on for hours on end or overnight.

https://www.amazon.co.uk/BRAND-OP-EBT2-ONE-BUTTON-TIMER-ELECTRONIC/dp/B07CT11W6W/ref=asc_df_B07CT11W6W/?tag=googshopuk-21&linkCode=df0&hvadid=375456255828&hvpos=&hvnetw=g&hvrand=13424727891696683432&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=1007850&hvtargid=pla-818909378379&psc=1&th=1&psc=1&tag=&ref=&adgrpid=77211061152&hvpone=&hvptwo=&hvadid=375456255828&hvpos=&hvnetw=g&hvrand=13424727891696683432&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=1007850&hvtargid=pla-818909378379

John.G

https://www.boards.ie/discussion/comment/119519415#Comment_119519415

The problem with a priority system is that if someone is using the non priority shower and someone starts using the priority one is that the non priority one is then switched out, a non priority system is where whichever shower is on, remains on. I would think that most systems are non priority.

Dayo93

https://www.boards.ie/discussion/comment/119538562#Comment_119538562

I didn't know it gave one shower priority over the other , I thought if shower 1 was on it would not allow shower 2 to be switched on a vice/versa. Haven't tried to put the 2 on together since switch was installed. Previous owner had 2 electric showers installed but no switch.

Sleeper12

There are different types of switches. Priority switches give priority to one shower. Non priority switches don't give priority. It's first come, first served.

thedart

Get a 16kva suppply and get rid of the poverty priority switch.

unkel

https://www.boards.ie/discussion/comment/119545448#Comment_119545448

LOL you can't run 2 electric 9-10kW showers from a 16kva supply at the same time

thedart

https://www.boards.ie/discussion/comment/119545486#Comment_119545486

Let’s do the maths lol, what’s 9kw in amps lol? Am I doing the lol right lol.

John.G

2x9kw = 18kw = 18kva @ unity PF?

2011

^^^ That is the maths alright!

John.G

https://www.boards.ie/discussion/comment/119544390#Comment_119544390

Have a look at your DB, a non priority will have 2 sensing relays as well as two contactors, a priority system will only have one sensing relay + 2 contactors, there will be 1A or similar marked on the sensing relay, you can do a practical test anyhow.

thedart

Having two 9kw showers going at full capacity which never happens but let’s keep with the analogy of text book non real life here as it’s seems to roll will have no issue on a 16kva supply.

Subzero3

Just get a gravity fed power shower and you won't need anything extra.

2011

https://www.boards.ie/discussion/comment/119546719#Comment_119546719

Please explain what you mean by "full capacity". You know that turning down the temperature dial still means that they draw the full load, right? It is not compariable to a cooker where a diversity factor can be applied.

These showers are either on or off. When on each will draw 9 kw of power so if both are on expect the combined load to be 18kW. Can a 16kVA supply support this? Sometimes, but not always.

Expecting a 16kVA supply to support this is not advised to put it mildly!

It is as simple as that.

cnocbui

https://www.boards.ie/discussion/comment/119530975#Comment_119530975

If you have a tank with hot water in it, you can ditch the whole electric shower nonsense and install a 3 bar pump and decent shower fittings which will give you a better showering experience overall. I installed such a pump in my house and plumbed it so that the whole hot and cold water circuits are via the pump, so every tap and toilet benefits from the increased rate of flow and pressure. After flushing, a toilet cistern refills in seconds; running hot water in the kitchen sink is fast so you don't have to go away and read a chapter in a book.

There are two showers and both can work simultaneously, though balancing the temperature is tricky. The main glich was that the pressure was a bit much for the toilet cistern inlet valves in that they couldn't close properly so kept fililing and overflowing and the pump kept running, but a trip to a plumbing supply revealed that the valves have a replaceable plastic flow restrictor and that you can get a high pressure one for very little. Fitting these was a doddle and solved the prolem.

unkel

https://www.boards.ie/discussion/comment/119545509#Comment_119545509

Are you trolling giving terrible advice on purpose or are can you not do maths taught in early primary school?

John.G

https://www.boards.ie/discussion/comment/119546719#Comment_119546719

Normally a electric shower has three power settings, 1 is no element powered = cold shower, 2 is one element powered = 5kw, 3 is two elements powered = 9kw, my shower has never been run on 5kw in the 15 years its been installed so in most cases reduced capacity never happens.

Calahonda52

36 kW Combi boiler, job done, no wires crossed

thedart

https://www.boards.ie/discussion/comment/119550049#Comment_119550049

Good to hear a knowledgeable poster in the breakdown of showers. Even at full capacity 37 amps approx I can’t see 74 amps tripping a 80 amp main mcb. That’s the maths.

2011

https://www.boards.ie/discussion/comment/119550738#Comment_119550738

I see that your calculation ignores the fact that homes have more electrical loads than just the shower. It also conveniently ignore the fact that most people use instantaneous showers at the highest setting. This is particularly the case in the winter.

Also a 9kW load draws just over 39.1 amps at unity power factor and more than that at lower power factors, not the 37 amps quoted.

This means that turning on a kettle, a washing machine etc. while the 2 showers are on would exceed 80 amps and that is before base loads are even considered.

Not only ill advised but against the regulations. Selecting the correct main fuse rating starts with calculating the design current properly.

thedart

https://www.boards.ie/discussion/comment/119551285#Comment_119551285

You said earlier that electrical showers are either on or off. You will break the chain with the back pedalling.

39.1 x 2 is still less than 80 amps. Maths are the maths.

I know several homes with 6kw induction hob, air to water, 2kw oven, 2 kw instant hot water and that’s before I mention they have a shower. That’s on a 12kva supply. Your argument is weak.

2011

https://www.boards.ie/discussion/comment/119551321#Comment_119551321

As John.G (the "knowledgeable poster" that you quoted) said: "my shower has never been run on 5kw in the 15 years its been installed so in most cases reduced capacity never happens."

In other words, diversity can not be applied to instantaneous showers.

Comparing this to a cooker and other laods that a diversity factor can be appleid to is a false equivalence.

thedart

https://www.boards.ie/discussion/comment/119551440#Comment_119551440

You are the only one comparing a shower to a cooker, why I don’t know. The maths speak for themselves.

2011

https://www.boards.ie/discussion/comment/119551485#Comment_119551485

Look at post numer 25 for the answer to your question.

Regarding maths 9000/230 = 39.13 not 37 (which is what you calculated).

No doubt you think this advice from Safe Electric is incorrect too:

"Q3 - I have been asked to install a shower in an existing installation doI need to be aware of anything?

A. Your installation should comply with annex 63B ensuring that you verify the mains tails, the main bonding are adequately sized. Also ensure that there is not already another shower already fitted if so a priority unit may be required. "

From this link:

https://safeelectric.ie/contractors/wp-content/uploads/sites/2/2018/09/2016may_news.pdf

thedart

https://www.boards.ie/discussion/comment/119551551#Comment_119551551

I shall contact safe electric on that interweb link. You should realise 230 would not be a average voltage in domestic houses. We regularly see 240 in rural locations.

2011

https://www.boards.ie/discussion/comment/119551600#Comment_119551600

I realize that some homes in Ireland can see 240 volts, yes. This only defeats your argument further. Let me explain, a 9kW shower units have a fixed resistance of around 5.9Ω

When a higher voltage is applied across a fixed resistance the current increases, otherwise known as "Ohm's Law".

See link:

https://en.wikipedia.org/wiki/Ohm%27s_law

Mathematically Ohm's Law can be expressed as I = V/R.

Where I = current, (amps)

V= voltage, (V)

R = Resistance, (Ohms)*

So at 230 volts the current = 230/5.9 = 39 amps (approx)

....and at 240 volts the current = 240/5.9 = 41 amps (approx)

* Impedance is considered equal to resistance for the above calculation to simplify the calculation. As the frequency is fixed this impedance is alos a constant.

Secondly, the main fuse is there to protect the cable. The rating of this fuse should not be considered the limiting factor. The limiting factor is the "connection capacity". This means that the maximum switched load should not exceed this value. Clearly two 9kW loads exceed this.

An enhanced single phase supply is 16 kVA which equates to 70 amps, see link:

https://www.esbnetworks.ie/new-connections/understanding-connection-capacity

I also see that you have decided to ignore all other electrical loads when calculation the design current for the installation. It is highly likely that a home with two instantaneous showers will have other loads which could be in circuit at the same time, such as:

• Fridge
• Cooker
• Kettle
• Immersion
• Lights
• Boiler
• Washing machine
• Dish washer

^^^What is the rationale for ignoring the other loads?

John.G

I was delighted with my house voltage which for many years was ~ 245V at the running shower terminals which gave me a 10.2kw shower, 9*(245/230)^2, in the past year or so it has fallen back to a more normal voltage of 235/238V, certainly noticeable in the shower in the winter with a mains temperature of ~ 7/8C.

Re two shower houses: I think the sensor(s) are set relatively low maybe around 4/5A, 1.0kw, be interesting if sensors set to say 24A (5.5kw) were available as you could then get two shower operation if set to 1/2 power during say 3 months of the summer with mains temp of at least 15C vs say 8C in winter, you would still get ~ 70% of the full power winter flowrate.

2011

We are going around in circles here. I think this thread has run it’s course.

It is clear that 18kW + all of the other house loads will exceed the 16kVA (and 70 amps) threshold.