2 electric showers

[17thman]

A client wants 2 electric showers, both at 9kw. Now I have talked to him about having a hot feed one from a tank (3kw) heater (no combi) as 78 amps, plus cooker and all, will trip cut out. He is having a think but i am too. Anybody got the simplest way of ensuring that only one shower can be used at a time, such as running the supply through a manual switch/changeover situated on the ground floor to choose the up or down shower. Old parents living in a downstairs part of house with younger part of the family in the rest of house using the upstairs bathroom.

Thanks

 

[Chri5]

3 pole change over switch for manual use.

Pretty sure it can be done automatically (so only one can be used at a time) via a contactor.

I'm sure one of our more learner-ed guys will put me right on this

 

[rebuke]

You could presumably put in a 2-way switch driving a contactor which supplies the two showers (switch would probably have to go outside the bathroom unless you can get a 2-way pull cord switch).

You'd need some way of indicating whether the shower has power or not so the user knows whether to flick the switch, but a neon of some sort should be easy enough.

However, given that doing this would mean that one user could switch a shower off while another is using it anyway, would it not be easier just to inform the user that they can't use both at once, and then supply both showers from the same breaker so that if they do it only trips the breaker and not the entire house power?

 

[Chri5]

A design with built in over load isn't really a kosher way of doing it.

So waiting for a 40/45a RCD to pop, isn't really the way forward.

 

[trey]

I have something similar. A 45A electric flow boiler and a 37A electric shower. I solved the problem using a contactor that cuts out the boiler like a thermostat would.

In your clients case you could do something similar, but you'll have to find a contactor that can take the current for 9kW. If you do get a solution make sure that they get electric showers with motorised on off. That way if someone tries using one shower while the other is on the shower won't start, rather than just getting them very wet with ice cold water.

 

[17thman]

Thanks, the problem with instucting them is that is you can not rely on them using them singularly and built in overload protection seems wrong. If automatic, it could lead to "shower wars", bursting out of the bathroom in the nod and screaming upstairs. On individual mcb's the cut out could blow. Manual seems the lesser of two evils,

 

[tSpark]

I personally would always try and steer a customer away from fitting a second electric shower, Even if you can only use one at once, whats the point? you might aswell wait for the first electric shower to come free!!
Usually if a family is going out (for a meal etc) they are all getting ready at the same time so you can bet your last pound they'll want to use the showers at the same time,

I would always suggest a mixer, or if compatible with hot water system a power shower. You can get some decent wall mounted models for about the same price, They go in the same place as an electric shower the only difference is you need a hot feed but the biggest difference is, some of them only pull about two amps so you save on cable costs straight away, and your not heating water, you have already got sat in a tank (in most cases).

 

[Steve]

There is a very clever (but complex) way of powering two showers with an automatic changeover, which uses the pullswitches to energise contactor for the relevant shower. But the contactor will not close until the other contactor is off - both contactors need an aux normally closed contact, which powers the other contactor via the relevant pullswitch. It also has the added bonus of being able to use smaller cable to wire the shower switch, and a different switch altogether. Shower switches, IMO are an inherently bad design.

Something like this:

Criticism welcome - have i missed anything?

 

[17thman]

ingenious steve. I much appreciate it. So 1 shower user cannot dispupt the other until switch is opened. there would probably be a need for double pole isolation maybe?

 

[Steve]

I thought that. The whole lot could be fed remotely with a 50A MCB (as a submain), then split this locally with A CU, with MCBs to the two showers and a small MCB for the control circuit. Possibly house the contactors in the CU, depending on location of the showers and switches. The DP switch of the local CU allows total isolation.

One shower cannot interrupt the other, but if someone is using one shower, the pullswitch for the other shower can be turned on ready for when shower one is turned off.

Of course, this relys on them using the pullswitches, and is a relatively expensive solution!

 

[holmslaw]

..

 

[Steve]

Indeed there isn't a simple solution to that holmsaw, but my method goes some way to automating things as much as possible. Perhaps use a contact on the actual shower unit, instead of the pullswitch, to tell the system that the other shower cannot have power. This way, its not relying on pullswitches. But I appreciate warranties would be void if we started poking around inside shower units and attaching bits here and there.

Oh, and I'd mount the contactors on a big wooden board, just for the fun

 

[AMEdinburgh]

Thank you Steve, as I think you have solved my earlier post "Triton Body Drier" as essentially this is exactly what we would have with a body drier and an autoclave, both rated at 9KW.

No one seems to fault your design and so I'm most grateful too.

 

[ban-all-sheds]

Criticism welcome - have i missed anything?

What happens if you remove the power to the entire shower environment, pull both switches to On, and then restore the power?

 

[sparkyspike]

The same thing if two people pull the switch at the same time?