Unusual electrical installation query - 2 consumer units

[DrSee]

I've got a power shower (A) at one end of the house and that has

switched supply to the pump in the middle of the house. I'm installing another power shower (B) in a new extension which has separate consumer unit. I want to utilise the same pump and have switched supply coming from shower room (B) aswell.

The intention is, that either shower, when switched on, can activat the pump.

Is there a problem with phase or differential potential if bot switches are "on" at the same time - bearing in mind the two supplie come from different consumer units (but both are on the same externa supply and meter). One consumer unit has RCD, the other old fashione fuses.

Thanks

-- DrSee

[Andy Hall]

This isn't an acceptable or safe way to connect this up. For example, if there were a fault in the circuit supplying (A) it could still receive a supply via (B) and the pump.

There are several alternatives. Here are three:

- Rewire such that the same circuit supplies both switches and the pump.

- Use a relay on the new circuit - i.e. switch the coil from (B); and then have the contacts on circuit (A) in parallel with the existing switch

- Replace the pump with a flow activated one.

[Chip]

On Sun, 23 Oct 2005 21:29:59 +0100,it is alleged that DrSee spake thusly in uk.d-i-y:

Quick response would be "yes, there's a serious safety issue with that, it's lethal"

A contactor or 2 may be the way to go with this, but there are significant implications with even having supplies from 2 different CUs in the same enclosure, and having them connected to the same terminals on a wiring device is totally out I'm afraid. The danger of electrocution or fire due to a miswire is large, and even if these events don't happen, tripping of the RCD would occur immediately you connected the wiring.

Although this is a DIY Group, in this case I would suggest an electrician, the potential dangers make the cost worthwhile.

[John Rumm]

Yes! This is a *very bad idea*.

Adding a flow switch to energise the pump might be the simplest solution.

[DrSee]

Thanks for the advice guys. I did suspect that it was not on.

The pump already has a low pressure flow switch but I want to be abl to isolate it easily from both shower rooms.

I th>

I think you mean a form of relay switch so that the circuits are kep totally independant yet one can switch the other. Can you point me i the direction of such a device.

Maplins have a range:-

this what you mean? Obviously I need 240v but which one is mos appropriate? Many thanks

-- DrSee

[Matt Beard]

Please don't do it!

If nothing else, consider the poor plumber, in a couple of years time, who is called out to fix a faulty shower pump (by now you have moved house and the new owner doesn't understand the setup). He flips the power off at the CU, then sets about dismantling the pump. A minute or so later, big bang small amount of smoke and exit plumber stage-left!

[DrSee]

There is an existing isolating switch just next to the pump. An modifcations to the wiring before this will still leave this isolato in situe. I do not now intend having two supplies, just one supply from one CU with relay switching from the shower rooms. I now need to know which relay switch(es) would be most appropriate. Thanks DrSe

-- DrSee

[Dave Plowman (News)]

I'd go for an octal base type. You can get bases for these with screw connections. DPDT types handle 10 amps and should cope ok with a pump.

They're a pretty universal design and places like TLC sell them too.

[John]

Why? If it works it works if it doesn't it needs sorting. Extra superfluous switches are of no practical use at all. You should however have means of isolation near to the pump for use in a maintenance situation. I can see no justification in having a device intended to respond automatically to a demand then put a switch in its way to prevent this response. If your system has a drip or other such problem which causes the pump to run due to pressure loss (A negative head pumpset) at times other than needed, then fix it (or whatever other leak is present). Perhaps you like to switch off your automatic pir security lights during the day too?

[DrSee]

I understand what you are saying, however, the existing shower (A) ha a pump isolator switch wired in conjuntion with the light in the showe room.

So to use shower (B) I would have to turn on the light in shower (A first. It would be more convenient to be able to switch it on from shower (B aswell

-- DrSee

[Gizmo]

And you wonder why they brought in Part P

Jes' !!

[Clive Dive]

I like that!; 'potential dangers'...very good!

[DrSee]

Well, you'll all be relieved to know that, with the advice offere here, I've decided to do away with all complicated switching method and simply use a dedicated switched fused spur to power the pump an use the low pressure flow switch to activate it from either shower. This means disconnecting a redundant circuit and not adding any more. Happy guys? :

-- DrSee

[John]

It would be more convenient to remove the light interlock and use the flow/pressure switch

[John]

good idea!