contactors

[Big_Spark]

C.K.....if someone has used 20A contactors on a 40A potential load then they are a fool and to answer your question, YES it is under-rated.

Regarding the technical issue of connecting two circuits in this way, yes, as I said in my original reply, it is possible to interlock two contactors so that when one has power, the other does not, in fact this is relativly simple to achieve if you have anything like a reasonable understanding of electrical circuit to understand the wiring diagram or the principles behind a described method for doing this.

 

[c.k.]

Thank you for your reply.

 

[Big_Spark]

Update on this matter.

I have asked this question of the NICEIC Technical helpline and the reply I got was this.

Yes, electrically it is doable, and you could almost certainly make it comply with BS7671, however as such an install is open to abuse we would not consider it good design or good practise. The other aspect of this is what would be the position of the supply authority. Should a fault occur, or tampering, that alllows both showers to work together, the supply cable would get warm, the head damaged and the Supply authority may be inclined to prosecute or disconnect the supply. As a member of Staff of the NICEIC this is not something we would like to see in a domestic installation, the potential dangers outway the potential benefits, especially when installation costs are accounted for.

As this is the stance of the NICEIC on this matter, I will say no more on it as I am not about to encourage someone to undertake a task that I feel is above their technical knowledge or ability to understand, the dangers that could be introduced by doing this make giving out any such information on a public forum outway the discussion benefits.

C.K, sorry if this is not the answer you want to hear, but as a contractor I could be held legally liable for advice given out, and the NICEIC would certainly not be impressed with advise getting in to the wrong hands or a similar scenario.

 

[ban-all-sheds]

I've given this some thought, and I can see a way to wire it up with two DP 2-way (i.e. changeover) contactors and a couple of switches to control them.

It works fine - there is no way to have both showers on at once, and neither switch can preempt the other.

BUT - I can still see what I would term a "race-condition" where if both switches were off, and were simultaneously turned on, both contactors would cycle rapidly between off and not off (but not necessarily on), so some more thinking is needed......

BTW - I'm not entirely convinced by NICEIC's argument - they say it can be done, and it can be made to comply with the regs, but they don't like it because it is open to abuse, faults or tampering. Virtually any installation is open to those things. My CU is not locked to me - I can abuse it or tamper with it and possibly cause the head to be damaged, but I don't think NICEIC deprecate the use of unsealed CUs. Or do they?

 

[Big_Spark]

I've given this some thought, and I can see a way to wire it up with two DP 2-way (i.e. changeover) contactors and a couple of switches to control them.

Ban, if you really think about this properly, then you can actually achieve it with two contactors and a pair of 6A pull cords

Edited to correct my earlier typo..sorry!!

 

[ban-all-sheds]

I'm looking for a solution which does not have any switching outside of the 2 bathrooms. Each bathroom to have a switch which controls its shower. If bathroom A is on, operating the switch in B is to have no effect on A, and is not to be dangerous. And vice-versa. The only cooperation required is for people to remember to turn their shower off when finished so that the switch in the other bathroom becomes operational.

A single switch to control which bathroom has power is trivial and I wasn't going to bother - that can be done with 1 switch and 1 contactor, or just a 45A changeover switch....

Apart from the race condition, my idea works fine - the first bathroom to request the lock gets it, and the 2nd one has to wait until it is released. Only if they both go for the lock at the same instant does it all get a bit flaky. This is extremely unlikely to happen with people operating the switches, but not so unlikely if there was a power cut, and both switches were left in the on position when power was restored. I'm wondering if an additional contactor in one of the loops would introduce enough delay in one side to prevent the problem, but I don't like it - it's untidy.

 

[Big_Spark]

Bad post typo by be earlier, my post should have ended..and a pair of 6A pull cords

One in each bathroom of course!! Sorry, I was rushing to go to the pub!!

 

[ban-all-sheds]

So let me see if I've got this straight - I said I had a design with two contactors and a couple of switches, and you said that if I thought about this properly, then I could achieve it with two contactors and a couple of switches.......

 

[Big_Spark]

So let me see if I've got this straight - I said I had a design with two contactors and a couple of switches, and you said that if I thought about this properly, then I could achieve it with two contactors and a couple of switches.......

I'm looking into this at the moment..in between doing a lot of other things, and I am coming to the conclusion that it will not work with two contactors and two pullcords

 

[ban-all-sheds]

I'm looking into this at the moment..in between doing a lot of other things,

me too..

and I am coming to the conclusion that it will not work with two contactors and two pullcords

Well it almost works. But that's a bit like saying I almost avoided that pedestrian...

I'll email you my sketch...