how to wire 2 electric showers on the same circuit

[mecca76]

Hi I'm an apprentice electrician just finished Phase 2 , and today me and a forth year apprentice added a new shower to a house but added it on the same circuit utilizing electrical interlocking in the board so only one shower at a time can run.
I have learned basic motor control using contactors and switches NO/NC etc but haven't come across this way of using contactors i had a quick look at the wiring of the extra consumer unit but should of drawn a diagram down because now i have forgotten how it was wired and i cant work out how it is done, i have a brain block when trying to work out how the showers control the contactors if that is how its done. How if one is on the other can not come on and vice versa.
Can any one shed some light with a diagram or something as both my boss has no patience to help me and the the 4th year has too much of an ego and just fobs me off making me feel like the scum at the bottom of his shoe who knows nothing! I'm sure as soon as i see how it is done i will be like "oh ye its so damn simple" but its been a busy week and I'm tired so my brain's 'Mush' but I have to know how its done other wise it will keep bugging me.

thanks.

 

[GaryMo]

How are you selecting shower A or shower B? Two position selector switch?

If so then Shower A is fed via contactor A, Shower B is fed via contactor B.

From the selector switch (position A) wire through a N/C auxiliary contact on contactor B then to A1 (240v coil) on contactor A.
Again, from the selector switch (position B) wire through a N/C auxiliary contact on contactor A then to A1 (240v coil) on contactor B.

So, you want to use shower A, you select position A on the selector switch. Contactor A can only energise if contactor B isn't energised, hence the N/C contact. If contactor B for some reason had latched in then the N/C contact would be in an open position and contactor A would not energise.

This is electrical interlocking.
It's always a good idea to utilise a mechanical interlock as well for backup should one of the N/C contacts fail and the contactor latches in.

 

[briwire]

GaryMo's posting sounds spot on. On the mechanical interlocking. Sometimes in between the contactors sits an extra interlock so that if one contactor is energised it mechanically prevents the other form going in.

I'm disgusted that a tradesman is unwilling to help or pass on information to an apprentice. Have you told him directly that you are unsure, and could he show you how to do it. Any decent trademan would be more than willing to help.

Do you have any more information on the parts used?

 

[mecca76]

Thanks for the reply's Im pretty sure there was no selector switch to select A/B shower was just your standard 10 square from the CU to the pull cords And no switch near CU.
I didn't actually ask my boss properly about this set up as it was mainly the higher level apprentice i work with who wouldnt help me. But in the past my boss really seems to have no patience used to snap the answer at me which is hard to understand sometimes as I'm from England originally and the strong Irish accent can be a little fast for me, anyway enough ranting i will be more direct and ask him tomorrow. And if i feel i'm not learning properly working for him i will have to look else where for a new employer
Regarding the Contactors below are a couple of photos i took with my mobile as i was interested in the set up but there not good enough to see the wiring routes. I see the RCBO for the Shower circuit, and the 6A MCB for the control circuit but from there I'm not sure where the wires are going, or how the control produced. Maybe you can enlighten me especially on the smaller Grey interlocks with there use along side the larger Contactors in the photos.

 

[breezer]

its something to do with what ever those things are either side of the contactor

my guess is they are some type of current sensing device to operate the contactor

which ever one comes on first gets the supply

 

[mecca76]

ye i was just thinking that aswell as it had a symbol on the front which looked like a contactor symbol with the switch state symbol but had (I) for current on it or something like that.
Makes a bit more sense now.
So the current sensor in the small contactors is the select switching as such.
So if Shower A draws current through current sensor contactor A the N/C contact on it for the control circuit is connected to the main contactor for Shower B then opens the circuit and de-energizes it, so no power for Shower B and vice versa. Down side is the contactors are constantly energised. And the sensors must be specific to the current drawn as i remmember now that there was a problem when we tested the set up out and both were powering on at the same time so the little grey contacts must have to be regular contactors so when the pull cord is pulled to close the circuit the small contactor is energised and then opens the control circuit path to the other shower.
Correct me if I'm completely wrong here.

 

[breezer]

probably.

without seeing what they are its hard to tell

 

[GaryMo]

Have you got a make and model number of the possible current sensing devices?

 

[mecca76]

unfortunately not but the make im guessing would be the same as the others in the board 'Garo' no idea of No part and cant see it on the website.
Don't think i will be back there again, but if i am ill check it all out again. and write down details as it defiantly a good one to remember.

 

[Steve]

Use the macro focus on your camera if available, for close ups.

Part number probably written on the part.

 

[securespark]

I believe you when you say the other guy is trying to make you look like you know nothing.

However, I believe that he knows nothing - you have more knowledge than him.

Why? Because if he knew something (and really wanted to make you look small) then he'd be telling (or showing) you how to do it.

The very fact that he hasn't speaks volumes to me.

Move companies. Your boss sounds like the sort of boss you could do without. Get one who cares.

 

[GaryMo]

^^^^^^ I totally agree.