Wiring Brain Teaser

[SparkyChick]

This is another real life problem that I fixed this week and it lead onto quite a lengthy chat in the van about the components used, how they work etc. so I figured I'd post it for you guys to have a punt at.

The problem....

If any of you know Cardiff, you'll know all the apartments etc. that have gone up around the bay. Quality buildings It seems that some of them include air handling units that are running 24/7 providing forced ventilation. These units have, if you will, an overdrive mode that is engaged under certain conditions to greatly increase the air flow rates.

In the apartment in question, overdrive mode is triggered by the bathroom light, the en-suite light and the kitchen light. Unfortunately the 'controller' for this appears to be a pile of poop, with inadequately rated components that are failing, resulting in weird behaviour (the fan stuttering between normal and overdrive) and/or not going into overdrive at all.

The switching is handled by the 'controller' located in a plastic adaptable box by the consumer unit. It has 5 cables coming into it.

3 x 1.5mm single and earth - These provide a switched live supply from the 3 lights that trigger overdrive
1 x 1.5mm twin and earth - This provides the supply for the fan
1 x 1.5mm three core and earth - This provides the connection to the fan (Brown = Permanent Live, Grey = Neutral, Black = Switched live for overdrive mode)

For clarity, the lights are on a different MCB to the fan, but neither have any RCD protection. What the current controller consists of is largely irrelevant, just know that when one of the lights is turned on, it supplies 230v to the overdrive conductor in the 3C+E cable.

Have a punt at drawing up a wiring diagram that achieves the desired results with no unintended consequences

 

[Loki]

Hi @SparkyChick ,


Ok so here's my attempt at your latest brain teaser.

Spoiler

 

[SparkyChick]

Hi @SparkyChick ,

Ok so here's my attempt at your latest brain teaser.

Nice diagram... but think about the very last paragraph of my post... "that achieves the desired result with no unintended consequences", it's very important.

 

[Loki]

Nice diagram... but think about the very last paragraph of my post... "that achieves the desired result with no unintended consequences", it's very important.

Spoiler

Oh yeah ive just realised in my drawing if any one of the lights is on the switch wire will feed the other lights & they will turn on also lol

 

[SparkyChick]

When these things are going on, please put your comments/thoughts/questions etc. in a spoiler so people can choose to read it... or not

 

[Lucien Nunes]

Spoiler: It's a bit cheeky

Not having a neutral for the three trigger inputs that is electrically separate from the fan neutral. I know the current only needs to be tiny, but it shouldn't borrow the neutral by design, surely?

 

[SparkyChick]

Not having a neutral for the three trigger inputs that is electrically separate from the fan neutral. I know the current only needs to be tiny, but it shouldn't borrow the neutral by design, surely?

I wouldn't call it a cheeky spoiler... valid point is a better description, and one that, I'll be honest, didn't really cross my mind at the time.

Both the lighting and the fan are supplied by MCBs on a non-RCD portion of the board, and I only replicated with contactors what a PCB with relays was already doing, but yes it's not an ideal situation really.

I suspect it wouldn't be too much of a problem to put it right as the CU isn't too far away (read inches).

Something for me to consider more carefully the next time something like this comes up. Thanks for pointing out my error

 

[Jay 1987]

Here’s my attempt...

 

[Jay 1987]

The

Here’s my attempt...

the things in the middle are contactors (normally open) which need 230v supply

 

[Lucien Nunes]

Good so far, but there are some connections missing from the contactors. If you replace the anonymous rectangles with the standard symbols for coil and contacts, this will be immediately obvious.

You obviously have a clear grasp of what you want to achieve with the drawing and it conveys the information well, so I'd urge you to move to the next level, using correct circuit symbols and putting away the multicoloured pens .

 

[Jay 1987]

Good so far, but there are some connections missing from the contactors. If you replace the anonymous rectangles with the standard symbols for coil and contacts, this will be immediately obvious.

You obviously have a clear grasp of what you want to achieve with the drawing and it conveys the information well, so I'd urge you to move to the next level, using correct circuit symbols and putting away the multicoloured pens .

Good so far, but there are some connections missing from the contactors. If you replace the anonymous rectangles with the standard symbols for coil and contacts, this will be immediately obvious.

You obviously have a clear grasp of what you want to achieve with the drawing and it conveys the information well, so I'd urge you to move to the next level, using correct circuit symbols and putting away the multicoloured pens .

That took me 3 hours to work out lol seriously.....

 

[davesparks]

Here’s my attempt...

You've got the right idea, and I'm pretty sure you are on the right track to a suitable solution.

However you have created what is known as a borrowed neutral here, this is a very dangerous thing to do.
Your coil connections take a live from one circuit and a neutral from a different circuit. You must always connect to the correct neutral for the circuit you have used the live from.

I know this may sound abrupt or a bit harsh, and I don't want to put you off, but borrowed neutrals are very dangerous.

 

[Lucien Nunes]

True enough; however, according to SparkyChick's description that Jay will have followed, it was wired like that with the borrowed neutral, as I also mentioned above. So the original installers and makers of the relay gubbins are to blame for it!

 

[SparkyChick]

True enough; however, according to SparkyChick's description that Jay will have followed, it was wired like that with the borrowed neutral, as I also mentioned above. So the original installers and makers of the relay gubbins are to blame for it!

Absolutely, but I should have picked up on it and corrected it. Mistake on my part.

 

[Lister1987]

Absolutely, but I should have picked up on it and corrected it. Mistake on my part.

Play it cool, it was intentional and you were testing everyone.....right? ?