Wiring Brain Teaser

[Jay 1987]

Here’s my second attempt.....

No rectangles
No coloured pens

hahahah

 

[davesparks]

Here’s my second attempt.....

No rectangles
No coloured pens

hahahah

It's a good clear diagram which I find pretty easy to read.
But it may not work exactly as you are expecting it to.

If you were to turn on all three lights by their switches, and then turn off light 2 only by its switch, what will happen?
It may help to sketch what happens on the diagram with a pencil,

 

[Lucien Nunes]

Much more professional... but wrong!

Problem 1: Exactly as DS says. It's to do with where you are getting the feed to the contactor terminal 1's from.

Problem 2: The fan is supposed to drop back to low speed when none of the lights / contactors are on. But you have done something that will prevent this working...

You're close.

 

[Jay 1987]

Much more professional... but wrong!

Problem 1: Exactly as DS says. It's to do with where you are getting the feed to the contactor terminal 1's from.

Problem 2: The fan is supposed to drop back to low speed when none of the lights / contactors are on. But you have done something that will prevent this working...

You're close.

You make me laugh lucien lol

I don’t know where to go from here but I’ll look
and try again!

 

[Jay 1987]

It's a good clear diagram which I find pretty easy to read.
But it may not work exactly as you are expecting it to.

If you were to turn on all three lights by their switches, and then turn off light 2 only by its switch, what will happen?
It may help to sketch what happens on the diagram with a pencil,

It's a good clear diagram which I find pretty easy to read.
But it may not work exactly as you are expecting it to.

If you were to turn on all three lights by their switches, and then turn off light 2 only by its switch, what will happen?
It may help to sketch what happens on the diagram with a pencil,

Would I turn off the high powered mode also ?

 

[Lucien Nunes]

OK, I just looked on a bigger screen. Problem 2 is not as I stated. I thought the contactors were switching the fan neutral, which would have stopped it running at low speed with all the lights off. You have actually drawn a link from the supply N to the fan neutral commoning terminal, so I was mistaken about that. But, then, what is the wiring to terminals 3 & 4 supposed to achieve?

 

[Jay 1987]

OK, I just looked on a bigger screen. Problem 2 is not as I stated. I thought the contactors were switching the fan neutral, which would have stopped it running at low speed with all the lights off. You have actually drawn a link from the supply N to the fan neutral commoning terminal, so I was mistaken about that. But, then, what is the wiring to terminals 3 & 4 supposed to achieve?

Yes I found that problem out I have the supply Line going th

OK, I just looked on a bigger screen. Problem 2 is not as I stated. I thought the contactors were switching the fan neutral, which would have stopped it running at low speed with all the lights off. You have actually drawn a link from the supply N to the fan neutral commoning terminal, so I was mistaken about that. But, then, what is the wiring to terminals 3 & 4 supposed to achieve?

so now your saying I have a problem with supply for terminal 1 also what is the point of terminal 3 and 4 ?

 

[Jay 1987]

It's a good clear diagram which I find pretty easy to read.
But it may not work exactly as you are expecting it to.

If you were to turn on all three lights by their switches, and then turn off light 2 only by its switch, what will happen?
It may help to sketch what happens on the diagram with a pencil,

I don’t know mate from what I can see high powered mode would still work even if I turned off switch number 2. The only thing I can see as a potential Problem is terminal 2 may still be energised. But I don’t see how that affects anything when the light switch is off the circuit is broken. that means the coil should de-energise.

 

[Lucien Nunes]

Yes. You don't want to switch the neutral as the fan runs all the time, so you don't need the second pole (3 & 4) of the contactors. At the moment you have wired those contacts up, but then short-circuited them with a link from the supply neutral to the N commoning terminal. So those connections are completely redundant. The coils' A2 terminals and the fan need a neutral, and that's it.

But the problem Davesparks highlighted is what is commonly called 'backfeeding'. Suppose switches 1 & 2 are turned on, energising both of their contactors. Each will send a feed from the light switch through terminals 1 and 2 into the fan SL and the fan will speed up. So far so good. But when switch 1 is turned off, its light and contactor coil are still connected to the fan SL, which is still live as switch 2 and contactor 2 are still energised. What happens?

E2A having seen your last post. Yes, terminal 2 will still be energised from the other switch(es) that are on. Now consider that current will flow either way through the contactor contacts...

 

[Jay 1987]

Yes. You don't want to switch the neutral as the fan runs all the time, so you don't need the second pole (3 & 4) of the contactors. At the moment you have wired those contacts up, but then short-circuited them with a link from the supply neutral to the N commoning terminal. So those connections are completely redundant. The coils' A2 terminals and the fan need a neutral, and that's it.

But the problem Davesparks highlighted is what is commonly called 'backfeeding'. Suppose switches 1 & 2 are turned on, energising both of their contactors. Each will send a feed from the light switch through terminals 1 and 2 into the fan SL and the fan will speed up. So far so good. But when switch 1 is turned off, its light and contactor coil are still connected to the fan SL, which is still live as switch 2 and contactor 2 are still energised. What happens?

E2A having seen your last post. Yes, terminal 2 will still be energised from the other switch(es) that are on. Now consider that current will flow either way through the contactor contacts...

Mate, I’ve had enough today I’ll get back to you tomorrow

 

[davesparks]

I don’t know mate from what I can see high powered mode would still work even if I turned off switch number 2. The only thing I can see as a potential Problem is terminal 2 may still be energised. But I don’t see how that affects anything when the light switch is off the circuit is broken. that means the coil should de-energise.

The coil should de energise, but it won't.
The switch will be off (open) but the relay will remain energised because it will backfeed from the other switched lives.
The relay will be latched in that position, and the light will also stay on, until all three light switches are turned off.

Having terminal 1 directly connected to the coil defeats the purpose of the relay being in the circuit.

 

[Jay 1987]

Here’s my third attempt, taking into consideration all the feedback!

 

[Jay 1987]

Here’s my third attempt, taking into consideration all the feedback!

Is this attempt right? Or is it still wrong ?

 

[Lucien Nunes]

Spot on. Each light controls only the coil on its contactor. All three contactors have their contacts in parallel so that any one of them energised will operate the fan.

Of course, the neutrals of the contactor coils should really go back to the lighting circuit because neither that nor the fan circuit can be correctly isolated because of the interconnection by the 'borrowed' neutral. But that is how it was installed as we considered above.

One final point about the drawings. Consider the difference between
a) a wiring diagram and
b) a circuit diagram or schematic.

The wiring diagram shows each physical wire and where it connects to. This is good for showing how something is assembled and is used in production environments. Complex diagrams can be cluttered and difficult to follow. Put into words: N to Con 1 A2. Con 1 A2 to Con 2 A2. Con2 A2 to Con 3 A2. Etc.

The circuit diagram shows symbolically how things are connected together, in the clearest possible way, without specifying where each wire runs. This is good for engineering and troubleshooting purposes. In words: Con 1, 2 & 3 terminals A2 are all connected to N.

Get a working knowledge of both conventions...

 

[Jay 1987]

Spot on. Each light controls only the coil on its contactor. All three contactors have their contacts in parallel so that any one of them energised will operate the fan.

Of course, the neutrals of the contactor coils should really go back to the lighting circuit because neither that nor the fan circuit can be correctly isolated because of the interconnection by the 'borrowed' neutral. But that is how it was installed as we considered above.

One final point about the drawings. Consider the difference between
a) a wiring diagram and
b) a circuit diagram or schematic.

The wiring diagram shows each physical wire and where it connects to. This is good for showing how something is assembled and is used in production environments. Complex diagrams can be cluttered and difficult to follow. Put into words: N to Con 1 A2. Con 1 A2 to Con 2 A2. Con2 A2 to Con 3 A2. Etc.

The circuit diagram shows symbolically how things are connected together, in the clearest possible way, without specifying where each wire runs. This is good for engineering and troubleshooting purposes. In words: Con 1, 2 & 3 terminals A2 are all connected to N.

Get a working knowledge of both conventions...

Thanks lucien, it was a bit of a slog, but got there in the end!

I believe understanding diagrams really opens up your electrical design abilities,which in turn makes you a better spark. This is something I really enjoy.

it would be great if more of these tasks could be set. I have no commercial 3phase experience yet, but it would be good to know how installations work in that type of environment.

maybe yourself or another mentor could put some scenarios together that would require circuit drawings or calculations for commercial.

that would be great

Never the less thanks for the support.

jay