Understanding the common wire

[Gas engineer]

Hi,

I’ve asked this question to people I work with but have different answers, so thought I’d try here. What is a common wire and what does it do?

Thanks.

 

[Spoon]

Welcome to the forum mate.
Is your question regarding house wiring in particular?
The 'common' wire is usually the neutral wire in houses.

 

[Bobster]

It depends what the "common" wire your are referring to is doing.

In a nutshell it is a wire that is common between multiple places.

For example a 2 light switches that each switch on one lamp. The common wire could be the feed from the supply. It could supply both switches. The independent switch wire from each switch would then go to it's corresponding lamp.

 

[Pete999]

Welcome

 

[davesparks]

Hi,

I’ve asked this question to people I work with but have different answers, so thought I’d try here. What is a common wire and what does it do?

Thanks.

You're going to have to give a bit of context to this as your question doesn't make much sense at the moment.

In a control circuit you may have a common live which connects to the common terminal of multiple different switches, sensors and relays.


The common terminal on a multimeter is the terminal which is common to all test modes, it's usually the black/negative terminal which is used in all test ranges with the red/positive lead being moved to different sockets.

 

[Edtwozeronine]

I've only ever noted common being on testers, is it more of an electronics thing than an electrical thing?

 

[Bobster]

I've only ever noted common being on testers, is it more of an electronics thing than an electrical thing?

Never noticed the C, L1, L2 on light switches? Guess what the C stands for?

 

[Spoon]

Never noticed the C, L1, L2 on light switches? Guess what the C stands for?

Cake???

 

[Bobster]

Cake???

Close but no Cigar.

 

[Gas engineer]

Hi all,

I should have been more spe, I apologise. It’s in relation to central heating wiring.

 

[Spoon]

Close but no Cigar.

well bugger me.... (not literally....)

 

[Silly Sausage]

Never noticed the C, L1, L2 on light switches? Guess what the C stands for?

To sum up (I think!), it's a wire, connection ... whatever, that is shared.

That, or it's cable manufactured on Merseyside.

 

[Deleted account]

Common in a heating system is the fixed live ( sometimes but not always permanently live) in a switch device i.e. Room stat, cylinder stat, programmer port valves etc...

 

[davesparks]

Hi all,

I should have been more spe, I apologise. It’s in relation to central heating wiring.

You don't normally describe any particular conductor as being the common conductor in a central heating system.

You have various switch contacts which are normally labelled as being the common for that particular switch,such as in thermostats, relays etc.
In this case the common contact is the contact which you normally connect the incoming Live to, this could be a permanent live or a switched live from an upstream device. For example a switched live from the programmer would normally connect to the common of a thermostat.

 

[MJPD29]

It is generally a bit like an Input contact, under most circumstances the common will flow to the normally closed (n/c) but then when switched by say a contactor or switch will move onto the normally open (n/o). If I knew how to add a picture it would probably help the vague description lol

 

[GMES]

Katie price

 

[Edtwozeronine]

Never noticed the C, L1, L2 on light switches? Guess what the C stands for?

Man makes a good point, innit!

 

[FatAlan]

Generally situated below the Jacob Rees-Mogg wire.

 

[FatAlan]

Generally situated below the Jacob Rees-Mogg wire.

 

[PEG]

Generally situated below the Jacob Rees-Mogg wire.

Stop it....he's my lad's hero