T for tap. Thanks! I suspected it meant something logical but had no clue.

The A designation might refer back to the days of tubes and, well, relay power supplies.

Early tube components had two batteries, the A and B. "A" was six or twelve volts and lit up the filaments, which gave off electrons that were drawn to the plate. The plate was charged with the B battery. I've seen 45 volt and 90 volt batteries for this purpose. Ever hear of "B+"? That's the voltage on the plate from the B battery.

As electronics got converted to line-powered devices, the reference to batteries because a reference to supply voltages, and they were soon called filament supply and B+. The origin of the terms was forgotten. Everybody referred to the plate voltage as B+; nobody referred to a B supply; and nobody referred to the filament voltage or supply as A. I ran across that reading some old tech texts.

So maybe that's where A comes from for the relay coil, as it's the main voltage that causes something to happen.

A1 and A2 are the control contacts as mentioned above. You could have addition Terminals like AUX1 and AUX2 with are obviously auxiliary contacts with you want to control another contactor or equipment (I have seen them label A1 and A2 as well). You could go to any real electrical wholesaler (not a HD or Mom & Pop Hardware store) and the person at the desk would gladly answer your question regarding your contactor.

...well, I think it was becoming obvious that the guy at the counter of his electrical house was not very knowledgeable....

Installed and working like a champ.

+1

The A is for Armature!!!

Hmmm. An armature is a moving part. On the other hand, it's

So maybe the essence of armature is COIL, not MOVING, as I thought.

And "N" is for newbie, someone who responds to thread that is one and a half years old.

Eh, gotta start somewhere. I may or may not have done the same thing when learning about online forums...

That is definitely a newbie thing. What puzzles me is oldtimers here getting irritated when they then add responses, then catch on a couple of posts later to the fact that they're wasting their time and get pissed off about it! At least that didn't happen this time.

Seems like a good thread for an initial post. Well since the poster's user name is "ElectricNEWB", I guess the label "newbie" just might fit.

Having read through this thread while on my own quest to learn/verify the terminal naming conventions for contactors, I for one was quite glad to see the rationale for the "A1" and "A2" designations laid out. Something that none of the non-newbies had previously managed to provide.

And ElectricNEWB's post certainly added more value than yours (or mine, for that matter).

So belated thanks to ElectricNEWB for sharing and sorry if anyone is offended by resurrecting an old thread. But then again the ability to find these old threads via internet search engines adds considerable value to these forums. At least for some of us...

It’s so weird, I was just looking up contactor wiring over the weekend for a project I’m working on and saw this post 4 items down....funny thing was it wasn’t related to anything but A1-A2 contactor on a 24v timer delay.

Pretty crazy how well google ranks RC!

Well let's see what Wikipedia, that most authoritative of sources, has to say on the matter:

"In electrical engineering, an armature is the power-producing component of an electric machine. The armature can be on either the rotor (rotating part) or the stator (stationary part) of the electric machine.

The armature interacts with the magnetic field (magnetic flux) in the air-gap; the field component can comprise either permanent magnets, or electromagnets formed by a conducting coil, such as another armature (i.e., doubly-fed electric machine).

The armature, in contrast, must carry current, so it is always a conductor or a conductive coil, oriented normal to both the field and to the direction of motion, torque (rotating machine), or force (linear machine). The armature's role is twofold. The first is to carry current crossing the field, thus creating shaft torque in a rotating machine or force in a linear machine. The second role is to generate an electromotive force (EMF)."

So the contactor/relay is an example of a electromagnetic linear machine in which the ends of the conducting coil comprising an armature are commonly labeled 'A1' and 'A2'.

Now I can rest easy for a while.

Hey, guys, another comedian has joined us!

Like I said: it's a coil.

The EMF is not generated by the armature. Instead, the armature and associated parts convert mechanical power to electrical power. Electrical power is not made out of nothing, while the armature spins without needing force applied to it!

Nah, I don't think so. An electromagnetic linear machine's output would be motion with some power behind it (I can't think of a better way to express that). A relay's "output" is the closing of switch contacts solely so that electricity can flow elsewhere.

I hope so.