What is the difference between a regular contactor, and one "w/shunt"?

Shunt,, sounds like a medical device,, I`m waiting to hear more

In electronics, a shunt is a device which allows electric current to pass around another point in the circuit. The term is also widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage.

Shunts as circuit protection
When a circuit must be protected from overvoltage and there are failure modes in the power supply that can produce such overvoltages, the circuit may be protected by a device commonly called a crowbar circuit. When this device detects an overvoltage it causes a short circuit between the power supply and its return. This will cause both an immediate drop in voltage (protecting the device) and an instantaneous high current which is expected to open a current sensitive device (such as a fuse or circuit breaker). This device is called a crowbar as it is likened to dropping a metal tool called a crowbar across a set of bus bars (exposed electrical conductors).

What you are asking is what it the difference between a 2 pole contactor and a single pole contactor. The answer is nothing. Any application that you could use a 2 pole you can use a single pole. The single pole is usually found in residential A/C units. The single pole has a couple of benefits in my opinion. One a 2 pole contactor one pole can either wear out or actually become welded shut, this will prevent the other pole from making contact and starting the unit. Obviously a single pole doesn't have this issue but if the contact does get welded shut, because of the 'shunted' side the unit will have constant power.

Are you talking about a "Back EMF protection"? Voltage that's release into the power supply when DC coils turn off. Another term may be a snubber. AC protection of coils is not normally required.

Contact protection for AC and DC can be different as well.

There is such a thing as a "Shunt Ammeter"

OK, bendgregg,I hope its clear to you now,, dosen`t sound like anything I`ve run across or anything I`ll need in the future,,

Thanks ltemetellu

To elaborate by what I mean by single pole, there is 2 sets of terminals (2 on the load side and 2 on the line side) with one shorting bar between L1 and T1. The other side L2 and T2 would have a "shunt" or metal strip connecting the contacts.

Mark: Totally have to disagree with you on the single pole/double pole contactor thing.

Why is that? It is a very common component in residential A/C systems

http://members.cox.net/canon01/contactor2.jpg

I was kind of thinking of a shunt as Mark described it. But I don't actually know the definition of a true shunt. This is very interesting knowledge of all here. Keep it coming and hopefully the asker will post a pic of what they are talking about.

I tried, for the first time, to post a pic. It shows up on y screen but not sure if I did it correctly. Can any of you see it?

Mark I was answering while you were posting the pic of the ac contactor. Thank you for showing what I was thinking of. This was my first thought when I read the original question. Are we correct in calling this a shunt, and if not, what would it be called.

MGD, I've always just referred to it as a shunt and everyone that I know in the trade seems to do the same. Now if it is the correct terminology I have no idea but it seems to be the accepted term.

What did you think of the humor post, I'm still laughing. I actually made this one up myself. Not sure if that's a good or a bad thing. Don't think ill quit my dayjob for commedy, but if I could come up with stuff like that on a regular basis, I would think about it.

Mark:

I've never seen one of them. Quite ODD I must say.
2 pole contactors to me have two poles that move and are used for 240 systems. They provide a 100% disconnect of both sides of the 240 when off, otherwise the motor or whatever has 120 on an end of it.

Line tstats are just as odd. They switch 1 pole with temperature and both at the off position.

1 pole contactors have 1 pole that moves and are used for 120 systems.

3 pole contactors have 3 poles that move and are used with 3 phase systems.

Auxiliary contacts cause problems too. A 1 pole contactor with an AUX contaxt is not a 2 pole contactor.

That thing is a new beast. It just makes wiring it a bit neater.
Now I know.

Honeywell calls it a (1 pole, 1 with shunt), so it must be 2? I give up. I think I like the 1.5 pole contactor designation better.
I thought if you had one pole contactor and subtracted a pole you would have 1 left. In this case you have -1 left. Silly.

Product (http://customer.honeywell.com/honeywell/ProductInfo.aspx/DP1025A5005)

what did you think of the humor post, im still laughing. i actually made this one up myself. Not sure if thats a good or a bad thing. Dont think ill quit my dayjob for commedy, but if i could come up with stuff like that on a regular basis, i would think about it.I saw it... keep practicing, and hold on to that day job at least a li'l longer... :p

Yes it will constantly supply one leg of the 240 but as I'm sure you know that the circuit won't be completed until the second leg is energized. These types of contactors are fairly common, more than likely because they are cheaper.

I saw it...keep practicing, and hold on to that day job at least a li'l longer...:p

Oh come on, it wasn't that bad.

But I bet you laughed a little on the inside.

Well... maybe a little. You got to start somewhere.

Show us how its done.

The shunt as it is being called is used in many cases to allow 120 volts through at all times to keep the windings in the compressor warm. I is a cheap way to have a built in crankcase heater. Class for today is over.

Its user free

I always stock 2 pole contactors and wire them, for friends and family, as a single pole. If they ever go bad, I just use the other pole the next time they call me back. Bosses don't like this practice because you can't sell a new contactor when you have to go back.

The price difference is like $1.80 single vs double.

There really is a good reason why manufacturers started using a single pole but I'm drawing a blank as to why. If I remember I'll post it later.

Oh, I did remember. Manufactures actually found a single pole was more reliable than a double and cheaper too. Only 2 points to foul out. Only 2 points for an earwig to crawl under and a bit cheaper t0o manufacture. A two pole contactor actually has 4 point of contact, two on each pole.