Allen Bradley select switch

[blackandredwarrior]

how to understand CAM, i am using 800T-XA, if i select KB7 cam X O O, what this means?

A NO contact block in that position will close when turned to the left. It will be open in center or right. A NC block would be open to the left and closed to the center and right.

 

[blackandredwarrior]

what is the difference between KB7 and KC7?

You have to look at each block type and position. Circuit A, White side, there is no different. With Circuit B, the NO contact being closed to the right would now be closed in the center position, but open in the right position. You would have to compare each row going down to see all of the differences.

 

[angi]

so what we need:
for Start, X OO
for Stop, XXO
is it right? so which cam we need to use?

 

[ASF]

That's right. But I can't see one on that table (although it's making me cross eyed trying to look at it too much!). I still maintain that it'd still be far easier just to get a piggyback contact and use your existing contact block. It'll be cheaper and likely in stock as well.

 

[angi]

how to understand "contact block suffix code", C, H, B, A?

 

[angi]

i only see A, B, AV, BV, there is no C, H

 

[angi]

what does Circuit A/B mean?

 

[ASF]

Circuit A/B I think likely means that you have the two circuits on your block. Like you described before, when you turn the switch one way, the top contacts close - so that's circuit A. When you turn the switch the other way, the bottom contacts close - that's circuit B. Not sure about the suffix

 

[angi]

KC7
A:XOO
B:OXO
can not be used for 3 wire control, there is no XOO and XXo combination.

 

[ASF]

Thought so. Once again, go for a piggyback contact block.

 

[TConnolly]

If you are trying to stuff two functions in one hole then consider a pull to start, push to stop button. This is a fairly common arrangement. If this isn't what you are trying to do then never mind.

 

[blackandredwarrior]

so what we need:
for Start, X OO
for Stop, XXO
is it right? so which cam we need to use?

I believe that you have everything you need. But you need to test it to make sure. Are you wiring this in hardwire or going to a PLC?

Circuit A & B is when you have two circuits like you do on an 800T-XA contact block. This contact should be on the "white" side of the switch.

With the switch in the center maintained position one block (the A circuit, and these should be marked) will be open and the other will be closed. When you turn it to the left, the NO contacts should close, and the NC contacts should stay closed. When you turn it to the right the NO contacts should stay open, and the NC contacts should open. I *think* this should work for what you want.

The way that I think you want to wire the circuit is so that your control power comes into the NC contact first. Then jump to the NO contact. Out of the NO contact you go to your motor controller. Now what you will normally do is also take a wire from between the the NO and NC contacts and run that through the starter auxiliary to the coil to "seal in" the circuit when you release the knob.

If you do this when you turn the knob to stop it will drop the circuit out. Well, it should. Unless I'm wrong which I think I have been before, but I could be mistaken.

If you note what kind of motor controller you're using it might change things (for example a VFD, or a PLC.)

 

[blackandredwarrior]

i only see A, B, AV, BV, there is no C, H

I think, but I'm not positive is the first contact block would be "A", then "B". That would fill up the first layer. Then you move to the second layer, and that is "C" and "H". You then choose which blocks you want it what position. Now my local AB dealer doesn't stock assembled operators. We get whatever the base operator (knob and cam) then whatever contact blocks we need. I guess it makes it easier for them to carry more options, but less in stock items.

The contact block types (option "f") actually keep going into the next column to the right.

 

[jraef]

To start off, I'm going to state that this is a very poor design concept for a 3 wire Start - Stop control circuit, for the very simple reason that if you want to turn something off in a hurry, having to find, grab and twist a switch, as opposed to slapping an extended head button, can possibly result in loss of limb or life. There is a REASON why Push Buttons are used and why this is not a popular combination.

So right off the bat, I strongly urge you to reconsider the advice from TConnolly (post #26) in using a Push-Pull switch for this: momentary Pull to Start, spring return to Center, momentary Push to Stop, often also used with an integral red light wired to illuminate when the starter is energized. 800T-FXN6A7 is the non-illuminated version, it has the exact contact arrangement you are looking for, 800T-FXNQH2RA7 is the same thing but with a Red LED light in the center. One hole, 3 functions, no added risk.

If you insist on pursuing this foolishness of using a selector switch, the KE7 cam is the one that will get you what you want, with 2ea XA contact blocks, one on the White side, the other on the Black side. Wire Circuit A-Black as your Start, wire circuit B-White as your Stop. Center position; circuit A-Black (Start) is open, Circuit B-White (Stop) is closed. Turn to the Right (Start), Circuit A-Black closes, circuit B-White remains closed. Turn to the Left (Stop), Circuit A-Black remains open, Circuit B-White opens.

If you want to experiment with the switch you already have, you might be able to use a Late-break NC contact, 800T-XD4, stacked onto one side or the other. That's how they get the Push-Pull to work that way, because it changes the operating distance of the plunger. Years ago there used to be a MUCH more complex target chart depicting all possible combinations of cams and contact blocks, but that was from a day long past before people just began to use inexpensive solid state logic devices to do this sort of stuff.

 

[ASF]

Agree with the sentiment above, but if there's any risk of harm involved, selecting a PB over a switch is not even close to an acceptable risk mitigation strategy. As far as a control measure goes, that's so far down the list it's not even worth a mention. The start/stop control should only ever be for control, safety should be taken care of by a risk assessment and proper procedure - eliminate, substitute, engineer, administrative, PPE. An e/stop comes after ALL of that, and then your start/stop controls even later.