How to wire a knob switch?

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  • Thread starter SEGFAULT1119
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In summary, this knob switch has two sets of contacts, one set is open when the knob is turned one way, and the other set is open when the knob is turned the other way. There may be a center position where all sets of contacts are open. The knob is on an old machine that we got, and we can't find a schematic for it. We need help understanding one of the contacts, and we're hopeful that someone can help us.
  • #1
Hello,

I was wondering if I could get some help understanding the wiring of a knob switch (Link 1 and 2). It's on an old machine that we got and I can't find any schematic for switch. The purpose of the switch on the machine is to raise or lower a steel arm. There are actually two boxes (switches) to support these features. If I could get some help understanding one, then I think I can figure out the rest.

Thanks in advance!

Link 1: http://www.radwell.com/Buy/ALLEN BRADLEY/ALLEN BRADLEY/800TJ91C19
Link 2: https://www.ebay.com/itm/Allen-Brad...lock-600V-AC-Max-Pilot-HVY-Duty-/401412825653
 
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  • #2
That looks a lot like an old knob switch in my junk drawer. It has two sets of contacts. One set is closed when the knob is turned one way, the other set is closed when the knob is turned the other way. There may be center position where all sets of contacts are open. One set of contacts is closest to the know, the other set is farthest away. Each set of contacts can be one, two, or more pairs.

Disconnect the wires (label them first), connect an ohmmeter, and start knob turning.
 
  • #3
@jrmichler is correct on the knob. 2 normally open sets of contacts, one set operates in each direction, with a spring return to center (off).
I can't find what the contacts are in the ebay listing though. Is the ebay part one you are looking to use to replace the other one? if you need replacement contacts for the 800tj91c19 I can get you that info tomorrow when I get to work. these usually are multipart switches. one part is your contact block (2 n.o. momentary in your case) and an operator which can be a push button, a spring return turn knob (your case) , a maintained turn switch or an e-stop(manual reset). Unless you broke the operator, you can just replace the contact block. One other piece of info needed is the diameter of the mounting hole ( 18mm, 22mm,26mm or 30mm)
 
  • #4
@jrmichler @wirenut
Thank you for responding.
The people who put the machine together modified the knob, so the knob has two relay boxes of the same type (in the previous links). Before I posted the thread, I had tried to test the contacts using an ohmmeter as jrmichler suggested but I couldn't make sense of the results. For example, the ones that I expected to be NO were closed regardless of the position of the knob.

@wirenut, I don't know if the knob is still functional or not. The machine is really old so it might be already broken :)).

I'm going to give it another try today and I'll be back if I still can't figure it out.

Thanks!
 
  • #5

1. How do I determine the correct wire gauge for a knob switch?

The wire gauge for a knob switch depends on the amperage rating of the switch and the length of the wire. It is important to consult the manufacturer's instructions or a wire gauge chart to select the appropriate wire gauge for your specific knob switch.

2. Can I use a knob switch for both AC and DC circuits?

No, knob switches are designed for either AC or DC circuits, not both. It is important to check the specifications of your knob switch to determine if it is suitable for your specific circuit.

3. How do I connect the wires to a knob switch?

The specific wiring instructions will vary depending on the type and model of knob switch you are using. However, in general, the wires are typically connected by stripping the insulation off the end of the wire and wrapping it around the terminal screw, tightening the screw to secure the wire in place. It is important to follow the manufacturer's instructions for proper wiring.

4. Is it necessary to use a ground wire with a knob switch?

Yes, it is important to use a ground wire with a knob switch to ensure safety and proper functioning. The ground wire provides a path for excess electricity to safely travel in the event of a short circuit.

5. Can I wire multiple knob switches together?

Yes, it is possible to wire multiple knob switches together in a circuit. However, it is important to consult the manufacturer's instructions and use proper wiring techniques to ensure the circuit is safe and functional.

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