How to wire a knob switch?

  • Electronics
  • Thread starter SEGFAULT1119
  • Start date
  • #1

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 2:

Answers and Replies

  • #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
Gold Member
@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.

  • #5
jim hardy
Science Advisor
Gold Member
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