I'm not sure if I'm understanding the question correctly, but if its marked as Normally Open then that refers to its state of rest, i.e. not being operated by a finger or whatever. If the switch has two output terminals, say one of each type, they should be clearly marked Normally Open or Normally Closed, either on the switch itself or the datasheet. As a last resort (or a good idea with a switch of unknown provenance!) just a quick check with a multimeter will clear things up.

Hi lynne, Jon's reference is correct, take a door bell push button for instance, it will be n/o i.e. it will be normally open however you wire it up and only closes when someone pushes it to ring the bell (or chimes/whatever)

Regards Nick.

Hi Lynne . The switches I sent you the numbers for are standard 22mm panel switches, internationally used.  They do make a smaller one ,which I think is 16mm . Most of the contacts you will require are N/O open contacts until pressed. These are all for things like start, jog, reverse. They are all inputs on a vfd from 1 common output . The N/C will be required for the stop button. Most of mine were N/O & I think I used 2 N/C ones. Depends on your particular vfd wiring. Hope this helps.

Steve.

Edited By Steviegtr on 17/02/2020 12:42:31

Here's a link for switches. IDS also stock switch enclosures, 4-core shielded power cable, potentiometers etc for controlpendants

Link

Regarding 'low-voltage' versus 'High-voltage' switches – when considering voltage only from a safety perspective you can use Hi-Volt switches on lo-volt applications, but vide-versa requires that the switch working voltage be good enough for the requirement – all obvious I suppose.

But what is not obvious is switch current rating interchangeability. Generally it is NOT advisable to use a high current ( 10A or more, and sometimes even a 5A) switch in lo-current, signal applications, without knowing the mechanical makeup of the contacts.

Many GOOD signal switch specs will give the MINIMUM switched current required. This is to ensure that the contacts remain 'clean' and within contact resistance specs. Most lo-current signal switches have wiping contacts, or at the very least, a firm spring snap contact action. This helps to keep the contact clean and break through any tarnish or oxidation layer.

Hi current switches used correctly have a degree of arcing at the contact which clears the surface of debris, oxidation, etc. Signal switches have not such luxury and rely on the wiping action.

Few, if any, low cost switches used for signal application are hermetically sealed and the contacts may be silver plated only, as that is the cheapest way to reach a contact resistance spec. That silver coating will oxidise and become non-conductive after a while. If you are really cheap, your switch only has brass contacts, which will tarnish as badly. Likewise, the volatiles in the molded plastic housing leach out and coat the contacts with an oily film.

If ignored, some months, years later, the switch appears intermittent .

A cheap switch is just that..

Spending a few bob less on crummy switches just postpones the expense.

If you have problems with intermittent switches, NEVER use silicon spray on signal switch contacts! NEVER!

NEVER Q20 either.

Only use WD40 if you have a really wet, corrosive environment, but even then…WD40, leaves a thin oil residue which attracts guff.

Use a NON-OILY spray – some carburettor cleaner sprays are good, but they may not be kind on the switch plastics.

Joe