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Switches

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Lynne17/02/2020 11:51:06
79 forum posts
27 photos

I am looking for momentary switches to build a remote panel for recently purchased vfd. Have been given ebay reference by a fellow member of the group. Many switches are referred to as 1no/1nc or vece vesa. Am I correct in thinking that no/nc is dependant on how they are wired up? Also switches sourced from China appear to be a much larger switch arrangement than switches that are sourced/made in the UK, and I am puzzled, why? Can anyone explain why. Regards Lynne

Jon Lawes17/02/2020 11:57:47
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353 forum posts

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.

Clive Brown 117/02/2020 12:03:47
357 forum posts
9 photos

Inverter Drive Supermarket have all the switch-gear that you will need for making up a remote panel for a VFD. The components, eg pushbuttons, contacts etc are purchased separately and join together to give a wide range of switch types, push-button colours etc etc.

Nicholas Farr17/02/2020 12:08:12
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2125 forum posts
1028 photos

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.

Martin Kyte17/02/2020 12:13:45
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1679 forum posts
25 photos

1no/1nc is

1 pair of contacts normally open and 1 pair normally closed.

Wire the pair you want.

regards Martin

Steviegtr17/02/2020 12:41:30
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827 forum posts
187 photos

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

SillyOldDuffer17/02/2020 13:04:20
5370 forum posts
1090 photos

There are three variants of the single momentary push switch:

  1. One with 3 terminals that is normally open on one terminal and normally closed on the other. Pressing the switch breaks the normally closed (NC) connection, and makes the normally open (NO) connection. This type can be wired as either NC or NO.
  2. Two active terminals that are always NC
  3. Two active terminals that are always NO

Don't get type 2 and 3 mixed up, the mistake can only be fixed by buying the other switch! You don't want the motor to run when it should be stopped, or that will only run when the change gear cover is removed. Getting type 1 the wrong way round is easily mended by swapping the wire to the other terminal.

Switches from China are much the same size as any other. Small switches for low voltage, low current and big ones for switching power; thousands of them in all shapes and sizes. VFD control switches can be tiny, but don't skimp on anything carrying real power like the NVR, main ON/OFF, or contactor.

Dave

Lynne18/02/2020 14:03:02
79 forum posts
27 photos

Thanks for all your responses. Martin gave me a very clear answer to my main question. My further musing was that pictorially , chinese switches appeared much larger and more complex looking than many uk versions, any particular reason for this. I now realize that the switches I have looked at are in the voltage ranges 220V to 415v. The outputs from the VFD are 10 and 24v. So do I need to look for switches that clearly specify these ranges , or are the others OK to use? I've looked at InverterDrive web, and I cannot see any low voltage switch gear, plenty of 230/240v gear. So some clarity on the subject would be useful for me. Thanks, Lynne

Gavin Freeman 118/02/2020 14:43:30
12 forum posts

As a rule, you can use high voltage switches for low voltage applications but not the other way round!

I've made VFD control panels with these or similar;

https://www.ebay.co.uk/itm/22mm-NO-NC-Momentary-Panel-Mount-DPST-Control-Push-Button-Switch-AC-220V-LED/173833190213?hash=item287943fb45:m:mhMdQStVId-IXE6UujeCezw

Checking the ones I have, they are rated at 440v but are only switching 12v

A simple three pin toggle switch is required for forward and reverse.

Depending on what VFD you use and how it is programmed, you may want to include a relay in the start circuit so as to act as a NVR switch

Clive Brown 118/02/2020 15:19:16
357 forum posts
9 photos

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

Link

Lynne20/02/2020 23:38:30
79 forum posts
27 photos

Thanks for all the help and info. Lynne

Joseph Noci 121/02/2020 09:14:49
603 forum posts
859 photos

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

Clive Foster21/02/2020 10:52:10
2032 forum posts
73 photos

When it comes to workshop electrical controls I'm a considerable fan of push button carrier assembles for V3 microswitches.

Although it can be a bit more cumbersome if space is limited and, possibly, a little more expensive overall V3 size microswitches are readily available in a wide range of current and voltage ratings so its quite easy to select an appropriate one for the job. If of reputable make they are very reliable over many thousands of operations and not terribly expensive. If one does go down or if you decide to reuse "the one I made earlier" for another job the switch unit can easily be changed for another more appropriate rating if needed.

If your Google-Fu is a bit under the weather today carriers can take a bit of finding but are not terribly expensive for example the ZF range from **LINK** , **LINK** , I have used versions of the Honeywell carrier and cap device **LINK** in the past but they have gotten expensive and the range smaller in recent years. A DIY version looks easy enough to make.

I have also used the lever action type with an external toggle to make a stay on or off version. The flexible lever makes a nice spring to keep the toggle in the right place.

With a separate switch its pretty easy to seal things against liquid splashes, airborne dust et al too.

Clive

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