If I go to a different brand and order a switch with two normally open contacts, I will many times get a switch with two normally open contacts, just as the drawing shows. It was up to the person ordering the parts to determine whether an operator would reverse the action of the contact block. It was not unusual to have an operator which held a normally open contact closed in normal operation. Our diagrams always showed the contacts in the as installed or as assembled position. In some product lines the single contact blocks were interchangeable with the two contact blocks. Then came the contact blocks with only one set of contacts. You are inadvertently making my point.īack in the day when I was doing a lot of control work, ordering parts, designing new circuits, repairing, troubleshooting etc., All of our selector switches used contact blocks with one set of normally open and one set of normally closed contacts.
#On off switch symbols how to#
Jimmy Carter RE: How to draw a 2-position selector switch and its contacts? (IEC world) ScottyUK (Electrical) 21 Feb 18 06:00 I can understand the use of a Hand/Automatic switch in an application where the designer does not want the possibility that a Hand/Off/Automatic switch may be forgotten in the off position. Two position switch versus a three position switch. That way you get the switch that you wish to use and the field technician has a drawing that he can understand. Included in the note that we discussed may be a bill of material that calls up the switch with the confusing description. Remember that one purpose of the diagram is to aid in troubleshooting. I suggest that if we lack a symbol to show normaly-open-held-closed then a normaly closed symbol most clearly describes the action of the circuit. I think that a lot of our confusion has been caused by a misleading catalogue description. I still think option "E" most clearly demonstrates the action of the switch as installed.
IMO, option "A" is the clearest of all Link Jimmy Carter RE: How to draw a 2-position selector switch and its contacts? (IEC world) JuanBC (Electrical) In the NEMA convention we have, in addition to normally open and normally closed, symbols for "normally open, held closed" and "normally closed, held open" A convention that works is to draw the switch shown the first position and show the other one or two positions with dotted lines, Show the contacts in the first position as solid and in the other one or two positions as dotted. That was the standard for many years until Switch operators appeared with two normally open contact blocks mounted side by side.
The contact block, when mounted to a push button had one set of normally open and one set of normally closed contacts and that is how either a hand/auto switch or a hand/off/auto switch would be drawn.
Well for many years in the NEMA world we use an operator with a single cam operating a double contact block. Kcress - RE: How to draw a 2-position selector switch and its contacts? (IEC world) JuanBC (Electrical) I CADded three other symbols that all failed their byzantine machinations by various details which this did not. But, I only spent about two hours puzzling this mess out. You can't continue that symbolism without mirroring the contact. Why "completely shocking"? Note they (freakishly) show the dashed side of their Vs as being the ON position and that mechanically associates with physically shoving the dashed-to-contact in that direction to physically operate it. I actually think they've dropped them for saner pastures. Texas Instruments has lost many of our component selections due to the vapid IEC symbols they use. IEC symbolism is so bad that I and several other engineers I know will simply exclude any and all integrated circuit offerings for our designs if they're provided in IEC. Input.cmn-toggle-round + label:before, input.I can well understand a lot of people being shocked, electrocuted too, with these lame symbols.
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