Hi itsmoked and electricpete;
Actually both conventions are correct but refer to different devices.
The original symbol refers to what used to be the oiltight line of pushbuttons and selector switches. There are a lot of newer designations for bushbutton lines now in use.
The symbol you are using is as you state, two single pole contact blocks mounted on a single operator (Selector switch or push button.) There is another variation that is a double throw. The symbol is similar, but only one horizontal line is shown to indicate the movable contact and the dots are shown closer together. In industrial control diagrams, the symbols you have shown are widely used and widely understood. You will find those symbols used in the motor starter wiring diagram booklets given out by most motor control manufacturers.
In my GE Control catalogue, 1995 issue, the convention is used for both the wiring diagrams of the motor starters and to describe the action of the various push buttons and selector switches.
A couple of hints, Keith. The contact blocks do not have to be shown in the drawing adjacent to each other. In the case of interlocked pushbuttons for a reversing starter or a two speed starter, the normally closed section of the switch can be shown in a different line and offset to one side or the other. The sections are joined by a dotted line. For selector switches with a lot of contacts, the contacts can be shown in seperate locations, threaded together with a dotted line. It is considered good form to keep the switch sections as close together as is consistent with the circuit. You can usually arrange your diagram to keep your dotted lines reasonably short and limit as much as possible lateral shifts in location.
For selector switches with a lot of contacts, a "Truth table" is often shown to indicate the connections in each position.
The convention suggested by electricpete is also familiar to me but it is a different device. The magnetic motor starters supplied for the HVAC industry used to commonly have a light duty "Hand-Off-Auto" switch mounted in the cover. The physical arrangement of the switch and the symbol are just as shown by electricpete.
I haven't used it for awhile, but I still have the old template with all those symbols on it.
The symbols you have, Keith, work quite well with horizontal ladder type schematic diagrams. Drawing in the jumpers is valuable as it leaves no ambiguity for either the panel assembler or the service technician.
I understand your dislike for a different standard from what you're used to. I feel the same way when I run up against something like a Carrier Container Unit and try to figurew out a control sequence from a schematic in an unfamiliar format.
Those symbols that you dislike used to be and probably still are CEMA standards for Industrial Control Systems. (CEMA is the Canadian eqivalent of NEMA and I understand is almost identical)
Respectfully
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