HOA switch operation

[Rho_HV]

I feel really dumb for asking this but can someone check this truth table for this 3 position HOA (Hand-Off-Auto) switch? My understanding is that position of X determines when contact is energized; for example, "normally open" contact set of "13-14" closes when HOA is in Auto, nd so on....



X=closed
0=open

Cantact	Hand	Off	Auto
33-34	X	O	O
43-44	X	O	O
63-64	X	O	O
13-14	O	O	X
21-22	X	O	X
51-52	X	O	X
73-74	O	O	X

 

[retirede]

21-22 and 51-52 are closed in the Off position. Should be O X O.

 

[Rho_HV]

21-22 and 51-52 are closed in the Off position. Should be O X O.

Then what difference makes if you use NO or NC set of contacts; either way contacts close when in position and open when not. It'll be the same if you replace 21-22 with 23-24.

 

[retirede]

Then what difference makes if you use NO or NC set of contacts; either way contacts close when in position and open when not. It'll be the same if you replace 21-22 with 23-24.

Depends on construction of the switch. I would assume that the switch in the drawing has N.O. contacts in the 2 positions I mentioned that are held closed by the actuator when in the off position. If you mount N.C. contacts there, they would function X O X.

 

[GoldDigger]

You cannot tell just from the schematic part of the diagram what the truth table of the switch is, although you can rule out some possibilities.
The letters in parentheses to the left of each contact pair gives you that row of the truth table.

 

[topgone]

I feel really dumb for asking this but can someone check this truth table for this 3 position HOA (Hand-Off-Auto) switch? My understanding is that position of X determines when contact is energized; for example, "normally open" contact set of "13-14" closes when HOA is in Auto, nd so on....

View attachment 17483

X=closed
0=open

Cantact	Hand	Off	Auto
33-34	X	O	O
43-44	X	O	O
63-64	X	O	O
13-14	O	O	X
21-22	X	O	X
51-52	X	O	X
73-74	O	O	X

IIRC, the convention in numbering of contacts is (was): second digit ending in 1-2 --> normally closed and contacts numbered with 2nd digit ending in 3-4 --> normally open.

From your truth table:
"Hand" selection will "close" (X) contacts 33-34, 43-44, and 63-64
"OFF" selection will close (X) contacts 21-22 and 51-52
"AUTO" selection will "close" (X) contacts 13-14 and 73-74

 

[retirede]

You cannot tell just from the schematic part of the diagram what the truth table of the switch is, although you can rule out some possibilities.
The letters in parentheses to the left of each contact pair gives you that row of the truth table.

Back when I was drawing control circuits (a long time ago!), the convention where I worked was to draw the switch in a neutral position (usually center in the case of a 3 position switch) and draw the contacts closed that were actually in a closed state in that position.

We would then draw each of the other positions in a dashed line left and right of center. From there we would draw a dashed line vertically through each conductor and draw an 'X' where each dashed line intersected a conductor whose contact was closed in that position.
Hard to explain, maybe I'll have time to upload a diagram later.

The OP's schematic is just another way to represent that using the letters in parentheses.

 

[Rho_HV]

Back when I was drawing control circuits (a long time ago!), the convention where I worked was to draw the switch in a neutral position (usually center in the case of a 3 position switch) and draw the contacts closed that were actually in a closed state in that position.

We would then draw each of the other positions in a dashed line left and right of center. From there we would draw a dashed line vertically through each conductor and draw an 'X' where each dashed line intersected a conductor whose contact was closed in that position.
Hard to explain, maybe I'll have time to upload a diagram later.

The OP's schematic is just another way to represent that using the letters in parentheses.

It took me a lot longer than it should have but I figured it out. In H position H and O are triggered, in O position none and A position O and A. I thought just one contact is triggered in each position (H in H, O in O and A in A).

Confused the crap out of me.

 

[retirede]

Back when I was drawing control circuits (a long time ago!), the convention where I worked was to draw the switch in a neutral position (usually center in the case of a 3 position switch) and draw the contacts closed that were actually in a closed state in that position.

We would then draw each of the other positions in a dashed line left and right of center. From there we would draw a dashed line vertically through each conductor and draw an 'X' where each dashed line intersected a conductor whose contact was closed in that position.
Hard to explain, maybe I'll have time to upload a diagram later.

The OP's schematic is just another way to represent that using the letters in parentheses.

Like this:

 

[Jraef]

Like this:
View attachment 17486

That is the old "JIC" schematic representation used in North America, now known as "NEMA" schematics, although NEMA is not really an enforced standard. The other one, using specific numbering of terminals, is the IEC schematic standard derived originally from the German DIN standards.

Topgone is correct, in the IEC standard anything ending in 1-2 is NC, anything ending in 3-4 is NO, then the first digit pertains to its physical location on the device itself. So 13-14 means it is a NO contact on the fist position of the switch, in this case the first tier, left side looking at it from the inside of the panel. 21-22 would be next to it on the right side of the first tier, 33-34 would be NO second tier left side, 43-44 would be NO 2nd tier right side, etc. etc., based on the switch holding only two contact blocks per tier. If the switch holds 3 per tier, as Siemens switches do, the physical location changes slightly, but the standard is still very specific as to what that is (I can't remember though if it is 1, 2, 3 left to right, or 1, 3, 2, because that puts 1 and 2 as always being in the same spot regardless of brand). It's actually a very "rational" system (as the Germans like to say) once you are taught (and can remember) how it works.

 

[retirede]

That is the old "JIC" schematic representation used in North America, now known as "NEMA" schematics, although NEMA is not really an enforced standard. The other one, using specific numbering of terminals, is the IEC schematic standard derived originally from the German DIN standards.

Topgone is correct, in the IEC standard anything ending in 1-2 is NC, anything ending in 3-4 is NO, then the first digit pertains to its physical location on the device itself. So 13-14 means it is a NO contact on the fist position of the switch, in this case the first tier, left side looking at it from the inside of the panel. 21-22 would be next to it on the right side of the first tier, 33-34 would be NO second tier left side, 43-44 would be NO 2nd tier right side, etc. etc., based on the switch holding only two contact blocks per tier. If the switch holds 3 per tier, as Siemens switches do, the physical location changes slightly, but the standard is still very specific as to what that is (I can't remember though if it is 1, 2, 3 left to right, or 1, 3, 2, because that puts 1 and 2 as always being in the same spot regardless of brand). It's actually a very "rational" system (as the Germans like to say) once you are taught (and can remember) how it works.

Yep - I remember my old symbol template having "JIC" stamped on it! It's all coming back to me now (I think) - 1979 was a long time ago.......