Standard for drawings showing relay contacts are deenergized?

[tom baker]

Is there a NEMA or other standard for drawings showing relay contacts are drawing in the deenergized state?

 

[sameguy]

I think it is called the "normal" state.
Like normaly open, normaly closed, how it is out of the box.
What are you asking?

 

[weressl]

Is there a NEMA or other standard for drawings showing relay contacts are drawing in the deenergized state?

Contacts are show in their off-shelf AND deenergized state. In other words not only is it the question of deenergized, but pushbuttons are shown 'unpushed', limit switches unactivated, etc. Multiposition switches, such as rotary switches usually have some sort of indication which position are they in, that is usually a solid dot next to the position, or vertical dashed lines with dots at the swicth position intersecting with the horizontal solid or dashed position of the contact.

 

[SG-1]

Tom, this is IEEE Std 315A-1986 & ANSI Y32.2-1975. There may be later versions.

 

[DANIEL LAWLOR]

Should the 'Traffic Signals' industry be any different?

Should the 'Traffic Signals' industry be any different?

Gentlemen:

Recently, two local manufacturers of traffic signal controller cabinets have indicated to me that they typically show relay contacts - on their schematic diagrams - in whichever state corresponds to a 'normal' or 'healthy' operating conditions, as required to indicate power flow to the signal lights.

As such, some relays are shown on the schematics as 'energized' whereas others are not. This means that a NO contact is shown as closed on the diagram.

I've been told that this is common in the 'traffic signals' business despite the fact that it is in direct contravention to IEEE/ANSI standards and the standards that I've worked with outside the traffic world.

Traffic signals cabinets are commonly constructed to NEMA TS1 and TS2 standards for many (but not all) municipalities across North America; these standards however do not appear to address schematic drawing conventions.

A little internet research produced a copy of the City of Los Angeles, Department of Transportation, Model 332 schematic which indeed shows relay contacts in their energized state.

At the end of the day I suppose that this is acceptable as long as there are notations on the schematics which explain the conventions being employed.

Nevertheless, I still this practice rather strange and I am wondering if anyone can explain why this is done, what the origin of the practice is, how wide spread it is or if there is some documented 'standard' which dictates this way of doing things.

Thanks very much,

:?

 

[pfalcon]

Contacts are show in their off-shelf AND deenergized state. In other words not only is it the question of deenergized, but pushbuttons are shown 'unpushed', limit switches unactivated, etc. Multiposition switches, such as rotary switches usually have some sort of indication which position are they in, that is usually a solid dot next to the position, or vertical dashed lines with dots at the swicth position intersecting with the horizontal solid or dashed position of the contact.

Um, yea. I'll stick with the above and continue to INSIST that anyone submitting drawings to me abides by it. I refuse to accept poor practice because somebody from 1912 made the original drawing and no one has seen fit to update it.

 

[hurk27]

Gentlemen:

Recently, two local manufacturers of traffic signal controller cabinets have indicated to me that they typically show relay contacts - on their schematic diagrams - in whichever state corresponds to a 'normal' or 'healthy' operating conditions, as required to indicate power flow to the signal lights.

As such, some relays are shown on the schematics as 'energized' whereas others are not. This means that a NO contact is shown as closed on the diagram.

I've been told that this is common in the 'traffic signals' business despite the fact that it is in direct contravention to IEEE/ANSI standards and the standards that I've worked with outside the traffic world.

Traffic signals cabinets are commonly constructed to NEMA TS1 and TS2 standards for many (but not all) municipalities across North America; these standards however do not appear to address schematic drawing conventions.

A little internet research produced a copy of the City of Los Angeles, Department of Transportation, Model 332 schematic which indeed shows relay contacts in their energized state.

At the end of the day I suppose that this is acceptable as long as there are notations on the schematics which explain the conventions being employed.

Nevertheless, I still this practice rather strange and I am wondering if anyone can explain why this is done, what the origin of the practice is, how wide spread it is or if there is some documented 'standard' which dictates this way of doing things.

Thanks very much,

:?

I think it had to do with the multi-contact timers that they used to use, Washers and dryers are still drawn like this, but have a time line and contact position for the timer.

 

[weressl]

Um, yea. I'll stick with the above and continue to INSIST that anyone submitting drawings to me abides by it. I refuse to accept poor practice because somebody from 1912 made the original drawing and no one has seen fit to update it.

That's the kind of progressive attitude I'll take any day......:happyyes:

 

[pfalcon]

I think it had to do with the multi-contact timers that they used to use, Washers and dryers are still drawn like this, but have a time line and contact position for the timer.

I'm familiar with the time graphs for contacts. They come as a supplement to the main drawing. None of the time graphs I've seen attempt to show an actual circuit.

 

[petersonra]

I don't know just what the convention is some times.

I try to use the out of box, de-energized, and not engaged model in my drawings.

However this is not always clear to the end user.

I have seen drawings from instrument manufacturers that show N/C relay contacts drawn as NO, because that is the way they drew it 50 or 75 years ago and they are just not going to change it.

There are actually standard (or at least fairly commonly used) symbols for showing held closed or held open type contacts, but it is not always clear just what that means in a particular instance.

A lot of times other people are supplying a lot of the switches being used on a project and often we do not even know what they are. I have been known to show 4 wires going to a pressure switch because it may need power. I usually show it as a box with no terminal designations. Just hot, N, (or DC + and -) ground, and signal. They can figure it out in the field if I put on the drawings that the signal is "on" when a certain condition occurs. Even so, it is not unusual for the thing to have a signal that only works one way and it is different than I anticipated.

These days a fair number of switches are electronic and there is some way to set how the signal reacts to the process. How do you even try to show that kind of thing?

 

[sameguy]

In the power off state, ladder logic, id contacts