# floats on a drawing



## gpop (May 14, 2018)

A low level shut of float wired as fail safe would be normally open when hanging and closed when submerged. E.G when the liquid level drops the float will open shutting of the controls.

On a drawing would it be shown as normally open or normally closed?


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## joebanana (Dec 21, 2010)

N.O. The "normal", "not actuated" mode would be the standard drawing representation.


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## splatz (May 23, 2015)

I often think of the "normal" condition as the condition when it's sitting on the shelf in the supply house. That works fine for say relay contacts with the coil not energized.

When you apply that same sitting-on-the-shelf idea to a float, well, it doesn't really work does it, it would depend how it landed on the shelf.

The convention for "normal" for a float is not-floating - hanging in an empty tank. The schematic symbols










make perfect sense when you think about this kind of float










more so than this kind of float


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## 460 Delta (May 9, 2018)

All of our water heater [boiler] tanks have them, and they are referred to as a NO switch. I have one style of float used on weighed water holding tanks that will screw into a 1/2" port. The switch is Either NO or NC depending on how you orient [turn] the switch in the port. It's pretty cheap through Stephens Manu. and it is used "off label" by me in other applications.


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## gpop (May 14, 2018)

I had a engineer trying to tell me that it was a Normally open float but drawn as Normally closed to represent the non alarmed state. 
The parts list does show 2 x N/O floats so it kinda made sense but it seemed wrong especially as our specs call for 3 wire float's


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## splatz (May 23, 2015)

gpop said:


> I had a engineer trying to tell me that it was a Normally open float but drawn as Normally closed to represent the non alarmed state.
> The parts list does show 2 x N/O floats so it kinda made sense but it seemed wrong especially as our specs call for 3 wire float's


So his thinking is define "normal" as "not alarmed." I think I see the logic but I do not know if I like that idea. If you go that way, the same SPST float is a NO used as a low alarm and a NC used as a high alarm, that seems like it could be confusing. With a SPDT three wire float, the red wire could be NO for a low alarm or NC for a high alarm. 

But I guess if everyone understands and uses the same convention everywhere in the system maybe it would be OK.


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## Navyguy (Mar 15, 2010)

I was always taught to refer to them as "open on level increase" or "close on level increase". The theory for this explanation is because they "float", so if it is not "floating" it is in its rested state.

Cheers
John


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## wcord (Jan 23, 2011)

The age old question. 
Did a pipeline compressor station, where the instrumentation engineer designated his contacts as 00, 01, 10 or 11.
His logic was to try to show the status of the contact either in a power on or power off situation.
Confusing as hell


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## emtnut (Mar 1, 2015)

There are 2 different symbols for each switch (NO and NC)
It's been common to draw them in the 'process normal state' where I have worked. But you can tell by the symbol what the 'de-energized or normal state' is.


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## oldsparky52 (Feb 25, 2020)

Navyguy said:


> I was always taught to refer to them as "open on level increase" or "close on level increase". The theory for this explanation is because they "float", so if it is not "floating" it is in its rested state.
> 
> Cheers
> John


Whenever I had ordered one, that was the conversation that was had, "open on level increase" or "close on level increase".


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## paulengr (Oct 8, 2017)

wcord said:


> The age old question.
> Did a pipeline compressor station, where the instrumentation engineer designated his contacts as 00, 01, 10 or 11.
> His logic was to try to show the status of the contact either in a power on or power off situation.
> Confusing as hell


Uhh yeah and I suppose he is one of those guys that has the tagline "there are 10 kinds of people in the world, those who understand binary and those who don't?" (binary 10 = 2)

This is like the absolutely stupid red/green logic where NFPA 79 and a lot of plants make red "stop" and green "running" while the switchgear guys make red "unsafe" (energized) and green "safe" (de-energized). So on MCC's, I've seen it labeled either way depending on whether the guy who did it was into power distribution or controls.


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## Bird dog (Oct 27, 2015)

paulengr said:


> Uhh yeah and I suppose he is one of those guys that has the tagline "there are 10 kinds of people in the world, those who understand binary and those who don't?" (binary 10 = 2)
> 
> This is like the absolutely stupid red/green logic where NFPA 79 and a lot of plants make red "stop" and green "running" while the switchgear guys make red "unsafe" (energized) and green "safe" (de-energized). So on MCC's, I've seen it labeled either way depending on whether the guy who did it was into power distribution or controls.


There is also such a thing as explanatory notes on drawings. Well I guess on GOOD drawings.


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## oldsparky52 (Feb 25, 2020)

gpop said:


> our specs call for 3 wire float's


Are they combo NO/NC ?


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## ScooterMcGavin (Jan 24, 2011)

It can also be drawn showing the “held” condition. In your case a fail safe low level would be normally open held closed. So it would be drawn as Diagram A. It’s really useful on limit switches when your dealing with situations like open vs not closed valves.


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## emtnut (Mar 1, 2015)

scameron81 said:


> It can also be drawn showing the “held” condition. In your case a fail safe low level would be normally open held closed. So it would be drawn as Diagram A. It’s really useful on limit switches when your dealing with situations like open vs not closed valves.


The limit switch is a good example.
We used NO on both open and closed limit switches.
On our control diagrams, the NO close limit was shown as closed, and the NO open limit switch was shown as open.
ie, they were shown with the pump being off, but the symbol was correct for both switches as being NO contacts.


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## Navyguy (Mar 15, 2010)

scameron81 said:


> View attachment 152876
> 
> It can also be drawn showing the “held” condition. In your case a fail safe low level would be normally open held closed. So it would be drawn as Diagram A. It’s really useful on limit switches when your dealing with situations like open vs not closed valves.


I would bet the farm that symbol A and D don't exist. At least I have never seen them before.

The only place I have seen "Normally Open Held Closed" (NOHC) or "Normally Closed Held Open" (NCHO) is on limit switches. And they only place I have seen them used is on guarded equipment and when I took a refrigeration course about a million years ago I think they were common there... maybe pressure or liquid level... (don't really remember).

Symbols are normally drawn in their rested state... so the NCHO and NOHC confuse the hell out of people. I never really understood them myself even after all these years.

Cheers
John


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## emtnut (Mar 1, 2015)

Navyguy said:


> I would bet the farm that symbol A and D don't exist.


Is it a nice farm ??? 

Relay contacts are shown in their off states, because there is only the one symbol for NO and NC.
Float and limit switches have separate symbols for NO and NC, and the reason is so you can show them in their normal 'process off' state.


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## gpop (May 14, 2018)

oldsparky52 said:


> Are they combo NO/NC ?


Yes one common wire then either N/O or N/C


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## gpop (May 14, 2018)

scameron81 said:


> View attachment 152876
> 
> It can also be drawn showing the “held” condition. In your case a fail safe low level would be normally open held closed. So it would be drawn as Diagram A. It’s really useful on limit switches when your dealing with situations like open vs not closed valves.



It might be time to change the standards to including foot notes and to insist on larger symbols on the diagrams. Honestly A and C when printed on a A4 sheet will look the same unless we increase the size.

Always fun when the panel builders, programmer and electrician get confused as it makes my job doing the start-up way more interesting.


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## oldsparky52 (Feb 25, 2020)

Navyguy said:


> I would bet the farm that symbol A and D don't exist.


I think I have D in my toilet bowl.  Of course controlling H2O and not electrons.


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## Navyguy (Mar 15, 2010)

emtnut said:


> Is it a nice farm ???
> 
> Relay contacts are shown in their off states, because there is only the one symbol for NO and NC.
> Float and limit switches have separate symbols for NO and NC, and the reason is so you can show them in their normal 'process off' state.


The farm is nice! I have lost it several times in my life, but it is self-generating and I have the option to lose it over and over!

I am not sure I am following you. There are two separate symbols for NC and NO. Everything is drawn in its "off" state.

Now I would say that I have seen some interesting variations on a schematic drawing that don't conform to a typical control drawing, but I am sure @gpop was talking about a control drawing and a not any hybrid schematic or functional drawing.

Cheers
John


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## emtnut (Mar 1, 2015)

Navyguy said:


> I am not sure I am following you. There are two separate symbols for NC and NO. Everything is drawn in its "off" state.


It may not be a standard at all. I have seen drawings do it both ways. I never gave it much thought apart from that using (for example) a 'close on rise' pressure switch, as long as the switch part of the drawing is below the connecting line, you know it's a close on rise. So you have the choice to show the 'process' state.

For the most part, from my experience with consulting engineering companies, they showed the process state.

Now maybe that's part of the problem, they were engineers 

Cheers John,

Wayne


( I just said John Wayne !!!! )


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## emtnut (Mar 1, 2015)

gpop said:


> A low level shut of float wired as fail safe would be normally open when hanging and closed when submerged. E.G when the liquid level drops the float will open shutting of the controls.
> 
> On a drawing would it be shown as normally open or normally closed?





> I had a engineer trying to tell me that it was a Normally open float but drawn as Normally closed to represent the non alarmed state.


Just so I'm clear on what I said earlier ...
The low level switch (since you said failsafe), is a NO switch. It has to be shown as that on the drawing.
What I was saying, is it doesn't really matter if you show it as 'A' or 'B' . It's still a NO float switch.
If the engineer is saying it should be drawn as 'C' (or 'D'), then he is wrong.


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## bill39 (Sep 4, 2009)

I quickly learned to NOT draw limit switches as NO-held closed or NC-held open. Many electricians would wire them wrong apparently because they did not understand or were not familiar with the held open or held closed concept......or just thought I had drawn it wrong.

As a retired electrician & controls engineer I encourage the liberal use of notes on a drawing to avoid confusion. This would certainly help in the OP’s case.


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## Bird dog (Oct 27, 2015)

bill39 said:


> I quickly learned to NOT draw limit switches as NO-held closed or NC-held open. Many electricians would wire them wrong apparently because they did not understand or were not familiar with the held open or held closed concept......or just thought I had drawn it wrong.
> 
> As a retired electrician & controls engineer I encourage the liberal use of notes on a drawing to avoid confusion. This would certainly help in the OP’s case.


Would it be a good idea to have cut sheets included(?)...?
I know I struggled with controls. Every electrician is not well versed in controls. There are a lot of electricians who can wire but can't troubleshoot. Great post @bill39 .


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## bill39 (Sep 4, 2009)

Bird dog said:


> Would it be a good idea to have cut sheets included(?)...?
> I know I struggled with controls. Every electrician is not well versed in controls. There are a lot of electricians who can wire but can't troubleshoot. Great post @bill39 .
> 
> 
> things but the cotrol drawings should





bill39 said:


> I quickly learned to NOT draw limit switches as NO-held closed or NC-held open. Many electricians would wire them wrong apparently because they did not understand or were not familiar with the held open or held closed concept......or just thought I had drawn it wrong.
> 
> As a retired electrician & controls engineer I encourage the liberal use of notes on a drawing to avoid confusion. This would certainly help in the OP’s case.


No doubt cutsheets are are valuable for mounting purposes & other


Bird dog said:


> Would it be a good idea to have cut sheets included(?)...?
> I know I struggled with controls. Every electrician is not well versed in controls. There are a lot of electricians who can wire but can't troubleshoot. Great post @bill39 .


No doubt cutsheets are are valuable for mounting purposes, etc., but the control drawings should not only have the correct symbol shown but also show the detailed connection info such as the switch’s terminal numbers or wire colors.

Including these details eliminates sooo many checkout & startup issues.
It is NOT the electrician’s job to interpret drawings by trying to figure out what the engineer wants. The prints should clearly detail that information.


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## VELOCI3 (Aug 15, 2019)

joebanana said:


> N.O. The "normal", "not actuated" mode would be the standard drawing representation.


Drawings reflect “shelf state” unless otherwise notated. Shelf state referring to the device condition while un-powered. (Not the equipment but the components used within)

I’ve used drawings that don’t follow this either. 

Trust but verify. [emoji854]


Sent from my iPad using Tapatalk


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## bill39 (Sep 4, 2009)

You & I both know that but the newly minted chemical engineer who thinks he can also do electrical work doesn’t know that.....and worse you cannot tell him what is right!


VELOCI3 said:


> Drawings reflect “shelf state” unless otherwise notated. Shelf state referring to the device condition while un-powered. (Not the equipment but the components used within)
> 
> I’ve used drawings that don’t follow this either.
> 
> ...


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## gpop (May 14, 2018)

bill39 said:


> You & I both know that but the newly minted chemical engineer who thinks he can also do electrical work doesn’t know that.....and worse you cannot tell him what is right!


I try not to focus on right or wrong as basically any one higher than me doesn't understand what the problem is and everyone else is a contractor so i get to have the final say.

Its interesting to know that you could draw it in a held state and if the engineer had done that or added a note it wouldn't be a problem (or should i say wouldn't be his problem). On this job the float was not even drawn correctly as it was shown as a N/C contact labeled as LL-FS. It only took me 5 minutes to change 3 wires and run the tests to prove it worked then the engineer printing out a updated diagram reflecting the change so all is well. Of course we still had to do the blame sharing which is where the original post started. 
Now we understand the problem we will simply update the standards to avoid doing it again. Nice to know that it does happen to other people and there's a few option on how to correct it.

Next pissing contest is for a valve that claims a amp draw of 0.57 locked rotor that eats 6 amp micro relays. Again a easy fix but someones got to eat the blame. That's probably going to be me as i approved the parts and to be honest on paper it still looks like it should work. Technically it does work for around a month before it welds the relay.


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## emtnut (Mar 1, 2015)

gpop said:


> I try not to focus on right or wrong as basically any one higher than me doesn't understand what the problem is and everyone else is a contractor so i get to have the final say.
> 
> Its interesting to know that you could draw it in a held state and if the engineer had done that or added a note it wouldn't be a problem (or should i say wouldn't be his problem). On this job the float was not even drawn correctly as it was shown as a N/C contact labeled as LL-FS. It only took me 5 minutes to change 3 wires and run the tests to prove it worked then the engineer printing out a updated diagram reflecting the change so all is well. Of course we still had to do the blame sharing which is where the original post started.
> Now we understand the problem we will simply update the standards to avoid doing it again. Nice to know that it does happen to other people and there's a few option on how to correct it.
> ...


Glad it worked out.

I can relate to the issues with NO held closed contacts for the electrician wiring things up. But my experience with most controls was in the maintenance end.
Wondering why a pressure switch wasn't closed in a circuit at 3am on a call out is pretty easy to troubleshoot when the drawing says what it should 'normally be at'. Ie, elevated Alum tank, vs pressure fed system. And we had both at various plants.
After a couple of years, you don't need the prints anyways ... you just know the system, what breaks, and how to fix it!

For the relay driving the valve solenoid, look into 'Fly back diodes' . The inductive kick back kills the relay.


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## just the cowboy (Sep 4, 2013)

Great topic, I have been doing machine control for over forty years and this always comes up. Here is my 2 cents.
Two different things I see in this post.
First is NO-HC, NO, NC-HO, NC 








I was taught to show it in a machine ready to run mode, but control power off. Example is use (A) for a hydraulic tank that is full of oil. Low level would trip shutoff, same with a pressure switch and machine air is on.

Second is for fail safe I was taught it should "not be able to run if wires are ripped out or contacts go bad", so this makes ALL fail safe switch applications NC. If you are seeing a signal during normal operation it is not fail safe.
Example; Water on floor switch's in my vaults are wired NC, Description is "NO water on floor". Same with High pressure switch's wired NC and called "NOT high pressure".

Cowboy


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## emtnut (Mar 1, 2015)

Thanks Cowboy, I was starting to feel all on my own here !


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## gpop (May 14, 2018)

emtnut said:


> For the relay driving the valve solenoid, look into 'Fly back diodes' . The inductive kick back kills the relay.



Great idea but unfortunately this is a 120v ac motor driven valve so i considered 10 x rotor locked amps to be worst case on inrush plus i figured the 6 amp relay probably had a safety margin so i didn't consider it a problem until a month later when they started to fail.


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## emtnut (Mar 1, 2015)

gpop said:


> Great idea but unfortunately this is a 120v ac motor driven valve so i considered 10 x rotor locked amps to be worst case on inrush plus i figured the 6 amp relay probably had a safety margin so i didn't consider it a problem until a month later when they started to fail.


For an AC motor, a snubber on the relay should fix it up.


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## VELOCI3 (Aug 15, 2019)

just the cowboy said:


> Great topic, I have been doing machine control for over forty years and this always comes up. Here is my 2 cents.
> Two different things I see in this post.
> First is NO-HC, NO, NC-HO, NC
> View attachment 152920
> ...


Yes I wire things like leak sensors and all contacts that don’t have built in supervision in the NC position. This way the point is supervised. There is an alarm if the contact changes state or someone cuts the wire. 


Sent from my iPhone using Tapatalk


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## bill39 (Sep 4, 2009)

VelocI3: All valid points that I agree with. The trick is that many system integrators have hired inexperienced designers that do not take failsafe into consideration, maybe don’t even understand the concept. Their drawings show the electrician how to wire things. Then you have the programmer, who may or may not be the same guy who drew up the prints.

Many times I’ve seen wiring changed because the programmer hadn’t familiarized themselves with the drawings and say “Well, that’s not how I programmed the PLC, HMI, and stated it in the training material.” So failsafe gets thrown out the window because it “easier” for the electrician to change it than to change everything else.

FYI: if you have read many of my posts then you may think that I do not have a very high opinion of programmers. That would be true.


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## emtnut (Mar 1, 2015)

VELOCI3 said:


> Yes I wire things like leak sensors and all contacts that don’t have built in supervision in the NC position. This way the point is supervised. There is an alarm if the contact changes state or someone cuts the wire.
> 
> 
> Sent from my iPhone using Tapatalk


In my line of work it was either rodents, or a backhoe !

Sometimes ice and even conduit shift would do it too.


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