E-stops

[brewerinc]

I have several old school mechanical assembly men that are used to having their e-stops wired so that when pushed in (activated) there is no light and when pulled out (de-activated) is lit up. My schooling and understanding of NEC code is that the e-stop should not be lit up if pulled out (de-activated) and if pushed in (activted) should be lit up red indicating a e-stop condition is present. Could someone else weigh in here and clarify this?

 

[iwire]

The NEC is silent on this.

I also think it would be a bad idea to try to change what they are used to.

 

[brewerinc]

So basicaly its up to the user to determine what they want the red e-stop light to indicate? Sounds confusing and I would think that there would be some type of code on this topic so that all machines with e-stops would fall into the same type of operation no matter who built it.

 

[wireguy8169]

one problem with an estop ligting up when activated is "what if the lamp is burned out", if the machine is getting ready to run and the lamp is out the operator may note this and put in a request for a work order to change the lamp. And I agree with iwire unless its an issue don't change it some may use that as a toubleshooting tool and though it can be overcome why mess with what has worked unless you have too.

 

[markstg]

The NEC is silent on this.

I also think it would be a bad idea to try to change what they are used to.

Iwire is correct, changing what they are use to will only confuse everyone, or worse, some one way some the other.

I've seen at a facility Green used for Motor Running and at another Green for Motor Stopped.

Best to stick to the convention used for the site.

How about circuit breaker position lights...We do Red Closed; Green Open.

 

[iwire]

So basicaly its up to the user to determine what they want the red e-stop light to indicate?

I am not really saying that, all I am saying is that is not what the NEC addressees'.

The NEC will tell us how we have to wire the E-stops but not where to put them or how they will operate.

I think there is a good chance it would be addressed in NFPA 79: Electrical Standard for Industrial Machinery

http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=79

There are some members here that know NFPA 79 very well and they may be able to help you more than I can.

 

[qcroanoke]

The NEC is silent on this.

I also think it would be a bad idea to try to change what they are used to.

I agree, NEC does not adress this.
Nor would I try to change what they are used to.
What you are proposing makes sense, but what if the bulb's filament had broken from vibration or some other reason since it was last operated? How would you know what E-stop had been activated?
The way it is now only two things could make the bulb go out. Bad bulb or an E-stop activated.
We often design our alarm circuits normally closed to open on alarm that way even if it is only a broken wire we will get an alarm.

 

[wireguy8169]

So basicaly its up to the user to determine what they want the red e-stop light to indicate? Sounds confusing and I would think that there would be some type of code on this topic so that all machines with e-stops would fall into the same type of operation no matter who built it.

I agree with you on keeping things common but light or no light does not really influence the safety aspect of an estop. With all the different types of switching used in estop circuits it would not work to make all have lights cause some are not even that type of switch could be a micro switch if there is a jam up between some rollers or something.
I did not see anything in the code on your question and can't think of any reason for there to be, unless it was an industry standard that all estops have a light but doubt that will be the case.

 

[markstg]

This is the colors from NFPA 79:

RED - Danger or alarm, abnormal condition requiring immediate attention

YELLOW (AMBER) - Attention, caution / marginal condition. Change or impending change of conditions

GREEN - Machine ready; Safety

WHITE - Normal Condition Confirmation

BLUE - Any function not covered by the above colors

 

[markstg]

I agree, NEC does not adress this.
Nor would I try to change what they are used to.
What you are proposing makes sense, but what if the bulb's filament had broken from vibration or some other reason since it was last operated? How would you know what E-stop had been activated?
The way it is now only two things could make the bulb go out. Bad bulb or an E-stop activated.
We often design our alarm circuits normally closed to open on alarm that way even if it is only a broken wire we will get an alarm.

If the E-stop is a mushroom head maintained type Pushbutton, Push to Trip, the one Pushed In would be the E-Stop that activated the trip. If the E-Stops are momentary than you couldn't tell. That of course is if all is hardwired. If they are wired to a PLC than any kind of capture of the events could be done.

 

[brewerinc]

My concern or reasoning for this is that I was brought into this company/position to automate a few of their processes. In doing so I have incorporated a few handling robots that also have e-stops that when pushed in are illuminated with a red light. I think it would be confusing for the end user/customer to which this machine would be going to have two different e-stop light conditions. With my background being 18 years in the automotive controls industry I found this to be true with each of their machines as well.

 

[brewerinc]

E-stop is a standard Square D 9001 series two position iluminated push/pull switch with a KA1 pair of contacts. This is typicaly what I use for my e-stop circuits.

 

[billsnuff]

NFPA 79 - 9.2.5.3. Stop, 9.2.5.4. E-Stop and 10.7 Devices for Stop and E Stop

I don't see anything for the indicatior lite, but just did a quick scan.

lite on lite off, don't bet the apple fritter on it. (I agree with Bob.)

 

[petersonra]

My experience is that many, maybe the majority of estop pbs are not lit at all.

They are commonly lit in some plants and industries to help in locating the open PB, but its not anything to do with any code. Just practice in that plant.

IMO, it is more important to monitor the PB with a PLC input so you can more quickly determine what PB was tripped. The lights are not real easy to see from more then 10 or 15 feet away, except in the dark.

 

[wireguy8169]

My concern or reasoning for this is that I was brought into this company/position to automate a few of their processes. In doing so I have incorporated a few handling robots that also have e-stops that when pushed in are illuminated with a red light. I think it would be confusing for the end user/customer to which this machine would be going to have two different e-stop light conditions. With my background being 18 years in the automotive controls industry I found this to be true with each of their machines as well.

At that point if your the person in charge you may just have to make a command desicion if you feel its in the best interst of customers and your product. So if your the boss looks like you have the green light to have the redlight anyway you like...:grin:

 

[Jraef]

Also you need to understand that unlike "general" industrial systems, robots DO have a safety standard that they adhere to, developed by the the RIA (Robot Industry Assoc.) and administered by ANSI as the American National Safety Standard ANSI-RIA R15.06-1986, "Industrial Robots and Industrial Robot Systems - Safety Requirements." In there I believe they do have definite descriptions of E-stop safety circuits but I'm still not sure they deal with illumination specifically. Most of the illuminated ones I see are yellow rings around the button, illuminated when the button is pressed (stop) so that you know immediately that it was an EMO (Emergency Off) command as opposed to some other safety detection system trip.

What I am saying is that Robots may not be a good example of how other E-Stop circuits should work because they have a somewhat unique set of requirements.