Stop button required or not ?

[brother]

I dont recall the exact nfpa article or if it is just an OSHA issue, but is a stop button for the controls of the loading dock platform required? I always thought they were. What we found is a loading dock that the start/go button is a momentary contact has to be held in to operate the platform, basically when you release the start button the motor stops. The issue here is that the start button had gotten stuck and the platform/motor would not stop running. The staff had to rush to the disconnect to shut it off. It was once wired with the stop button but it was bypass/ no longer part of the circuit.

Since the pushbutton was momentary , I was told that this was not required. For safety reasons I thought they were required, even if its not an 'e- stop mushroom', just for some of the reasons that happen above when the button got stuck and the motor wouldnt stop.

What NEC article says this, or is it a NFPA 79 control issue, or OSHA safety?

 

[tom baker]

The NEC is an installation standard. Your application is as you suggest NFPA 79 and or OSHA. But stop buttons are always wired in series, and when on button is pushed it drops out the power in a holding circuit, denergizing the motor contractor. A simple solution is to have a maintained stop contact in series with the momentary start button.

 

[ptonsparky]

IDK about required, but a maintained position Stop is a danged good idea. That and a disconnect at the motor.

 

[paulengr]

IDK about required, but a maintained position Stop is a danged good idea. That and a disconnect at the motor.

NFPA 79 states stop buttons need to be a single action on a dedicated button. And that reset should be a different action. Some mushroom head stop buttons are push to engage (open circuit) and twist to release or they have a guard so you have to reach around it to pull the button back out.

 

[petersonra]

I don't see how NFPA 79 covers a loading dock platform.

I don't see how this is a particularly dangerous situation when it gets to one end or the other it is going to stop anyway either because it hits a hard stop or because there's a limit switch there that tripsit. I don't have an issue with having an e-stop push button but I'm not sure that as a safety measure is really needed.

What troubles me about this situation is someone has hacked the original design. The other thing that bothers me is apparently according to your original post this thing has happened more than once. That is extremely unusual. How could multiple push buttons fail that are not used all that much. They are typically rated for a lot of operations. Like Millions Maybe. It makes me wonder if someone is abusing the button by jamming a stick in it or something.

 

[ptonsparky]

We had to insert a timer into a process where I just happened to notice the screw driver still wedged into the run PB. 15-20 seconds was all it needed to be held. To much work, I guess.

 

[paulengr]

I don't see how NFPA 79 covers a loading dock platform.

I don't see how this is a particularly dangerous situation when it gets to one end or the other it is going to stop anyway either because it hits a hard stop or because there's a limit switch there that tripsit. I don't have an issue with having an e-stop push button but I'm not sure that as a safety measure is really needed.

What troubles me about this situation is someone has hacked the original design. The other thing that bothers me is apparently according to your original post this thing has happened more than once. That is extremely unusual. How could multiple push buttons fail that are not used all that much. They are typically rated for a lot of operations. Like Millions Maybe. It makes me wonder if someone is abusing the button by jamming a stick in it or something.

NFPA 79 is a voluntary standard, not required. Contrary to popular belief E-Stops are not required except on hydraulic presses. But as far as where the goofy stop button requirements come from that’s all NFPA 79 and tribal knowledge. The OP question was about stop buttons.