Multiple start buttons

tmerc65

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Jun 2009
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I’m currently working on a wire processing machine. Basically an unwind, coating, heating and rewind running relatively slow (25 Feet/min). My question is during the threading process the operator would like the ability to start and stop the machine at various locations. NFPA 79-9.2.5.2.4 states that if multiple starts are present then all start control devices shall be actuated concurrently, so multiple start buttons will not work. My question is if we introduce a THREAD MODE that limits line speed to the machine and is selected and enabled at the main operator station can I then have several locations that have a THREAD SPEED button that is only active in this mode. Of course there would be a STOP and E-STOP at the same location. We have looked at JOG push and hold buttons but some of the products take two hands to wrestle, and allowing a second operator to control the JOG or start and stop seems more of a safety issue then multiple start buttons.
 
QOUTE
My question is during the threading process the operator would like the ability to start and stop the machine at various locations. NFPA 79-9.2.5.2.4 states that if multiple starts are present then all start control devices shall be actuated concurrently, so multiple start buttons will not work.
QUOTE END

It may be best to copy the whole paragraph here. I find this confusing and ambiguous. I only have NFPA Natl Elect Code handy.

You can have multiple start stop and jog stations wherever you want and however many you want.
I would wire ALL stops in series then the starts in parallel and the jogs in parallel. Takes a little more wire but the advantage is that ANY stop will stop the machine. E stops should be in a completely separate circuit and depending on you machine safety classification may have to have additional controls.

Having one guy jog a machine while another is doing something inside it ie threading can be dangerous but sometimes is a fact of life. It comes down to guys who can work well together and trust the guy on the button. Classic example is setting something with crane - one guy guiding and another on crane control.

VERY frequent occurance in maintenance work - have done with a lot of interlocks jumpered out.

Dan Bentler
 
NFPA 79
9.2.5.2.4
On machines requiring the use of more than one control station to initiate a start, the following criteria shall be met:
1) Each control station shall have a separate manually actuated start control device.
2) All required conditions for machine operation shall be met.
3) All start control devices shall be in the released (off) position before a start operation is permitted
4) All start control devices shall be actuated concurrently.

This indicates to me that I can not use a start button in multiple locations unless all the start buttons are pushed at the same time. I have personally done CE marked machines that only 1 start button could be active at any given time and this was selected from a master control location. The NFAP 79 version of this sounds even more restrictive then CE.
 
Perhaps you are trying to apply a restrictive standard that is intended for another purpose?

Does your machine have the requirement:
On machines requiring the use of more than one control station to initiate a start

I don't believe this is intended to apply to all machines that have more than one control station but specifically to ones that *require* multiple stations to initiate a start. The obvious example is the dual palm switch system to assure operator's hands are not in the machine before starting. Criteria 3 is the "anti-tiedown" common in those systems.
 
I know this may be playing semantics but…
Your remote buttons will actually be “jog” buttons and I am assuming they will be momentary contacts. They could also call for a lower then normal run speed.
This is not really classified as a “Machine Start” Control.
 
NFPA 79
9.2.5.2.4
On machines requiring the use of more than one control station to initiate a start, the following criteria shall be met:
1) Each control station shall have a separate manually actuated start control device.
2) All required conditions for machine operation shall be met.
3) All start control devices shall be in the released (off) position before a start operation is permitted
4) All start control devices shall be actuated concurrently.
This indicates to me that I can not use a start button in multiple locations unless all the start buttons are pushed at the same time. I have personally done CE marked machines that only 1 start button could be active at any given time and this was selected from a master control location. The NFAP 79 version of this sounds even more restrictive then CE.

I too believe that this is applicable to machines where two start buttons must be pressed simultaneously to start. An example is a punch press.

I do not believe this applies to your machine.

IF I recall correct the JOG switch on a punch press was not a two hand control. HOWEVER on many machines I saw it could only be used by means of a key switch to allow for JOG and only used when setting up dies.

Dan Bentler
 
Just an idea (not relating to any particular regulations etc).
If you have multiple operating postions/ control stations on the machine you could do the following:

Each control station has Estop, start, jog enable keyswitch, jog enabled lamp and a jog forward, and jog reverse button. The idea being that all jog buttons are normally disabled. The first key switch to activate on a station will enable jog mode ONLY on that station. A second keyswitch active anywhere could then disble jog mode; maybe flashing the lamps to indicate why its not working??

Just an idea.
 
Firebrd10 – The semantics is what I was going for with the thread (reduced speed) approach. 📚

Melliss / leitmotif – I would like to believe you trust me. But the wording is multiple control stations and not multiple start devices. Two hand control devices are also covered in a separate section of NFPA 79.

My customer is the one that brought this up and actually willing to work with me and try to figure this out, but it got me thinking (and I’m known for over thinking) about this. No one I know has encountered an issue with multiple starts, except in the CE world, and I was wondering if anyone on this forum has.
 
I think the key word in the spec is "requiring". To me that means it's describing a machine where the start signal from all of the control stations must be asserted in order to start.

What you're describing is a machine where the start signal from any of the control stations can start the machine.

Does NFPA have anything to say on the subject of what types of machines "require the use of more than one control station to initiate a start"?
 
Please do not take my word for it, it's just a suggestion of something you might want to investigate further.

The point I was trying to make is the wording is:
requiring the use of more than one control station to initiate a start

It's not simply "with more than one control station". It specifically says that the mutliple controls stations are *required* to initiate a start. I take this as a more generalized form of the two palm button system, to cover situations where more than one operator has to press a start button to get the machine going perhaps? It just doesn't sound like a reasonable requirement for any situation with more than one control station.
 
Just one more tidbit of the NFPA 79 Standard before I never quote another machine with this as a requirement.

9.2.7.5
Where a machine has more than one operator control station, measures shall be taken to ensure that only one control station shall be enabled at a given time. Indication of which operator control station is in control of the machine shall be provided at locations where necessary for the safety requirements of the machine
Exception: A stop command from any one of the control station shall be effective where necessary for the safety requirements of the machine.

This brings this standard much closer to the European CE standards. ☯
 
The question I have is what is the definition of a control station? To me, it is where an operator can change the operating mode of the machine, i.e., from jog to run.

I am of the opinion that a REMOTE box with a start/stop/e-stop is not a control station.
 
The question I have is what is the definition of a control station? To me, it is where an operator can change the operating mode of the machine, i.e., from jog to run.

I am of the opinion that a REMOTE box with a start/stop/e-stop is not a control station.

I think this brings up a good question ie just what is being discussed here?

I have been thinking on this and am believing I need to go buy a copy of the manual / code.

Based on a few years in Safety and Health work where multiple codes were applicable this would not be the first confusing poorly written code I have seen. It is best of course to read the definitions which in some cases only adds to confusion.

What really bugs me is that NFPA is comprised of people in the electrical business and still are able to make it confusing for others when they in theory should remember instances where NEC writing phraseology cause confusion.

Dan Bentler
 
The way the code is being referred to here seems ludicrous. ALL of our equipment has multiple operator control stations, each OCS can initiate motion somewhere. That must be, we have lines hundreds of feet long, and several stories high.

Of course, we do have a single point "Line Start" pushbutton, but there are multiple jog, progressive jog, thread, and progressive thread buttons and foot pedals.

I really tend to come down on the side of that requirement is meant for a machine that has a two-hand safety system myself, like a press, or a shear. Not a production line.
 
Originally posted by rdrast:

Of course, we do have a single point "Line Start" pushbutton,...

But that is exactly the OP's point. He currently has multiple Line Start buttons. One of his possible courses of action is to move to thread or jog buttons.

Given the context I'm not sure what they are talking about in that paragraph. I'm inclined to agree with Steve Bailey's assertion that this only applies to machines where a valid risk assessment or operational requirements REQUIRE that more than one start button is required to start the machine. In that case points 1 and 2 are just general operational safety points and points 3 and 4 are a quasi-anti-tiedown requirement.

Keith
 

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