Estop Question

I have an OEM panel that has 1 estop on the main panel door and 1 remote estop. Most controls are 24 volt but there is one 120 volt output card.

They have 120 volts ac going through both estop buttons which are the key locking type that have to be reset with a key.

The estops drop out the coils on 2 AB safety relays /contactors and they break 120 volts feeding the ac output card and 24 volts feeding the dc output card.

They have no reset button as soon as you pull the estop out the safety relay / contactor has power again but when i't actuated it does give an input to the plc that estop was hit and outputs turn off in the plc and it drops out the start logic in the plc so the machine has to be restarted.

Looks like they are using the locking estop as their method of reset but things could restart when it's pulled back out if for some reason the plc did not get the input to drop out the start / hold logic in the plc.

Is this really safe? Just want opinions on the design. I think we may need to change it?

I'm no expert, but what is deemed "safe" depends on a risk assessment, not gut feeling. If the OEM has done a risk assessment and they feel that that solution is "safe" then it is safe.

If you want to change the OEM's design, then you should do a risk assessment. If you change the OEM's design then I'd think some liability would fall on your company in the event that something goes wrong.

Again, I'm not expert, just my understanding (which could be wrong)

Depends on the machinery I suppose, I prefer to have an E-Stop open a MCR or multiple MCRs, which cuts the power to VFDs and motor starters. Still have a E-Stop input to the PLC for logic purposes, to turn off other devices, say for valves that will not change back to OFF on their own. but the actual safety device is hard wired to the coils on MCRs

What you are describing sounds like it could be construed as a "software" safety.

I guess an example would be a 480 Volt motor contactor, say the contacts get welded together, Press an E-Stop and the coil of the contactor is turned off, but the motor stays running because the contacts are welded together, This is but one situation where a MCR would be beneficial.

Lets not turn this into another ramble about safety.
As dmroeder has stated as all other similar posts state.
######## RISK ASSESSMENT ########
this has been a standard to all European/British/Australian/American/(Forgive me if I left a country out)countries.
EDIT - for many years


To say any one method that does or does not include a Safety relay/PLC/Programmable Relay can mislead people reading this post.

Some countries safety systems are still back in the 70's
in most cases the old system did not fail often..
BUT IT DID FAIL

Have a look at AB/PILZ/SICK/JOKAB/.....web sites
They have really good replications of the Safety guide lines
most of which are translated from the listed countries requirements.

Who exactly is turning this into a "ramble" about safety?

iraiam said:

Who exactly is turning this into a "ramble" about safety?

Click to expand...

As dmroeder has stated as all other similar posts state.
######## RISK ASSESSMENT ########
this has been a standard to all European/British/Australian/American/(Forgive me if I left a country out)countries.
EDIT - for many years


Sorry but this is a paragraph meant to be read together
not paraphrased

Yeah search for SIL / PL
and most of times you will have to use safety relais, and double estop buttons.

I know this will be impertinent, but aren't guns killing more people in America than safety would ever do electrical?

Tim,

After reading your post several times and typing my response several times, I must ask What is a keyed e-stop?
Electrical machinery must be designed in accordance with the following:

NFPA 79 - Electrical standard for electrical machinery and
NFPA 70E - Arc Flash codebook.
NFPA 70 - electrical code book.

At some point you MUST buy these books and start studying them.

regards,
james

James Mcquade said:

Tim,
I must ask What is a keyed e-stop?

Click to expand...

I presume:

Tim,

if the e-stop is like the picture posted by Zimmer, then i advise strong caution with the following reasons.

1. what does the machine do?
2. if someone gets hung in the machine, how will he get out with the e-stop circuit locked out?
3. what are the state osha and local regs pertaining to this type of e-stop?
4. if the machine is going out of state,what are their regs?
5. what does the risk assessment dictate?

regards,
james

James Mcquade said:

Tim,

if the e-stop is like the picture posted by Zimmer, then i advise strong caution with the following reasons.

1. what does the machine do?
2. if someone gets hung in the machine, how will he get out with the e-stop circuit locked out?
3. what are the state osha and local regs pertaining to this type of e-stop?
4. if the machine is going out of state,what are their regs?
5. what does the risk assessment dictate?

regards,
james

Click to expand...

Generally speaking, these days, it seems almost good practice to have a RESET button on an estop. There is something in NFPA 79 that "..restoration of power shall not reset the estop...", which is what you get when you don't have a dedicated RESET. Easy to do.

Zimmer said:

I presume:

Click to expand...

Yes that's it. Therea re 2 of these and when hit they open a 700S-CF620DC and the 120 vac for the ac output modules is broken with the 700S-CF620DC and so I guess they key will qualify as a reset?

They sell lots of these machines so I guess it's legal and it works but it seems like a bottom of the barrel method of doing it IMHO.

To put it simply.
There is No "I Guess" with machine safety

"I guess it is ok fo a five year old to drive a car down a freeway at 100 miles per hour with no one else in the car."

Our point

Do a Risk Assessment or get a professional to do it.

Don't get caught by saying " it's been like that for years" that makes the statement that you accept liability because you knew of the issue.

Where does the legal burden of responsibility lie? Neither Tim nor his company designed this machine or its controls. He sees something that looks a little odd to him. Does that suddenly make him legally responsible? Taking your 100 MPH 5-year old, iant, if I see him driving down the freeway am I legally responsible for stopping him? Am I even legally compelled to report it? We shouldn't confuse morality with legality. They are often two different things.

Having said that, the e-stop is not designed the way I would have done it. But if the OEM performed a risk assessment and determined this level of protection is sufficient I can't say any differently without doing a risk assessment myself. For all I know this machine is surrounded with 6" battleship steel walls and has a 1/4" hole for parts to drop in on top and a similar hole for parts to drop out on the bottom. Regardless of the hazard identification the physical risk mitigation may not require any additional electronic mitigation. What you have may already be overkill. We just don't know.

Keith