How do you handle new E-Stops?

When you're doing a project, especially small ones how do you handle designing the emergency stop circuit?

It's my understanding that the customer is responsible for telling the designer what category (SIL #??) the machine is rated for and that rating determines the basic design of the circuit.

It is also my understanding that a typical system integrator (us) does not have the knowledge or certification to make the decision as to what the hazard level is.

One of the areas where this causes problems is in bidding a job and putting enough money in the bid to cover unknown material costs. I guess we'd have to put some kind of CYA verbage in the the quote letter.

Thanks in advance for your answers.

If it's a custom machine or cell, I believe that the customer needs ownership even if they are not capable of figuring it out for themselves. This can be accomplished by having them signing-off on the completed risk analysis. Once that is done, your design must meet those requirements. As for who is best suited to complete the risk analysis, I think the machine/cell designer(s) need to do this.

If you're competing with someone who is willing to gloss over this and thereby supply an unsafe or incomplete system and a customer who accepts that, you may not really want that job anyway.

IMHO

dogleg43,

All new machinery must comply with NFPA 70 - electrical code,
NFPA70e - are flash, and NFPA79 - electrical standard for industrial machinery.

Through the years the area in assigning responsibility of who does what is ever so thin.

An oem who is building a new piece of equipment is responsible for doing a risk assessment. They then in turn goto the customer and discuss their findings with them (maintenance, operators, engineering, safety, and management) for any improvements.

A systems integrator who is building a control panel with controls to go onto any piece of equipment must also do the same. It doesn't matter if they are building the control panel for a new machine for themselves to sell, as a subcontractor to a machine shop, or for an existing piece of equipment in a factory, a risk assessment must be done and any problems found in the equipment must be dealt with and addressed.

All parties involved must agree on the risk assessment. If the customer refuses to fix any issues or concerns, a document must be drawn up and signed by the customer releasing your company, its employees, and their family members (yes, I do mean family members) of any liability in regards to those issues.

This document will NOT release your company in failing to abide with the rules noted above.

This is from personal knowledge and experiences from working with an oem for almost 20 years and I am prevented from saying anything further.

Things may have changed, but assuming that you do not have to do a risk assessment is foolish in my opinion. When someone gets injured or killed, all eyes will be on the company that made the machinery, controls, did the installation, everything. You better have all your bases covered as best you can to avoid legal issues.

regards,
james

dogleg43,

The primary things an E-Stop must do are:
Drop all power to all areas of any machinery
Stop all motion, motors, drives, etc.
Require an action by someone to reset the E-Stop condition (reset PB on E-Stop safety relay)

Always remember that you have to make it Idiot-Proof, and realize you are probably underestimating the quality of idiots HR can hire.

James Mcquade said:

dogleg43,

.......All new machinery must comply with NFPA 70 - electrical code,
NFPA70e - are flash, and NFPA79 - electrical standard for industrial machinery........

regards,
james

Click to expand...

Yes, I agree with you. This particular project is modifying an existing control system and the consulting engineers specified an emergency stop PB. No other details. My thought is that the consultants should have included that rating in the spec's or are responsible for telling us what it is now that we have raised the question.

Since this is a retrofit(upgrade) they are responsible for telling you what is lacking and detail what needs to be done. Specifying an E-stop pb by itself just doesn't cut it in my opinion. Is there a safety relay in place? Mcr by itself?
I don't know the particulars of your system, so I would ask them for details on what the system is lacking and ask for specifics.

I think that when you do an upgrade, you must look for current violations and address those issues, that's my opinion.

james