An ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis, operating efficiencies and cost savings, as well as all relevant safety standards, such as those from NFPA, ANSI, RIA, IEC, ISO and OSHA. About J.B. Titus.
Machine Safety: My main disconnect e-stop isn’t red with a yellow background
July 05, 2012
Does my main disconnect functioning as an e-stop need to be red with a yellow background?
This has long been an active area of discussion in manufacturing. In fact, using a main disconnect as an emergency device for removal of power has a long history. Some of us might remember when machines evolved to having their own machine mounted motor and or drive. Soon after this evolution the crow bar circuit emerged for emergency stopping a machine. I expect young folks today would laugh at seeing someone pick up a crow bar and throw it at the three main leads shorting out the current. An e-stop was born!
Fast forward to today and realize that the discussion about main disconnects being used as an e-stop device was only recently updated in NFPA 79 – 2007, Clause 10.7.4 Local Operation of the Supply Disconnecting Means to Effect Emergency Stop. The last updated NFPA 79 – 2012 made no changes to these requirements. The requirements of this Clause are:
10.7.4.1 The supply disconnecting means shall be permitted to be locally operated to serve the function of emergency stop as follows:
(1) Where it is readily accessible to the operator
(2) Where it is of the type described in 5.3.2(1), 5.3.2(2), or 5.3.2(3)
10.7.4.2 Where used as an emergency stop, the supply disconnecting means shall meet the color requirements of 10.7.3.
10.7.4.3 Disconnecting (isolating) electrical devices as described in 5.5.4, where accessible to the operator, shall also be permitted to serve the function of emergency stop. _____________________________________________________________
The additional requirements that I understand are that every machine needs to have at least one e-stopping device as determined by the risk assessment, that it needs to be red with a yellow background per 10.7.3 and that it needs to be accessible by the operator. ANSI B11.19 – Performance Criteria for Safeguarding normatively references NFPA 79 – 2007 as required.
Is anyone still confused?
Your comments or suggestion are always welcome so please let us know your thoughts. Submit your ideas, experiences, and challenges on this subject in the comments section below. Click here controleng.com/blogs if you don't see a comments box, find, and click into: Machine Safety: My main disconnect e-stop isn’t red with a yellow background, and scroll down.
Related reading and articles:
Contact: www.jbtitus.com for “Solutions for Machine Safety”.
For more than 30 years, J.B. Titus has advised a wide range of clients on machine functional safety solutions, including Johnson + Johnson, Siemens, General Motors, Disney, Rockwell Automation, Bridgestone Firestone, and Samsung Heavy Industries. He holds a Bachelor of Business Administration degree from Oklahoma University in industrial management and an MBA from Case Western Reserve University in marketing and finance. He is a professional member of the American Society of Safety Engineers and is OSHA-certified in machine guarding. Titus is also TUV-certified as a Functional Safety Expert and serves on several American National Standards Institute, National Fire Protection Association, and National Electrical Manufacturers Association national safety and health standards committees. Reach him at jb(at)jbtitus.com and via www.jbtitus.com.