Machine Safety: My main disconnect e-stop isn’t red with a yellow background
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?
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