Electrical safety issue 2

[thinker]

Our customer's (major automotive manufacturer) local safety
standard states the following requirement to main power
disconnect switch: " OPERATING HANDLE SHALL BE PERMANENTLY
AFFIXED TO THE DISCONNECT SO THE HANDLE IS IN CONTROL OF THE
DISCONNECT AT ALL TIMES, INCLUDING WHEN THE ENCLOSURE DOOR
IS OPEN". Was this requirement originated from any of more
general standards (like National El.Safety Code or NFPA) or
this is just local initiative?

 

[busbar]

One online comparison for molded-case breaker accessories is:

“Type SM Safety Handle Mechanism”

http://www.cutler-hammer.eaton.com/unsecure/cms1/IL_14439E.PDF

A slang term for these is “flange operator”.

“Universal Rotary Handle Mechanism”

http://www.cutler-hammer.eaton.com/unsecure/cms1/SA29D02SE.PDF

A slang term for the second assembly is “rod operator”. Safe to say many plant-floor electricians feel that rod operators are, without question, blue-ribbon trash in any form.

 

[MakeItSpin]

Busbar gives two examples of disconnects commonly used in industrial panels. Lots of the "rod operator" types don't allow lockout like the example he sites does. When you open the door, your lockout point essentially goes away.

NFPA 70E, "5-1.3.1 Individual Qualified Employee Control Procedure." concerns this. Basically it allows a qualified individual to NOT apply a lock if the live parts are adjacent to the disconnecting means. Is it good practice? Probably not. And good luck with OSHA if they see someone doing it.

 

[thinker]

Thank you Busbar and MakeItSpin. A little bit more details
on our problem. We (as a system integrator) supplied a third party converter.It has input molded case CB (1200 A frame) with door mounted handle and OUTSIDE lockout provisions. When the door is open, nothing prevents the CB to be turned ON, and this is specifically prohibited by customer local standard (see my original posting). Since there is no way around safety inspection, we try to force the converter vendor to modify their system (install another
CB with provisions to lock out the CB when the door is open.
It would be easier to apply pressure on vendor if we knew that these provisions are required not only by local standard, but also by, say NFPA.(Suprisingly, this converter
is UL listed).

 

[gigahertz]

The only way that is acceptable as a locking mechanism under any code is if the external lock also prevents opening the door to get to the breaker. Check under definition of lockout in any code ...

 

[meihm]

Another alternative would be to provide a microswitch that shunt trips the circuit breaker when the door is opened.

 

[buzzp]

What meihm has stated is used widely in the industries I am familiar with.

 

[busbar]

Thinker, you may be hard pressed to find a differentiation between the two linkage styles in root safety documents. The requirement most likely is a line item in a purchase order or related procurement documents and not contained a generic consensus-safety standard. IMO, one aspect of this is timely troubleshooting and machine restoration. Rod operators generally are or soon become a repeated, mechanically squirrelly headache for open-cover machine operation during energized troubleshooting. An open switch makes the task of simple voltage and current measurements impossible.

buzzp and meihm, I mean no personal offense, but a shunt-trip feature does not meet the requirement for lockout, and seems to exist primarily because control-equipment vendors can “sneak” the shunt-trip or undervoltage-release mandate into their specs, but alas, as a convenient 'no-expense-for-me' accessory. They can get away with not having to pay for this, using the infamous “by others” scapegoat clause. An equally pathetic ‘safety’ mechanism are solenoids that keep hinged control-panel doors from opening during energized operation. Again, such a feature often makes voltmeters and ammeters completely useless for troubleshooting efforts.

 

[stevenal]

One standard easily found is OSHA 1910.147:

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9804

Look at the definitions as gigahertz suggested.

I'm not sure if this or any standard helps you apply the pressure you want. Just because a third party supplied a convertor that does not meet the definition of "energy control device" doesn't relieve anyone's responsibility of ensuring that such a device is installed upstream.

 

[MakeItSpin]

NFPA 79 "Electrical Standard for Industrial Machinery" 2002 Edition "5.3.3.1.", requires the disconnect to be capable of being locked in the open position independent of the door position. It also states that the disconnect must be operable by qualified persons without tools independent of door position.

Read the ROP if you're interested in their logic.

 

[thinker]

Thank you MakeItSpin.Your reference is precisely what I needed. I did not know about 2002 edition of NFPA 79.
Interesting, that 1997 edition we have, does not address this issue in all details. Your info was a great help!

 

[Antje]

Hi busbar,

You used the term "Energized Troubleshooting" could you or someone else please explain what this means.

Thank you.

 

[xnuke]

It's hard to take voltage or current readings on a circuit that is deenergized, so to find a fault you might need the circuit to be live. That is what is meant by energized troubleshooting. In my opinion, lockout/tagout is not meant for troubleshooting by authorized personnel with proper training, but meant to protect affected personnel or equipment from a dangerous condition that could exist if the power was still applied to the equipment. Almost all the troubleshooting I've ever done has been on energized circuits.

Incidentally, we had a contractor's electrician that opened a MCC bucket where the flanged disconnect switch was locked out. Because the electrician had "violated the lockout", i.e., he could operate the circuit breaker handle at will, he was summarily dismissed and blacklisted from ever working at our company again, even though he did not and would not shut the breaker. This goes back to the requirement that the equipment be locked out regardless of the door position.

There are pieces of lockout equipment that could be attached to the breaker handle directly instead. One solution may be to have the person performing the lockout turn off the disconnect, then open the door and lock the breaker off, carefully avoiding incoming power circuits. This way, the electrician could not have operated the breaker, and the operator's safety would not be violated by opening the door. I know this raises the question of an untrained operator working in the vicinity of the live incoming power, but I believe the risk is minimal. After all, the person should be trained on how to properly lockout the equipment, so these hazards could be addressed at this time. (If fuses were used instead of a breaker they could be pulled safely as they should be downstream of the disconnect.)


xnuke

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[busbar]

xnuke covered it well. Think of it this way. A multimeter is almost a universal tool for troubleshooting. A basic model measures voltage, current and resistance—but voltage and current disappear when power is removed. There is no replacement for tracking the many logic states and analog levels that occur in normal or malfunctioning machine operation.

In 99NEC110-26, three dimensions are addressed: height, width and depth, as is accessibility and lightning level in the workspace. “Working space for equipment… likely to require examination, adjustment, servicing, or maintenance while energized…”

Unfortunately, some have suffered serious injuries and grisly deaths as a result of inadequate working space.

 

[Antje]

Thank you ever so much for your competent, clear and swift answers. It's now even clear to me (non-native speaker of English and absolute blockhead as far as electrical engineering is concerned).

Best regards,
Antje

 

[skiier]

Did someone say "start-up" and "debug" or "troubleshooting"? Guess what. This is probably the most dangerous time of machine operation.
Working in the automation industry I have seen people run to turn off disconnects - in an emergency during start-up and debug - that had their handles pulled out because they were mounted on the main control enclosure door which was open! Most times some maintenance staff or programmer will have the enclosure doors open. These programmers are generally responsible for the design of the controls and are not usually there after the initial debug and start-up. They don't really become aware of normal maintenance and lockout procedures and the hazards involved so in the past safety design problems in the initial installs went unnoticed. So what happened in the industry is that a bad design - used industry wide for years - only became apparent after an emergency, or death, occurred.
Most major automotive manufacturer's spec that the actuator for the disconnect must always be on the disconnect.
Most rules or specs have pretty obvious reasons for their development and implementation, sometimes it takes time for them to be apparent however.