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 Post subject: Steps for Establishing an Electrically Safe Work Condition
PostPosted: Wed Nov 29, 2017 12:28 pm 
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2018 NFPA-70E 120.5 lists 8 steps for establishing and verifying an electrically safe work condition (and says they are to be performed in order).

It does NOT include what the industry calls “Try Out”, even though this is required in 120.4(B)(5) Verification, which states,
Quote:
“The equipment operating controls, such as push-buttons, selector switches, and electrical interlocks shall be operated or otherwise it shall be verified that the equipment cannot be restarted.”


Is anyone aware of any reason why this requirement isn’t integrated into the 8 steps?


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 Post subject: Re: Steps for Establishing an Electrically Safe Work Conditi
PostPosted: Fri Dec 01, 2017 7:43 am 
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...crickets chirping...


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 Post subject: Re: Steps for Establishing an Electrically Safe Work Conditi
PostPosted: Thu Feb 01, 2018 12:19 pm 
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Its says in (7) to use adequately rated test equipment to test each phase to verify that it is de-energized.
“The equipment operating controls, such as push-buttons, selector switches, and electrical interlocks shall be operated or otherwise it shall be verified that the equipment cannot be restarted.”
You are complying with 120.4(b)(5) when testing with test equipment(meter) to verify lack of voltage.
The issue with "Try Out", is that it doesn't verify the lack of voltage, it just verifies that the machine won't operate. The machine not operating is fine for operations folks, who need to clear a jamb in the equipment, by locking and trying. But if you are going to be exposed to live electrical parts you need to verify with a meter etc, otherwise you have not established a safe work condition.
With the tryout method, you could disconnect a 3phase service, try it and it would not operate, but there could be a single phase or auxiliary supply that is still live. The machine will not operate, but the machine is not in an electrically safe condition. Verification is always required if you are going to be exposed to live parts.


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 Post subject: Re: Steps for Establishing an Electrically Safe Work Conditi
PostPosted: Sat Feb 03, 2018 10:17 am 
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From a practical point of view agreed. MULTIPLE times I've done "try out" and it utterly failed to work for electrical work. Among the reasons:
1. Wrong starter, buttons, etc. This is also true for general lockouts. It is a very scary feeling if you ever violate this and find yourself holding onto a live 2400 VAC line that is badly corroded and barely holding onto the terminal. In defense of my stupidity, I did check for absence of voltage at the disconnect for the transformer where it was marked on both the primary and secondary sides. Up in the ceiling the conduits had been "swapped" at some point in the past due to a prior transformer failure and were never swapped back.

2. It does not address conditions where there are multiple voltage sources, particularly shared control power. This one "bites" a lot of people.

3. Just because the handle moves on a circuit breaker or a disconnect and at least 1 phase manages to open doesn't mean that all of them did. Really common in plants that still have some of the old 1960's-1970's infrastructure buildout era that are now mechanically questionable.

4. All kinds of interlock arrangements making it appear that things are de-energized when in fact they aren't. Often times it is basically just dumb luck that the motor does not appear to start manually and it turns out to be very much alive. I've also seen more than once with common control power where the "running" feedback in the control room comes from starter auxiliary contacts and operators can energy the starters and are confused by the idea that it's "running" when it's locked out.

It should be noted that "try" is actually in OSHA Subchapter S but there is a slight difference. That regulation requires QUALIFIED personnel to do the actual "try" although Subchapter S lockouts do reference Subchapter J lockouts and does allow you to "mix" lockouts as long as you do all the activities that are unique to one or the other. Most of the time that means mechanical trades can use electrical lockouts. Electrical trades can't really use mechanical lockouts except for the lock part because testing for absence of voltage and grounding are extra steps that are required for general lockouts.


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