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 Post subject: loto procedure
PostPosted: Fri Apr 17, 2015 2:18 pm 

Joined: Sun Oct 07, 2012 11:15 am
Posts: 7
Is it necessary to ground a mcc bucket as part of a loto as stated in 70e ? As I see it it can be a problem for some QW who may not have any electrical experience. Something like this should be left to the people who do electrical work every day. Would this type of loto be for something like a main in a mcc ,not a bucket ?


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 Post subject: Re: loto procedure
PostPosted: Sun Apr 19, 2015 9:14 pm 
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Location: North Carolina
bure961 wrote:
Is it necessary to ground a mcc bucket as part of a loto as stated in 70e ? As I see it it can be a problem for some QW who may not have any electrical experience. Something like this should be left to the people who do electrical work every day. Would this type of loto be for something like a main in a mcc ,not a bucket ?


It says where it is required. That is, when potential hazards exist. This is not just a 70E requirement. It is also an OSHA requirement for this in the U.S.

Workers coming from a medium or high voltage environment, especially utilities, would question why anyone would ever question this. Those working below 1 kV typically would question why it would ever be necessary. The answer is...it depends on whether or not hazardous voltages (induced or stored) may exist. If they do, then grounding is required, even if it's just a one-time discharging effort.

There are several sources of potential energy to watch out for:
1. Shielded cables (underground application) may have stored charge in their insulation (its a capacitor).
2. Someone decides to hook up a generator to a panelboard without a transfer switch or at least opening the main breaker.
3. Lightning, even several miles away.
4. Upper line drops accidentally onto a lower line.
5. Common practice to tag out only (not LOTO) so someone decides to ignore clearance tags and re-energizes line, accidentally or intentionally. This is typically only a problem for utilities.
6. Wind blowing through wires will induce a charge in some cases.
7. Two parallel lines form a transformer. With a long enough run, and especially with the older outdated practice of grounding and working "between grounds" (forming a ground loop), induction can energize a line that is grounded when not using single point grounding.
8. Capacitors in the system with stored charge.
9. Ground potential rise from nearby electrical structures (more induced effects).

If you walk through this list and don't find a reason to ground, consider not doing it.

Grounding can be pretty hazardous by itself. Two specific instances come to mind. Some sites use a "grounding truck" which is essentially a switchgear module with a shorted bus on it. Racking it in grounds the bus. It can also cause a massive bolted fault if racked into a live line. Second instance is that when removing grounds, quite often they draw a substantial arc where induced voltages are present but little or no arcing when connecting initially.


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