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 Post subject: Label 'Generic' Pull boxes?
PostPosted: Mon May 02, 2016 3:01 pm 

Joined: Mon Aug 24, 2015 10:24 am
Posts: 28
See attached for a common item I run across at our facility - 4160V, 480V, 208V, pull boxes with screw on lids that are not identified. Many have the voltage warning label but not much else. Should I be planning to label such clearly accessible boxes with arc flash labels?

I realize that NFPA 70E Table 103.7(C)(15)(A)(a) doesn't require labeling assuming all is well, but if I was investigating a circuit path I'm sure I could wind up needing to get into this box without being 100% sure of the circuits inside nor of what kind of condition the wiring methods are in inside. What would you do?

Thanks,
Brian


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 Post subject: Re: Label 'Generic' Pull boxes?
PostPosted: Tue May 03, 2016 11:13 am 
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See NEC 110.16: " Electrical equipment, such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers that are in other than dwelling units and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment."

Two key concepts here. The first is the phrase "such as". The equipment list is an EXAMPLE, not a comprehensive requirement.

For instance disconnect switches, especially the fused variety, are not included on the NEC list but clearly meet the definition of requiring maintenance.

The second concept is that it is LIKELY to require some kind of work while it is energized. As an example it is not standard practice for most plants to open and service a motor peckerhead while it is energized. In this case a peckerhead does not require a label.

A true "pull" box where wiring merely runs through a box without termination within the box also typically doesn't require servicing while energized so again, no label.

But where we get into equipment that has terminals and/or junctions which is specifically designed for servicing clearly would require a label if it is serviced while energized. Again this does somewhat depend on what your plant practices are.

A final concept is that of time. Even if equipment under consideration meets all the requirements above when it is being serviced if you have equipment that rarely gets servicing of any kind (say at least a year or more between servicing), then it may not meet the definition of likely. For instance it would not be unusual to find some kind of panel such as say one that has terminals that allow termination of a cable that is only allowed for underground service to one that is rated for more general purpose service that is rarely opened or serviced in any way.

The whole concept here is that electricians should NOT have to go pull the single line prints and check what the incident energy is (or ask someone else who is qualified to do so) the vast majority of the time but it is acceptable if this happens on an infrequent basis.

Many plants have some kind of "default rule". Usually this means that for instance the assumption is that any unmarked panel is automatically considered 1.2 cal/cm^2 and may or may not also have an automatic voltage assumption, or that unmarked panels are to be treated according to the tables in 70E instead of following the label. Having a default rule like this drastically reduces the number of panels that have to be labelled but there are two caveats to it. The first is that the tendency is that if there's no label, have at it...don't think about the consequences. The second caveat is that a label can be missing, obscured (depending on the approach), or simply missed during the last labeling campaign. Thus the correct result is to use the follow up mechanism but with a "default rule", this does not happen.

Frequently the "default rule" is used in conjunction with a very strict interpretation of the NEC label rule though so that for instance a lot of "utilization equipment" (loads and boxes associated with loads) does not get a label. Only the distribution equipment (panelboards, MCC's, switchgear, disconnects, and similar equipment) gets a label.

The reverse case (label everything) also has a downside. This means that most plants will have a huge number of "lighting panel labels" with a label that basically says the panel is not a significant hazard. If it looks like all the other labels, the tendency will be to get complacent and ignore arc flash labels altogether.


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 Post subject: Re: Label 'Generic' Pull boxes?
PostPosted: Mon May 09, 2016 8:58 am 
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Posts: 119
But..........
Until you open it up to see that it is "just a pull box",.......
It is sort of "Schrödinger's Pull box", it both is and isn't
I once opened one, only to find a set of three MV PTs, connected to switchgear on the other side of the wall.


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 Post subject: Re: Label 'Generic' Pull boxes?
PostPosted: Mon May 09, 2016 9:48 am 
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Location: Port Huron, Michigan
JKlessig wrote:
But..........
Until you open it up to see that it is "just a pull box",.......
It is sort of "Schrödinger's Pull box", it both is and isn't
I once opened one, only to find a set of three MV PTs, connected to switchgear on the other side of the wall.


Then label it as to what it is. It never hurts to have a label like "Pull Box for XXXX Cables", for instance.


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 Post subject: Re: Label 'Generic' Pull boxes?
PostPosted: Mon May 09, 2016 1:46 pm 
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There is always an element of an "unknown" for any industrial plant. Even the most perfect labeling system with an electrical group that always does exactly what they are supposed to do in the most professional manner over time can run into trouble. The label can fall off for instance.

It is the same problem as the element of the unknown when opening a door. And even if it has a label even in the best of plants, that doesn't mean anything. Examples:
1. Two 2300:480 transformers fed by two fused MV disconnects and feeding two fused disconnects for isolation purposes. Electrician (that's me) opens 2300 V disconnect, observes blades open, and uses a tic for good measure. Electrician also opens and inspects 480 V fused disconnect and uses a meter to verify absence of voltage on the 480 V end. Electrician goes to open transformer and it was NOT dead. It was very difficult to trace out conduits in this area but suffice to say that previous modifications and the fact that one of the two identical transformers had failed so someone swapped leads (and conduits) so the transformer labels ended up switched. No good way to detect this no matter how hard you try.
2. Electrician went to work on a well that had a contactor and small relay external to the MCC nearby. Electrician (again, that's yours truly) locks out the disconnect labelled "Well". Conduits all run underground so no way to trace anything. Nothing visually wrong and at the time the pump is not running. Fortunately electrician checked for absence of voltage and found the starter was energized! What had happened was that at some point the MCC bucket failed so they went to another bucket as a temporary measure and had marked the bucket with magic marker. Over time the marker faded and since the original phenolic label wasn't removed, it was no longer obvious at least externally that the bucket internally was stripped and devoid of anything except a disconnect.
3. And the most notorious, most difficult situation that I'm just going to describe in general terms..."common neutrals", which is especially all to often common in control panels and results in all kinds of floating ground/neutral problems, things being energized when they shouldn't, etc.

To be fair, I've probably opened thousands of panels over the last 20 years. Out of those a small handful contain some interesting surprises like equipment which is located where it would not be expected to be found. Not to say that it's good practice or the right thing but it is mostly harmless. Once in a great while poor labeling turns into a potentially hazardous situation but there always has to be an accumulation of errors...more than one thing goes wrong...before lack of a label turns into a potentially hazardous situation. And even then as in the two cases above, absolute adherence to both energized and de-energized procedures works correctly every time it is followed.

So yes I'd agree that label issues are "safety issues" but they are administrative controls. Like all administrative controls they generally improve safety but by themselves failure of an administrative control should never result in a serious safety issue, with one exception. Although there is some redundancy built in to them, certain procedures like lock-out-tag-out and confined space entry can be fatal if not followed correctly but in most cases this is not the case.


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