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 Post subject: In your opinion, do rubber boots like these affect I.E.
PostPosted: Wed Aug 01, 2018 5:08 am 
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We have a handful of old installations on campus using single phase oil filled cans to make three phase power like you see in the pics below. We put the orange rubber boots over the paddles several years ago. In recent years we've determined in most cases we cannot open the doors on our pad mounted transformers while energized due to too high of incident energy. We discussed installing rubber boots on the paddles like you see in the pics below on our pad mounts too.

In your opinion, would doing this eliminate exposure to live parts?

We have over time converted most of our pad mount to external oil sample ports and drains so we can now take samples without opening the doors and we buy new transformers with the external drain but you still cannot see the gauges or see if you have a spare conduit or how feasible it is to add another feeder etc.

Thoughts?


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Wed Aug 01, 2018 12:35 pm 
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I'll let others speak regarding the covers.

The installation depicted violates the two action rule implicit in the codes. Pad mounted equipment is built so the door must be opened and an elbow be pulled before one is exposed to medium voltage. In a substation, live parts are guarded by height or secondary guards once one gets past the fence. Here it appears there is only a single door keeping unauthorized folks away from the exposed primary bushings.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Wed Aug 01, 2018 12:46 pm 
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Here's a photo of an inadequate, easily moved secondary guard. I understand the janitor was given a key so he could mop up after the rain blew in through the door vent. All gone now.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Wed Aug 01, 2018 1:49 pm 
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The rubber boots will help protect against inadvertent shock and could prevent an arc flash event.

The item I don't understand is your statement
Quote:
In recent years we've determined in most cases we cannot open the doors on our pad mounted transformers while energized due to too high of incident energy.


How was the determination made? What voltage are the secondaries of the padmount transformers? NESC Table 410-1 lists padmount transformers as 4 cal/cm2 up to 600V and 601V to 1000V as 6 cal/cm2. IMO that is not too high of incident energy as PPE is readily available and utilities open many padmount secondary doors with no incidents.

I do like that you are ordering the transformers with sampling ports that are accessible from the outside.

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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Thu Aug 02, 2018 6:18 am 
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stevenal wrote:
I'll let others speak regarding the covers.

The installation depicted violates the two action rule implicit in the codes. Pad mounted equipment is built so the door must be opened and an elbow be pulled before one is exposed to medium voltage. In a substation, live parts are guarded by height or secondary guards once one gets past the fence. Here it appears there is only a single door keeping unauthorized folks away from the exposed primary bushings.


My pics are to show the boots, not the pad mounts install I'm asking about. Oh, and in the pics the primary bushings are insulated. You can open the door to the secondary side of a pad mount without opening the primary side door. Have no idea what you are talking about.

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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Thu Aug 02, 2018 6:22 am 
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wbd wrote:
The rubber boots will help protect against inadvertent shock and could prevent an arc flash event.

The item I don't understand is your statement
Quote:
In recent years we've determined in most cases we cannot open the doors on our pad mounted transformers while energized due to too high of incident energy.


How was the determination made? What voltage are the secondaries of the padmount transformers? NESC Table 410-1 lists padmount transformers as 4 cal/cm2 up to 600V and 601V to 1000V as 6 cal/cm2. IMO that is not too high of incident energy as PPE is readily available and utilities open many padmount secondary doors with no incidents.

I do like that you are ordering the transformers with sampling ports that are accessible from the outside.


I'll have to look into the NESC section you cite. Arc flash analysis yields much higher than 4 cals on the secondary usually. I have witnessed a secondary L-G fault on a pad mount secondary with my own two eyes that did not clear the primary protection. It did not clear until we reopened the primary feeder switch.

Oh, and we have 480Y/277, 208Y/120 and 240V delta pad mounts. All primaries are 12,470V delta.

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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Thu Aug 02, 2018 6:29 am 
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stevenal wrote:
Here's a photo of an inadequate, easily moved secondary guard. I understand the janitor was given a key so he could mop up after the rain blew in through the door vent. All gone now.


Where we still have single phase cans they are in vaults behind 2 locked doors. The first door is into a mechanical or electrical room accessible only to our maintenance staff. The second door, the vault door, is keyed only accessible by our high (medium, really) voltage electricians and me.

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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Thu Aug 02, 2018 8:36 pm 
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bbaumer wrote:
wbd wrote:
The rubber boots will help protect against inadvertent shock and could prevent an arc flash event.

The item I don't understand is your statement
Quote:
In recent years we've determined in most cases we cannot open the doors on our pad mounted transformers while energized due to too high of incident energy.


How was the determination made? What voltage are the secondaries of the padmount transformers? NESC Table 410-1 lists padmount transformers as 4 cal/cm2 up to 600V and 601V to 1000V as 6 cal/cm2. IMO that is not too high of incident energy as PPE is readily available and utilities open many padmount secondary doors with no incidents.

I do like that you are ordering the transformers with sampling ports that are accessible from the outside.


I'll have to look into the NESC section you cite. Arc flash analysis yields much higher than 4 cals on the secondary usually. I have witnessed a secondary L-G fault on a pad mount secondary with my own two eyes that did not clear the primary protection. It did not clear until we reopened the primary feeder switch.

Oh, and we have 480Y/277, 208Y/120 and 240V delta pad mounts. All primaries are 12,470V delta.


IEEE 1584 is valid when you have a much smaller enclosure than your typical padmount with three vertically oriented bus bars in close proximity, around 25 mm for 480 V systems for instance. There is nothing whatsoever about a padmount transformer represented by that data.

NESC relied on testing actual equipment for doing their testing. It shows MUCH lower incident energy compared to IEEE 1584 calculations. The tests were for the most part performed by and published by EPRI. Any EPRI report over 10 years old (and some even more recent) is available for download for free. EPRI compared the actual test results to IEEE 1584 and quickly came to the conclusion that actual testing is necessary for accurate results for this type of equipment. They did several tests representing various extremes and took the worst case values which are used in the NESC tables.

So given a choice between actual testing and a computer generated number that is clearly not representative of the actual equipment, which one would you trust?


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Thu Aug 02, 2018 8:46 pm 
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stevenal wrote:
I'll let others speak regarding the covers.

The installation depicted violates the two action rule implicit in the codes. Pad mounted equipment is built so the door must be opened and an elbow be pulled before one is exposed to medium voltage. In a substation, live parts are guarded by height or secondary guards once one gets past the fence. Here it appears there is only a single door keeping unauthorized folks away from the exposed primary bushings.


Where is this implicit anywhere? Air termination cabinets were used for years before separable connectors and are still used extensively on the low voltage end because separable connectors are limited to 600 A. Seperable connectors came along for underground terminations both underground and at risers, vaults, and similar locations. Most of the vault equipment in the City of Charleston, SC, for instance spends almost it's entire life underwater due to high water tables. Utilities recently started using separable connectors everywhere because it makes disconnecting transformers much easier compared to removing bolts on lugs for quick changeouts. And that's for medium voltage.

Not only that but there is clearly only one barrier on the power cable for my laptop and most flexible cords have the same status. In lighting panels once you remove the outer ring, that's it, it's all very much exposed.

NEC rules with regards to fences and doors harken back to a bygone era of truly "live front" equipment where once you open the door to the electrical room, everything is wide open.

http://i114.photobucket.com/albums/n278 ... G_0486.jpg

NEC also requires signage sometimes (and sometimes not) on cable trays where once again the conductors are kind of hanging out there for the entire world to see with no secondary barrier at all.

I can go on but the fact of the matter is that NEC generally requires some kind of tool to access medium voltage conductors whether it's a key, a screw driver, a wrench, or a bucket truck. Once you get past the first layer especially in older equipment, there is no protection at all in many cases.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Mon Aug 06, 2018 10:15 am 
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bbaumer wrote:


.. Oh, and in the pics the primary bushings are insulated.


Agreed, they are insulated by air, easily bridged through contact. There is a voltage gradient along the bushing surface, from ground potential at the bottom to line potential at the top. This surface is and must be considered live.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Mon Aug 06, 2018 12:49 pm 
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PaulEngr wrote:

Where is this implicit anywhere?


Put together NESC 110 and 124

PaulEngr wrote:

Not only that but there is clearly only one barrier on the power cable for my laptop and most flexible cords have the same status.


I did say "medium voltage."

PaulEngr wrote:

I can go on but the fact of the matter is that NEC generally requires some kind of tool to access medium voltage conductors whether it's a key, a screw driver, a wrench, or a bucket truck. Once you get past the first layer especially in older equipment, there is no protection at all in many cases.


NEC requires the use of listed equipment, and I don't think you will find any listed live-front medium voltage padmount equipment that doesn't employ a secondary barrier. But use a pole-mount transformer in a way the manufacturer never intended, and all bets are off.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Mon Aug 06, 2018 12:58 pm 
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bbaumer wrote:
Where we still have single phase cans they are in vaults behind 2 locked doors. The first door is into a mechanical or electrical room accessible only to our maintenance staff. The second door, the vault door, is keyed only accessible by our high (medium, really) voltage electricians and me.


Two actions. Good. Thought I was seeing daylight coming through the door in the last photo.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Wed Aug 08, 2018 8:26 am 
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I'm following up on this subject as earlier today we had a presentation from a pad mounted transformer manufacturer. He was sharing information on some of their strategies to reduce incident energy at the transformer secondary. He was showing calculated IE over well over 100 cals and clearing times of around 6 seconds in his SKM model. I asked him if he knew anything about testing that showed in reality much lower IE due to the large bus gap and open space in the secondary cabinet causing arcs to self extinguish very rapidly. He did not.

One other thing to add, a couple years ago our oil testing company started to refuse to take samples on energized pad mounts due to too much IE at the secondary and that's when we decided to go with the remote ports.

In any case, after the discussion I looked up a couple of the things referenced by some in this thread and found the following links those, like me, who were not previously familiar, might want to check out.

Thanks to all who took the time to reply.

EPRI Testing: https://ieeexplore.ieee.org/document/6107577/

NESC T410-1 Presentation: http://industrial.tecgen.com/files/ced5 ... c-2012.pdf

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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Wed Aug 08, 2018 9:21 am 
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First off, NESC applies to generation, transmission, and distribution. It is different from NEC. No Listing requirement shows up in NESC unlike NEC. Generally speaking equipment is built to ANSI standards rather than UL. The medium voltage UL section is very generic in nature.

OK, reading the 2017 version of NESC...

110A requires an enclosure of some kind (fence or building) with locked gates/doors and a sign. This is to prevent access by "unauthorized persons". The content of the sign is not stated as it is in NEC.
110B essentially requires noncombustible materials, good ventilation, and protection from weather on buildings and similar enclosures.
110C requires adequate support (foundations).

124 requires all potentially energized equipment to be insulated, guarded, or inaccessible. It's a much longer version of "exposed" requirements, and goes into more detail on construction. In some ways it is a more generalized version of the "finger safe" IEC rule which is intended for smaller enclosures with close access. But since all personnel are authorized, it is acceptable for instance to use even a simple guard rail around exposed equipment.

So I might be missing something here but taking 110 and 124 together it becomes obvious that suitably guarded enclosures around live equipment (e.g. a padmount transformer termination chamber) meets the requirement with a lock. Similarly in some ways, outdoor overhead style substations are also acceptable with fences and equipment positioned in what would be in 70E terminology not be considered accessible. In both cases you could make a case that it requires two actions to access...unbolting/unlocking the door, and opening the door, and perhaps 3 actions for overhead switchgear if you include using a ladder but I'm not seeing "2 layers" here...nothing like both opening a locked outer door to a switchgear room and then opening the door to a cabinet. It seems no different from the NEC 110B requirement for a locked room/enclosure but no second barrier is required either.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Wed Aug 08, 2018 1:32 pm 
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The scope of the NESC extends beyond T, D, &G. See 011A8.

When I speak of two actions, I don't include opening or defeating the lock separately from opening the thing it secures. In the case of the substation, the first action is to get past the fence. The second action is to gain altitude to get to those energized parts guarded by height, or to get past the secondary guard for those things that aren't. For overhead lines outside the sub, two actions aren't required, but the height is much greater.

The commercial padmount items I've seen likewise require two actions. See this specification for a live-front padmount capacitor for example: https://dta0yqvfnusiq.cloudfront.net/westernunderground/2015/08/2-12a.pdf


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Thu Aug 09, 2018 11:00 am 
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That's not the typical "padmount" equipment I've seen in the Eastern U.S. Here we can really break it down into "live front" and "dead front".

In both types, the outer doors are frequently if not almost always bolted shut with a pentagon 13/16" bolt head and there is also provision for a padlock which is almost always used. Sometimes I run into one without the pentagon bolt, particularly in industrial equipment where they freak out about the "oddball" bolt that is the same bolt head used on manholes, vaults, and I've even been told it's used in some fire department equipment.

Once the doors are open with "dead front" equipment there are several wells that accept elbow connectors (IEEE 386). The grounds, drains, etc., are all exposed even if it is "dead front". This construction design originated with underground equipment so it uses the same connectors and sealed designs.

With "live front" equipment, that's pretty much it. There might be phase barriers but usually there are simply bus bar stabs with NEMA bolt patterns and that's it. This design basically came from overhead "tank" style transformers with open bushings on top and the only thing new is a built-in enclosure (aka air termination compartment) surrounding the stabs.

Beyond that quite often I see a bunch of vinyl tape or sometimes rubber and vinyl tape, or a lot of duct seal wrapping the bus bars and connectors and then wrapped up in several layers of vinyl tape to make it look "neat", with or without some kind of rubber "boots", air gaps and all. Since there is no shield and over 1000 V you can carry surface charges, none of this garbage is doing anything, barely counting as a "covered" conductors, but it shows up where low voltage contractors, particularly older ones, attempt to do medium and high voltage work, often skipping out on drains and any attempt at voltage stress relief as well, figuring more insulation will somehow fix the tracking problem that their work causes. I'm not counting any of this stuff since none of it meets any kind of standard and just causes me a lot more work to strip it all off for access and then cleaning it all off to restore the connection to manufacturer recommended practices.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Thu Aug 09, 2018 4:14 pm 
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Not always implicit I guess. In the case of pad-mounted equipment, NESC 381G2 is quite explicit regarding the two actions. Been in the code since '73.


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 Post subject: Re: In your opinion, do rubber boots like these affect I.E.
PostPosted: Fri Aug 10, 2018 5:08 am 
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stevenal wrote:
Not always implicit I guess. In the case of pad-mounted equipment, NESC 381G2 is quite explicit regarding the two actions. Been in the code since '73.


Ahh, you got me there. That's cool, learned something new. So now being an engineer I have to explore all the nuances and ins and outs of something new.

Let's review first the structural context of that rule since it seems to more or less come out of nowhere. NESC is organized into 5 parts. Part "0" (it doesn't have a label) applies generally. If the "2 action" rule was intended to be universally applied it would be in this section like the Rule 09x section for grounding. Part 1 which contains rule 110 and 124 is for generating stations. The "2 action" rule appears to be supported by but is not implicit in these rules. In fact they are more like a variation on how NEC is structured. I'll cover that later. Part 2 is for overhead supply and communication lines. No "2 action" rule. Might be able to make a case for "very remote" overhead access but this is certainly not the intent. It only becomes "very remote" because the lines are not fixed and we have to tag into account sag under all conditions as opposed to wiring that is supported continuously as in general construction or underground wiring so the distances of necessity must be much larger. Part 3 is for underground supply and communication lines. Rule 381G is in THIS section only. Part 4 covers operating rules for all supply and communication lines so no equipment design rules are in this section.

The pertinent part of Rule 381G is:

"Access to exposed live parts in excess of 600 V shall require two separate conscious acts. The
first shall be the opening of a door or barrier that is locked or otherwise secured against unauthorized entry as required by Rule 381G1. The second act shall be either the opening of a door or the removal of a barrier."

That pretty much states and clarifies the "2 action" rule.

So fence or door to the room, then another door over the enclosure itself. I think I see now how the padmount distribution transformers meet this requirement without a building or fence. The high voltage side has a separate door that is covered by the outer low voltage door so you have to open the low voltage side to access the high voltage side. Signage is often an afterthought. I'd say 90% of the ones I see that Duke and Dominion own don't have any kind of "danger" signs. Maybe they did at one time but not over the years. The doors themselves meet the internal barrier requirement. Simple and efficient without excess parts.

Going over to the utilization side (NEC), the rules are similar but there are also major differences:

"110.31 Electrical installations in a vault, room, or closet or in an area surrounded by a wall, screen, or fence, access to which is controlled by a lock(s) or other approved means, shall be considered to be accessible to qualified persons only. The type of enclosure used in a given case shall be designed and constructed according to the nature and degree of the hazard(s) associated with the installation.For installations other than equipment as described in 110.31(D), a wall, screen, or fence shall be used to enclose an outdoor electrical installation to deter access by persons who are not qualified."

Note the wording here. Except for the last sentence which applies only to some but not all outdoor equipment yards, a lock is NOT required. The whole purpose of this rule is to support live front construction...bare bus bars and open insulators without any enclosures at all where the locked doors and gates are quite literally the "enclosure" protecting unqualified personnel from exposure to energized work. We need to prevent access to exposed equipment elsewhere in NEC and other Codes so this rule confers that special status. This rule does not require a locked door/fence, only conveys the "qualified personnel" status. Furthermore, this is not a "2 action" rule by any stretch since the equipment can be energized, live, and exposed for all the (qualified) world to see.

110.31(B) explains indoor locations accessible to unqualified persons and simply requires "Indoor electrical installations that are accessible to unqualified persons shall be made with metal-enclosed equipment. Metal-enclosed switchgear, unit substations, transformers, pull boxes, connection boxes, and other similar associated equipment shall be marked with appropriate caution signs."

Note that the sign goes on the equipment, not the fence/building doors. With metal enclosed equipment frequently there are two doors on the front. Draw out switchgear obviously meets the "3 action" rule with an outer door, the draw out mechanism, and the shutters to get access to live bus. But go around to the back side and remove the cable entry access door and it becomes only a "1 action" rule. Metal enclosed equipment is sometimes "2 action", sometimes "1 action".

I also checked the ANSI Codes for metal enclosed and metal clad equipment. There is definitely not a "2 action" rule anywhere implicitly or explicitly in those Codes. It definitely implicitly exists as a "3 action" rule for metal clad draw out switchgear but not for anything else and even then it only applies to the front, not the back.

Outdoor installations fall under 110.31(C) which states, "Outdoor electrical installations that have exposed live parts shall be accessible to qualified persons only in accordance with the first paragraph of this section and shall comply with 110.34, 110.36, and 490.24." Unlike NESC there is no elevation or fencing requirement. You can put a barrel style pole mount transformer with open bushings on the ground and have open bus bars or cables right up to it, surrounded by an outer fence. Not that in this day and time I really recommend that construction technique, and I hate working on them, but they meet Code.

Finally, 110.31(D) covers what would be the most equivalent to the situations described in NESC 110 and 124. It is for outdoor equipment accessible to unqualified pesonnel including John Q. Public: "Ventilating or similar openings in equipment shall be designed such that foreign objects inserted through these openings are deflected from energized parts. Where exposed to physical damage from vehicular traffic, suitable guards shall be provided. Nonmetallic or metal-enclosed equipment located outdoors and accessible to the general
public shall be designed such that exposed nuts or bolts cannot be readily removed, permitting access to live parts. Where nonmetallic or metal-enclosed equipment is accessible to the general public and the bottom of the enclosure is less than 2.5 m (8 ft) above the floor or grade level, the enclosure door or hinged cover shall be kept locked. Doors and covers of enclosures used solely as pull boxes, splice boxes, or junction boxes shall be locked, bolted, or screwed on. Underground box covers that weigh over 45.4 kg (100 lb) shall be considered as meeting this requirement."

This rule is clearly intended as a "1 action" rule but goes above and beyond NESC fence/door requirements as far as limiting access to John Q. Public.

So in summary the "2 action" rule applies to underground and thus vault entry padmount equipment under NESC (voluntary). It doesn't apply to other conditions within the NESC nor to NEC installations, and isn't a regulatory requirement either. But it certainly explains the door arrangement on padmounts. It never really made sense to me because sometimes I need to do something on the primary side which I can do without energized work when it uses elbow connectors (no exposed wiring) but I'm stuck having to do energized work because I have to open the secondary side which often just has NEMA 4 hole pads just so that I can access the primary side.


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