The Sufficiency of NEC rules

[Sahib]

The POCO neutral is multi-grounded. So the ground return current can be substantial. This can give rise to touch and step voltage issues, which are serious as regards swimming pools and cattle farms. But the NEC grounding and bonding rules should be sufficient to solve these issues and where they lack, the rules might have been amended long back to afford increased effectiveness. But still do such rules of the NEC lack in any important aspect of protection? Your inputs please.

 

[iwire]

Thanks for starting your own thread to discuss this.

I will get things rolling by pointing out that the NEC is a minimum standard. In many cases good design goes beyond the required minimums.

90.1 Purpose.

(A) Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.

(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.

FPN: Hazards often occur because of overloading of wiring systems by methods or usage not in conformity with this Code. This occurs because initial wiring did not provide for increases in the use of electricity. An initial adequate installation and reasonable provisions for system changes provide for future increases in the use of electricity.


(C) Intention. This Code is not intended as a design specification or an instruction manual for untrained persons.

 

[Sahib]

iwired:
It is not something to be improved upon NEC minimum requirements but a conflict with it such as below

grounding and bonding rules of NEC actually make conditions worse in some cases, and it is a definite problem particularly with dairy farmers even when there is a little impedance in a typical multi grounded neutral.

I wonder what the CMP has so far done about it.

 

[iwire]

iwired:
It is not something to be improved upon NEC minimum requirements but a conflict with it such as below



I wonder what the CMP has so far done about it.

The CMP votes on proposals from outside parties. If you have an improvment in mind, substantiation to back it up and the cost to benefit ratio was good it would likely be accepted.

Keep in mind that the NEC has no say on the US distribution system and we are stuck with a multi grounded neutral distribution system.

 

[Sahib]

Keep in mind that the NEC has no say on the US distribution system and we are stuck with a multi grounded neutral distribution system.

Thanks for your reply.

Stray currents all over the land of US mainly due to multi grounded neutral distribution system.

The question is

Do step and touch voltages rise to objectionable/dangerous levels in cattle farms/swimming pools in some cases due to any defect in installation or any deficiency in NEC rules to be brought under the scrutiny of the CMP?

 

[iwire]

The question is

Do step and touch voltages rise to objectionable/dangerous levels in cattle farms/swimming pools in some cases due to any defect in installation or any deficiency in NEC rules to be brought under the scrutiny of the CMP?

That is too vague of a question for me.

Perhaps you could point to a specific NEC code section that is causing the problem or could be safely changed to reduce the problem?

 

[Sahib]

That is too vague of a question for me.

Perhaps you could point to a specific NEC code section that is causing the problem or could be safely changed to reduce the problem?

Then kwired may answer because he stated it:

grounding and bonding rules of NEC actually make conditions worse in some cases, and it is a definite problem particularly with dairy farmers even when there is a little impedance in a typical multi grounded neutral.

In response to which this thread was started.

 

[kwired]

Let me start with the entire reply mentioned:

I have no doubt it works, grounding and bonding rules of NEC actually make conditions worse in some cases, and it is a definite problem particularly with dairy farmers even when there is a little impedance in a typical multi grounded neutral.

Step potential for a person is shorter than it is for a cow, plus they are standing in/on urine, water, and other waste with no shoes, boots or other electrical insulation. And if they are touching a metal object with their mouth/nose it may be even farther distance from that point to their back feet meaning more potential voltage. Fairly low voltages will cause a drop in milk production and even cause health issues with the cows. If the voltages are high enough they will feel it and this can cause them to not even want to approach feed or water or enter the milking parlor or other areas which makes even more problems for the dairy farmer.

Many times there is a problem the cows can feel but people can not - partly because we do not stand in same conditions barefooted with four feet on the ground - and with such a spread between feet. Following NEC helps minimize potential but does not make this current go away. When you have animals that weigh 1000 pounds or more, nothing ever gets broken either - just ask the people that work in these places and they will disagree.

The more earth connections there are in the system you have the more stray paths potentially can develop. If the earth return is from one single point to another single point (the point here may be a large point) then you have a different situation than if you have multiple connections to earth and every one of those is bonded to premises wiring systems.

Following NEC does help minimize effects, that is why the rules are the way they are. Abnormal conditions still come up, things do break down. These animals are heavy enough that they break things you never thought they could, might take a little time but it happens.You also have a corrosive atmosphere to work against you.

Swimming pools and art 547 buildings are designed to help protect against these problems, get away from those installs and there are situations where NEC grounding and bonding rules can make things worse. We read on occasion where someone was electrocuted in a lake around a dock with electric power. We even get questions on this forum about people feeling current around this kind of area - even when they turn off all the power supplying the area. Problem in most of those cases isn't a defect in their equipment it is the fact their equipment is bonded via an equipment grounding conductor which is eventually bonded to the POCO MGN making it an extension of the conductor carrying the offending current. We can provide additional protection in a swimming pool or an art 547 building without too much trouble - but with some potential for failure but around natural bodies of water this becomes very impractical if not impossible.

The topic of discussion in the other thread involved single wire earth return high voltage distribution - at least at the point where I made the comment that got this thread started. IMO intentionally making the earth the only return path for a load is inviting even more troubles in the types of areas mentioned. SWER may work better for longer path of a single load, but if you were to run it in a dense population area you would likely have all kinds of stray voltage problems as it has so many unintended paths to follow. And any area similar to a swimming pool or something like a dairy barn will be one of the first places to notice problems.

 

[Sahib]

Swimming pools and art 547 buildings are designed to help protect against these problems, get away from those installs and there are situations where NEC grounding and bonding rules can make things worse.

So if the building electrical design is per NEC specification, it is free from stray voltage problems.

intentionally making the earth the only return path for a load is inviting even more troubles in the types of areas mentioned.

No. See your own reply and my comment based on it above.

any area similar to a swimming pool or something like a dairy barn will be one of the first places to notice problems.

In Alaska SWER distribution system has been permitted. Has the authority prohibited swimming pools and dairy farms in nearby places where this distribution system has been installed?
No. For the same reason they permitted such installs for conventional multi grounded distribution systems: the installs shall conform to NEC.

 

[rbalex]

It's only a little more than 15kM from Bethel to Napakiak, Alaska; there's virtually nothing between them. Certainly no dairies; the closest is about 700kM away. There will be a swimmingpool in Bethel; it will be indoors and highly isolated from any effects ofthe SWER.

 

[cowboyjwc]

Had an issue last week, where we couldn't get the neutral/ground to clear. Ended up that it was on the utility side. They had bonded the neutral at the transformer. Have never had that issue before. But I also couldn't convince the contractor to remove the "neutral disconnect link" he simply kept removing the "bonding jumper" and from what I could tell that should have worked, but I may be mistaken.

 

[don_resqcapt19]

Had an issue last week, where we couldn't get the neutral/ground to clear. Ended up that it was on the utility side. They had bonded the neutral at the transformer. Have never had that issue before. But I also couldn't convince the contractor to remove the "neutral disconnect link" he simply kept removing the "bonding jumper" and from what I could tell that should have worked, but I may be mistaken.

I don't understand. If it is a grounded system there will always be a neutral to earth bond at the transformer and at the service disconnect.

 

[cowboyjwc]

I don't understand. If it is a grounded system there will always be a neutral to earth bond at the transformer and at the service disconnect.

At the main service, once you pull the disconnect link there should be no continuity between the ground and the neutral.

 

[don_resqcapt19]

At the main service, once you pull the disconnect link there should be no continuity between the ground and the neutral.

I am still confused at where you have this continuity. If you are looking at the neutral on the load side of the service neutral disconnect, then I don't see how anything at the utility side would make any difference.

If you are looking at the utility side of the neutral, then you will have a path via the service grounding electrode and the utility grounding electrode. In many cases this will not be a low impedance path, but there are a number of conditions that are normal and would create a low impedance path.

 

[kwired]

So if the building electrical design is per NEC specification, it is free from stray voltage problems.

Stray voltages do not disappear, they are shunted around the users of swimming pools, in art 547 buildings they are shunted around the animals, yet we still have things that happen from time to time that gives a hole in the so called protection. Lets just say when around cattle there is a lot of BS, and a lot of BS ends up happening too. Original installs do not remain in original condition for very long, if you don't believe me you need to work around these kind of places and it will not take very long to figure that out. All the equipotential bonding is good, but you still need to avoid unnecessary neutral current as much as possible, then when something goes bad or gets broke the risk is a little lower.

No. See your own reply and my comment based on it above.

See what Bob said - there is not much around in many parts of Alaska to have an effect on. And for a little sarcasm, pretty much everyone in Alaska has a swimming pool.

It's only a little more than 15kM from Bethel to Napakiak, Alaska; there's virtually nothing between them. Certainly no dairies; the closest is about 700kM away. There will be a swimmingpool in Bethel; it will be indoors and highly isolated from any effects ofthe SWER.

In Alaska SWER distribution system has been permitted. Has the authority prohibited swimming pools and dairy farms in nearby places where this distribution system has been installed?
No. For the same reason they permitted such installs for conventional multi grounded distribution systems: the installs shall conform to NEC.

Utility company installs are not covered in the NEC.

 

[Sahib]

Stray voltages do not disappear, they are shunted around the users of swimming pools, in art 547 buildings they are shunted around the animals, yet we still have things that happen from time to time that gives a hole in the so called protection. Lets just say when around cattle there is a lot of BS, and a lot of BS ends up happening too. Original installs do not remain in original condition for very long, if you don't believe me you need to work around these kind of places and it will not take very long to figure that out. All the equipotential bonding is good, but you still need to avoid unnecessary neutral current as much as possible, then when something goes bad or gets broke the risk is a little lower.

It is a matter of maintenance issue and not a case of failure of grounding and bonding rules of NEC for the step and touch potentials to reach objectionable/dangerous levels in dairies/swimming pools.

See what Bob said - there is not much around in many parts of Alaska to have an effect on. And for a little sarcasm, pretty much everyone in Alaska has a swimming pool.

Unfortunately, the performance of SWER of Bethel is not satisfactory and so the authority is not willing to provide SWER in other places of Alaska.

Utility company installs are not covered in the NEC.

That is true. It is also true that NEC does not have specific provisions for safeguard against stray currents from SWER distribution systems because there is no increased hazard from them.

 

[electrofelon]

That is true. It is also true that NEC does not have specific provisions for safeguard against stray currents from SWER distribution systems because there is no increased hazard from them.

I am not sure there is much the "NEC" could do to mitigate stray current from a utility distribution system short of requiring every structure to have an elaborate and extensive grounding and bonding grid like a cell tower site. It is not the NEC's job to solve all of humanity's problems. The are any number of things that the NEC would "like" to see but that are beyond their scope and control.

 

[Sahib]

I am not sure there is much the "NEC" could do to mitigate stray current from a utility distribution system short of requiring every structure to have an elaborate and extensive grounding and bonding grid like a cell tower site. It is not the NEC's job to solve all of humanity's problems. The are any number of things that the NEC would "like" to see but that are beyond their scope and control.

The thread discussion is about the sufficiency of NEC rules to mitigate stray current irrespective of its source and not about whether the rules have an all covering protective feature.

 

[kwired]

Here is what NEC requires in 547 - the dairy barn installation:

547.10 Equipotential Planes and Bonding of Equipotential Planes.


The installation and bonding of equipotential planes shall comply with 547.10(A) and (B). For the purposes of this section, the term livestock shall not include poultry.


(A) Where Required. Equipotential planes shall be installed where required in (A)(1) and (A)(2).


(1) Indoors. Equipotential planes shall be installed in confinement areas with concrete floors where metallic equipment is located that may become energized and is accessible to livestock.


(2) Outdoors. Equipotential planes shall be installed in concrete slabs where metallic equipment is located that may become energized and is accessible to livestock.


The equipotential plane shall encompass the area where the livestock stands while accessing metallic equipment that may become energized.


(B) Bonding. Equipotential planes shall be connected to the electrical grounding system. The bonding conductor shall be solid copper, insulated, covered or bare, and not smaller than 8 AWG. The means of bonding to wire mesh or conductive elements shall be by pressure connectors or clamps of brass, copper, copper alloy, or an equally substantial approved means. Slatted floors that are supported by structures that are a part of an equipotential plane shall not require bonding.

Here is what NEC requires in 680 the swimming pool installation:

680.26 Equipotential Bonding.


(A) Performance. The equipotential bonding required by this section shall be installed to reduce voltage gradients in the pool area.


(B) Bonded Parts. The parts specified in 680.26(B)(1) through (B)(7) shall be bonded together using solid copper conductors, insulated covered, or bare, not smaller than 8 AWG or with rigid metal conduit of brass or other identified corrosion-resistant metal. Connections to bonded parts shall be made in accordance with 250.8. An 8 AWG or larger solid copper bonding conductor provided to reduce voltage gradients in the pool area shall not be required to be extended or attached to remote panelboards, service equipment, or electrodes.




(1) Conductive Pool Shells. Bonding to conductive pool shells shall be provided as specified in 680.26(B)(1)(a) or (B)(1)(b). Poured concrete, pneumatically applied or sprayed concrete, and concrete block with painted or plastered coatings shall all be considered conductive materials due to water permeability and porosity. Vinyl liners and fiberglass composite shells shall be considered to be nonconductive materials.




(a) Structural Reinforcing Steel. Unencapsulated structural reinforcing steel shall be bonded together by steel tie wires or the equivalent. Where structural reinforcing steel is encapsulated in a nonconductive compound, a copper conductor grid shall be installed in accordance with 680.26(B)(1)(b).


(b) Copper Conductor Grid. A copper conductor grid shall be provided and shall comply with (b)(1) through (b)(4).


(1) Be constructed of minimum 8 AWG bare solid copper conductors bonded to each other at all points of crossing. The bonding shall be in accordance with 250.8 or other approved means.


(2) Conform to the contour of the pool


(3) Be arranged in a 300-mm (12-in.) by 300-mm (12-in.) network of conductors in a uniformly spaced perpendicular grid pattern with a tolerance of 100 mm (4 in.)


(4) Be secured within or under the pool no more than 150 mm (6 in.) from the outer contour of the pool shell


(2) Perimeter Surfaces. The perimeter surface shall extend for 1 m (3 ft) horizontally beyond the inside walls of the pool and shall include unpaved surfaces, as well as poured concrete surfaces and other types of paving. Perimeter surfaces less than 1 m (3 ft) separated by a permanent wall or building 1.5 m (5 ft) in height or more shall require equipotential bonding on the pool side of the permanent wall or building. Bonding to perimeter surfaces shall be provided as specified in 680.26(B)(2)(a) or (2)(b) and shall be attached to the pool reinforcing steel or copper conductor grid at a minimum of four (4) points uniformly spaced around the perimeter of the pool. For nonconductive pool shells, bonding at four points shall not be required.




(a) Structural Reinforcing Steel. Structural reinforcing steel shall be bonded in accordance with 680.26(B)(1)(a).


(b) Alternate Means. Where structural reinforcing steel is not available or is encapsulated in a nonconductive compound, a copper conductor(s) shall be utilized where the following requirements are met:


(1) At least one minimum 8 AWG bare solid copper conductor shall be provided.


(2) The conductors shall follow the contour of the perimeter surface.


(3) Only listed splices shall be permitted.


(4) The required conductor shall be 450 mm to 600 mm (18 in. to 24 in.) from the inside walls of the pool.


(5) The required conductor shall be secured within or under the perimeter surface 100 mm to 150 mm (4 in. to 6 in.) below the subgrade.


(3) Metallic Components. All metallic parts of the pool structure, including reinforcing metal not addressed in 680.26(B)(1)(a), shall be bonded. Where reinforcing steel is encapsulated with a nonconductive compound, the reinforcing steel shall not be required to be bonded.


(4) Underwater Lighting. All metal forming shells and mounting brackets of no-niche luminaires shall be bonded.


Exception: Listed low-voltage lighting systems with nonmetallic forming shells shall not require bonding.


(5) Metal Fittings. All metal fittings within or attached to the pool structure shall be bonded. Isolated parts that are not over 100 mm (4 in.) in any dimension and do not penetrate into the pool structure more than 25 mm (1 in.) shall not require bonding.


(6) Electrical Equipment. Metal parts of electrical equipment associated with the pool water circulating system, including pump motors and metal parts of equipment associated with pool covers, including electric motors, shall be bonded.


Exception: Metal parts of listed equipment incorporating an approved system of double insulation shall not be bonded.




(a) Double-Insulated Water Pump Motors. Where a double-insulated water pump motor is installed under the provisions of this rule, a solid 8 AWG copper conductor of sufficient length to make a bonding connection to a replacement motor shall be extended from the bonding grid to an accessible point in the vicinity of the pool pump motor. Where there is no connection between the swimming pool bonding grid and the equipment grounding system for the premises, this bonding conductor shall be connected to the equipment grounding conductor of the motor circuit.


(b) Pool Water Heaters. For pool water heaters rated at more than 50 amperes and having specific instructions regarding bonding and grounding, only those parts designated to be bonded shall be bonded and only those parts designated to be grounded shall be grounded.


(7) Fixed Metal Parts. All fixed metal parts shall be bonded including, but not limited to, metal-sheathed cables and raceways, metal piping, metal awnings, metal fences, and metal door and window frames.
Exception No. 1: Those separated from the pool by a permanent barrier that prevents contact by a person shall not be required to be bonded.


Exception No. 2: Those greater than 1.5 m (5 ft) horizontally of the inside walls of the pool shall not be required to be bonded.


Exception No. 3: Those greater than 3.7 m (12 ft) measured vertically above the maximum water level of the pool, or as measured vertically above any observation stands, towers, or platforms, or any diving structures, shall not be required to be bonded.


(C) Pool Water. An intentional bond of a minimum conductive surface area of 5800 mm2 (9 in.2) shall be installed in contact with the pool water. This bond shall be permitted to consist of parts that are required to be bonded in 680.26(B).

The dairy barn wired to NEC minimum does not have near the detailed bonding requirements as a swimming pool.

When it comes to maintenance, every dairy barn always has fully qualified and high knowledge maintenance electricians on staff 24/7:happyno:

 

[don_resqcapt19]

It is a matter of maintenance issue and not a case of failure of grounding and bonding rules of NEC for the step and touch potentials to reach objectionable/dangerous levels in dairies/swimming pools. ....

Not really. The utilities use a multi-grounded neutral system that puts the earth in parallel with the utility primary grounded conductor, and yes there are phase to neutral loads on our utility distribution systems.

The voltage drop on the primary grounded conductor can be high enough to become objectionable in dairies and maybe even dangerous in pools. This voltage will appear between anything connected to the electrical grounding system and "remote earth" (defined as outside of the influence of a grounding electrode and often said to be 50 or more feet from a grounding electrode). This issue is the reason that the NEC added the perimeter surface bonding rule for pool decks.