Wiring Methods and Swimming Pools - So What Is A Corrosive Environment?
With the 2020 National Electrical Code updates right around the corner and the dust finally settling on the code panel meetings in San Diego, CA we code users begin to reflect on a few of the changes that are taking place with wiring methods used in swimming pool environments. This article will attempt to shed some light on those developments.
For a few code cycles now the code user (and code developers) have struggled with the term "corrosive environment" and how it applies to the swimming pool environment. We all collectively understand that the "condition of use" in those environments, such as pool rooms and locations where pool treatment chemicals are stored and of course the pool pump equipment is located do have an elevated potential for being a higher than normal environment where corrosion can take place. However, once we begin to look at these environments and the existing wiring methods permitted within them do we begin to question why no standards exist to provide a detailed evaluation of the environment. Let me go into that in more detail.
Let us paint the scenario for the reader so as to better illustrate the "condition of use" involved. We have a single-family dwelling with a swimming pool and associated pump and recirculation equipment, chlorine or bromine tablet or liquids and, where applicable, their injectors as well as the storage containers for those chemicals. Based on the 2020 NEC that location would be considered a "corrosive environment" based on the proposed language :
This is a considerable change to the definition found in the 2017 NEC under section 680.14(A). In fact, it still remains unclear as to what exactly constitutes such a "corrosive environment" based on the concentrations of such chemicals unlike how we clearly define "combustible dust" in Article 100. We can all agree the environment does warrant an elevated consideration similar to those of exterior locations where the same existing wiring methods are currently used, except of course for the chemicals in the pool sanitation process.
Traditionally the NEC has permitted Rigid Metal Conduit (RMC), Intermediate Metal Conduit (IMC), Polyvinyl Chloride Conduit (PVC) and Reinforced Thermosetting Resin Conduit (RTTC) in these locations without any formal investigation to their suitability for the "condition of use" that the code- making- panels seems to believe is a highly corrosive environment. But let's not stop there and actually look at the "other" electrical equipment permitted to be installed in these areas without any concern about their suitability.
These pool rooms typically contain electrical pool distribution panels with plastic circuit breakers, which are terminated onto exposed bus assemblies with exposed conductor terminations. The luminaries typically found in these rooms are not rated for a "corrosive environment" as expressed in the definition found in Article 680. Let's not forget to mention that the majority of the pool equipment is PVC that does come in indirect or direct contact with the chemicals being used. And it only serves as a good reminder that none of the actual wiring methods expressed in 680.14(B) for the 2017 NEC or the proposed 680.14 in the 2020 NEC have actually been evaluated for those environments as well because no standard exists to cover the swimming pools "corrosive environment" area and the leading NRTL's are aware of it.
While we are on the topic of wiring methods, and of course that was the title of this article, lets examine the current NEC proposed language for the wiring methods permitted in a "Corrosive Environment".
As you see above the language has changed or is proposed to change. The rule opens with the following statement: "Wiring methods in a corrosive environment" shall be listed and identified for use in such areas." and ends with the list of existing wiring methods that have technically been "grandfathered" into the rule. The reason I say "grandfathered" is because none of the wiring methods in the list have been evaluated for the harsh condition that the CMP believes exists. However, let's focus on a wiring method that is excluded from that list that has proven it's merit in those harsh environments for years.
During the 2017 NEC development process as well as in the current 2020 development process of the NEC it was presented that PVC Jacketed or Covered Type MC (Metal-clad) Cable should be included in that list. Let's examine the facts from the position of the National Electrical Code, the electrical industries minimal safety standard as well as the actual product standard, UL 1569.
1) UL 1569 states in section 13.2 that "steel" armor must have corrosive resistant zinc applied to the strip much in the same fashion as with RMC and IMC. So while the aluminum version doesn't have the same protection you will see later that the PVC Jacketing or Covering will provide that protection.
2) Section 330.10(A)(11) of the 2017 NEC states "In wet locations where a corrosion resistant jacket is provided over the metallic covering and any of the following conditions are met." The most often used method used to comply with this rule is by using insulated interior conductors that are listed for use in wet locations, such as THHN/THWN-2 or XHHW-2. In fact, it was argued during the 2017 NEC NITMAM stage that both indoor or outdoor wet locations can be considered a corrosive environment. So clearly the entire intent of the PVC Jacketing or Covering over the metal armor meets this intent.
3) Section 330.12, which is the "uses not permitted" section of this article clearly prohibits the use of Type MC in locations where it is subject to physical damage or destructive corrosive environments. However, it does permit that Type MC is acceptable in these environments if protected by material resistant to the condition. This is where the PVC Jacketed or Covered come into play. Remember, there is no related UL/ANSI Standard for the harsh pool environment to test against.
4) Back to that UL 1569 Standard for a second. It has been stated for years by some folks very close, if not intimate with that standard, that UL 1569 already permits Type MC Cable with a PVC Jacketed or Covering to be used for connections to swimming pool motors in those same "conditions of use" without any problems. In fact, some folks even argue that some "special" testing takes place in UL 1569 that demands that manufacture place the wording "Suitable for use in swimming pool motor circuits" on PVC Jacketed or Covered Type MC when used for swimming pool motors.
However, a close examination of section 40.1(o) in UL 1569, it states that manufacturers who produce such a cable assembly "may" mark the cable assembly "may be marked" with that statement but doesn't require it and clearly nothing in that standard or any other standard demands any additional testing to take place. Wait, is the standards telling me PVC Jacketed or Covered Type MC Cable is ok for use with pool pump motors as permitted in 680.21(A)(1) of the NEC for decades without any concerns?
In light of the information above those who are aggressively against the use of Type MC with a PVC Jacketing or Covering then turned to the connectors as their target for the weakness. We reached out to one of the leading manufacturers of connectors to address this question and they stated while there is no formal testing for this specific "pool environment", they feel that the existing connectors rated for wet locations would be sufficient for this application. When that effort was squashed they then turned to the armor and said it provided a Grounding Path and the potential corrosion to that armor could be detrimental to that path which was ultimately explained to that member that normal PVC Jacketed or Covered Type MC Cable armor is not considered such a path but is bonded by virtue of the fittings to meet the bonding requirements. Also, they were reminded that Rigid Metal Conduit (RMC) is in fact permitted to serve as the Equipment Grounding Conductor (EGC) by section 250.118(2) and are routinely found damaged and that traditional Type MC Cable has an internal EGC to ensure that connection remains reliable.
In an effort to clarify the durability of the PVC material used on Type MC this author reached out to individuals at IPEX, leaders in the non-metallic pipe and fitting industry since 1951. IPEX also publishes an industry-leading guide called the "IPEX Chemical Resistance Guide" used to determine the various factors in the chemical attack onto PVC material along with may other materials. It was made clear to this author that the chlorine used in pools is actually chlorine water with an approximate concentration of chlorine of 10-13%. This is a far cry from pure chlorine liquid, which would destroy any of the permitted wiring methods currently allowed. The chart provided documented proof that PVC is resistant to the attack of chlorine water and of course since 90% of the pool pumps, recirculation systems and storage containers are PVC themselves this would make total sense. They also went on to explain that PVC material in the presence of Boric Acid, Bromine-AG , and Hydrochloric Acid also has no negative affect on the PVC material.
In an effort to get to the bottom of this PVC issue once and for all (wrong) Encore Wire set up a controlled test in our DAP Certified UL Lab to study the effects of long term exposure (12 months) of Type MC , both PVC Jacketed or Covered Aluminum and Steel Armor products in a harsh chemical environment. The worst case scenario was to use hydrochloric acid vapor in its purest form knowing the vapor would envelope the samples and with the normal Texas heat, create condensed liquid from that vapor that would be deposited on the samples over the test period. The samples also included both standard Type MC in their aluminum and steel forms.
Long story short, the aforementioned results were presented in full detail to CMP 17 and provided undeniable proof that even after 12 months of exposure in our environment here in Texas where temperatures reached over 100 degrees on a regular basis, that no negative effects appeared on any of the samples with the PVC Jacketed or Covered Type MC Cable.
Lastly, let's examine the 2020 NEC proposed language for section 680.14 and what I believe permits (my opinion) the use of PVC Jacketed or Covered Type MC Cable.
Clearly, Type MC Cable is listed and when it is PVC Jacketed or Covered it is also evaluated for direct burial applications in locations we have determined are also corrosive environments or otherwise why put a jacket or covering on it in the first place. The allowances, or should I say permission is given in the previously discussed section 330.10(11) and 330.12(2) for the use in those such environments covers that opening sentences permission to use PVC Jacketed or Covered Type MC Cable. It is also my personal opinion that the new language proposed in section 680.2 only describes the locations to be considered a "corrosive environment" and adds nothing to define it.
Under additional analysis, the second sentence simply offers "grandfathered" recommendations of those untested wiring methods to be considered acceptable wiring methods that have again yet to be evaluated for the "condition of use" described by CMP 17 as a "Corrosive Environment".
Conclusion - There is no doubt that these environments can increase the potential for a corrosive environment. However, it has been proven with test data and the leading chemical resistance guides that the PVC Material placed on cables or raceways can provide an adequate protection against a corrosive environment. In fact, it could be argued that Type MC Cable with a PVC Jacket or Covering is the only wiring method with adequate testings for these specific "conditions of use".
Paul W Abernathy, CMECP®
Paul W Abernathy, CMECP®
Notice : NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association and are used for educational purposes only. All "NEC®" inserts are used for clarity and educational purposes and are not altered from their original format as expressed in the NFPA 2nd Draft Public Comment Stage.
