Question 1. Does Article 555 NEC specifically require the use of marine power (listed marine power outlets), or can shore power receptacles be installed in individual enclosures in accordance with 555.19(A)(1) and 555.11? For example, an individual meter base nippled to a 6-circuit sub panel then nippled to a weatherproof  FS box for the shore power receptacle with a weatherproof cover. — J.P.

Answer 1.  Article 555 of the 2002 NEC does not specifically require the use of marine power outlets. That is one of several options that are found in 555.19(A)(1). A locking- and grounding-type receptacle rated not less than 30 amperes or more than 50 amperes may also be installed in a listed weatherproof enclosure or in a listed enclosure that is protected from the weather. Your example mentions an FS box with a weatherproof cover, so you need to make sure that the assembly also complies with the last sentence of 555.19(A)(1). 

Additionally, your example mentions an individual meter base nippled to a 6-circuit sub-panel. If this meter is not the utility meter and is installed at each individual slip on the load side of the service disconnecting means, the installation would have to comply with 250.142(B), Exception No. 2. A disconnecting means is required not more than 762 mm (30 in.) from the shore power receptacle and is to be located ahead of the receptacle in the supply circuit. 

These requirements are based on the 2002 NEC, but you should remember that if you are working with the 1999 edition, these items can be found in NFPA 303 as well. — Robert McCullough, CMP-19

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Answer 2.  Section 550-23(b) allows the service equipment for a manufactured home to be located in or on the unit where all of the conditions (1) through (4) are met. As such, there is nothing in 550-6 that would prohibit this installation. The specific grounding rules found in 550-11 are applicable to an installation where the service equipment is located away from the unit and a distribution panelboard is installed within the unit. This would be the case for a mobile home, as the service equipment is not permitted to be located in or on the unit.

Much of the confusion in applying these rules stems from the fact that many people tend to interchange the terms mobile home and manufactured home. The definitions in 550-2 tell us that the two are treated the same unless specifically indicated otherwise. When it comes to the service equipment, we find a case where the distinction is indicated. Section 550-23(a) is specifically titled Mobile Home Service Equipment, and 550-23(b) is titled Manufactured Home Service Equipment. 

For the 2002 edition, 550-23 has been renumbered 550.32, and 550.32(B) has added language that states where the service equipment is not installed in or on the unit, the installation shall comply with the other provisions of this section. This would then trigger in the grounding requirements which are now found at 550.16.

It is important to understand that the NEC is not the primary document used for the construction of manufactured housing. The construction requirements are found in the HUD Part 3280 rules. These rules reference the NEC where the HUD rules do not specifically state a requirement. As part of an ongoing project, NFPA 501, Standard on Manufactured Housing, has been rewritten with the intent of becoming the primary referenced rules in the HUD document. The changes you see in the 2002 NEC were developed from NFPA 501. To see where all this leads us, 501 section 9.3.11(3) contains the identical provisions as section 550.32(B) of the NEC. In addition, NFPA 501, 9.4.10 and 9.4.11, specifically allow for the service equipment to be installed on the manufactured home.

In summary, the answer to your question is yes, provided all the conditions in 550-23(b) are met and the unit is, in fact, a manufactured home bearing the HUD label. Dealing with different units that are seemingly identical can be a challenge, and I hope this answer is useful to you.  — Robert McCullough, CMP-19

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Question 3. A journeyman industrial electrician with ten years of experience in the food industry, I recently switched from a vegetable processing operation to a milk processing plant. While the use of rigid aluminum raceway is familiar to me, along with effects of high pressure wash down including high strength cleaning chemicals, I was surprised to find that the milk processing plant uses stainless steel tubing as the preferred raceway for electrical conductors. The tubing is purged and welded to additional lengths of stainless steel tubing as well as elbows and boxes.

While this makes an impressive looking raceway, I am curious as to how this is allowed seeing that no such wiring method appears in the NEC. The plant engineer assures me that this is the preferred method among dairies and is perfectly acceptable.

Would you send me any information about the use of this method? Is another set of code rules involved with the dairy industry? Is this method an NEC violation? The small community has no electrical inspector. In that case who is considered to be the authority having jurisdiction? —J. E.

Answer 3. The first part of your question deals with a wiring method in a milk processing plant. This may or may not fall under the scope of Article 547. If this plant is a part of or an area adjacent to the milking operation or confinement area, then this would be covered in 547.1 and the wiring methods set forth in 547.5 would be applicable. Section 547.5(A) permits, in addition to the specific wiring methods listed, other cables or raceways suitable for the location. Since you indicate that the area is subject to high-pressure wash down and high strength cleaning chemicals are used, you would refer to 300.6 in general for protection against corrosion. That section states that the materials used must be suitable for the environment encountered. Sections 110.2 and 110.3(A) provide guidance to the AHJ regarding suitability.

If the plant is a separate building where animals are not present and the product is brought in for final processing, Article 547 would not apply and the general rules of the Code would apply subject to any installation restrictions for the particular environment encountered. You specifically mention the use of stainless steel tubing as the wiring method used in your facility and express concern that this wiring method does not appear in the NEC. In order to address this concern it is necessary to differentiate between tubing and conduit. If in fact conduit has been used, stainless steel is an acceptable material. Refer to the definition of rigid metal conduit (RMC) contained in 344.2 where the last sentence states, "Special use types are silicon bronze and stainless steel." Stainless steel conduit is covered by UL Standard 6A; and 344.6 requires the conduit to be listed. Another point of concern would be your comment that the stainless steel is welded to additional lengths. Section 300.18(B) does not permit metal raceways to be welded unless specifically designed for this so the UL standard should be reviewed to see if this application is permitted. If stainless steel tubing rather than conduit has been used, I would be concerned about the suitability of this for use as a raceway based on the listing requirements as well as the effectiveness as an equipment grounding conductor.

Now to "milk" this answer further, I will try to address your other questions. You ask if there is another set of rules involved with the dairy industry. The rules that govern any electrical installation depend on how your particular state or jurisdiction regulates such installations. If the political jurisdiction has adopted requirements for installation codes, you would have to look at that adoption and see what rules are in place. There are some areas in the country that specifically exempt agricultural industries from any regulation. Others may adopt codes without a mechanism for enforcement; in which case, the onus for compliance is on the building owner. Since you state the small community has no electrical inspector, that may be the case. This brings us to your last question — who is considered to be the AHJ? As I stated previously, you have to find out if the political jurisdiction has adopted any regulations covering electrical installations and, if it has, has an entity been designated to enforce the regulations. In looking at the definition of authority having jurisdiction in Article 100, the AHJ could be an organization, office or individual. The FPN for this definition contains examples of who could possibly be considered the AHJ and it is worth noting that in some cases this could be the building owner. So to "herd" all this together and head back to the barn, can this wiring method be used? Following the guidelines of 110.2, the definition of approved in Article 100, and 90.4, the AHJ could choose to accept this installation. I would hope that the AHJ would not take this approval process lightly. — Robert McCullough, CMP-19

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