Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to firstname.lastname@example.org. Answers are based on the 2014 NEC.
On a public works project, entire portions of the facility require all conductors in rigid metal conduit (RMC). To eliminate threading of conduit that is cut to fit the installation, we are using some threadless fittings. Set-screw-type fittings are the easiest and cheapest. When using threadless fittings outdoors, is the set-screw-type permitted, or do we need to use compression-type fittings? Is it permitted to install set-screw-type fittings in concrete, provided all of the couplings are duct-taped before the concrete pour?
Requirements for threadless couplings and connectors used with RMC are located in Section 342.42(A). The general rule is that they be made up tight. Where installed in wet locations, threadless fittings must be installed in accordance with Section 314.15, which requires fittings listed for use in wet locations. Applying duct tape over set-screw-type fittings in concrete is not permitted. Fittings permitted for use in concrete must be of the “concrete-tight” type. To meet these requirements, it is essential that you purchase the correct fittings. Most fittings listed for use in wet locations will also be concrete-tight. A quick review of manufacturer specifications online will provide you with multiple compliant options to purchase the correct type of fitting.
Fire pumps in multibuilding campus-style complexes
We are working in a new building under construction on a large college campus, and the permitted use of a feeder to supply the fire pump has generated many questions and discussions. The question of reliability has been discussed, as well as how to install the disconnecting means for the feeder supplying the fire pump. We have been going in circles with the engineer on how to size the disconnecting means for the feeder. Do we need to size the circuit breaker to handle the locked-rotor current? Additionally, do we need to isolate the circuit breaker to an enclosure that does not supply other equipment? We want to get this right but do not want to increase the cost of the installation unless it is necessary. Can you provide some input?
This is an interesting question that has ties to another NFPA standard. For clarity, before we examine the NEC requirements, it must be understood that NFPA 20 has purview over the performance of an electrically driven fire pump. The NEC, NFPA 70, has purview over the electrical installation requirements and must structure them to meet the performance-based requirements in NFPA 20. See the informational note immediately after Section 695.1, Scope, that explains to the reader that this article contains extracted material and the relevant NFPA 20 sections are noted in brackets for the NEC user to locate the extracted requirement.
The reliability requirement in Section 695.3 comes directly from Section 9.3.2 of NFPA 20, and the annex material in A.9.3.2 provides significant information on the reliability requirement for the normal source. Permission to use a feeder as a normal power source in a multibuilding campus style complex in Section 695.3(C) comes from NFPA 20 Section 9.2.2(4). The requirements for the feeder disconnecting means are in Section 695.4(B)(1)(b), which states that the feeder disconnect and overcurrent protective device installed under the provisions of 695.3(C) are permitted to comply with the other provisions of this Code. This means that the requirement for sizing the overcurrent device to handle locked-rotor current in 695.4(B)(2) and the requirements for the disconnecting means in 695.4(B)(3)(a) do not apply. These NEC rules are extracted from sections 9.2.2 and 9.2.3 in NFPA 20, which specifically omits the multibuilding campus-style complex feeder from the disconnect and overcurrent protection requirements as seen in 695.4(B)(2) and (B)(3)(a). Additional clarity is needed in the NEC and may occur in the 2017 Code-revision cycle.
Outline form of the NEC, article placement
I understand that the NEC is separated into chapters, with the first four being general in nature and applying to all installations and the last three being special with modifications. In Chapter 5, Special Occupancies, most of the articles within are occupancies with the exception of Article 590 for temporary wiring. Why is temporary wiring in Chapter 5?
As stated in your question, the outline form of the NEC consists of the introduction in Article 90 and eight chapters. This arrangement and outline is found in Section 90.3. Chapters 1 through 4 are general and apply to all electrical installations. Chapters 5, 6 and 7 are special and simply modify or supplement the rules in chapters 1 through 4 as needed. Chapter 5 is titled “Special Occupancies,” and all but two of the articles address specific types of occupancy. Article 504, Intrinsically Safe Systems, does not address an occupancy but is logically positioned with the other “hazardous location” articles. I agree with your objection to the placement of Article 590, Temporary Installations, in Chapter 5, as it is more properly located in Chapter 7, Special Conditions.
An installation of “temporary power and lighting” does not imply a special occupancy; it is, in my opinion, a special condition. The need for temporary power and lighting is limited and exists only where there is a lack of permanent power. The use of Article 590 is limited in the amount of time permitted as seen in Section 590.3. New buildings and structures will need temporary power when being constructed, as will existing buildings as they are renovated. I suggest that you submit a public input to revise the NEC. Get involved!
Unused openings in panelboards
On a recent job, we had multiple panelboards that were not completely full of circuit breakers, and we purchased “blanks” that snapped in to fill the holes. The owner’s representative took exception to the use of the blanks and stated that they were noncompliant and wanted us to fill the empty spaces in the panelboards with spare circuit breakers. We argued back and forth, but it was just easier to add the circuit breakers to make the customer happy. Does the NEC prohibit the use of circuit breaker blanks in a panelboard? Are we required to fill the panelboard with circuit breakers?
In Section 408.7, the NEC requires unused openings in switchboards, switchgear and panelboards to be closed using “identified closures” or other “approved means” that provide protection substantially equivalent to the wall of the enclosure. The “identified closures” (blanks) are in most cases optional items supplied by the panelboard manufacturer to close unused openings. The term “Identified (as applied to equipment)” is defined in Article 100 as being recognized as suitable for the specific purpose. The accompanying informational note informs the Code user that suitability for a specific purpose may include an investigation by listing and labeling. Where a manufacturer supplies circuit breaker blanks as an accessory, they are considered to be identified closures.
All panelboard manufacturers sell identified closures, commonly referred to as blanks, to fill unused openings for circuit breakers. Adding spare circuit breakers would certainly be an approved means to close the unused openings, but would not be required. In a situation such as this, it would be beneficial to provide the owner with the panelboard manufacturer’s list of accessories, which would include the identified closures permitted in Section 408.7.
Warning signs for pull and junction boxes over 1,000V
In a bid package that we recently reviewed, there was a note to place warning signs on all pull and junction boxes for conductors rated at 1,000 volts (V) or more, as required by the NEC. This is a common practice in our area, and we have been applying this type of warning label for as long as I can remember. Is this an NEC requirement?
Yes, the marking requirement is found in Section 300.45 and applies to all points of access to conductors in conduit and cables. This requirement is in Part II of Article 300 and applies only to systems over 1,000V, nominal. As written, it applies to all points of access, which includes more than just pull and junction boxes. The requirement for the warning sign is prescriptive and must contain the following:
DANGER—HIGH VOLTAGE—KEEP OUT
It is important to note that the sign must be applied in accordance with 110.21(B), which provides additional requirements for all field-applied hazard markings, which includes all required signs that state “caution,” “warning” or “danger.”