Electrical systems from the AHJ’s viewpoint
Electrical inspectors see a lot of mistakes that can be easily avoided. This inspector points out a few quirks of the code.
As an inspector and authority having jurisdiction (AHJ), I frequently encounter installations that do not comply with code. There are also many common mistakes I regularly see, including routine misinterpretations of code, or aspects that sometimes just get overlooked.
Prior to working as an inspector, I was an electrical installer. What I was led to believe was code turned out to be industry practices. After beginning my career as an AHJ, I’ve learned a lot more about what’s really in the code. I have often said that it would be nice to see an installation per plan, but that doesn’t happen often enough. Almost everyone I’ve ever met in the field changes the engineer’s drawings in one fashion or another.
It is not my intention to imply that I can design or install systems better than the next guy. There are many different types of systems and a lot of different sizes of systems. What appears to be missed more often than not is sufficient information on a set of drawings to help the field work go smoothly. This, and a knowledgeable installer, can reduce the number of flaws considerably.
Following is a short list that may be looked at as either common mistakes or misapplications of the code.
1. As the code is arranged, one would hope that the more specialized the system, the more specialized and experienced the installer. One common mistake seen in the field is sometimes largely dependent on the installer’s knowledge of applying the code. For example, there are not many residential installers qualified to work on the electrical system for a hospital, gas station, or other commercial facilities. Having the right technician for the installation always produces a better chance of the code being applied correctly.
2. There is a common design issue that everyone who has ever installed an electrical system has had to face: the dimensions of the electrical equipment room (see Figure 1).
That’s right—“All the power in the world, in an itty-bitty living space,” as Aladdin puts it.
Usually the equipment fits, or there may have to be minor changes to the layout. Yet it’s the electricians that will service this system later that get left out of the loop. I understand that there’s rarely a large budget for an electrical room or, more specifically, its long-term operation and maintenance. Equipment rooms have little function to the occupants (except when inappropriately used as a janitor closet or place to store boxes of Christmas decorations).
NEC Article 110.26, Spaces About Electrical Equipment, provides all of the general requirements. It tells us that “Sufficient access and working space shall be provided and maintained about all electrical equipment to permit ready and safe operation and maintenance of such equipment.” The clearances to follow in this section of the code are mandatory distances for personnel safety. It may be prudent for the designers and owners to consider increasing these minimum clearance requirements.
The issue here is that the rooms are only large enough to take into account what is shown on the initial design. At times, the initial design doesn’t even include sufficient space for the equipment shown on the drawings.
To allow for future expansions, it may be prudent for the designers and owners to consider the need for additional equipment. For example, the code does not include provisions for future expansion, correct? NEC Article 90.1(B), Adequacy, clarifies that “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.”
If a designer has a piece of equipment where, in the planning stages, there are spaces for “spares,” maybe those “spares” should also be allowed the same clearance areas as the main section of equipment. Future equipment will eventually replace the spare and will need to be installed somewhere in the building (see Figure 3).
3. Single-line drawings frequently need more information than is typically provided. The single-line is the heart of the entire electrical system. An enormous amount of information is needed to perform a thorough single-line inspection, which will ultimately lead to approval to energize the system.
Some design professionals prefer to include pertinent information in several tables on a separate page. While that works well for larger systems, most of the information for smaller systems can be provided on one single-line page. The information needed can range from the obvious voltage, ampere, and number of phases, to each overcurrent device in the system single-line, conduit size, wire size, etc. The single-line drawing, along with all the panel schedules, provides most of the information needed. Frequently, equipment AIC (amperes of interrupting capacity) ratings get left out. Most of the time, this information is provided on the panel schedules. For instance, 480/277 V, 3-phase, 4-wire, 225 amp, MCB 22,000 AIC provides the voltage, phases, amperes, main circuit breaker with 22,000 AIC. Yet often this information is missing and the installation is changed to a main lug or 10,000 amps of interrupting capacity. It also helps to have the actual interrupting short circuit current rating (ISC) or available fault current at each point of the wiring system while reviewing a single-line.
4. Another common mistake is the compatibility of systems within the structure. For instance, consider the integration of electrical, architectural, and mechanical systems.
Within any structure there are numerous separate systems that together constitute the functionality of the building. One primary concern of the code is the ability to safely evacuate all occupants. Keeping this in mind, the overlay of different systems should be a major priority when designing electrical systems. Frequently there are conflicts with separate systems, and the size and location of such systems become an area of concern.
The need to coordinate systems during design plays a major role in the emergency egress lighting system. Depending on the type of occupancy in the structure, there could be many objects obstructing the view of occupants attempting to evacuate the building. In a large warehouse the means of egress may be visible before any equipment is installed, but the ability to find the exits may become considerably more difficult after all the equipment has been put in place. In these cases, the designer may not be given the tenant improvement plans at the time the initial emergency egress lighting study has been performed. I recently performed inspections on a manufacturing operation. After the production equipment was installed, the exit signs were not visible at the locations necessary for safe evacuation. This situation required a costly change due to the specification requirements of the equipment used at the site.
One of the most common code violations observed in the field is when fire-resistive construction has been effectively de-rated during the electrical installation. Electrical panels and large junction boxes may be installed on, but not in, rated walls. The 2009 International Building Code (IBC) section 713.3.2, Membrane Penetrations, allows an aggregate area of 100 sq in. of opening in 100 sq ft of wall area. Electrical panels installed in this manner do not comply. These limitations often create difficult field fixes and costly changes in an effort to maintain the fire-resistive nature of the wall.
During the design phase, the design team should review the architectural drawings to identify any potential conflicts between such systems. The architectural drawings should show whether a wall will be rated or not, and whether systems not allowed to be installed in such walls can be relocated.
Also, building equipment, such as mechanical systems and the specifications required for those systems, sometimes conflict in size. I have frequently seen mechanical plans with systems sized for 480 V only to find the main system voltage does not exceed 208 V .
5. I frequently see separately derived ac systems without the required grounding system re-established at the point of the separately derived system. In many cases, this information could be on the single-line drawing. Whether the separately derived system is a generator set or a transformer or even a battery set, when it supplies a new ac system, the grounding means must be established as required by NEC Article 250.30. If this information were shown on the drawings, it would be more likely to be properly installed when required. The opportunity to install the bare copper conductor in the earth ahead of time instead of after the fact—once the structure is built—could result in better grounding means. The Southern Nevada jurisdictions require concrete-encased electrodes as the main grounding electrode. If a transformer was not considered during the initial design, it can be difficult to impossible to install concrete-encased electrodes as an afterthought. In situations like this, other means of grounding can be used.
6. Rules of thumb about how to determine when voltage drop should be calculated should never be used for accurate voltage drop. Some of today’s equipment is very sensitive to the system voltages. Frequently, there is a note on the electrical drawings indicating that voltage drop calculations have been performed. But it would also be helpful if a length is provided, specifying when additional calculations would be needed. There are obviously changes that could occur in the routing of the conduit system that would add numerous feet to the system. Once calculations have been performed based on a predetermined length scaled from the drawings, and the system exceeds that length, the engineer has the option of recalculating the voltage drop and making the necessary revisions.
7. Harmonics in electrical systems is becoming more of a design challenge due to the sensitive equipment used in many projects. Dedicated neutral conductors are needed more and more for systems that are computer based. The use of mitigating harmonic transformers would be a great choice for systems on the Las Vegas Strip, where there are thousands of computer-based slot banks. The distorted current waveform created by nonlinear loads can cause many problems in electrical distribution systems. The use of harmonic mitigating phase shifting transformers can reduce the imbalance in such systems.
8. Parallel wiring methods are a common noncompliant arrangement (see Figure 2). Article 310.4 allows conductors to run in parallel. Subsections B through E expand on that requirement. I have encountered systems installed in parallel with one conduit installed overhead and the other installed underground. That is an incorrect interpretation of the code; consequently, the installer had to abandon one conduit system and have both systems installed in the same manner.
9. The technology in photovoltaic systems cannot be ignored (see Figure 5). The availability of alternative renewable energies has come a long way over the past several years. A need for the equipment to perform over a longer life span will make more effective systems. There are still difficulties in the environment that the technology could overcome. Longer-life photo-arrays that can resist sand, dust, and wind elements will create a more sustainable system. Providing a system that increases the percentage of performance in each photo-array while decreasing the maintenance needed to operate will be available in the near future.
Installers, take note
Other than what’s mentioned here, I don’t see a lot of design flaws. As any inspector, I see things that often get missed in the course of installing the electrical system. Here are two examples.
The need for insulating fittings or smooth transitions for conduits with conductors larger than #4 AWG frequently gets overlooked. NEC Article 300.4(G) requires “Where raceways contain 4 AWG or larger insulated circuit conductors and these conductors enter a cabinet, box, enclosure or raceway, the conductors shall be protected by a substantial fitting providing a smooth rounded insulated surface, unless the conductors are separated from the fitting or raceway by substantial insulating material that is securely fastened in place.” This includes conduits emerging from grade. Frequently, underground feeders can be seen lying on the edge of a conduit with sharp edges, with no insulating fitting, and no sealing compound.
This also holds true for bonding for more than 250 V (see Figure 4). Where systems have more than 250 V to ground and there are concentric or eccentric knockouts, bond bushing may be required. NEC Article 250.97 requires “For circuits over 250 V to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).” This is often missed in the field.
Loper has been with the City of North Las Vegas for 11 years and is presently a combination inspector. Prior to that, she worked as an electrician in California and Nevada. She is certified as a plan checker and combination inspector. She is also recognized as a master electrician by the International Code Council (ICC).
- Events & Awards
- Magazine Archives
- Digital Reports
- Global SI Database
- Oil & Gas Engineering
- Survey Prize Winners
- CFE Edu