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. Send questions to firstname.lastname@example.org. Answers are based on the 2017 NEC .
GFPE, alternative methods?
Can I use technology other than standard ground fault protection of equipment (GFPE) to meet the requirements of 230.95? We have a job with a 1,600-ampere (A) service at 480/277 volts (V), and the owner wants to install an arc energy reduction method that works incredibly fast. My understanding of GFPE in the Code is that it is only required to prevent arcing faults that destroy the equipment. It seems redundant to install both. Can an inspector approve this instead of standard type GFPE?
Section 230.95 requires GFPEs for all solidly grounded wye-connected services of more than 150V to ground but not exceeding 1,000V phase-to-phase for each service disconnect rated at 1,000A or more. With respect to your question, the key here is the requirement in 230.95(A) for the setting of the GFPE. When considering the application of other technologies to meet the requirements of 230.95, an inspector will want to know if these requirements are met.
This section requires the maximum setting for the GFPE to be set at 1,200A and the maximum time delay for the GFPE to open the disconnect at 1 second for ground fault currents equal to or greater than 3,000A. This is the reason typical GFPE protection is provided with current transformers (CTs) on all circuit conductors to monitor current to ground.
Before we go any further in response to this question, we must look deeper into these numbers. As the question mentions, the technologies available today are designed to reduce arc energy, but they do not necessarily monitor ground fault current. The requirement in 230.95(A) mandates a setting to recognize ground fault currents at not more that 1,200A. New arc energy reduction technologies do not act just because a CT sees a value of current to ground; they monitor the system and act only to open an arcing fault. Section 230.95 also permits ground faults over 3,000A to persist for one second (60 cycles).
For example, the present requirement will permit an arcing fault at 15 kiloamperes, phase to ground, on a 480/277V system for 60 cycles. This means the present requirement permits the equipment to be destroyed. This requirement is outdated by new technologies and, in my opinion, needs to be revised. I have been questioned many times on why the threshold for GFPE protection is 1,000A. It is typical to see multiple service disconnects as permitted in 230.71. This allows for a 480/277V, 1,200A service to be installed with three 400A service disconnects, which eliminates the need for GFPE. The possibility of an arcing fault destroying the 400A disconnects is exactly the same as that in a disconnect rated at 1,000A or more.
When considering new arc-reduction technologies, it must also be understood that not all methods to reduce arc energy are always active. Some need to be engaged. For example, an energy reduction maintenance switch will provide protection only from an arcing fault when it is engaged. There are other technologies such as energy-reducing active arc flash mitigation systems, which are active at all times and do not need to be engaged.
You are correct in that 230.95 exists to prevent the loss of equipment and that the new technologies are superior in protecting the equipment from burn down. The problem is the requirements of 230.95(A) must be met. Where an inspector fully understands: (1) the reason 230.95 exists, (2) that new arc reduction technologies are capable of performing better than standard GFPE protection, (3) the capabilities of the arc-reduction technology applied and (4) that the system is active at all times, the inspector can approve the installation by exercising 90.4. This is an example of “special permission” as Article 100 defines because the objective of 230.95 would be met with equivalent (superior) protection against an arcing burn down.
Wound rotor motor
While taking a quiz in a prep class for my electrical contractor’s license, I made an error on a question dealing with motors. I checked Table 430.52 for non-time-delay fuses to get the rating of the motor branch circuit, short-circuit and ground-fault protection. The question referenced a wound rotor motor. I missed that. All of the induction-type motors other than wound rotor size the protective device at 300 percent. However, a wound rotor motor must be sized at 150 percent. All of these motors are induction-type motors. What is the difference? Why 50 percent for this type of motor?
Wound rotor motors are typically used for loads with a high starting torque. These motors are very different from the typical squirrel cage motors, which have the rotor windings permanently shorted. There are brushes on a rotor in a wound rotor motor into which impedance can be inserted. When the motor is started, the impedance is placed in series with the rotor windings, which increases the torque and lowers the starting current at the same time. This lower value of starting current requires the branch circuit, short-circuit and ground fault protective device to be set at a lower value to protect the motor.
Swimming pool gas water heaters
Are hard-wired natural gas water heaters for swimming pools required to have GFCI protection? My question is really based on the replacement of older units.
Yes, 680.28 requires circuits operating at a voltage above the low-voltage contact limit to be provided with GFCI protection. Low-voltage contact limit is defined in 680.2. Any voltages that exceed: 15V (rms) for sinusoidal AC, 21.2V peak for nonsinusoidal AC, 30V for continuous DC or 12.4V peak for DC that is interrupted at a rate of 10–200 hertz will require GFCI protection.
Grounded conductor termination
I have been installing and upgrading services in dwelling units for over 25 years. For many years, it was permitted to land the neutral with the grounding conductor in service equipment. We were told some time ago that the Code changed and that was no longer permitted, but we were never told why. We cannot find such a requirement in the Code.
The requirement you are referring to is in 408.41, which requires each grounded conductor (neutral) to be terminated within the panelboard in an individual terminal that is not also used for another conductor. This requirement is safety driven, and the intent is to ensure, if the grounded conductor of a branch circuit is removed from the terminal bar in the service equipment, the associated equipment grounding conductor is still in place, providing an effective path for ground fault current.
We are installing fluorescent lighting fixtures end to end. In some cases, there are as many as 24 fixtures in a single run. The drawings show at least two and, in some cases, three circuits for each run. Is it permitted to install a multiwire branch circuit and run it through all of the fixtures?
Yes, 410.64(C) specifically permits luminaires that are designed for the purpose to be installed in that manner, and one multiwire branch circuit is permitted if it supplies the connected luminaires. In this installation, the luminaires are not required to be listed as a raceway. Note that additional requirements apply. Section 210.4(B) requires all multiwire branch circuits to be provided with a means of simultaneous disconnect. This can become a design issue.
For example, a three-pole circuit breaker supplying one of these lighting circuits will open the entire multiwire branch circuit, and the whole run of luminaires will be de-energized. If that is undesirable, two-wire circuits should be considered, and only two circuits are permitted in any section. Section 210.5(C) requires ungrounded conductors to be identified where more than one nominal voltage system exists. Section 410.130(G) requires fluorescent luminaires with double-ended lamps that contain ballasts to be provided with a disconnecting means that will allow for safe ballast maintenance. Where a multiwire branch circuit supplies a ballast, 410.130(G)(2) requires the disconnecting means to simultaneously break all of the supply conductors to the ballast, including the grounded conductor.
Outdoor air conditioner receptacle
On a recent job, I installed a 30A, 208V receptacle for an air conditioning unit. These are smaller units and are designed to be easily relocated outside of office trailers. This unit is located outside of three trailers in a fenced-in location with two other air conditioning units. None of the existing receptacles are provided with GFCI protection. None of these receptacles are accessible to the public. Why am I required to provide GFCI protection for a receptacle that the public has no access to?
The requirement you are referring to is in 210.8(B) for other than dwelling units. All single-phase receptacles installed outdoors rated at 50A or less and 150V to ground or less must be provided with GFCI protection. The title of 210.8 is “Ground Fault Circuit Interrupter Protection for Personnel.” The protection required here is not specifically directed at the general public. It is for everyone, including those that will maintain the equipment.