What Is The Maximum Amount Of Service Switches Allowed Per Nec

In my opinion, two locations within the ability distribution system present unique challenges for the electrical worker, service entrance equipment and the equipment directly on the secondary of a transformer. The 2020 version of the NEC but took a leap forward for at least ane of these two locations with changes to a rule that has been a long-standing requirement for many years – the six (six) disconnect rule institute in 230.71. This discussion would be amiss if we covered the changes in 230.71 without touching on the changes in 230.62(C), barrier requirements for service equipment because the journey for that which nosotros come across in 230.71 began due to NEC-2017 changes requiring line-side barriers for service panelboards.

Before we move forward in this expanse, please recognize that what is learned about the hazards in service equipment and the new requirements for these locations tin can be used to aid increment prophylactic for like applications elsewhere. A prime example is the equipment found directly on the secondary side of power distribution transformers regardless of their location in the organization. As this discussion progresses, we will close with how this information can exist leveraged in other than service equipment.

Photo 1. A panelboard with a main breaker that has lineside barriers installed, reducing the likelihood of shock and arc flash.

The Kickoff

To understand the journeying to the changes in the vi-disconnect rule seen in NEC 2020, we must first await back to NEC 2017 with the changes made in 408.3, and more specifically, the exception to 408.3 that had to be created. Section 408.3 as role of NEC-2017 reads every bit follows

408.3 Support and Arrangement of Busbars and Conductors.

(A) Conductors and Busbars on a Switchboard, Switchgear, or Panelboard. Conductors and busbars on a switchboard, switchgear, or panelboard shall comply with 408.3(A)(ane), (A)(2), and (A)(3) every bit applicable.

(1) Location. Conductors and busbars shall be located then as to exist free from physical impairment and shall be held firmly in place.

(2) Service Panelboards, Switchboards, and Switchgear. Barriers shall be placed in all service panelboards, switchboards, and switchgear such that no uninsulated, ungrounded service busbar or service terminal is exposed to inadvertent contact by persons or maintenance equipment while servicing load terminations.

Exception: This requirement shall not utilise to service panelboards with provisions for more than one service disconnect within a unmarried enclosure every bit permitted in 408.36, Exceptions one, 2, and 3.

The above exception language generated questions and concerns nigh the safety of existing practices for service equipment. This exposed the safety concerns of equipment constructed such that a line-side barrier is not practicable, specifically panelboards, with 6 disconnects installed within.

NEC-2020 has recognized the importance of these barriers and moved this barrier requirement into Article 230 for services. This new requirement can exist found in 230.62(C) titled "Barriers." This action expanded the barrier requirement to all service archway equipment and reads as follows:

230.62(C) Barriers.

Barriers shall be placed in service equipment such that no uninsulated, ungrounded service busbar or service terminal is exposed to inadvertent contact by persons or maintenance equipment while servicing load terminations.

Note that the exception previously a role of 408.3 has been removed, which is indeed at the heart of the changes found in 230.71 of NEC 2020. The significance of this can only be realized once we understand what the hazards are at this location in the power distribution system.

An example of a panelboard with a line-side barrier installed is shown in effigy 1.

Figure 1a. Configuration includes the assumption of 50kA available at the upstream panelboard with the 400A feeder circuit breaker for the 225kA transformer. Conductor lengths are limited in size, such that the available fault current at the downstream 208V panelboard is 16,807A. Incident energy results may vary depending upon the upstream OCPD selected.

Figure 1b. Configuration includes the assumption of 50kA available at the upstream panelboard with the 400A feeder circuit breaker for the 225kA transformer. Conductor lengths are limited in size, such that the available fault current at the downstream 208V panelboard is 16,807A. Incident energy results may vary depending upon the upstream OCPD selected. The higher calories/cm2 have been moved from equipment with a high likelihood of access to equipment with a much lower likelihood of access increasing safety for the electrical worker. — Figure 1b. Configuration includes the assumption of 50kA available at the upstream panelboard with the 400A feeder circuit breaker for the 225kA transformer. Usher lengths are express in size, such that the available error electric current at the downstream 208V panelboard is xvi,807A. Incident energy results may vary depending upon the upstream OCPD selected. The higher calories/cm2 have been moved from equipment with a high likelihood of access to equipment with a much lower likelihood of admission increasing safety for the electrical worker.

Agreement The Hazards

The rubber concern for this blazon of equipment — service panelboards with provisions for more than than one service disconnect within a single enclosure — is existent and had to be addressed at some point in the history of the NEC. The hazards for this equipment include but are not limited to the following:

The only way to de-energize this service equipment is to call the utility to disconnect the service.
When 6 disconnects are in the same enclosure, the act of turning off all of the disconnects provides no level of isolation of power for the electrical worker as the energized common charabanc will remain exposed unless disconnection at the utility has been performed.
Incident free energy is high because the just upstream OCPD is on the line side of the utility transformer sized to handle inrush current, which volition non open speedily on downstream arcing currents
When the deadfront of the panel is removed, the electrical worker is looking directly at exposed copper or aluminum unprotected bus. The likelihood and severity of an electrical safety event are high for the electrical worker.

The hazards of daze and arc flash are two existent hazards electrical workers face every day. Establishing an electrically prophylactic working status and reducing incident energy relies on upstream overcurrent protective devices and/or switches. Regarding service entrance equipment, the electrical worker doesn't have direct access to the upstream overcurrent protective device, and the upstream overcurrent protective device is in a location in the distribution organisation where arcing currents are low enough that clearing times are long. Justified energized piece of work in this equipment presents a real safe challenge to the electrical professional.

Outside of the obvious concerns of shock, an understanding of an arc flash upshot within an enclosure should be understood to fully cover the electric take chances. Should an arc flash event occur in service archway equipment, fifty-fifty those with a main overcurrent protective device, the enclosure experiences a rapid release of a plasma cloud that can quickly escalate the event to the lineside lugs of a panel with a main or the main coach of the panel for those without a chief. This "lineside propagation" of the arc wink places the immigration time solely in the hands of the upstream overcurrent device.

From Old to New

It was in 1937 that the NEC began the journey into permitting upwardly to 6 services. Historical documents illustrate this determination every bit follows:

"Paragraph (c) of Section 401 of this affiliate is to be amended by added text to allow for special permission to have more than than one gear up of service conductors run to a single building having a multiple occupancy."

There were other historical decisions fabricated at this time, including changes in Department 405 that permitted the utility meter, if installed outdoors, to exist placed ahead of the service switch and the service fuse. In improver, this edition introduced the structure of the NEC, most of which is what nosotros still know today.

"The principal trunk of the rearranged Lawmaking is prepare forth in ten Chapters as our Appendix indicates. Chapters 1 to iv are of general application. Chapters 5, vi, and seven apply to special occupancies or equipment and to other special weather condition. Their provisions, equally is stated in the Introduction, are supplementary to or amendatory of the general rules. All previous editions of the Code take resorted to this method of avoiding repetition in text. Affiliate 8 deals with communication systems–radio and signaling. Affiliate 9 will contain merely tables and diagrams with necessary cantankerous-references to the rule material of the previous capacity. Chapter 10, similarly to Chapter nine, is a drove, merely instead of tables and diagrams is of requirements for details of construction of materials and equipment rather than of installation or appropriate employ."

In 1937, the alter to let more 1 service recognized that having one disconnect for a construction may not exist the safest approach. The apparent discussions at that time revolved around one disconnect to some structures that would kill power to elevators and other important items within the structure, causing other types of safety concerns. The 1937 report on changes says the post-obit with this regard.

"The changes in the regulations equally to service conductors and service entrance equipment annals increasing recognition and acceptance of the view that the burn department no longer (if information technology ever was the practice) proceeds immediately when responding to an alarm of fire to the basement to cut off all current and put premises into darkness and prevent utilise of elevators or other important aids to their operations. In many buildings, the quantity of electricity used makes the "unmarried-stroke" opening of a disconnect for the unabridged supply a dangerous if not physically impossible operation. In smaller premises, diversity of use and kinds of supply employed may make a single disconnect undesirably complicated and perchance hazardous.

A corollary to this development is the subdivision of overcurrent protection and the omission, for some applications, of a single unit of a rating corresponding to the capacity of the service conductors."

New changes found in 230.71(B), Ii to Vi Service Disconnecting Ways, is changing what the electrical industry has known and used for many years and now provides options for providing a structure with half-dozen service disconnects. None of these options allow the installation of a panelboard with vi disconnects within. In my opinion, this is a celebrated moment for the NEC as information technology has changed a practice that has been in place for more than 80 years.

The options provided for in these installations include the following:

(ane) Separate enclosures with a master service disconnecting ways in each enclosure:

Examples of applications meeting this option could include fusible switches. Some could make the argument that a six panelboards with a master would exist 6 separate enclosures with a main service disconnect in each enclosure, which leads u.s. to the next option.

(2) Panelboards with a primary service disconnecting means in each panelboard enclosure

This pick is the item that specifically removes the power to have a panelboard without a main. This particular tells us that a service panelboard must have a master service disconnecting means.

The adjacent option addresses switchboards, and in my opinion, information technology is very straight forward.

(three) Switchboard(s) where in that location is only 1 service disconnect in each divide vertical section where there are barriers separating each vertical section.

And finally, that last option addresses two separate types of service equipment, notably switchgear and metering centers.

(iv) Service disconnects in switchgear or metering centers where each disconnect is located in a separate compartment.

It is option 4 that, in my stance, may see more than modifications moving forward into the next version of the NEC. The first step that could exist made to meliorate this item is to carve up switchgear from metering centers as, after all, the new Informational Note 1 notes that metering centers are really addressed in UL 67, which is the UL standard for Panelboards. 1 could make an statement to include metering centers as part of option 2 which addresses panelboards or address this equipment as a new choice five. The NEC is like a fine wine. It just keeps getting better with time.

These changes accommodate the requirements institute in 230.71, as noted in a higher place facilitating the barriers of line-side service usher terminations.

Closing

The changes we see at service equipment are all about reducing the likelihood and severity of electrical hazards. It facilitates the application of line-side barriers, which helps with both aspects of electrical hazards of arc flash and shock.

Equally I noted in my opening paragraph, nosotros tin can learn from this discussion and leverage this knowledge in other similar areas of the power system. The presence of a transformer in between a panelboard and the side by side upstream overcurrent protective device, as shown in Figure 1a, presents a claiming to incident energy at the downstream console. Based on this discussion, the incident free energy at the downstream panelboard, equally shown in Effigy 1a, is a double-digit number placing the electrical worker in a very caustic environment.

The placement of barriers on the lineside of the principal OCPD in that console tin can significantly decrease the likelihood of an event, only it does not enable the reduction of the calculated incident free energy. It is worth noting that a uncomplicated change to the pattern can significantly increase prophylactic for the electrical worker. Figures 1a and 1b illustrate what can exist achieved with a design modify and presents a generic design option that can be used both at the service and at the secondary of any power distribution transformer. The premise of this change is to button the college incident free energy into an enclosure that is rarely accessed by an electrical worker providing lower incident energy and the ability to easily establish an electrically safety working condition at equipment with a high likelihood of existence accessed. The focus of designs tin exceed blank minimum code requirements, but together with the principles that the NEC brings to the table, and knowledge of hazards, blueprint approaches tin create a safer workplace.

References