ION ORACLE - NEC Basics

NEC BASICS

Compliance

In this unit, we will jump into some of the basics surrounding PV as they appear in the NEC. The purpose of this is to help senior designers and compliance specialists understand all the code specifics behind the design process and electrical caclutations and help with electrical disputes with AHJs and Utilities as applicable.

1 | PHOTOVOLTAIC SYSTEMS (PV)

690.12 Rapid Shutdown of PV on Buildings

690.13 PV System Disconnecting Means

690.31 Wiring Methods and Materials

2 | OVERCURRENT PROTECTION

690.8-9 Inverter Output Circuit Current & Device Ratings

240.4 Protection of Conductors

3 | ELECTRICAL INSTALLATION GENERAL REQUIREMENTS

110.3 Examination, Identification, Installation, Use, and Listing of Equipment

110.6 Conductor Sizes

110.9 Interrupting Rating

110.11 Deteriorating Agents

110.14 Electrical Connections

110.25 Lockable Disconnecting Means

310.12 Single-Phase Dwelling Services and Feeders

4 | ELECTRICAL GROUNDING AND BONDING

690.47 Grounding Electrode System

250.4 General Requirements for Grounding and Bonding

250.52 Electrodes Permitted for Grounding

250.66 Size of Alternating-Current Grounding Electrode Conductor

250.118 Types of Equipment Grounding Conductors

250.122 Size of Equipment Grounding Conductor

5 | INTERCONNECTED ELECTRIC POWER PRODUCTION SOURCES

705.11 Supply-Side Source Connections

705.12 Load-Side Source Connections

705.13 Power Control Systems

6 | MARKING AND LABELING

690.54 Interactive System Point of Interconnection

690.56 (C) Buildings with Rapid Shutdown

705.10 Identification of Power Sources

705.12 Load-Side Source Connections

1 | PHOTOVOLTAIC SYSTEMS (PV)

NEC 690 is the main code governing electrical design and installation standards for PV Specifically. Most of the basic criteria we will cover in this unit will intersect with NEC 690.

690.12 Rapid Shutdown of PV on Buildings

This section of the code talks about PV disconnecting means.

To begin, it is important to establish some terms used in the code language to better understand it:

(A)(2) Controlled Conductors: These are the electrical circuits within PV systems installed on or in buildings. The code mandates that these circuits have a rapid shutdown function to reduce the risk of electric shock for firefighters.

(C) Initiation Device: This is the device that starts the rapid shutdown function. When this device is in the "off" position, it means that the rapid shutdown is active for all connected PV systems. For one or two-family dwellings, this initiation device should be easily accessible outside the building. It can be any of the following:

Service disconnecting means
PV system disconnecting means
Readily accessible switch that plainly indicates whether it is in the "off" or "on" position.

To satisfy these conditions, we use either a breaker type disconnect or a knife handle type AC disconnect.

690.13 PV System Disconnecting Means

Means shall be provided to disconnect the PV system from all wiring systems including power systems, energy storage systems and utilization equipment and its associated premises wiring.

(A): PV System disconnecting means shall be installed at a readily accessible location.

(B): Each PV system disconnecting means shall plainly indicate whether in the open (off) or closed (on) position and be permanently marked "PV SYSTEM DISCONNECT"

Notice that in most cases, 690.12 and 690.13 can be satisfied using a single disconnect. In some cases, some AHJs or utilities may require an AC disconnect in addition to the PV breaker used for interconnection if that interconnection is occurring on in indoor panel; this is because of the guidelines highlighted in 690.13(A).

690.31 Wiring Methods and Materials

(A) Wiring Systems: All raceways and cable wiring methods included in the code, other wiring systems and fittings specifically listed for use in PV arrays and wiring as part of a listed system shall be permitted.

Circuit conductors shall be guarded or installed in type MC cable or in a raceway.

In the examples to the right, we have two examples of approved interior attic runs:

The top is the most common type used here at ION.
- NM-B is approved for open air use in attics and through walls as long as there is no risk of exposure to moisture or outside damage.
- Unfinished areas such as attics and basements allow for direct exposure as long as NM-B is properly secured to structural members every 24".
The bottom photo is an example of an interior run using type MC cable:
- MC cable is simply FMC prefilled with THHN single conductor cables.
- THHN is never approved for open air use, so it will always need to be contained in a raceway.

These next examples to the right show common exterior conduit runs.

The top is a less common roof conduit run:
- This is usually only chosen when there is no attic access to complete an interior homerun.
- In this example, cables, typically THHN, is being ran through type FMC.
- The FMC is equipped with the proper PVC jacked for weather proofing.
The bottom photo is a very common example of exterior wall conduit:
- This will be seen on virtually every install.
- THHN running through EMT.
- EMT should be fastened at every 6' and within 24" of any entrance/exit to an enclosure or another raceway.

(B) Identification and Grouping: PV system circuit conductors shall be identified at all termination, connection, and splice points by color coding. Where the conductors of more than one PV system occupy the same junction box or raceway with a removable cover(s), the PV system conductors of each system shall be grouped separately by cable ties or similar means at least once and shall then be grouped at intervals not to exceed 1.8m (6ft).

For PV we use the typical color coding and grouping:

Ungrounded Conductor:

black or red

Grounded Conductor:

white or gray.

Equipment Grounding Conductor (EGC):

green or bare

2 | OVERCURRENT PROTECTION

690.8-9 Inverter Output Circuit Current & Device Ratings

690.8 (A)(1)(e) Inverter Output Circuit Current: The maximum current shall be the inverter continuous output current rating.

To the right is an example of a typical string inverter spec sheet (top) and a microinverter spec sheet (bottom). The maximum continuous output current is what would be used for calculations regarding backfeed and OCPD ratings.

For more information on reading equipment specs, refer to Equipment Listings and Specs

690.9 (B)(1) Device Ratings: Overcurrent devices, where required, shall be rated in accordance with the following: not less than 125% of the maximum currents calculated in 690.8(A)

Example: 19 module system using IQ8+ inverters

(19) x 1.21 = 22.99A

22.99A x 1.25 = 28.74 A

Continue to 240.4 for an explanation of how to size the OCPD for 28.74.A

240.4 Protection of Conductors

(B) Overcurrent Devices Rated 800 Amperes or Less: This section allows for the use of the next higher standard overcurrent device rating for conductors rated at 800 amperes or less.

So in the example above, we would need to round up to the next higher standard overcurrent device rating since an OCPD rated for 28.74A does not exist.

30A Overcurrent Protection Device (OCPD) Needed

3 | ELECTRICAL INSTALLATION GENERAL REQUIREMENTS

110.3 Examination, Identification, Installation, Use, and Listing of Equipment

(A): In judging equipment, considerations such as the following shall be evaluated:

(1) Suitability for installation and use in conformity with this code.

(2) Mechanical strength and durability, including, for the parts designed to enclose and protect other equipment adequacy of the protection thus provided.

(3) Wire-bending and connection space

(4) Electrical insulation.

(5) Heating effects under normal conditions of use and also under abnormal conditions likely to arise in service.

(6)Arcing effects

(7) Classification by type, size, voltage, current capacity, and specific use.

(8)Other factors that contribute to the practical safeguarding of persons using or likely to come in contact with the equipment.

(C) Listing: Product testing, evaluation, and listing (product certification) shall be performed by recognized qualified electrical testing laboratories and shall be in accordance with applicable product standards recognized as achieving equivalent and effective safety for equipment installed to comply with this Code.

For more on equipment listings see Equipment Listings and Specs

110.6 Conductor Sizes

Conductor sizes are expressed in American Wire Gage (AWG) or in circular mils.

The table to the right (NEC table 310.16) shows typical ampacity ratings per wire gage:

An important thing to note is that conductors have different temperature ratings which can affect ampacity ratings.
Also note that this graphic only shows the table ratings for coper type conductors and not aluminum or copper clad aluminum.

For more about sizing wires, wire temperature ratings, correction factors, see Advanced NEC

For a vast majority of jobs at ION, AWG will be used for sizing conductors, but occasionally circular mils is used to size wire for extended trenching where wires need to be upsized.

110.9 Interrupting Rating

Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that is available at the line terminals of the equipment.

Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that must be interrupted.

What is interrupting Rating?

The interrupting rating is commonly referred to with several terms that mean the same thing:

Interrupting rating (IR)
Ampere interrupting capacity (AIC)
Ampere interrupt rating (AIR)

The interrupting rating is defined in the NEC® as “the highest current at rated voltage that a device is identified to interrupt under standard test conditions.”

In other words, the highest current that a piece of equipment, typically a circuit breaker, without sustaining extreme damage.

So if a breaker has an ampacity rating of 200A and an interrupting rating of 35000A, this is what it means:

When the threshold of 200A of current passes through the breaker, it will cause the breaker to trip.
The breaker will continue to interrupt fault current without combusting up to 35000A of current.
- If somehow the fault current were to exceed 35000A, this would cause a catastrophic equipment failure and the breaker would combust.

110.11 Deteriorating Agents

Unless identified for use in the operating environment, no conductors or equipment shall be located in damp or wet locations; where exposed to gases, fumes, vapors, liquids, or other agents that have a deteriorating effect on the conductors or equipment; or where exposed to excessive temperatures.

Equipment not identified for outdoor use and equipment identified only for indoor use, such as "dry locations," "indoor use only," "damp locations," or enclosure Types 1, 2, 5, 12, 12K, and/or 13, shall be protected against damage from the weather during construction.

Mainly, this applies to indoor rated equipment:

They should never be located outdoors.
They should never be located in bathrooms.

The example to the right shows an indoor rated panel mounted outdoors which would be in direct violation with this code.

110.14 Electrical Connections

This section of the code goes over quite a bit of information. Here is a condensed version of the code language:

Handling Dissimilar Metals:
- Connectors and materials should be suitable for the type of conductor being used, and dissimilar metals should not be mixed without proper identification or precautions.
Connector Identification:
- Connectors for finely stranded conductors must be identified for the specific conductor class or classes.
Terminal Connections:
- Secure connections should be made using appropriate pressure connectors, solder lugs, or splices to flexible leads. Certain exceptions are allowed for smaller conductors.
Splicing Rules:
- Conductors must be spliced using appropriate splicing devices, and soldered splices must be mechanically and electrically secure without solder first. All splices and joints should be insulated properly.
Temperature Considerations:
- The temperature rating of conductors should be coordinated to avoid exceeding the lowest temperature rating of any connected termination, conductor, or device.
Equipment Provisions:
- Equipment termination provisions for different circuit ratings should be followed based on specific temperature and ampacity regulations, as outlined in the code.
Separate Connector Usage:
- Pressure connectors installed separately must not exceed the ampacity listed and identified temperature rating of the connector.
Terminal Connection Torque:
- Terminal connection torque values should be followed as indicated by the equipment manufacturer's instructions, using an approved means to achieve the specified torque value.

110.25 Lockable Disconnecting Means

If a disconnecting means is required to be lockable open elsewhere in this Code, it shall be capable of being locked in the open position. The provisions for locking shall remain in place with or without the lock installed.

When you see Visible Lockable AC Disconnect on a plan set, it is stating that the equipment is capable of accepting a mechanical lock meant to lock the equipment in the open (off) position.

310.12 Single-Phase Dwelling Services and Feeders

For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, service and feeder conductors supplied by a single-phase, 120/240-volt system shall be permitted to be sized in accordance with 310.12(A) through (D).

For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, single-phase feeder conductors consisting of two ungrounded conductors and the neutral conductor from a 208Y/120 volt system shall be permitted to be sized in accordance with 310.12(A) through (C).

(A) Services. For a service rated 100 amperes through 400 amperes, the service conductors supplying the entire load associated with a one-family dwelling, or the service conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the service rating. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.

(B) Feeders. For a feeder rated 100 amperes through 400 amperes, the feeder conductors supplying the entire load associated with a one-family dwelling, or the feeder conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the feeder rating. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.

(C) Feeder Ampacities. In no case shall a feeder for an individual dwelling unit be required to have an ampacity greater than that specified in 310.12(A) or (B).

For more about sizing wires, wire temperature ratings, correction factors, see Advanced NEC

4 | ELECTRICAL GROUNDING AND BONDING

690.47 Grounding Electrode System

(A) Buildings or Structures Supporting a PV System. A building or structure(s) supporting a PV system shall utilize a grounding electrode system installed in accordance with Part III of Article 250.

250.4 General Requirements for Grounding and Bonding

(A)(1) Electrical System Grounding: Electrical Systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

(A)(3) Bonding of Electrical equipment: Normally non-current-carrying conductive materials enclosing electrical conductors or equipment or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

(A)(5) Effective Ground-Fault Current Path: Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault occurs to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.

250.52 Electrodes Permitted for Grounding

(A) Electrodes Permitted for Grounding:

Metal Underground Water Pipe
Metal in Ground Support Structure(s)
Concrete-Encased Electrode
Ground Ring
Rod and Pipe Electrodes

250.66 Size of Alternating-Current Grounding Electrode Conductor

The size of the grounding electrode conductor at the service at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system of a grounded or ungrounded AC system shall not be less than given in table 250.66.

Table 250.66

250.118 Types of Equipment Grounding Conductors

The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:

A copper, aluminum, or copper-clad aluminum conductor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
Rigid metal conduit
Intermediate metal conduit
Electrical Metallic Tubing
Flexible Metal tubing.

250.122 Size of Equipment Grounding Conductor

(A) General: Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.22. The equipment grounding conductor shall not be required to be larger than the circuit conductors supplying the equipment.

(B) Increase in Size: If ungrounded conductors are increased in size for any reason other than as required in 310.15(B) or 310.15(C), wire-type equipment grounding conductors, if installed, shall be increased in size proportionately to the increase in circular mil area of the ungrounded conductors.

5 | INTERCONNECTED ELECTRIC POWER PRODUCTION SOURCES

705.11 Supply-Side Source Connections

(A) Output Rating: The sum of the power source continuous current output ratings on a service, other than those controlled in accordance with 705.13, shall not exceed the ampacity of the service conductors.

(B) Conductors: The power source output circuit conductors from the service conductors point of connection to the first overcurrent protection device shall be sized in accordance with 705.28 and in no case sized smaller than 6 AWG copper or 4 AWG aluminum. These conductors shall be installed in accordance with 230.30 or 230.43.

(C) Overcurrent Protection: The power source output circuit conductors shall be protected from overcurrent in accordance with 705.30. If fuses are not integral with the disconnecting means, the disconnecting means shall be located on the service side of the fuses. Where the power source output circuit conductors make their connection to the service outside of a building, they shall be protected by overcurrent devices in a readily accessible location outside the building or at the first readily accessible location where the power source conductors enter the building. Where the power source output circuit conductors make their connection to the service inside a building, they shall be protected with one of the following methods:

(1) With an overcurrent device located within 3 m (10 ft) of conductor length in dwelling units and 5 m (16.5 ft) in other than dwelling units from the point of connection to the service

(2) In other than a dwelling unit, with an overcurrent device located within 20 m (71 ft) of conductor length from the point of connection to the service, provided that cable limiters installed in all ungrounded conductors are located within 5 m (16.5 ft) of conductor length from the point of connection to the service

(D) Connections: The connection of power source output circuit conductors to the service conductors shall be made using listed connectors as described in 110.14 and comply with all enclosure fill requirements Any modifications to existing equipment shall be made in accordance with the manufacturer's instructions or the modification must be evaluated for the application and have a field label applied. For meter socket enclosures or other equipment under the exclusive control of the electric utility, only connections approved by the electric utility shall be permitted.

(E) Ground-Fault Protection: For connections rated 1000 amperes or more to solidly grounded wye services exceeding 150 volts to ground but not exceeding 1000 volts, phase-to-phase, ground-fault protection meeting the requirements of 230.95 shall be provided.

705.12 Load-Side Source Connections

The output of an interconnected electric power source shall be permitted to be connected to the load side of the service disconnecting means of the other source(s) at any distribution equipment on the premises. Where distribution equipment or feeders are fed simultaneously by a primary source of electricity and one or more other power source and are capable of supplying multiple branch circuits or feeders, or both, the interconnecting equipment shall comply with 705.12(A) through (E). Where a power control system (PCS) is installed in accordance with 705.13, the setting of the PCS controller shall be considered the power-source output circuit current in 705.12(A) through (E).

(A) Dedicated Overcurrent and Disconnect: Each source interconnection of one or more power sources installed in one system shall be made at a dedicated circuit breaker or fusible disconnecting means.

(B) Bus or Conductor Ampere Rating: The power source output circuit current multiplied by 125 percent shall be used in ampacity calculations for 705.12(B)(1) through (B)(3).

(1) Feeders: Where the power source output connection is made to a feeder, the feeder shall have an ampacity greater than or equal to 125 percent of the power-source output circuit current. Where the power-source output connection is made to a feeder at a location other than the opposite end of the feeder from the primary source overcurrent device, that portion of the feeder on the load side of the power source output connection shall be protected by one of the following:

a. The feeder ampacity shall be not less than the sum of the primary source overcurrent device and 125 percent of the power-source output circuit current.

b. An overcurrent device at the load side of the power source connection point shall be rated not greater than the ampacity of the feeder.

(2) Taps: Where power source output connections are made at feeders, all taps shall be sized based on the sum of 125 percent of all power source(s) output circuit current(s) and the rating of the overcurrent device protecting the feeder conductors for sizing tap conductors using the calculations in 240.21(B).

(3) Busbars: One of the following methods shall be used to determine the ratings of busbars:

(1) The sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar.

(2) Where two sources, one a primary power source and the other another power source, are located at opposite ends of a busbar that contains loads, the sum of 125 percent of the power-source(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed 120 percent of the ampacity of the busbar. The busbar shall be sized for the loads connected in accordance with Article 220.

(3) The sum of the ampere ratings of all overcurrent devices on panelboards, both load and supply devices, excluding the rating of the overcurrent device protecting the busbar, shall not exceed the ampacity of the busbar.

(4) A connection at either end of a center-fed panelboard in dwellings shall be permitted where the sum of 125 percent of the power-source(s) output circuit current and the rating of the overcurrent device protecting the busbar does not exceed 120 percent of the current rating of the busbar.

(5) Connections shall be permitted on switchgear, switchboards, and panelboards in configurations other than those permitted in 705.12(B)(3)(1) through (B)(3)(4) where designed under engineering supervision that includes available fault-current and busbar load calculations.

(6) Connections shall be permitted on busbars of panelboards that supply lugs connected to feed-through conductors. The feed-through conductors shall be sized in accordance with 705.12(B)(1). Where an overcurrent device is installed at the supply end of the feed-through conductors, the busbar in the supplying panelboard shall be permitted to be sized in accordance with 705.12(B)(3)(1) through 705.12(B)(3)(3).

(D) Suitable for Backfeed: Fused disconnects, unless otherwise marked, shall be considered suitable for backfeed. Circuit breakers not marked "line" and "load" shall be considered suitable for backfeed. Circuit breakers marked "line" and "load" shall be considered suitable for backfeed or reverse current if specifically rated.

(E) Fastening: Listed plug-in-type circuit breakers back-fed from electric power sources that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by 408.36(D) for such applications.

705.13 Power Control Systems

A power control system (PCS) shall be listed and evaluated to control the output of one or more power production sources, energy storage systems (ESS), and other equipment. The PCS shall limit current and loading on the busbars and conductors supplied by the PCS.

For the circuits connected to a PCS, the PCS shall limit the current to the ampacity of the conductors or the ratings of the busbars to which it is connected in accordance with 705.13(A) through (E).

(A) Monitoring: The PCS controller shall monitor all currents within the PCS. Any busbar or conductor on the load side of the service disconnecting means that is not monitored by the PCS shall comply with 705.12. Where the PCS is connected in accordance with 705.11, the PCS shall monitor the service conductors and prevent overload of these conductors.

(B) Settings: The sum of all PCS-controlled currents plus all monitored currents from other sources of supply shall not exceed the ampacity of any busbar or conductor supplied by the power production sources. Where the PCS is connected to an overcurrent device protecting any busbar or conductor not monitored by the PCS, the setting of the PCS controller shall be set within the ratings of that overcurrent device.

(C) Overcurrent Protection: The PCS shall provide overcurrent protection either by overcurrent devices or by the PCS including the functionality as an overcurrent device in the product listing.

Informational Note: Some PCS are listed to provide overcurrent protection.

(D) Single Power Source Rating: The rating of the overcurrent device for any single power source controlled by the PCS shall not exceed the rating of the busbar or the ampacity of the conductors to which it is connected.

(E) Access to Settings: The access to settings of the PCS shall be restricted to qualified personnel in accordance with the requirements of 240.6(C).

6 | MARKING AND LABELING

690.13 Photovoltaic System Disconnecting Means (B) Marking:

Each PV system disconnecting means shall plainly indicate whether in the open (off) or closed (on) position and be permanently marked "PV SYSTEM DISCONNECT" or equivalent. Additional markings shall be permitted based upon the specific system configuration. For PV system disconnecting means where the line and load terminals may be energized in the open position, the device shall be marked with the following words or equivalent:

WARNING ELECTRIC SHOCK HAZARD TERMINALS ON THE LINE AND LOAD SIDES MAY BE ENERGIZED IN THE OPEN POSITION

690.31(D)(2) Marking and Labeling Required: Unless located and arranged so the purpose is evident, the following wiring methods and enclosures that contain PV system conductors shall be marked with the wording PHOTOVOLTAIC POWER SOURCE by means of permanently affixed labels or other approved permanent marking.

690.54 Interactive System Point of Interconnection

All interactive systems points of interconnection with other sources shall be marked at an accessible location at the disconnecting means as a power source and with the rated AC output current and the nominal operating AC voltage.

690.56 (C) Buildings with Rapid Shutdown

Buildings with PV systems shall have a permanent label located at each service equipment location to which the PV systems are connected or at an approved readily visible location and shall indicate the location of rapid shutdown initiation devices. The label shall include the following words:

SOLAR PV SYSTEM EQUIPPED WITH RAPID SHUTDOWN. TURN RAPID SHUTDOWN SWITCH TO THE "OFF" POSITION TO SHUT DOWN PV SYSTEM AND REDUCE SHOCK HAZARD IN ARRAY.

110.21 Marking

(B) Field-Applied Hazard Markings:

Where caution, warning, or danger signs or labels are required by this Code, the labels shall meet the following requirements:

(1) The marking shall warn of the hazards using effective words, colors, symbols, or any combination thereof.

(2) The label shall be permanently affixed to the equipment or wiring method and shall not be handwritten.

(3) The label shall be of sufficient durability to withstand the environment involved.

705.10 Identification of Power Sources

A permanent plaque or directory shall be installed at each service equipment location, or at an approved readily visible location. The plaque or directory shall denote the location of each power source disconnecting means for the building or structure and be grouped with other plaques or directories for other on-site sources. The plaque or directory shall be marked with the wording "CAUTION: MULTIPLE SOURCES OF POWER." Any posted diagrams shall be correctly oriented with respect to the diagram's location. The marking shall comply with 110.21(B).

705.12 Load-Side Source Connections

(B)(3)(2) Busbars:

A permanent warning label shall be applied to the distribution equipment adjacent to the back-fed breaker from the power source that displays the following or equivalent wording:

WARNING:

POWER SOURCE OUTPUT CONNECTION

DO NOT RELOCATE THIS OVERCUURENT DEVICE

Equipment containing overcurrent device in circuits supplying power to a busbar or conductor supplied from multiple sources shall be marked to indicate the presence of all sources:

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