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Available Fault Current values at the service equipment can be obtained from the electric utility company.

#1) Available Fault Current.

Typical letter from the utility company providing the AFC at a given point.

#2) Available Fault Current and Characteristics of the...

The Ugly’s Electrical References guide has many tables and formulas commonly used by the electrician.

#3) Available Fault Current. Understanding the Calcula...

There are many programs to determine the available fault current at a given location but most just provide the final AFC value, not the math to back it up. What would be the available fault current at the service if the service entrance conductors are only 80 feet instead of 95?

#4) Available Fault Current. Example Calculation.

The interrupting rating is the highest current at rated voltage that a device is identified to interrupt under standard test conditions.

#5) Article 100 Definitions. Interrupting Rating.

This is a passive component and provides no overcurrent protection. It has a Short-Circuit Current Rating of 5kA or 5000 amps.

#6) Article 100 Definitions. Short Circuit Current Rat...

The time clock is a passive device that cannot protect itself against any fault occurring on the load that it controls.

#7) 110.9 Interrupting Rating of Defensive and Passive...

Overcurrent devices (top) must have an interrupting rating at least equal to the current that is available at the line terminals. Passive devices like the lighting contactor on the left require an interrupt rating at least equal to the current they are interrupting.

#8) 110.9 Interrupting Rating.

Circuit breakers are generally marked somewhere with their interrupting rating. If not marked, then they have a default value of 5,000 amperes.

#9) 240.83(C) Circuit Breaker Marking. Interrupting Ra...

The electrician must understand resistance, impedance and other circuit characteristics.

#10) 110.10 Circuit Impedance, Short-Circuit Current Ra...

Many factors need to be known in order to determine compliance with NEC 110.10.

#11) Available Fault Current. Applying It Downstream of...

The arc-flash hazard warning has nothing to do with the available fault current marking in 110.24.

#12) 110.16(A) Arc-Flash Hazard Warning. General.

The marking requirements apply when a 1200 amp or larger electric service is installed at other than dwelling units.

#13) 110.16(B) Arc-Flash Hazard Warning. Service Equipm...

This label provides the AFC and the date of the calculation.

#14) 110.24(A) Available Fault Current. Field Marking.

Changing the length or size of the service entrance conductors will also change the amount of available fault current at the service equipment.

#15) 110.24(B) Available Fault Current. Modifications.

Be mindful of the proximity of the utility transformer, generator or other sources of supply that contribute to the amount of available fault current.

#16) Available Fault Current and Remodel or Service Wor...

Be mindful of AFC values shown on the plans when measuring out and cutting feeders to length.

#17) Available Fault Current and Blueprints.

Refer to the image to answer the question.

#18) Available Fault Current on the Plans. Exercise 1.

Refer to the image to answer the question.

#19) Available Fault Current on the Plans. Exercise 2.

Refer to the image to answer the question.

#20) Available Fault Current on the Plans. Exercise 3.

Refer to the image to answer the question.

#21) Available Fault Current on the Plans. Exercise 4.

In a fully rated system, all OCPD’s have an AIC rating equal to or more than the AFC at their line terminals.

#22) Fully Rated Systems.

Series ratings can be between OCPD’s in the same enclosure or in separate enclosures.

#23) Series Rated Systems.

Often, a spare space in an older MDP is used if a new subpanel is added. For this one, the engineer has it easy since each switch shown is fused with common fuse sizes. Many modern series combinations will have a fuse at the MDP supplying a panelboard with breakers downstream. This series combination can be verified by the series rating book that comes with the new subpanel.

#24) 240.86(A) Series Rated Systems. Selected Under Eng...

Specific labeling is required for engineered series rated systems.

#25) 110.22(B) Engineered Series Combination Systems.

Unfortunately, the series rating book is usually one of the first things tossed into the trash by the electrician after the panelboard is installed. This one was fished out of the trash and placed at the switchgear after the inspector red tagged it during the final inspection.

#26) 240.86(B) Series Rated Systems. Tested Combination...

Specific labeling is required for tested series rated systems.

#27) 110.22(C) Tested Series Combination Systems.

Refer to the labeling inside the panelboard enclosure to verify a series combination.

#28) Verifying a Tested Series Rated Combination. Circu...

Use the panelboard manufacturers series rating chart to answer the question.

#29) Verifying a Tested Series Rated Combination. Fuses...

Over the years, maintenance persons have had their way with this panelboard. The panelboard had circuit breakers from different manufacturers as well as both 10k AIC and 22k AIC circuit breakers.

#30) NEC 110.3(B) and The Intermixing of Circuit breake...

In order to use a series combination here, since the motor is connected between the devices that are part of the series combination, the motor full load current would not be able to exceed 1% of the AIC rating of the 10k breakers.

#31) 240.86(C) Series Ratings. Motor Contribution Exerc...

Is the motor connected on the load side of the higher rated device and on the line side of the lower rated device in the series combination? If so, the motor full load current would not be able to exceed 1% of the AIC rating of the 10k breakers in order to have a code complaint series rated system.

#32) 240.86(C) Series Ratings. Motor Contribution Exerc...

Series rated electrical systems don’t generally work well when selective coordination is required. The fault on circuit 2 in Panel A should trip circuit breaker 2 before circuit breaker 6 in the MDP does.

#33) Series Ratings and Selective Coordination.

If circuit breakers used in a series combination have not been tested and verified, a whole lot of waiting and not much tripping can occur. As time goes by, higher and higher amount of AFC can make it through to the lower rated breaker.

#34) Circuit Breakers Protecting Circuit Breakers.

If fuses used in a series combination have not been tested and verified, a whole lot of waiting and not much tripping can occur. As time goes by, higher and higher amount of AFC can make it through to the lower rated breaker.

#35) Fuses Protecting Circuit Breakers.

The fuse chart can be used when protecting passive components, not selecting a series rated system. This chart shows that if a 400-amp RK-1 fuse was installed where the AFC was 40,000 amps, the fuse would let no more than 10,000 amps through before it blows. If the passive equipment being protected had a SCCR of 10k RMS, then this fuse could be used to comply with NEC 110.10.

#36) Fuse Protection of Passive Components.

This chart shows that if a 30-amp RK-1 fuse was installed where the AFC was 40,000 amps, the fuse would let no more than 1,800 amps through before it blows. If the passive equipment being protected had a SCCR of 5k RMS, then this fuse could be used to comply with NEC 110.10.

#37) Selecting a Fuse Because of its Current Limiting C...

This label was from an industrial chiller that had a SCCR of 5kA. The AFC was 65kA. The electrician was responsible to fill in the fuse type after using the fuse chart to ensure that the type of fuse marked on the label will never let through more than 5kA of AFC during a fault.

#38) Short-Circuit Current Ratings Dependent on Specifi...

This disconnect was installed ahead of an electric meter. It has a 200,000-amp SCCR when used with class J or R fuses. If class H or K fuses are used, it only has an SCCR of 10kA. The AFC on the line side of the switch determines which type of fuse will be needed.

#39) 230.82(3) Equipment Connected to the Supply Side o...

SPD’s are not allowed to be installed where their marked SCCR is exceeded by the available fault current.

#40) Surge-Protective Devices. Short-Circuit Current Ra...

An industrial control panel can be as simple as a couple of contactors or relays installed in an enclosure.

#41) Article 100 & 409.22 Industrial Control Panels.

Industrial control panels are required to be marked with their SCCR.

#42) 409.110 Industrial Control Panels. Marking.

This manual motor controller is marked with the SCCR.

#43) 430.8 Marking on Motor Controllers.

Now that the AFC has been calculated, the inspector can verify that the correct conductor type, size, and length has been installed in order to ensure that the SCCR of the motor control center is equal to or greater than the available short circuit current in compliance with NEC 110.9 and 110.10.

#44) 430.99 Motor Control Centers. Available Fault Curr...

Most HVAC multimotor and combination-load equipment will have a marked SCCR.

#45) 440.4 Marking on Hermetic Refrigerant Motor-Compre...

Now that the calculation has been performed, the inspector can verify that the correct conductor size, length and type has been installed in order to get the available fault current down to 5,000 amps to match the SCCR on the control panel.

#46) 440.10 HVAC Multimotor and Combination-Load Equipm...

The DC circuit breaker circled in red serves as the DC disconnect switch for this bank of storage batteries. The maximum available fault current derived from the stationary battery system and the date the calculation was performed must be field marked at the DC disconnect.

#47) 480.7 DC Disconnect Methods. Maximum Available Sho...

The elevator control panel shall not be installed where the available fault current exceeds its short-circuit current rating.

#48) 620.16 Elevators. Short-Circuit Current Rating.

After selecting the applicable combination from the nameplate, the SCCR, based on that combination must then be field marked on the exterior of the transfer switch.

#49) 700.5(E) Emergency System Transfer Equipment. Docu...

Extremely large or parallel generators can produce well over 10,000 amps during a fault condition.

#50) 701.4 Legally Required Standby Systems. Capacity a...

This automatic transfer switch is listed by UL and is suitable for use on emergency systems as required in NEC 700.5(C).

#51) 24.1-06-01-10. Requirements for electrical install...

There are many electrical products on the market that have not been listed or certified by a NRTL.

#52) 24.1-06-01-10. Requirements for electrical install...

Typical well drilling rigs require sufficient room to extend and operate.

#53) 24.1-06-01-10. Requirements for electrical install...

See North Dakota Laws and Rules pertaining to the use of aluminum conductors.

#54) 24.1-06-01-10. Requirements for electrical install...

The electrical system in this home must be evaluated for reconditioning or replacement after the flood waters recede.

#55) 24.1-06-01-20. Water damaged electrical equipment.

The means of egress consists of three separate components and is required to be illuminated at all times that the means of egress is available for use.

#56) 24.1-06-01-30. Markings of means of egress, illumi...

Combination smoke/carbon monoxide alarm.

#57) 24.1-06-01-40. Smoke alarms, heat alarms, fire ala...

Use the image to answer the question.

#58) 24.1-06-01-40. Smoke alarms, heat alarms, fire ala...

Use the image to answer the question.

#59) 24.1-06-01-40. Smoke alarms, heat alarms, fire ala...

Sunday lunch gatherings at church. Crockpot central.

#60) 24.1-06-02-10. (NEC 210) Branch circuits.

Two of the required circuits shall supply receptacle outlets on or near work counter area and so arranged that adjacent receptacles are not on the same circuit.

#61) 24.1-06-02-10. (NEC 210) Branch circuits.

The receptacle on the ceiling is not considered readily accessible since it can only be reached by portable ladder. See NEC Article 100 definition of “accessible, readily”.

#62) 24.1-06-02-10. (NEC 210) Branch circuits.

A perpendicular mast shall be fitted with storm collar flashing.

#63) 24.1-06-02-30. (NEC 230) Services.

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