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

#3) 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.

#4) 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.

#5) 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.

#6) 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.

#7) 240.83(C) Circuit Breaker Marking. Interrupting Ra...

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

#8) 110.10 Circuit Impedance, Short-Circuit Current Ra...

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

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

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

#10) 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.

#11) 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.

#12) 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.

#13) Available Fault Current and Blueprints.

Refer to the image to answer the question.

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

Refer to the image to answer the question.

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

Refer to the image to answer the question.

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

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

#17) Fully Rated Systems.

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

#18) 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.

#19) 240.86(A) Series Rated Systems. Selected Under Eng...

Specific labeling is required for engineered series rated systems.

#20) 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.

#21) 240.86(B) Series Rated Systems. Tested Combination...

Specific labeling is required for tested series rated systems.

#22) 110.22(C) Tested Series Combination Systems.

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

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

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

#24) 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.

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

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.

#26) 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.

#27) 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.

#28) 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.

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

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

#30) 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.

#31) Article 100 & 409.22 Industrial Control Panels.

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

#32) 409.110 Industrial Control Panels. Marking.

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

#33) 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.

#34) 440.10 HVAC Multimotor and Combination-Load Equipm...

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

#35) 620.16 Elevators. Short-Circuit Current Rating.

#36) Texas Laws and Rules 73.10. Definitions.

#37) Texas Laws and Rules 73.10. Definitions.

#38) Texas Laws and Rules 73.10. Definitions.

#39) Texas Laws and Rules 73.20. Licensing Requirements...

#40) Texas Laws and Rules 73.22. Licensing Requirements...

#41) Texas Laws and Rules 73.23. Licensing Requirements...

#42) Texas Laws and Rules 73.25. Continuing Education.

#43) Texas Laws and Rules Sec. 1305.002. Definitions.

#44) Texas Laws and Rules Sec. 1305.002. Definitions.

#45) Texas Laws and Rules Sec. 1305.003. Exemptions; Ap...

Table 130.5(C) Estimate of the Likelihood of Occurrence of an Arc Flash Incident for ac and dc Systems.

#46) NFPA 70E 130.5(C) Estimate of the Likelihood of Oc...

Table 130.5(C) Estimate of the Likelihood of Occurrence of an Arc Flash Incident for ac and dc Systems.

#47) NFPA 70E 130.5(C) Estimate of the Likelihood of Oc...

<p style="text-align: center;">Table 130.5(C) Estimate of the Likelihood of Occurrence of an Arc Flash Incident for ac and dc Systems.

#48) NFPA 70E 130.5(C) Estimate of the Likelihood of Oc...

<p style="text-align: center;">Table 130.7(C)(15)(a) Arc-Flash PPE Categories for Alternating Current (ac) Systems.

#49) NFPA 70E 130.7(C)(15)(a) Arc-Flash Hazard PPE Cate...

Table 130.7(C)(15)(a) Arc-Flash PPE Categories for Alternating Current (ac) Systems.

#50) NFPA 70E 130.5(C)(15)(a) Arc-Flash Hazard PPE Cate...

(Be sure to write down anything you want to remember, starting over erases all answers)

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