Guide to Equipment Grounding Conductor (EGC) Questions on NEC Electrical Exams

Equipment grounding conductors are critical components of electrical systems that provide a safe path for fault current. These questions frequently appear on electrical licensing exams because proper sizing of EGCs is essential for safety and code compliance. Understanding how to size EGCs, especially when dealing with motor circuits and various overcurrent protection devices, is crucial for passing your exam.

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Example Equipment Grounding Conductor Questions on NEC Electrical Exams

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A disconnect switch, with a 75 degrees C rating, fused at 300 A feeds a panel using PVC conduit. The minimum size of copper equipment grounding conductor is __________, if the circuit is 347/600 V, 3Ø, 4- wire using 500 kcmil THWN aluminum conductors.

A 30 HP, 460-volt, Design B, 3-phase motor is protected by an instantaneous-trip circuit breaker. The minimum size copper equipment grounding conductor for this motor circuit is __________ AWG.

In a commercial kitchen, a 50-amp, 240-volt circuit supplies a large electric oven. The aluminum equipment grounding conductor for this circuit must be no smaller than __________ AWG.

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How to Identify an Equipment Grounding Conductor Question on NEC Electrical Exams

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Key phrases to look out for:

• "Equipment grounding conductor"
• "EGC"
• "Ground wire size"
• "Minimum grounding conductor"
• "Motor circuit grounding"
• References to Table 250.122

When you spot these elements:

1. Determine if it's a standard sizing question or involves special cases
2. For motor circuits, note the type of overcurrent protection
3. Check whether copper or aluminum conductor is specified
4. Refer to NEC Article 250.122

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Equipment Grounding Conductor Articles: NEC 250.122

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To correctly apply NEC Article 250.122, focus on these main elements:

1. Standard Sizing (250.122(A)):
   
   • Use Table 250.122 based on rating of overcurrent device
   • Consider whether using copper or aluminum conductor
2. Motor Circuit Requirements (250.122(D)):
   
   • Size based on maximum permitted rating of a dual element time-delay fuse
   • Special considerations for instantaneous-trip circuit breakers
   • Reference Table 430.52 values when needed
3. Multiple Circuits (250.122(C)):
   
   • Single EGC must be sized for largest overcurrent device
   • Parallel EGCs must meet specific requirements
4. Installation Requirements:
   
   • Must be contained within same raceway as circuit conductors
   • Properly terminated at equipment
   • Continuous path back to source

Walkthrough for NEC Electrical Exam EGC Questions

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Standard EGC Sizing Question

A disconnect switch, with a 75 degrees C rating, fused at 300 A feeds a panel using PVC conduit. The minimum size of copper equipment grounding conductor is __________, if the circuit is 347/600 V, 3Ø, 4- wire using 500 kcmil THWN aluminum conductors.

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Step 1: Identify Key Information

• Overcurrent protection: 300 A fuse
• Conductor material for EGC: Copper
• Standard installation in PVC conduit

Step 2: Use Table 250.122

• Find row for 300 amp overcurrent protection
• Look in copper column
• For 300A protection, Table 250.122 requires 4 AWG copper
• Note: Circuit voltage and conductor types don't affect EGC sizing

The minimum size copper equipment grounding conductor required is 4 AWG.

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Motor Circuit EGC Question

A 30 HP, 460-volt, Design B, 3-phase motor is protected by an instantaneous-trip circuit breaker. The minimum size copper equipment grounding conductor for this motor circuit is __________ AWG.

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Step 1: Identify Special Requirements

• Motor circuit with instantaneous-trip breaker
• Must apply 250.122(D)(2)
• Table 430.250 FLC Table 30 HP, 460 volt = 40 amps
• Table 250.52(C)(1) maximum rating = 175% for dual-element fuse
• 40 amp x 175% = 70 amps
• Maximum dual element time-delay fuse rating: 70A

Step 2: Apply 250.122(D)(2)

• Size based on maximum permitted dual element fuse rating
• Not based on actual instantaneous-trip breaker size
• Use 70A rating for Table 250.122

Step 3: Use Table 250.122

• Find row for protection not exceeding 100A
• Look in copper column
• Minimum size required: 8 AWG

Step 4: Verify Code Compliance

• Meets motor circuit requirements
• Satisfies 250.122(D)(2)
• Provides adequate fault current path

The minimum size copper equipment grounding conductor required is 8 AWG.

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