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Master subpanel inspection requirements. Learn why neutral-ground separation is critical for safety, how to identify subpanels vs. main panels, and special grounding requirements for detached buildings.

Episode Overview

Subpanel grounding and bonding is different from main panel configuration—and these differences are critical for safety. This episode explains why neutrals must be isolated from grounds in subpanels and how to identify dangerous violations.

Why Subpanel Grounding is Different:

• IRC 2018 Section E3607.2: No grounding connections on load side of service equipment
• Neutral conductors carry current (normally at zero voltage)
• What happens when neutrals and grounds are improperly connected
• How wiring errors can energize the neutral conductor
• Shock risk from exposed bonded metal connected to neutrals

What Qualifies as a Subpanel:

• ALL panelboards downstream from service equipment
• Main lug panelboards (even if they're the "main panel" for the house)
• All outlets, junction boxes, and appliance disconnects
• Any location past the GEC connection point

Proper Subpanel Configuration:

• Neutral conductors connected to SEPARATE, ISOLATED neutral terminal bars
• Neutral bars NOT connected to enclosure
• EGCs connected to SEPARATE grounding terminal bars
• Grounding bars BONDED to subpanel enclosure
• Two most common bonding methods: mounted to enclosure or bonding strap/bar

Grounding and Bonding at Detached Buildings:

Single Branch Circuit (15-20 amps):

• No special grounding required if EGC present in cable
• EGC must be present in modern circuits

Multiple Branch Circuits or Feeder:

• Grounding electrode system REQUIRED
• NEW circuits: Must contain EGC, neutrals isolated from EGC
• EXISTING circuits without EGC: May remain, configure as main panel (neutrals and EGCs on same bars, both bonded to electrode and enclosure)

Typical Defects to Report

• EGCs and neutral conductors on same terminal bar (in subpanel)
• EGCs or EGC terminal bar not bonded to enclosure
• Neutral bar bonded to subpanel enclosure (should be isolated)
• Missing grounding electrode at detached building
• Detached building subpanel configured as main panel (with EGC present in feeder)
• Refer also to "Other Typical Defects Inside Enclosures" from Episode 03

Key Takeaways

• Subpanels = ALL panels downstream from service equipment
• Neutral and ground separation is a SAFETY requirement, not optional
• Improper bonding can energize exposed metal and cause shock
• Detached buildings have special grounding requirements
• Configuration depends on whether EGC is present in feeder

Critical Safety Principle

Current flowing on neutral conductors can become energized under fault conditions. Keeping neutrals isolated from grounds prevents this current from energizing exposed metal that people might touch.

IRC Code References

IRC 2018: E3607.2 (GEC connection location), E3607.3 (detached building grounding)

Visual Identification Tips

• Look for separate neutral and ground terminal bars
• Check if neutral bar is mounted directly to enclosure (WRONG in subpanel)
• Verify green/bare wires (EGCs) are separate from white wires (neutrals)
• Trace the grounding electrode conductor to its connection poin

For complete training with visual materials, practice exams, and certification support, visit nhiexamprep.com

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