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How Loss of the Neutral Connection in a Sub Panel Led to a Dangerous Electrical Shock InspectAPedia®  -     Case history of a neutral wire failure, improper joining of neutral and ground wiring in a sub panel, burning-up electrical ground wires, and a homeowner who received a nasty electrical shock How to inspect the electrical ground system: wires, grounding conductors, connectors, ground rods

This document describes a case history of loss of the neutral connection in an electrical panel combined with failure to isolate the neutral and ground buses leading to an electrical shock. While we have frequently updated and added to the material, in its original form this information was presented by Daniel Friedman - InspectAPedia.com, at the Hudson Valley chapter of the American Society of Home Inspectors - HVASHI Seminar 12 Sept 2002, Updated April 2006. Readers of this article should also be sure to review Safety Hazards and Safe Electrical Inspection Procedures for Inspectors examining Residential Electrical Systems. Sketch courtesy of Carson Dunlop.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Case History of an Electrical Ground Failure - Loss of a Neutral Connection in an Electrical Sub Panel Badly Shocks a Homeowner

What did all of these sub panel observations and electrical wiring errors mean?

When the air compressor motor was running it was producing a significant current on the compressor's neutral circuit.

The garage neutral circuit had no connection back to the main building (where it would have been connected to earth in the main panel, but because the owner had (improperly) bonded together the ground and neutral bus in his garage sub panel, the garage neutral circuit was indeed finding a path to earth through a small diameter (and thus overheated and dark) copper ground wire and a local grounding electrode.

The root causes of this electrical shock were:

Improper electrical wiring - bonding the ground and neutral wires together in the sub panel A binding steel screw in an aluminum wiring lug in the sub panel's incoming neutral wire connector - tightening the screw made the installer think he was securing the neutral wire when he was not. Because the garage electrical system was carrying current that should have been flowing only on the insulated neutral wires in the building, when the owner touched his grounded metal work bench and was also touching a damp floor, current flowed through the ground wire, through the metal work bench, through the owner, to earth. Sketch courtesy of Carson Dunlop. Our case study of a double fault involving loss of both the utility company ground and the local building ground shows how power can simply be lost in a building due to grounding system defects.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

See GROUND SYSTEM INSPECTION and Definition of Electrical Ground Terms. Also, see details about electrical grounding at Electrical Circuits, shorts, and at Electrical Wiring in Old Houses and at Electricity Basics - how it works.

ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR
ELECTRIC METERS & METER BASES
AMPACITY - the LIMITING FACTOR
ELECTRIC PANEL AMPACITY
ELECTRIC PANEL INSPECTION
ELECTRICAL BASICS
  Electricity Basics - how it works
  Electrical Circuit ID, Map & Label
  Electrical Circuits, shorts
  Electrical Code Basics
  Electrical Conduit Tips
  Electrical Definitions
  Electrical Grounding Basics
  Electrical Outlet-how to add
  Electrical Splices, how to make
  Electrical Tools & Tests
  Electrical Wire Stripping Tips
  Electrical Wiring Books & Guides
  Electrical Wiring in Old Houses
ENERGY SAVINGS in BUILDINGS
FEDERAL PACIFIC FPE HAZARDS
GROUND SYSTEM INSPECTION
  Why Grounding is Needed
  Gas Piping Ground Bond
  Table of Ground Wire Sizes
  False Ground at Receptacles
  False Neutral Connections
  Case History: Double Fault Leads to Loss of Power
  Case History:Loss of Neutral Shocks Homeowner
  Electrical Service Grounding Checklist
KNOB & TUBE WIRING
LIGHTNING PROTECTION
LOW VOLTAGE BUILDING WIRING
MAIN DISCONNECT AMPACITY

• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

More Information on Building Diagnostic Inspections and Repairs

• * Safety Hazards and Safe Inspection Procedures for Electrical and Home Inspectors at Residential Electric Panels
• Aluminum Wiring Information Website Aluminum Electrical Wiring Hazards and Repairs: in-depth authoritative info, photos, documents including selection of proper vs. ineffective repair methods. E.g.: Ideal 65 "Twister" purple connector fails in field and lab testing with aluminum wire.
• Ampacity of an Electrical Service: How to determine the electrical service size or ampacity entering a building
• Circuit Breaker, a bad one fails to trip failure at aluminum bus-to-circuit breaker connection - field report and photographs
• Electrical Panels, How to Inspect in Buildings, safety for electrical inspectors, electrical panel, fusing, wiring defects, defective products. Inspection Class Presentation
• Federal Pacific Electric (FPE) Stab-Lok Circuit Breaker Panel Hazards Website - Latent fire hazards, in-depth authoritative research, documents, advice on Stab-Lok electric panel and circuit breaker failures and what to do when this equipment is found in buildings.
• Lightning Strike Risk Assessment, Protection Systems & Services
• Multi-wire branch circuit inspection and defects
• Zinsco Electrical Circuit Breaker Failures: overheating, failure to trip, burn-ups involving Zinsco and certain Sylvania electrical panel components - page under development March 2006.
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
• "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
• "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
• "Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
• "Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
• "Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
• "Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.
• Rust and Corrosion in Electrical Panels, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels


• Directory of Home Inspectors accessible via internet
• Electrical System & Wiring Hazard Inspection, Detection, Cause, Remedy, Prevention - Main Electrical Page

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