RF Cafe Software

RF Cascade Workbook 2005 - RF Cafe
RF Cascade Workbook

Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel
RF & EE Symbols Word
RF Stencils for Visio

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2016
Webmaster:
Kirt Blattenberger,
 BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:
 AirplanesAndRockets.com

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !

Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes RF Cascade Workbook RF Stencils for Visio Shapes for Word Thank you for visiting RF Cafe!

Potential Neutral Conductor Hazards

This presentation was generated by Flour Hanford the U.S. Department of Energy.

The main point of this presentation is that the neutral wire (typically white in color) is unfortunately named in a way that implies it is harmless. Most people know that if you touch the black (or red or blue) wire, chances are you are going to receive an electrical shock. They also believe that it is safe to touch the white (neutral wire).

Under most conditions, this is true. However, that is only so if the path your body makes to ground is a significantly higher resistance to current flow than what the neutral wire path provides. This requires the neutral wire to have a complete path back to the service panel. If the neutral wire somehow gets disconnected from the neutral bar in the panel, your body becomes the only return path to ground for the electrical current.

So, the cardinal law of working around live circuits is to assume that the neutral conductor is at the same potential as the hot wire. I have worked on many live circuits in my life and have been bitten a couple times by open neutrals - it is not a good feeling. Just for the record, the highest AC voltage I have been hit by was a 3-phase 480 V supply to a commercial welder. The highest DC was from a 2 kV radar CRT display. I have been lucky - no permanent damage... other than mental  :-)

Potential Hazards
with Neutral Conductors


Neutrals Are Current Carrying Conductors

  • Neutrals are grounded but carry current under load.
  • The source of neutral current cannot always be identified.
  • Breaking a neutral under load could create a shock hazard.
  • Individuals contacting a lifted neutral potentially provide an alternate path to ground.
  • A broken neutral or lifted neutral could result in a shock or an arc.

Energized Neutral Examples

  • A neutral was misidentified and inadvertently opened creating an arc (ORPS EM-SR-WSRC-FTANK-2005-0009)
  • A circuit was moved to a different distribution panel, but the neutral was spliced in the original panel (ORPS EM-RL-PHMC-PFP-2005-0011)
  • An electrician received a shock after lifting a neutral from its bus bar. The neutral received its power through an emergency light that received power from another distribution panel. (ORPS SC-PNSO-PNNL=PNNLBOPER-2005-0018)

Configuration That Requires Additional Precautions:


Configuration that requires additional precautions - RF Cafe



Component Labels

Circuit breaker symbol - RF Cafe Circuit Breaker  
Circuit A symbol - RF Cafe Circuit A Ungrounded Conductor
Circuit B symbol - RF Cafe Circuit B Ungrounded Conductor
Grounded circuit symbol - RF Cafe Grounded Conductor (Neutral Conductor)
Ground symbol - RF Cafe Ground Notes:
  • 3 current carrying conductors in a raceway.
  • Copper ground wire omitted for simplicity.
  • Highlighted in yellow indicates energized.
Ballast/Flourescent light symbol - RF Cafe
        Ballast / Fluorescent Light
Ballast / fluorescent light symbol - RF Cafe Ballast / Fluorescent Light enclosure


The Multi-Wire Branch Circuit is an acceptable configuration according to the National Electrical Code (NEC) Section 210.4.


The Multi-Wire Branch Circuit


This circuit has also been referred to as:
  • The Edison Circuit
  • Common Neutral Circuit
  • Shared Neutral Circuit
  • These circuits are typically found on 120 / 240 volt single phase systems, but can be found on 208Y /120 and 277Y / 480 volt systems as well.
  • The Grounded Neutral wire carries the unbalanced load current. (“Grounded Conductor”)
Multi-wire branch circuit - RF Cafe



Neutral interrupted - RF Cafe


Use the following guidance when the neutral conductor must be interrupted:

  • Treat the neutral as energized even though the circuit is locked out at the source. (Use PPE that is appropriate for the hazard, i.e. gloves and eye protection)
  • Measure absence of voltage to ground immediately after lifting leads when more than one neutral is lifted from a device or when a splice is broken.
  • If known, Lock out both / all load breakers.
  • If both circuit breakers in a multi-wire branch circuit are not known?
    • Test the neutral circuit with a clamp-on type current detector to identify if the neutral is carrying current before lifting neutral leads or breaking a neutral connection.

    Emergency light - RF Cafe  NOTE:
    Current will exist only if one or more circuits sharing the neutral have a load energized at the time of measurement.


    When a common neutral hazard is discovered at a device:
  • Stop work and remove the hazardous condition or plan a new work package considering known energized conductors.
  • It should be corrected by installation of pigtails or other means, to maintain continuity of the neutral wiring in accordance with NFPA 70 National Electrical Code.
    Neutral connection - RF CafeCaution - RF CafeOther general precautions include:
  • Label the doors of lighting and power panels where common neutrals are known to exist.
  • This will alert LOTO planners and workers of potential problems.
  • Provide instructions in work packages where common neutrals are known to exist to remind workers to be alert to wiring that may indicate a common neutral and to maintain neutral circuit continuity.
  • Suspect a multi-wire branch circuit when three or more neutral conductors are spliced together in a junction box, outlet box, or lighting fixture.

Note: Some of the original PowerPoint slides contained animations, which have been omitted here. No important information is lost in the process.