1 / 18

Potential Hazards with Neutral Conductors

Potential Hazards with Neutral Conductors. Click to Advance. Neutrals are grounded but carry current under load. Neutrals Are Current Carrying Conductors. The source of neutral current cannot always be identified. Click to Advance. Potential Hazards with Neutral Conductors.

dannon
Download Presentation

Potential Hazards with Neutral Conductors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Potential Hazards with Neutral Conductors Click to Advance

  2. Neutrals are grounded but carry current under load. Neutrals Are Current Carrying Conductors • The source of neutral current cannot always be identified. Click to Advance

  3. Potential Hazards with Neutral Conductors • 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. Click to Advance

  4. 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) Click to Advance

  5. Configuration That Requires Additional Precautions: The Multi-Wire Branch Circuit Click to Advance

  6. Component labels For the purpose of this presentation, please review the following labels: Circuit Breaker Circuit A Ungrounded Conductor Circuit B Ungrounded Conductor • Notes: • 3 current carrying conductors in a raceway. • Copper ground wire omitted for simplicity. • Highlighted in yellow indicates energized. Grounded Conductor (Neutral Conductor) Ground Ballast / Fluorescent Light Ballast / Fluorescent Light enclosure Click to Advance

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

  8. The Multi-Wire Branch Circuit • This circuit has also been referred to as: • The Edison Circuit • Common Neutral Circuit • Shared Neutral Circuit Click to Advance

  9. The Multi-Wire Branch 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”) Click to Advance

  10. Multi-Wire Branch Circuit Ckt A Click to Lock Out Circuit “B” X Ckt B Click to Energize Circuits The desired technique used to remove a device Is to cut the neutral lead or disconnect the device leaving a neutral pigtail. (Click) Ckt A Good Work Practice! The Neutral Will Remain at Ground Potential Ckt B Ckt B Ckt A Click to Advance

  11. Multi-Wire Branch Circuit Ckt A Ckt B X Avoid Breaking The Neutral Bundle in a Multi-Wire Branch Circuit! If You Break The Neutral Bundle, It Will Become Energized From Circuit “A” (Click) You May See an Arc when disconnecting If You Contact The Neutral Conductor You May Feel A Shock. Click to Advance

  12. The Multi-Wire Branch Circuit • 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. Click to Advance

  13. The Multi-Wire Branch Circuit • Use the following guidance when the neutral conductor must be interrupted: • 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. NOTE: Current will exist only if one or more circuits sharing the neutral have a load energized at the time of measurement. Click to Advance

  14. The Multi-Wire Branch Circuit 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. Click to Advance

  15. The Multi-Wire Branch Circuit • Other 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. Click to Advance

  16. The Multi-Wire Branch Circuit • Other general precautions include: 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. Click to Advance

  17. The Multi-Wire Branch Circuit Other general precautions include: Suspect a multi-wire branch circuit when three or more neutral conductors are spliced together in a junction box, outlet box, or lighting fixture. 1 2 3 Click to Advance

  18. Potential Hazards with Neutral Conductors Questions or Comments? Contact Bobby Gray or Jerald Kinz Click to End Show

More Related