ANSI NEIS-169-2010 pdf download Arc-Fault Circuit Interrupters (AFCIs) and Ground-Fault Circuit Interrupters (GFCIs)
4.1.1 Multiwire Branch Circuits Single-pole AFCIs and GFCIs are not suitable for installation where loads are supplied from multiwire branch circuits. Multiwire branch circuits are circuits that share a common neutral conductor between two or more phase/line conductors that are supplied from different phases ofthe distribution system. Load currents are not balanced between individual phase conductors and the shared neutral conductor in mul- tiwire branch circuits. This steady-state imbalance causes nuisance tripping ofAFCIs and GFCIs. Single-pole AFCIs and GFCIs must directly compare balanced loads between an individual phase conduc- tor that has a dedicated neutral conductor. Two-pole AFCI circuit breakers may be available for multiwire branch circuits. Ifthe circuit breaker has a common trip, two circuits are de-energized when the AFCI detects an arc-fault. Ifthe circuit breaker has independent tripping between the two phase/line conductors, the shared neutral continues to carry load currents even though the one phase conductor is de-energized. Per 210.4(B) ofthe 2008 NEC, inde- pendent trip breakers are required to have a single point ofcommon disconnect.
4.2 Electrical Safety
a) Neglecting fundamental installation and mainte- nance requirements may lead to personal injury or death, as well as damage to electrical equipment or other property. All work and actions must conform to the requirements ofNFPA 70E, Standard for Electrical Safety in theWorkplace and State or Federal OSHA requirements.
b) Do not work on energized equipment. Do not enter equipment enclosures when components are energized. Electrically isolate conductors and equip- ment in accordance with established procedures and manufacturer’s instructions and recommendations. Guard energized conductors and equipment in close proximity to work.
c) Consider all ungrounded and grounded metal parts ofequipment and devices to be energized at the highest voltage to which they are exposed unless they are de-energized and tested in accordance with OSHA requirements.