National Electrical Code 2014

Chapter 3 Wiring Methods

Article 300 Wiring Methods and Materials

I. General

300.3 Conductors

(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment-grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

Os fios quentes e neutros devem estar na mesma pista para reduzir Acoplamento Indutivo . Você verá usando a Regra da mão direita , que os campos magnéticos criados pelos fios quente e neutro tendem a cancelar um ao outro. Reduzindo assim os efeitos do acoplamento indutivo.

I = direção do fluxo atual. B = direção do campo magnético.

O fio terra era necessário para funcionar na mesma pista, para fornecer um caminho seguro para a eletricidade viajar em caso de curto. Se um dos fios for danificado, é provável que o fio exposto tenha entrado em contato com o solo. Da mesma forma que um aterramento de equipamentos fornece proteção a um consumidor, a execução do solo na mesma pista fornece proteção semelhante em toda a extensão do circuito.

Enquanto, tecnicamente, executar um EGC separadamente de seu circuito é permitido pelo código a partir do 2014 NEC, conforme 250.130, parágrafo 2:

For replacement of non-grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

250.130 (C):

(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch- circuit extension shall be permitted to be connected to any of the following:

(1) Any accessible point on the grounding electrode system as described in 250.50

(2) Any accessible point on the grounding electrode conductor

(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates

(4) An equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates

(5) For grounded systems, the grounded service conductor within the service equipment enclosure

(6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure

e 300,3 (B) (2):

(2) Grounding and Bonding Conductors. Equipment grounding conductors shall be permitted to be installed outside a raceway or cable assembly where in accordance with the provisions of 250.130(C) for certain existing installations or in accordance with 250.134(B), Exception No.2, for DC circuits. Equipment bonding conductors shall be permitted to be installed on the outside of raceways in accordance with 250.102(E).

Eu preferiria um retrofit usando um disjuntor GFCI ou DFCI ou receptáculo GFCI conforme permitido em 406.4 (D) (2):

(2) Non-Grounding-Type Receptacles. Where attachment to an equipment grounding conductor does not exist in the receptacle enclosure, the installation shall comply with (D)(2)(a), (D)(2)(b), or (D)(2)(c).

(a) A non-grounding-type receptacle(s) shall be permitted to be replaced with another non-grounding-type receptacle(s).

(b) A non-grounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit interrupter-type of receptacle(s). These receptacles shall be marked "No Equipment Ground." An equipment grounding conductor shall not be connected from the ground-fault circuit-interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle.

(c) A non-grounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground-fault circuit interrupter shall be marked "GFCI Protected" and "No Equipment Ground." An equipment grounding conductor shall not be connected between the grounding-type receptacles.

porque tal retrofit é muito menos trabalhoso para o eletricista, será mais seguro (como alguém pode, sem saber, desconectar um EGC roteado separadamente e não conseguir reconectá-lo, enquanto a proteção de um GFCI está sempre presente) e não cria um loop de corrente maciço no caso de uma falta à terra de baixo nível, com sua resultante EMI magnética e possível captação magnética de tensões parasitas e RF.