Isolated ground receptacles are installed for the purpose of reducing electromagnetic interference on the grounded conductor. The insulated grounding conductor run with the circuit conductors and feeding the receptacle may pass through intervening panelboards without being terminated at the equipment grounding terminal bar. This conductor must terminate within the same building at an equipment grounding terminal of the service or system.
Complying with Code wording
This suggests the conductor should run to the location and be connected where the grounded conductor (neutral) and the equipment grounding conductor are connected, which is usually at the service location. However, that is not what the National Electrical Code (NEC) words say.
The isolated ground conductor could be connected to an equipment grounding terminal in any of the panelboards between the receptacle location and the service location. This might not accomplish the intended purpose, but it would satisfy the wording of 250.146(D).
“250.146 Connecting Receptacle Grounding Terminal to Box. (D) Isolated Receptacles. Where required for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means shall be permitted. The receptacle grounding terminal shall be grounded by an insulated equipment grounding conductor run with the circuit conductors. This grounding conductor shall be permitted to pass through one or more panelboards without connection to the panelboard grounding terminal as permitted in 408.20, Exception, so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service.
FPN: Use of an isolated equipment- grounding conductor does not relieve the requirement for grounding the raceway system and outlet box.”
Note that the conductor is permitted to pass through a panelboard, but it is not required to do so, and connecting it to an equipment grounding terminal in a panelboard remote from the service location would satisfy the requirement.
Placement of outdoor outlets
On another subject; 210.52 Dwelling Unit Receptacle Outlets, in the 2002 NEC reads: “(E) Outdoor Outlets. For a one-family dwelling and each unit of a two-family dwelling that is at grade level, at least one receptacle outlet accessible at grade level and not more than 2.0 m (6.5 ft.) above grade shall be installed at the front and back of the dwelling. See 210.8(A)(3).”
The phrase “accessible at grade level” clearly requires that the person for whom access is required is to be standing at grade level.
In the 2005 NEC (Proposal 2-235, Pg. 310, 2004 ROP, and Comment 2-136, Pg. 70-97, 2004 ROC) a second sentence will be added, reading: “For each dwelling unit of a multifamily dwelling where the dwelling unit is located at grade level and provided with individual exterior entrance/egress, at least one receptacle outlet accessible from grade level and not more than 2.0 m (6.5 ft.) above grade shall be installed.” [There is a typo in the ROC showing 6.5 in. instead of 6.5 ft.]
The proposal used the term “accessible at grade level” in proposing that an outside receptacle be required for multifamily dwellings at grade level, but the final version in the ROC uses the term “accessible from grade level.” This wording could be interpreted as making a receptacle not over 6.5 feet above grade installed on the exterior wall facing an outside porch, “accessible,” even though the porch itself is reached by a stairway of several risers. It would be accessible from grade, but not at grade. No doubt this will generate discussion until the next revision.
On this next item, I would like some feedback. 334.40(B) reads, in part: “(B) Devices of Insulating Material. Switch, outlet, and tap devices of insulating material shall be permitted to be used without boxes in exposed cable wiring and for rewiring in existing buildings where the cable is concealed and fished. Openings in such devices ... .”
The recognition of surface wiring devices for use with Type NM Cable dates back to at least the 1940 NEC. These plastic (boxless) devices were typically used in mountain cabins and other rustic locations. In the 1951 NEC the phrase “and for rewiring in existing buildings where the cable is concealed and fished” was added. The year 1951 was pre-ROP and ROC days, so I am asking: Where did this come from? Who proposed it and why did UL list these devices to be concealed in the walls with no boxes? EC
SCHWAN is an electrical Code consultant in Hayward, Calif. He can be reached at email@example.com.