OESC Code Rule 10-206(4)
Description of the change: Amend Rule 10-206(4)
Background
In OESC 2009 Rule 10-206 was amended to specify requirements for “different” instead of “isolated”
systems. However, the Ontario amendment, subrule (4) that recognized the effectively grounded metal
frame of a building as a grounding path, was not amended.
Rationale
The Ontario amendment, Rule 10-206(4) permits the effectively grounded metal structural frame of a
building as a grounding path to a grounding electrode for different systems at a facility. The effectively
grounded metal structural frame of a building as defined in Rule 10-004, is permitted to be used as
conductive paths to grounding electrodes, but cannot be considered as part of a grounding electrode.
The proposed reference to Rule 10-004 is added to provide clarification that the effectively grounded
metal structural frame of a building as shown in Photo 1 is defined by Ontario amendment 10-004.
Also, NEC Clause 250.52 (A)(2) recognize metal frame of the building or structure that is in direct contact
with the earth as a grounding electrode.
Photo1: Effectively grounded metal structural frame of a building
OESC Code Rule 10-206(4)
Code Proposal
10-206 Grounding connections for different systems at a facility (see Appendix B)
(1) Where, in addition to the system supplying the consumer’s service as described in Rule 10-204, one or more
different systems conforming to Rule 10-106(1) exist at a facility,
(a) each different system shall be connected to a separate grounding conductor
(i) at the transformer or other source of supply; or
(ii) at the first switch controlling the system.
(2) Notwithstanding Subrule (1), where the conductor to be grounded from each of two such systems terminates at
a common tie point, a single connection to a grounding conductor shall be permitted to be made
(a) at the tie point; or
(b) at the service equipment if one of the systems supplies the consumer’s service.
(3) Notwithstanding Rules 10-802 and 10-806, where a circuit is required to be grounded and is supplied from a
source having a rated output of 1000 V•A or less, the grounding connection shall be permitted to be made to
(a) the metal enclosure of the power supply, provided that the enclosure is connected to a bonding
(b) conductor; or
(c) the bonding conductor within the enclosure.
Add Rule 10-206(4) as follows:
(4) Notwithstanding Rules 10-802 and 10-806, where an isolated system or circuit a different system is required to
be grounded as required by Rule 10-106, the grounding connection shall be permitted to be made to the
effectively grounded metal structural frame of a building defined in Rule 10-004.