Section 10 rewrite: separately derived systems • Code File, October 2018
November 27, 2018 - This is my third and final column about the 2018 CE Code’s Section 10 rewrite (the first two were posted online in June and August). This time, I am focusing on rules related to the grounding of separately derived systems, such as generators and transformers.
The new definition of ‘separately derived system’ refers to an electrical system in which the circuit conductors have no direct connection to a supply authority system’s circuit conductors, other than those established by grounding and bonding connections.
A generator that supplies emergency power for a facility, for example, or a transformer that supplies a different voltage to parts of the facility would be considered a separately derived system.
Further, a generator connected to a supply authority via a transfer switch is also a separately derived system if all circuit conductors, including the grounded (neutral) conductor, are switched at a transfer switch.
A generator with a transfer switch that does not switch the grounded (neutral) conductor, however, is not a separately derived system. The grounding requirements for such systems are met by the grounding connection of the supply authority system to which they are conductively connected.
The grounding requirements of separately derived systems outlined in the 2018 CE Code are similar to those in the 2015 CE Code.
The grounded conductor of a solidly grounded, separately derived AC system must be connected to the equipment bonding terminal by a system bonding jumper; a grounding conductor; and it must have no connection to the non-current-carrying conductive parts of electrical equipment on the supply side or the load side where the grounding connection is made.
Grounding connections are permitted to be:
• at the source of a separately derived system;
• at the first switch controlling the system; or
• at the tie point of two separately derived systems.
Another change in Section 10 concerns grounding transformers. Transformers rated 750 V or less are permitted to be grounded by the system bonding jumper that is connected to the bonding conductor on the primary supply.
Grounding of portable, mobile and vehicle-mounted generators
Many questions have been asked about grounding requirements for portable, mobile and vehicle-mounted generators. Some of these generators have a terminal identified for the connection of a grounding conductor.
A new rule in the 2018 CE Code, i.e. Rule 10-214, explains a portable generator is not required to be connected to a grounding electrode if it has one conductor connected to the frame and is marked as “neutral bonded to frame.” Based on the Canadian standard for generators, CSA C22.2 No. 100-14, a portable generator assembly is rated at no more than 12 kW and 240 V and is equipped with receptacles only.
For mobile or vehicle-mounted generators, Rule 10-214 includes additional requirements. Vehicle-mounted generators do not need to be connected to a grounding electrode under the following conditions:
• The generator does not exceed a low-voltage (LV) rated output and has the neutral bonded to the frame.
• The generator’s conductive frame is connected to the vehicle’s conductive frame.
• The generator supplies only (a) electrical equipment installed on the vehicle, (b) electrical equipment that is cord-and-plug connected through receptacles mounted on the vehicle or on the generator or (c) both.
• The non-current-carrying conductive parts of the electrical equipment referenced above are supplied by a circuit incorporating a bonding conductor.
Based on Appendix B, Note to Rule 10-214 2, if a mobile or vehicle-mounted generator exceeds 12 kW and 240 V or is connected to fixed electrical installations, Rule 10-214 does not apply. That generator may act as a stand-alone power system or as a standby power source connected via transfer means, in parallel with one or more other power sources. It may be configured as a solidly grounded system, impedance grounded system or ungrounded system. The appropriate rules of Section 10 will apply.
This column originally appeared in the October 2018 issue of Electrical Business.
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