jar546
CBO
For those getting ready to go to the 2020 NEC. Let's start with the 2017 language.
2017 NEC Requirement:
(A) General. The service disconnecting means for each service permitted by 230.2, or for each set of service entrance conductors permitted by 230.40, Exception No. 1, 3, 4, or 5, shall consist of not more than six switches or sets of circuit breakers, or a combination of not more than six switches and sets of circuit breakers, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard or in switchgear. There shall be not more than six sets of disconnects per service grouped in any one location.
Then the changes.
2020 NEC Change:
230.71 Maximum Number of Disconnects. Each service shall have only one disconnecting means unless the requirements of 230.71(B) are met.
(B) Two to Six Service Disconnecting Means. Two to six service disconnects shall be permitted for each service permitted by 230.2 or for each set of service-entrance conductors permitted by 230.40. Exception No. 1, 3, 4, or 5. The two to six service disconnecting means shall be permitted to consist of a combination of any of the following.
(1) Separate enclosures with a main service disconnecting means in each enclosure
(2) Panelboards with a main service disconnecting means in each panelboard enclosure
(3) Switchboard(s) where there is only one service disconnect in each separate vertical section where there are barriers separating each vertical section
(4) Service disconnects in switchgear or metering centers where each disconnect is located in a separate compartment
Informational Note No. 1: Metering centers are addressed in UL 67, Standard for Panelboards
Information Note No. 2: Examples of separate enclosures with a main service disconnecting means in each enclosure include but are not limited to motor control centers, fused disconnects, circuit breaker enclosures, and transfer switches that are suitable for use as service equipment.
Rationale:
The safety and challenges of having more than one disconnect have been recognized and with these changes, the intent is to provide a safer installation by requiring installations in separate enclosures. By having a single disconnect to de-energize conductors and circuit parts in the enclosure except on the line side therefore reducing the possibility of inadvertent contact with energized parts. The terms used in part (B)(4), “metering centers” and “compartments” are not defined in the NEC or UL 67. This has created confusion from a design, installation, and inspection perspective.
The “six-disconnect rule” has been altered to no longer allow a single enclosure to house the grouped disconnects. The 2020 NEC requires separation as to supply each respective disconnect with its own individual “enclosure”, “vertical section, “compartment” depending on the application. The intention of this modification is to decrease the likelihood that personnel or tools could come in contact, inadvertent or otherwise, with an energized entity of the system while performing maintenance on a single disconnect. This reasoning is similar to the logic involved with the alteration of 230.62(C) where barriers are now mandated for all service equipment that falls under the purview of Article 230. This kind of contact with energized conductors by personnel or their tools could cause an arc-flash event. With the magnitude of energy that could be at these groups of disconnects, it is a precaution toward safety to mandate each disconnect to be provided with its own enclosure, vertical section, or compartment.
To design a system that has a service disconnect such as a fusible safety switch or enclosed breaker upstream of such a “metering center” would provide a safer installation for the electrical worker to de-energize the equipment prior to working on the equipment.
2017 NEC Requirement:
(A) General. The service disconnecting means for each service permitted by 230.2, or for each set of service entrance conductors permitted by 230.40, Exception No. 1, 3, 4, or 5, shall consist of not more than six switches or sets of circuit breakers, or a combination of not more than six switches and sets of circuit breakers, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard or in switchgear. There shall be not more than six sets of disconnects per service grouped in any one location.
Then the changes.
2020 NEC Change:
230.71 Maximum Number of Disconnects. Each service shall have only one disconnecting means unless the requirements of 230.71(B) are met.
(B) Two to Six Service Disconnecting Means. Two to six service disconnects shall be permitted for each service permitted by 230.2 or for each set of service-entrance conductors permitted by 230.40. Exception No. 1, 3, 4, or 5. The two to six service disconnecting means shall be permitted to consist of a combination of any of the following.
(1) Separate enclosures with a main service disconnecting means in each enclosure
(2) Panelboards with a main service disconnecting means in each panelboard enclosure
(3) Switchboard(s) where there is only one service disconnect in each separate vertical section where there are barriers separating each vertical section
(4) Service disconnects in switchgear or metering centers where each disconnect is located in a separate compartment
Informational Note No. 1: Metering centers are addressed in UL 67, Standard for Panelboards
Information Note No. 2: Examples of separate enclosures with a main service disconnecting means in each enclosure include but are not limited to motor control centers, fused disconnects, circuit breaker enclosures, and transfer switches that are suitable for use as service equipment.
Rationale:
The safety and challenges of having more than one disconnect have been recognized and with these changes, the intent is to provide a safer installation by requiring installations in separate enclosures. By having a single disconnect to de-energize conductors and circuit parts in the enclosure except on the line side therefore reducing the possibility of inadvertent contact with energized parts. The terms used in part (B)(4), “metering centers” and “compartments” are not defined in the NEC or UL 67. This has created confusion from a design, installation, and inspection perspective.
The “six-disconnect rule” has been altered to no longer allow a single enclosure to house the grouped disconnects. The 2020 NEC requires separation as to supply each respective disconnect with its own individual “enclosure”, “vertical section, “compartment” depending on the application. The intention of this modification is to decrease the likelihood that personnel or tools could come in contact, inadvertent or otherwise, with an energized entity of the system while performing maintenance on a single disconnect. This reasoning is similar to the logic involved with the alteration of 230.62(C) where barriers are now mandated for all service equipment that falls under the purview of Article 230. This kind of contact with energized conductors by personnel or their tools could cause an arc-flash event. With the magnitude of energy that could be at these groups of disconnects, it is a precaution toward safety to mandate each disconnect to be provided with its own enclosure, vertical section, or compartment.
To design a system that has a service disconnect such as a fusible safety switch or enclosed breaker upstream of such a “metering center” would provide a safer installation for the electrical worker to de-energize the equipment prior to working on the equipment.
