Thread: Disconnect for "sub" panel

I know that if there is a disconnect at the main service, one is not required at the downstream panel as the conductors are already protected. But is a disconnect required at the main service? (ie. a tap off of the main prior to the disconnect going to a panel that is protected with an overcurrent protection device)

I say that a tap is never allowed off of the main and that every conductor leaving a panel should be protected from the panel that it is leaving, including conductors going to another panel regardless of whether there is a OPD in the downstream panel or not. My argument is that should the conductors be damaged somehow between the panels, the disconnect in the upstream panel will protect them.

But I have seen/heard others who have said that as long as it is protected somewhere, it is fine. They point to the fact that the SEC to the main service is not protected until it enters that service panel.

Jerry??????

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• a/c disconnect

You're right Jon. First, you would have a double tap if there is no breaker, which would not be allowed. And, yes the wire size would not support the potential current load, so there should be a disconnect at the service panel.

Originally Posted by Jon Randolph

But is a disconnect required at the main service?

Complicated answer to a compound question, so I split it up.

Yes, a disconnect is required at the main service, that is one component of the "service equipment".

(ie. a tap off of the main prior to the disconnect going to a panel that is protected with an overcurrent protection device)

Now for the more difficult part of the answer.

There are several "tap" rules which may, or may not, apply.

I say that a tap is never allowed off of the main and that every conductor leaving a panel should be protected from the panel that it is leaving, including conductors going to another panel regardless of whether there is a OPD in the downstream panel or not.

First, we need to identify what types of taps you are referring to and where they are tapped off.

I.e., you stated "off the main", but is that on the line side of the main (the service entrance side) or the load side of the main (the feeder side)?

Service entrance conductors may have their overcurrent protection on their load side (at the main disconnect) instead of their line side (the meter), but your description creates a problem there as tapping the service entrance conductors simply adds another main, which must be located and grouped with the other mains.

If the service entrance side is tapped, that is okay (if done properly in the proper manner in the proper location), however, the main they are feeding needs to be grouped with the other mains, so little is accomplished for what you are describing.

If tapped off the load side of the main, they become feeder taps and then you have the following rules to follow:

From the 2008 NEC:
- 240.21 Location in Circuit.
- - Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (H). Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.
- - - (A) Branch-Circuit Conductors. Branch-circuit tap conductors meeting the requirements specified in 210.19 shall be permitted to have overcurrent protection as specified in 210.20.
- - - (B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors.
- - - - (1) Taps Not over 3 m (10 ft) Long. Where the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:
- - - - - (1) The ampacity of the tap conductors is
- - - - - - a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
- - - - - - b. Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
- - - - - (2) The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
- - - - - (3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.
- - - - - (4) For field installations where the tap conductors leave the enclosure or vault in which the tap is made, the rating of the overcurrent device on the line side of the tap conductors shall not exceed 10 times the ampacity of the tap conductor.
- - - - - - FPN: For overcurrent protection requirements for panelboards, see 408.36.
- - - - (2) Taps Not over 7.5 m (25 ft) Long. Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following:
- - - - - (1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.
- - - - - (2) The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side.
- - - - - (3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
- - - - (3) Taps Supplying a Transformer [Primary Plus Secondary Not over 7.5 m (25 ft) Long]. Where the tap conductors supply a transformer and comply with all the following conditions:
- - - - - (1) The conductors supplying the primary of a transformer have an ampacity at least one-third the rating of the overcurrent device protecting the feeder conductors.
- - - - - (2) The conductors supplied by the secondary of the transformer shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-third of the rating of the overcurrent device protecting the feeder conductors.
- - - - - (3) The total length of one primary plus one secondary conductor, excluding any portion of the primary conductor that is protected at its ampacity, is not over 7.5 m (25 ft).
- - - - - (4) The primary and secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
- - - - - (5) The secondary conductors terminate in a single circuit breaker or set of fuses that limit the load current to not more than the conductor ampacity that is permitted by 310.15.
- - - - (4) Taps over 7.5 m (25 ft) Long. Where the feeder is in a high bay manufacturing building over 11 m (35 ft) high at walls and the installation complies with all the following conditions:
- - - - - (1) Conditions of maintenance and supervision ensure that only qualified persons service the systems.
- - - - - (2) The tap conductors are not over 7.5 m (25 ft) long horizontally and not over 30 m (100 ft) total length.
- - - - - (3) The ampacity of the tap conductors is not less than one-third the rating of the overcurrent device protecting the feeder conductors.
- - - - - (4) The tap conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.
- - - - - (5) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
- - - - - (6) The tap conductors are continuous from end-to-end and contain no splices.
- - - - - (7) The tap conductors are sized 6 AWG copper or 4 AWG aluminum or larger.
- - - - - (8) The tap conductors do not penetrate walls, floors, or ceilings.
- - - - - (9) The tap is made no less than 9 m (30 ft) from the floor.
- - - - (5) Outside Taps of Unlimited Length. Where the conductors are located outdoors of a building or structure, except at the point of load termination, and comply with all of the following conditions:
- - - - - (1) The conductors are protected from physical damage in an approved manner.
- - - - - (2) The conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.
- - - - - (3) The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
- - - - - (4) The disconnecting means for the conductors is installed at a readily accessible location complying with one of the following:
- - - - - - a. Outside of a building or structure
- - - - - - b. Inside, nearest the point of entrance of the conductors
- - - - - - c. Where installed in accordance with 230.6, nearest the point of entrance of the conductors

But I have seen/heard others who have said that as long as it is protected somewhere, it is fine. They point to the fact that the SEC to the main service is not protected until it enters that service panel.

See all of the above.