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Santa Cruz County, CA, USA

I'm working on a project that requires an electrician to install a "disconnect" at a building/shed separate from my house (as per NEC 225.31). I'm unfamiliar with this term and would like a better understanding of what things could potentially be considered a "disconnect"?

Can someone elaborate on this? For example, can a simple wall switch be considered a "disconnect"? Or does it need to be something more robust such as a sub-panel?

2 Answers 2

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National Electrical Code 2014

Chapter 1 General

Article 100 Definitions

Disconnecting Means. A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.

This can include a switch, a circuit breaker, a cord and plug connection (sometimes), or a group of the aforementioned devices.

There are other stipulations within the code that dictate how these devices can, and cannot be used. But at the core of it, any device that can disconnect the conductors of a circuit from their source of supply, is a disconnecting means.

In the context of a separate building, typically either circuit breakers or a switch type device will be used.

Small panel Disconnect

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  • 1
    Everyone loves pictures!
    – mjohns
    Jul 9, 2015 at 15:32
  • The plural wording suggests that the mechanism disconnects neutral as well as hot (live) conductors - is that correct? Jul 10, 2015 at 10:43
  • @RedGrittyBrick Not typically, but there are devices that do disconnect the grounded (neutral) conductor as well.
    – Tester101
    Jul 10, 2015 at 10:55
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Toggle switches can be used as disconnects (typically in cases like 225.39(A) below). A very literal interpretation of the code below would allow for properly rated toggle switches to serve as your disconnect if your circuits are being fed directly from your main panel (because a sub panel would negate the need for another disconnect), but in the case of multiple circuits I think you would want to consider something more like a pull-type disconnect or circuit breakers.

I'll cheat here because I saw your other question: In the case of a 30A feeder to a sub panel, the breakers in your sub panel become your disconnect for each circuit, or, as pointed out in the comments, if you have a main breaker in your sub panel, this serves as a master disconnect.

225.33 Maximum Number of Disconnects.

(A) General. The disconnecting means for each supply permitted by 225.30 shall consist of not more than six switches or six circuit breakers mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard or switchgear. There shall be no more than six disconnects per supply grouped in anyone location.

(B) Single-Pole Units. Two or three single-pole switches or breakers capable of individual operation shall be permitted on multiwire circuits, one pole for each ungrounded conductor, as one multipole disconnect, provided they are equipped with identified handle ties or a master handle to disconnect all ungrounded conductors with no more than six operations of the hand.

and

225.39 Rating of Disconnect. The feeder or branch-circuit disconnecting means shall have a rating of not less than the calculated load to be supplied [...].

(A) One-Circuit Installation. For installations to supply only limited loads of a single branch circuit, the branch circuit disconnecting means shall have a rating of not less than 15 amperes.

(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the feeder or branch-circuit disconnecting means shall have a rating of not less than 30 amperes.

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    Individual breakers don't necessarily satisfy requirements: apparently some inspectors will allow it, others won't -- so check with them. Having a main breaker in your subpanel does definitely satisfy the requirement though. And the good news is that your local big box store, you're likely to find a small main panel including main breaker and a couple branch circuit breakers for cheaper than just a plain subpanel.
    – gregmac
    Jul 9, 2015 at 14:40
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    @gregmac I changed my code references to better address the single breaker/switch questions. In the end the AHJ/inspector rules, but one's interpretation of the code could leave room for using individual single pole devices. Having a main breaker is an excellent suggestion either way.
    – mjohns
    Jul 9, 2015 at 14:44
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    @gregmac Individual breakers only satisfy the requirement if they can disconnect all ungrounded conductors in 6 or less moves. For example, a panel with only 6 breakers. A panel with more than 6 breakers, where the handles are tied together in such a way that they are all turned off in 6 or less moves.
    – Tester101
    Jul 9, 2015 at 15:04
  • @mjohns The lockable provision is only applicable to installations over 1000 volts.
    – Tester101
    Jul 9, 2015 at 15:05
  • @Tester101, ah, you are correct. I missed the whole Section III heading. I will correct this. However, my answer does already mention the 6 moves-of-the-hand requirement.
    – mjohns
    Jul 9, 2015 at 15:07

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