What a Texas candidate needs to know about disconnecting means before test day

One named item, a long reach

The published content outline for the journeyman NEC Knowledge portion gives Control Devices and Disconnecting Means one of its 56 scored items. On the Calculations portion it gets one of 24. Read those two figures alone and this subject looks like a rounding error.

Now count how the questions are actually written. Of the 500 items in our bank, 52 mention a disconnecting means, and 31 of the 140 in wiring methods and installations do. They are filed under services, appliances, special occupancies and renewable energy, because the outline sorts items by the equipment in the stem and the disconnect rides along.

That is the most useful thing to know about this subject before test day. Study it as a named area and you're chasing one item. Study it as a question the code asks in twenty articles and you're working a share of almost every area on the paper, including the three heaviest at ten scored items each. The working space rules sit beside it, since both are about the person who arrives after you.

In sight from has two halves

Article 100 defines the term as a pair of conditions. One piece of equipment is in sight from another when it is visible from it and sits no further away than 50 feet. Eight items in our wiring area name the term, and one in the motor calculations area is built entirely on the pair.

That item puts a disconnect 60 feet from a motor with a clear line of sight and nothing in between, and records what people do with it. One wrong answer accepts the installation on the clear view alone, applying half the definition. One invents a 25 foot limit. One offers a lockable device as a way to stretch the distance, and that provision is a separate allowance with its own conditions.

So an installation can satisfy one condition and fail the other, and a stem with a wall in the plan view is testing that. A disconnect twenty feet from a controller with a partition between them passes on distance and fails on visibility. Visibility also gets assessed as built: a door kept shut is shut, shelving in front of a disconnect is in front of it, and the definition declines to ask what the installer intended.

The term is worth a tab for a second reason. Definitions, Theory and Plans carries three scored items on the knowledge portion, and a term defined in Article 100 that reappears in fifteen other articles is what a definition item gets built from.

The lock that stands in

Where the code lets a lockable disconnect substitute for one you can see, it buys the same protection by another route. You have no view of the handle from where you work, so the arrangement keeps anybody else from moving it while your lock is on.

The condition attached to that permission is the one candidates drop. 430.102(B) permits the motor disconnect to be remote where it can be locked in the open position, and 110.25 sets the terms: the provision for locking is installed on or at the switch or circuit breaker, and it stays there with or without a lock fitted. A hasp traveling in somebody's van fails that, and so does a breaker that only accepts a lockout accessory nobody left on site. A narrow exception covers cord and plug connected equipment.

The substitution comes on different terms in different places. In some articles a lock provision excuses a second disconnect entirely. In others it excuses only the one at the far end, and the near one still has to be visible from the work. So the answer for a given piece of equipment is found in the article covering it, which is the next section.

The equipment names the article

Disconnecting means is one idea written down separately in a dozen articles, each version tuned to the equipment it governs. For an open book test that works in your favor, because the equipment named in the stem tells you which article answers it. Identify the equipment, turn to its article, and read the part headed disconnecting means.

430.102 is the number to tab, because the rest of the book points back at it. 440.14 sends air conditioning equipment there and 430.208 sends motor circuits over 1000 volts there, so one tab answers three articles. Our bank item on a motor and controller in different rooms offers a lockable device in a panelboard as the whole answer, and that device is in sight of neither end of the job. Sizing the rest of that circuit belongs with motor circuits, and the worked arithmetic lives in the question set.

The numbers worth carrying in

Four figures do most of the work here, and three are close enough that the wrong one always looks reasonable:

• 50 feet, the distance half of in sight from, in Article 100.
• 115 percent of full load current, the minimum ampere rating for a motor disconnect under 430.110(A). Our bank item puts a 30 ampere switch on a 27 ampere motor, where the minimum is 31.05 amperes and the switch falls short by one.
• The same 115 percent taken on the whole group for a disconnect serving a combination load, under 430.110(C), with the currents summed first. No largest motor allowance applies, since everything that may run at once counts at full value.
• 300 volt-amperes or one eighth horsepower, the split in 422.31. At or below it the branch circuit overcurrent device is accepted as the disconnecting means. Above it the person working on the appliance needs to see what killed it or to lock it out.

The 125 percent that sizes motor branch circuit conductors under 430.22 is the figure most often dropped into a disconnect question, and our trap data records candidates using it on both 430.110 items. Keep the multipliers separated by what each one protects, since the conductor rule, the disconnect rule and the short circuit device rule all land on the same motor in one calculation. The overcurrent device side of that is a page of its own.

Readily accessible is different

Some disconnect rules ask for line of sight and others for ready access, and they're separate tests. Readily accessible means reaching something quickly without climbing over or under anything, removing obstacles, or fetching a portable ladder, and the definition treats keys differently from tools.

Our bank item puts a junction box above a lift out ceiling tile beside a service disconnect behind a locked door whose keys the building staff hold. The disconnect passes, because keys in the right hands leave ready access intact. The box fails, because lifting a tile is removing an obstacle and getting up there usually means a ladder. Candidates split on it in both directions.

Two more places show the same test. Article 240 asks that each occupant have ready access to the overcurrent devices protecting their own conductors, with named exceptions for continuous building management supervision and certain guest rooms. Article 690 keeps photovoltaic direct current circuits inside metal raceway or metal clad cable until they reach the first readily accessible disconnect inside the building, because a circuit live whenever there's light on the modules gets treated differently.

What this costs on the job

A disconnect in the wrong place is a rework item that surfaces at final inspection, and the fix is rarely short. Moving a unit disconnect on a roof means a new penetration, a new whip and a return trip with a crew that moved on. The rooftop condensing unit is the classic case, because it looks like a motor problem and gets answered from the air conditioning article, since the compressor is sealed with its motor and carries no horsepower rating for the motor tables to work from.

The plaque rule is the cheap one to miss. Where a building is supplied by more than one feeder or branch circuit, 225.37 asks for a plaque or directory at each disconnect naming the other supply and its load, and Article 230 says the same for services. Without it, the only way to learn that a second supply is still feeding part of the building is to find it energized.

Inspection is local. Cities in Texas keep the power to require inspections and to adopt local amendments to the code under Tex. Occ. Code 1305.201(a) and (c), and subsection (d) requires electrical work inside the city limits to follow all applicable local ordinances, so the governing text is the state adopted edition plus that city's amendments.

What to do before test day

About forty minutes covers this subject, and it buys a share of several areas at once:

1. Tab the definition of in sight from in Article 100, and read the distance figure out loud once so both halves stay attached.
2. Tab the disconnecting means part of Article 430, which is the fullest treatment in the book and the model the others follow.
3. Read the disconnect rules in Articles 422 and 440 back to back, since those two are most likely to arrive dressed as something else.
4. Where an item describes a layout, sketch it on your scratch paper before you read the options, because a wall is easier to see in a drawing than in a sentence.

None of that is arithmetic. These items reward reading and punish answering from a picture in your head of how the last job was wired, which is why the four shapes are worth recognizing: a described layout with a wall, a door or a distance in it; equipment named precisely, such as a hermetic compressor or a fixed appliance; a disconnect offered somewhere convenient, usually a breaker in a panel; and a cord and plug offered as the disconnect, where the real question is reach. The switch article split is worth reading alongside this, since the enclosed general use switch stayed in Article 404 when the wall devices moved.

Questions people ask

What does in sight from actually mean?

Article 100 defines it as a pair of conditions holding together. The equipment has to be visible from the other equipment, and it has to sit no more than 50 feet away. An installation can satisfy one and fail the other, which is what most items on this subject are built around. A disconnect 60 feet from a motor with a clear view of it fails on distance. A disconnect twenty feet from a controller with a partition between them fails on visibility. Visibility is judged as built, so a door kept shut and shelving stacked in front both count.

Can a lockable breaker replace a disconnect at the motor?

430.102(B) permits the disconnect to be remote where it can be locked in the open position, and 110.25 sets the terms for that. The provision for locking is installed on or at the switch or circuit breaker and remains in place with or without a lock fitted, so a hasp that travels in a van fails. A narrow exception covers cord and plug connected equipment. The permission also comes on different terms in different articles, so the answer for a given piece of equipment is found in the article covering it.

When does an attachment plug count as the disconnecting means?

Where the article covering that equipment permits it and where the connection is accessible. Both halves matter, and the second is the one dropped at rough in. Section 422.16 sets the conditions for cord and plug connection of built in dishwashers, waste disposers and trash compactors, giving a length range for each measured from the face of the plug to the plane of the rear of the appliance, and it asks for a reachable receptacle. A plug behind a built in oven that has to be pulled out of its cabinet first falls outside the permission.

Does a detached garage on a feeder need its own disconnect?

Yes. Article 225 carries the requirement for a building supplied by a feeder or a branch circuit, and it echoes the service rule: somebody working in the garage has to be able to kill everything in it without walking to another building, and a firefighter needs the same thing. The upstream overcurrent device protects the conductors, and protection is a different job from control. Our bank item offers doing nothing because the feeder is protected back at the house, and that option confuses the two.

How many exam items are actually about disconnects?

The published outline gives Control Devices and Disconnecting Means one of the 56 scored items on the journeyman knowledge portion and one of the 24 on calculations. The reach is much wider than that, because the outline files an item by the equipment in the stem. Of the 500 questions in our bank, 52 mention a disconnecting means, and 31 of the 140 in the wiring methods and installations area do. Preparing this as one small area undersells it by a wide margin.

Is a breaker behind a locked door readily accessible?

It can be. Readily accessible means reaching something quickly without climbing over or under anything, removing obstacles, or fetching a portable ladder, and the definition treats keys differently from tools. A service disconnect behind a locked door whose keys the building staff hold passes the test. A junction box above a lift out ceiling tile fails it, because the tile is an obstacle to remove and getting up there usually needs a ladder. Our bank item puts those two side by side for exactly that contrast.