Checked against primary sources 2026-08-24

The circuit comes off the nameplate and the service does not

Two numbers, two purposes, and an item that hands you both. The water heater is the appliance the code singles out, which is why it is the one that keeps appearing.

The circuit is sized from what is stamped on the appliance

A fixed appliance arrives with a marked rating on it, and under NEC 422.10 that marking is the input to the branch circuit. Not a table, not a horsepower, and not the figure that ends up in the service calculation later.

Where the appliance carries a marked maximum rating for the overcurrent device protecting it, NEC 422.11 makes that marking the ceiling for the device you install. The manufacturer has already done a calculation you are not being asked to repeat, and an item that quotes a marking is usually testing whether you will defer to it.

Where the appliance is motor operated, the motor rules reach into the problem and NEC 422.10 tells you when by sending you to Article 430. That is the point at which a question about an appliance turns into a question about motors, and the appliance article says so rather than leaving you to guess.

The storage water heater is singled out

For a fixed storage-type water heater at or below a stated capacity, NEC 422.13 puts the branch-circuit conductors and the overcurrent device at not less than 125 percent of the ampere rating of the water heater. Both of them, not one.

Read the section in your own book rather than a summary of it, because the wording moved and a lot of study material did not. Editions through 2017 called the water heater a continuous load and let the general branch circuit rules produce the multiplier. The editions since state the 125 percent directly and say nothing about continuous loads. Same number, different route, and the difference bites the moment an item asks you whether a water heater is a continuous load rather than what size circuit it takes.

The capacity threshold is a number in your book. Look it up rather than carrying it, because a tank above the threshold falls outside this section and an item can put one either side of the line deliberately.

Storage-type is doing work in that sentence too. A tankless heater is not what NEC 422.13 is written about, and it goes back to the general appliance rules along with everything else.

The reason for the margin is physical. A storage heater recovering after a shower runs its element flat out for a long stretch, and the conductors and the device sit in that heat for the duration. Reasoning from that beats remembering it.

Nameplate against calculated

This is where candidates lose the item, and it is not because the arithmetic is hard. It is because two articles are doing different jobs with the same number and the wording of the stem is the only clue as to which job you are in.

The branch circuit that feeds one appliance is sized in the appliance article from the marked rating. The service or feeder that supplies a building full of appliances is sized in Article 120, and Article 120 is allowed to be less pessimistic, because the odds of every appliance in a house running at once are not one.

Two sentences in Article 120 carry most of that difference. Under NEC 120.53 a demand factor may be applied to the nameplate rating of four or more appliances that are fastened in place, rated one-quarter horsepower or 500 watts and up, and served by the same feeder or service, with cooking equipment, clothes dryers, space heating, air conditioning and vehicle supply equipment kept out of it. And NEC 120.5(E) says the load calculation shall not require continuous loads to be calculated at 125 percent.

The disconnecting means

Part III of Article 422 is short and worth reading whole. NEC 422.30 is the sentence the rest of it hangs off. Every appliance gets a means that opens all of its ungrounded conductors at once.

• NEC 422.31 lets the branch circuit switch or overcurrent device be the disconnect, on a condition. Either it is within sight from the appliance, or it is capable of being locked in the open position, and the provision for locking stays on the device whether or not a lock is fitted to it that day.
• NEC 422.33 covers the cord-and-plug case. An accessible separable connector, or an accessible plug and receptacle, is the disconnect. Accessible carries the weight in that sentence, and the same section says a household range connection at the rear base qualifies where you can get at it from the front by pulling a drawer out. Where the connection is not accessible, the appliance falls back to NEC 422.31.
• NEC 422.34 lets a unit switch with a marked off position, one that is part of the appliance, be the disconnect where other disconnecting means are provided. What counts as other means is written per occupancy, and one-family, two-family, multifamily and other occupancies each get their own answer. That list is where the item is usually built.
• NEC 422.35 is a one-line knowledge item people drop. A switch or circuit breaker used as the disconnecting means is of the indicating type.

Whether a cord may be there at all is a separate question from whether the plug can be the disconnect, and Article 422 answers it separately. A cord is not a general permission to turn a fixed appliance into a cord-connected one.

Notice how much of the part is about the person rather than the equipment. That is the through line of every disconnect rule in the book and it is worth carrying from one article to the next.

Get the article right before you read anything

Appliance items are frequently articles-in-disguise items, and the wrong article costs you more time than the wrong arithmetic.

• Article 422 for appliances, which is the default and the one most stems land in.
• Article 424 for fixed electric space heating, including heating cable and a duct heater sitting in the same cabinet as something else.
• Article 430 for motors, reached through the appliance article when the appliance is motor operated.
• Article 440 for air conditioning and refrigerating equipment, which modifies the motor rules rather than replacing them.
• Article 120 when the stem is about a service or a feeder rather than about the appliance, including the demand treatment of a household range.

The range is the one to hold in mind. Its branch circuit is an appliance question and its contribution to a service calculation is a load calculation question, and the same appliance is answered from two different articles depending on which the item is asking about.

What to tab

1. Tab NEC 422.13 and write the capacity figure on the tab, not in your head.
2. Tab Part III of Article 422 and read the occupancy conditions under NEC 422.34 once, since that is the part of the disconnect rules an item can hide in.
3. Tab NEC 120.53 and NEC 120.5(E) together, since the pair of them are the whole reason the service arithmetic differs from the circuit arithmetic.
4. Work one water heater problem end to end, from nameplate watts through to conductor and device, so the 125 percent has somewhere to live other than a rule you half remember.

Half an hour, and it covers a slice of one of the three ten-item subject areas on the knowledge portion plus a recurring shape on the calculations portion.

What this page cites

• NEC 422.10 Branch circuit sizing for an appliance. The rating comes off the marked rating of the appliance, and a motor-operated appliance is sent to Article 430. source
• NEC 422.11 Overcurrent protection. Where a maximum overcurrent device rating is marked on the appliance, the device installed does not exceed it. source
• NEC 422.13 Storage-type water heaters. The branch-circuit overcurrent device and conductors for a fixed storage-type heater at or below the stated capacity are rated at not less than 125 percent of the heater. The 2017 edition was the last one that reached that figure by calling the heater a continuous load; the editions since state the 125 percent directly. The capacity figure is in your own book. source
• NEC 422.30 The general disconnecting means rule for appliances, and the opening sentence of Part III. All ungrounded conductors, opened together. source
• NEC 422.33 Cord-and-plug-connected appliances. An accessible separable connector or an accessible plug and receptacle serves as the disconnecting means, and the section carries its own provision for the connection at the rear base of a household range. source
• NEC 422.34 Unit switches with a marked off position, and the other disconnecting means each occupancy has to have before a unit switch counts. Read the occupancy list rather than the opening sentence. source
• NEC 120.53 Appliance load for dwelling units. Permits a demand factor on the nameplate rating of four or more appliances rated one-quarter horsepower or 500 watts and up that are fastened in place on the same feeder or service, and excludes cooking equipment, clothes dryers, space heating, air conditioning and electric vehicle supply equipment. Read off the 2026 page. source
• NEC 120.5(E) Percent Multiplier. States that load calculations shall not require continuous loads to be calculated at 125 percent. Read off the 2026 page. It does not remove the multiplier from the sections that size conductors and overcurrent devices. source
• NEC Article 440 Air conditioning and refrigerating equipment, which is where an appliance question goes when the appliance turns out to contain a sealed compressor. source
• 16 TAC 73.100 Texas adopted the 2026 edition effective 1 September 2026. Article 220 is vacant in that edition and the load calculation article is Article 120. source