NEC Questions and Answers - August 2016  



By Mike Holt for EC&M Magazine

Here's the follow up to yesterday's newsletter. This includes all of the answers to the questions sent, so you can see how you did.

Note: These questions are based on the 2014 NEC.

Q1. What are the Code rating requirements for outlet devices installed on a branch circuit?
A1. Lampholders connected to a branch circuit rated over 20A must be of the heavy-duty type [210.21(A)].

Author’s Comment:
Fluorescent lampholders aren’t rated heavy duty, so fluorescent luminaires must not be installed on circuits rated over 20A.

Receptacle Loading. A single receptacle on an individual branch circuit must have an ampacity not less than the rating of the overcurrent device [210.21(B)(1)].

Informational Note: A single receptacle has only one contact device on its yoke [Article 100]; this means a duplex receptacle is considered as two receptacles.

Multiple Receptacle Loading. If connected to a branch circuit that supplies two or more receptacles, the total cord-and-plug-connected load must not exceed 80 percent of the receptacle rating [210.21(B)(2)].

Author’s Comment:
A duplex receptacle has two contact devices on the same yoke [Article 100]. This means that one duplex receptacle makes it a branch circuit with multiple receptacles.

Multiple Receptacle Rating. If connected to a branch circuit that supplies two or more receptacles, receptacles must have an ampere rating in accordance with the values listed in Table 210.21(B)(3).

Table 210.21(B)(3) Receptacle Ratings
Circuit Rating Receptacle Rating




15A or 20A




40A or 50A



Q2. What loads does the Code allow on an individual branch circuit?
A2. An individual branch circuit is permitted to supply any load that doesn’t exceed the ampere rating of the branch-circuit [210.22].


Q3. What loads does the Code allow on a multiple-outlet branch circuit?
A3. In no case is the load permitted to exceed the branch-circuit ampere rating [210.23].

Branch circuits rated 15A or 20A supplying two or more outlets must only supply loads in accordance with 210.23(A).
15A and 20A Circuit. A 15A or 20A branch circuit is permitted to supply lighting, equipment, or any combination of both [210.23(A)].

Author’s Comment:
Except for temporary installations [590.4(D)], 15A or 20A circuits can be used to supply both lighting and receptacles on the same circuit.

Cord-and-plug-connected equipment not fastened in place, such as a drill press or table saw, must not have an ampere rating more than 80 percent of the branch-circuit rating [210.23(A)(1)].

Author’s Comment:
UL and other testing laboratories list portable equipment (such as hair dryers) up to 100 percent of the circuit rating. The NEC is an installation standard, not a product standard, so it can’t prohibit this practice. There really is no way to limit the load to 80 percent of the branch-circuit rating if testing laboratories permit equipment to be listed for 100 percent of the circuit rating.

Fixed Equipment. Equipment fastened in place (other than luminaires) must not be rated more than 50 percent of the branch-circuit ampere rating if this circuit supplies luminaires, receptacles, or both [210.23(A)(2)].

Question: Can a whole house (central) vacuum motor rated 13A be installed on an existing 20A circuit that supplies more than one receptacle outlet?
Answer: No, an individual 15A or 20A branch circuit will be required.

Q4. What Does the Code require in regard to branch circuits in the common areas of a multiple occupancy dwelling?
A4. Dwelling Unit Branch Circuits. Dwelling unit branch circuits are only permitted to supply loads within or associated with the dwelling unit [210.25(A)]

Common Area Branch Circuits. Branch circuits installed for public or common areas of a multi-occupancy building aren’t permitted to originate from equipment that supplies an individual dwelling unit or tenant space [210.25(B)].

Author’s Comment:
This rule prohibits common area branch circuits from being supplied from an individual dwelling unit or tenant space to prevent common area circuits from being turned off by tenants or by the utility due to nonpayment of electric bills.

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  • How long is a generator required to run after the normal power is restored per NEC. I cannot locate a time in the book. Thanks Dan

    Dan Knowles  September 15 2016, 1:56 pm EDT

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