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NEC Questions and Answers - Based on 2011 NEC
November 2013
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.
Q1. What are the Code rules regarding cord connection of dishwashers and trash compactors?
A1. A cord is permitted for a dishwasher or trash compactor if [422.16(B)(2)]:
- The cord has a grounding-type attachment plug.
- The cord length is at least 3 ft and not longer than 4 ft, measured from the rear plane of the appliance.
- The appliance receptacle is located to avoid damage to the cord.
- The receptacle is located in the space occupied by the appliance or in the space adjacent to the appliance.
- The receptacle is accessible.
Q2. What is the general rule that limits the use of flexible cords for the connection of appliances?
A2. Flexible cords are permitted to facilitate frequent interchange, or to prevent the transmission of noise and vibration [400.7(A)(6) and 400.7(A)(7)] (2)] and to facilitate the removal of appliances fastened in place, where the fastening means and mechanical connections are specifically designed to permit ready removal [400.8(A)(8) and 422.16(A)].
Author’s Comment: Flexible cords must not be used for the connection of water heaters, furnaces, and other appliances fastened in place, unless the appliances are specifically identified to be used with a flexible cord.
Q3. How are the branch circuit conductors and overcurrent protection sized for electric water heaters (120 gallons or less)? Please provide an example.
A3. An electric water heater having a capacity of 120 gallons or less is considered a continuous load, for the purpose of sizing branch circuits [422.13].
Author’s Comment: Branch-circuit conductors and overcurrent devices must have a rating of at least 125 percent of the ampere rating of a continuous load [210.19(A)(1) and 210.20(A)].
Question: What’s the calculated load for conductor sizing and overcurrent protection for a 4,500W, 240V water heater?
(a) 15A (b) 20A (c) 25A (d) 30A
Answer: (c) 25A
I = P/E
P = 4,500W
E = 240V
I = 4,500W/240V
I = 18.75A
Calculated Continuous Load for Conductor Sizing and Protection = 18.75A x 1.25
Calculated Continuous Load for Conductor Sizing and Protection = 23.44A
Q4. Does the NEC require GFCI protection of electric drinking fountains?
A4. Yes, electric drinking fountains must be GFCI protected according to 422.52.
Q5. How are the branch circuit conductors and overcurrent protection sized for fixed electric space-heating equipment? Please provide an example.
A5. For the purpose of sizing branch-circuit conductors, fixed electric space-heating equipment and motor(s) are to be considered a continuous load [424.3(B)].
Author’s Comment: The branch-circuit conductors and overcurrent devices for fixed electric space-heating equipment must have an ampacity not less than 125 percent of the total heating load [210.19(A)(1) and 210.20(A)].
Question: What size conductor and overcurrent device are required for a 9.60 kW, 240V fixed electric space heater that has a 3A blower motor with 75°C terminals?
(a) 10 AWG, 30A (b) 8 AWG, 40A (c) 6 AWG, 60A (d) 4 AWG, 80A
Answer: (c) 6 AWG, 60A
Step 1: Determine the total load:
I = VA/E
I = 9,6000 VA/240V
I = 40A + 3A = 43A
Step 2: Size the conductors at 125 percent of the total current load [110.14(C)(1), 210.19(A)(1), and Table 310.15(B)(16)]:
Conductor = 43A x 1.25
Conductor = 53.75A, 6 AWG, rated 65A at 75°C
Step 3: Size the overcurrent device at 125 percent of the total current load [210.20(A), 240.4(B), and 240.6(A)]:
Overcurrent Protection = 43A x 1.25
Overcurrent Protection = 53.75A, next size up is 60A 
For more NEC Practice, purchase Mike Holt's NEC Exam Practice Questions book based on the 2011 NEC.
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