Unit 6, Question 50, from MH EEP based on the 2017 NEC

[wdingman]

The question is: "What's the maximum size overcurrent protection device for a 2,500 W, 240 V water heater?"
The possible answers are (a) 15 A, (b) 20 A, (c) 30 A, or (d) none of these.

I selected (b) 20 A, but the answer key gives (a) 15 A. I think that the key might be wrong.

422.11(E) Single Non–Motor-Operated Appliance reads as follows:

If the branch circuit supplies a single non–motor-operated appliance, the rating of overcurrent protection shall comply with the following:

(1) Not exceed that marked on the appliance.​

(2) Not exceed 20 amperes if the overcurrent protection rating is not marked and the appliance is rated 13.3 amperes or less; or​

(3) Not exceed 150 percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes. Where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted.​

I think that (1) does not help because the OCPD size is not marked on the appliance, (3) should not apply because the appliance is not rated at more than 13.3 A (2,500 W ÷ 240 V = 10.42 A), and (2) should apply because the appliance is rated at less than 13.3 A. Therefore, I think that the answer should be (b) 20 A.

Am I missing something here?

 

[augie47]

FYI:In my Answer Key they showed 2500w @ 240 to be 10 amps hence the 15 amp answer.

 

[infinity]

422.13(IN) directs you to 422.10 but that doesn't seem to help much.

422.13 Storage-Type Water Heaters. A fixed storage-type water heater that has a capacity of 450 L (120 gal) or less shall be considered a continuous load for the purposes of sizing branch circuits.
Informational Note: For branch-circuit rating, see 422.10.

 

[Tulsa Electrician]

The question is: "What's the maximum size overcurrent protection device for a 2,500 W, 240 V water heater?"
The possible answers are (a) 15 A, (b) 20 A, (c) 30 A, or (d) none of these.

I selected (b) 20 A, but the answer key gives (a) 15 A. I think that the key might be wrong.

422.11(E) Single Non–Motor-Operated Appliance reads as follows:



I think that (1) does not help because the OCPD size is not marked on the appliance, (3) should not apply because the appliance is not rated at more than 13.3 A (2,500 W ÷ 240 V = 10.42 A), and (2) should apply because the appliance is rated at less than 13.3 A. Therefore, I think that the answer should be (b) 20 A.

Am I missing something here?

"If the branch circuit supplies a single non–motor-operated appliance, the rating of overcurrent protection shall comply with the following:
(1) Not exceed that marked on the appliance.
(2) Not exceed 20 amperes if the overcurrent protection rating is not marked and the appliance is rated 13.3 amperes or less; or
(3) Not exceed 150 percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes. Where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted."

I would say,
15 amp does not exceed 20 amp.
2500/240=10.4166
80% of 15= 12

Since this is considered a continuous load.
10.4166* 1.25.= 13.02
A 15 amp OCPD works

 

[HEYDOG]

I agree 15 amps would work. However, from what I have seen in many exam prep books, from many well respected authors is when the question ask for maximum, it is asking for the maximum allowed by code! IMHO I would go with 20 amps as the answer!