Need help with a two Question

[efournier]

1. What will have a larger short circuit current?

A) Motor Circuit
B) Lighting Circuit
C) or will they be the same

2. Do you count a Garage Door Opener in the calculation for a dwelling unit?

 

[charlie b]

The wording of Question 1 is not all that clear, but I think I understand the intent. When a short circuit occurs, there will be a high current flowing, but it comes primarily from the source. The nature of the load has no influence on the amount of short circuit current that the source will send through the fault point. However, a motor has its own ?source? of energy available: the spinning rotor. When you short circuit the supply to a motor, when the motor no longer has a voltage source that is driving it in circles, then the rotor starts slowing down. But during the first fraction of a second or so, the rotating part of the motor acts in conjunction with the stationary part to create a voltage of its own. The result is that the motor acts like a generator for a short time, and it sends some amount of short circuit current back to the fault point. So the correct answer is ?A.?

Most garage door openers are plug & cord connected. That means there needs to be a receptacle outlet nearby. I would not count that receptacle outlet as being any different from the rest of the receptacle outlets throughout the house and garage. In a dwelling unit, receptacle load is included in the ?3 watts per square foot? given in Table 220.12. That fact is stated in 220.14(J). So my answer is ?No.?

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