Quiz question has me stumped

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chicagosparky

Member
Location
Chicago, IL
Got a question wrong on an exam & still at a lost. Question is: "What is the ampacity of a #10 TW conductor in a conduit with 6 other current carrying conductors in an ambient temperature of 30 degrees C?"
So Table 310.15 (B)(16) shows #10 TW (60 C) is good for 30A.
Table 310.15 (B)(2)(a) 26-30 C has 1.0 as multiplier
Table 310.(B)(3)(a) 4-6 conductors has .8 as multiplier
30A x 1.0 x 0.8=24A [wrong answer]
Supposed to be 0.7 x 30A = 21A
Can't figure out why .7 is used as multiplier in lieu of .8
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I would be willing to bet a majority of folks who read that question make the same error !
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I would be willing to bet a majority of folks who read that question make the same error !

Yeah, it's like "A plane crashes on the border between two countries; in which country should the survivors be buried?" :D
 

sameguy

Senior Member
Location
New York
Occupation
Master Elec./JW retired
Yeah, it's like "A plane crashes on the border between two countries; in which country should the survivors be buried?" :D

I bet you think the answer is, survivors aren't buried.
No time constraint is put in so when the survivors do die they will be buried, in the country of their choice.
 

jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
Details are killers. I've learned that the hard way on many issues. :dunce:
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
And now for the real electrical exam

1. What color is a green ground screw?______________________

2. Electricity will leak out of pipes if you do not use rain tight fittings. T F

3. To trip a circuit breaker, you must stick out your foot as it walks by. T F

4. When dealing with conduit, the O.D. must exceed the I.D. or the hole will be on the outside. T F

5. A keyless fixture cannot be unlocked. T F

6. A circuit breaker reads "20" on the handle. This means it can trip 20 times before it is worn out. T F

7. If you plug something 110 volts into a 120 volt outlet, you will have 10 volts leakage. T F

8. When hooking up a 220 volt device, you must use 220 volt wire. T F

9. The gauge number of a wire is the number of plugs the wire can handle. T F

10. A flush mount device may only be hooked up to a toilet. T F

11. An ohm is a Hindu measurement of voltage. T F

12. Electrical Inspectors are also known as: _____________________

13. Service Entrance Conductors direct from the supply house with current already in them are very dangerous. T F

14. High voltage wire is used on upper levels of tall buildings whereas low voltage wire is usually found in the basement or underground. T F

15. If you have a molded-case circuit breaker, the mold can be washed off with warm soapy water. T F

16. Three ECs enter an empty room and lock the only entrance: the door. All have on a tool-belt with a regular screwdriver, a pair of lineman's pliers, and a roll of Scotch-33. The light overhead is supplied by a sinusoidal voltage source and the light has a 0.935% power factor. Harmonics are not a factor, but the Carnot Cycle might be. The next morning, all three ECs leave the room and lock the door behind them. How many ECs are left in the room? __________
 
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