Help with a textbook question about puting 5 fans on a 15 amp circuit.

eric_hoog

Member
I relaize this is probably very basic to most of you as I am a student doing a self study using Delmar's Standard Textbook of Electricity. But I just wanted to verify my answer to one of the practical questions I have came across. Any information, help, or tips would be greatly appreciated.

Well here it is:

#2 ? You are an electrician installing the wiring in a new home. The homeowner desires that a ceiling fan with light kits be installed in five different rooms. Each fan contains a light kit that can accommodate four 60-watt lamps. Each fan motor draws a current of 1.8 amperes when operated on high speed. It is assumed that each fan can operate more than three hours at a time and therefore must be considered a continuous-duty device. The fans are to be connected to a 15-ampere circuit. Because the devices are continuous duty, the circuit current must be limited to 80% of the continuous connected load. How many fans can be connected to a single 15-ampere circuit? How many circuits will be required to supply power to all five fans?

15 A * 0.8 = 12 A (80% of 15 A is 12 A so that is the max current allowed per circuit)

Each fan draws:
4*60W = 240 W (power used for lights on each fan)

On a 240 V circuit the lights would draw 1 ampere of current (I =P/E). With the motor the total current draw for each unit would be 2.8 A. So 12 A / 2.8 A = 4.2 units per circuit. So there could be 4 fan units on each circuit and would need 2 circuits.

On a 120 V circuit the lights would draw 2 amperes of current (I =P/E). With the motor the total current draw for each unit would be 3.8 A. So 12 A / 3.8 A = 3.15 units per circuit. So there could be 3 fan units on each circuit and would need 2 circuits.

I would assume that they would be using the 120 V circuit for this application but I included both voltages to cover everything. Does this sound correct you?

Also, I am very interested in pursuing a carreer in the electrical feild here in Canada. Other than going to school and getting a diploma (which I plan on doing) are there any suggestions, tips or information resources you can tell me about that would help me to facilitate my goal? If so please let me know it would be greatly appreciated. I'm currently studying Delmar's Standard Textbook of Electricity as I believe this is a great starting point.

Anyways, thank you a head of time for any help you can give me!
-Eric
 

Dennis Alwon

Moderator
Staff member
Since you are talking about equipment that is 120v then you should use 120V not 240V. In the real world I have never seen anyone consider lights in a residence as continuous however it does not hurt to do so. Obviously since the question asks that then you must use it.
 

eric_hoog

Member
Thanks for the reply! I did realize that the question sounded a little odd. I guess they are trying to ask them in such a way so you only apply what they have taught so far in the textbook. I was told that textbook was used in alot of the programs which I plan on taking. So far a good few of the questions have been quite vague. I think once I get further into the book they won't be quite so vague. But anyways much appreciated!
 

gndrod

Senior Member
Thanks for the reply! I did realize that the question sounded a little odd. I guess they are trying to ask them in such a way so you only apply what they have taught so far in the textbook. I was told that textbook was used in alot of the programs which I plan on taking. So far a good few of the questions have been quite vague. I think once I get further into the book they won't be quite so vague. But anyways much appreciated!
The question is not only a little odd, but not a reality when stringing a dwelling for both labor and economics of a project ...the example smacks of old method K&T stringing. In reality, there will be branch circuits instead of one 15amp BC. I do not believe the instructor has ever wired a house from the test question posed. Very misleading to find out if a student has a handle on loads and lighting calculations. There are better tutorial books than Delmar's.
(i.e. MH's and RBJ's) JMO
 
Last edited:

ActionDave

Moderator
Staff member
Also, I am very interested in pursuing a carreer in the electrical feild here in Canada. Other than going to school and getting a diploma (which I plan on doing) are there any suggestions, tips or information resources you can tell me about that would help me to facilitate my goal?
-Eric
Find a shop that is established in your area. One that has been around for a few years and has a reputation for doing good work. It may or may not be the place that has the shiniest trucks or most employees. Get hired there. Hang out with the guys who are in a good mood, not the ones who gripe about everything.

After you get hired do not try and impress anyone with how much you know or what you have read or studied. That does not mean you that you stop studying, just don't talk about it for a while. Do what you are told how you are told, not the way you think is better. It may or may not be correct. It doesn't matter. It's not for you to say. Don't ask, "Why?" just follow orders for at least four months.

When it comes time to ask questions ask things like, "Is it true that ...blah, blah, blah?" Or, "I read that...blah, blah, blah. What do you think?"

And above all, show up on time.
 

eric_hoog

Member
Thanks again for the replies! I'll certainly try to implement these ideas and try to find some more up to date books to study other than Delmar's. Much appreciated!

-Eric
 

BullsnPyrs

Senior Member
another way to increase your knowledge is to research everything you learn on the job in the code book. It puts a practicle application together with the code language. For me it is the easiest way to learn code.
 

Stevareno

Senior Member
Does the fan motor not have to be calculated at 125% for continuous duty? When I do that, I get the answer that you can only put two fans on a 15A circuit, therefore you need three 15A circuits for five fans.
 

mike1061

Senior Member
Find a shop that is established in your area. One that has been around for a few years and has a reputation for doing good work. It may or may not be the place that has the shiniest trucks or most employees. Get hired there. Hang out with the guys who are in a good mood, not the ones who gripe about everything.

After you get hired do not try and impress anyone with how much you know or what you have read or studied. That does not mean you that you stop studying, just don't talk about it for a while. Do what you are told how you are told, not the way you think is better. It may or may not be correct. It doesn't matter. It's not for you to say. Don't ask, "Why?" just follow orders for at least four months.

When it comes time to ask questions ask things like, "Is it true that ...blah, blah, blah?" Or, "I read that...blah, blah, blah. What do you think?"

And above all, show up on time.
That's pretty good advice.
Thanks
Mike
 
Top