Class question

[Newton his]

Just started my electrical class recently and the instructor asked a question and said find the answer anyway you can since no one knew. Can use google or anything else we can find to get the answer. The question was can you have a 600A service feed to 8 units in an apartment building? We already determined the building would need a 600A service and each unit will have 100A panels. We have to tell him yes it's possible or no and why.

 

[augie47]

In general, when dealing with students, rather than answering your questions outright we ask what you think the answer is and why. Your thought process is as important as the answer.

 

[Newton his]

Given that I have very little knowledge about this since it is my first week, just going by what I have learned over the last few days, I would guess yes. I have looked in my books (which it could be in there since I have limited knowledge of the books and ebooks in general) and could find anything. I only say yes because all 8 dwellings are not going to be running at the max load calculations for each unit at the same time.

 

[Ponchik]

That is true each unit can not be running at max load all at the same time. So the 600Amp service is good enough.

Now, did you guys do a load calculation to see what the calculated load is?

The instructor will probably ask you why the answer is YES or why the answer is NO.

So, without a load calculation all you can give him is your logical reasoning which sounds like a good answer to me since you only have 1 week of schooling.

 

[Newton his]

Yes we did the load calculations. For all 8 units it totaled about 560 if I remember correctly. We had figured everything out like we were suppose to. Then he said given the load calculation for for each unit to use 100A panel because you don't wanna use a panel smaller then that.

 

[augie47]

I agree, for your first week, that's a good answer.
Some Code references you might want to look at are: 220.40, 220.84 and since the question concerned the service size, 230.79.
A lot of instructors stress a "key word" method of finding answers... in this case the process could be: keyword: Service thus Art 230 then Service equipment (size or rating) to 230 Part VI 230.79.

 

[charlie b]

The question was can you have a 600A service feed to 8 units in an apartment building?

I agree with your conclusion that this type of installation can be done. It won't always be the right thing to do, but if the calculated load for the entire building is under 600 amps then you are OK. I think the instructor was trying to see if the students would get hung up on the notion of 8 panels, each rated at 100 amps, gives you a total of 800 amps, and that would be too much for a 600 amp service. Congratulations for not falling into that trap.

Welcome to the forum.

 

[K8MHZ]

I agree with your conclusion that this type of installation can be done. It won't always be the right thing to do, but if the calculated load for the entire building is under 600 amps then you are OK. I think the instructor was trying to see if the students would get hung up on the notion of 8 panels, each rated at 100 amps, gives you a total of 800 amps, and that would be too much for a 600 amp service. Congratulations for not falling into that trap.

Welcome to the forum.

No common area panel?

 

[charlie b]

No common area panel?

The instructor's question did not include one, so the expected "correct answer" would not include one.

 

[kingpb]

No common area panel?

And hence why my answer would be no. For the reason that not enough information is known about the house building load.