Need Help on Test Questions

[pressone]

Hi,

I have these test questions to answer. Can anyone help me? I am new to the electrical field and trying to learn a few new concepts. I appreciate any help.

1) What size conductors, conduits, and fuse are required for a continuous incandescent lighting load of 950 amps connected to a 120/208V, 3 phase 4 wire circuit (assuming Terminations are 75C)?

2) A conduit contains 8 wires consisting of two 3 phase 4 wire branch circuits serving a continuous fluorescent lighting load. If each circuit is protected by a 20a ocpd device, what size conduit, wire, and insulation type is required?

3) An 800 amps busduct rated at 22,000 amps RMS is protected by an 800a class L fuse. The available short circuit RMS current is 100,000 amps. Determine if the BUS rating of 22,000 amps is acceptable.


P.S. I want to thank suemarkp and mdshunk for helping me with the Branch Circuit solution.

Thank You!

[suemarkp]

Are these really test questions? Do you have a book where the concepts are explained? Can you take a shot at the answers and ask here about the parts you're not sure of?

Finally, these questions are kind of stupid. Who in their right mind runs 950 amps of 120V lighting? I'd be looking at 277V with this much load. Question 1 is not clear -- are we sizing a feeder or two feeders? You can't fit all those breakers into one panelboard, so what is to be sized? Question 2 may have multiple answers depending on the type wire you choose. There isn't one correct wire type, but for one that you pick you need enough conduit space to contain it and maintain proper fill rules.

[pressone]

Hi Mark,

Yes, these are the test questions - believe it or not. I do not think these are practical examples because of the values given. This is why I am confused. I have the 2005 Stallcup's Electrical Design Book and the NEC 2005 to reference for help, but do not know how to tackle these questions correctly since they are not practical. I hope you or someone out there can help direct me on how to tackle these questions.

Thanks!
George

[mdshunk]

To make the questions practical, assume modern (practical) installation materials. For instance, for question #1 assume copper, THHN, and EMT conduit. For question two, there are two "full boats" in that pipe (3 hots and a neutral, twice). Assume, again, THHN, Copper, and EMT. Question 3 requires an assumption as to the distance between the OCPD's and the buss duct. I don't know how to tackle that one without just pulling a distance from the sky. These are very poorly written questions.

[pressone]

I will approach the the questions in a practical sense. Thank You!

[Wgoodrich]

It looks like to me that if a teacher wrote these questions as a work practice test or an actual test the teacher needs to take a class in writing questions.

However I picked up the first two questions are seeking nonlineal loads mixing 4 wire wye systems both calling for special consideration of sizing the neutrals. This may be the subject sought in those first two questions. Poorly worded but that is what I picked up as what may be a trick to the question that the instructor may be trying to bring out to the students.

The third question root mean square yet is questing interupting rating of the overcurrent devices. Again not showing good test writing skills.

Actually the author of those test questions need to do a lot more study for themselves from the words in each question.

May just be questions read at a test then rewritten by memory from the student confusing the words in the original questions not recreating the questions accurately

Just my thoughts

Wg

[Under_Miner]

...The third question root mean square yet is questing interupting rating of the overcurrent devices...

:confused: :cheers: :hmmmm2:

[Wgoodrich]

He said; short circuit RMS current is 100,000 amps

Sorry I didn't give detail. I don't think the question was reproduced as originally written. RMS and 100 thousand amps does not relate to each other. I tried to read between the lines in what he was saying with the facts within his question. May have been way off but I tried.

Wg