Exam Prep / Study Help

[starbright28]

I was thinking the other day about iether have people PM you to get a list of questions that you could work off of to study for the test.

I was wondering if anyone has something sort of this typed up that they would be willing to say - yeah just PM me and I can get you some study material.

I have found by going through and doing some questions like that - it has helped me, but me - wanting to make sure I am really prepared, want more.

What everyone's thoughts?

 

[starbright28]

Or is this a bad idea.. I'm not getting any feed back.

 

[S'mise]

PM

PM

Amanda, I am not sure if this is a good aproach. How would you know if you can trust the questions and answers? The amount of miss-info out there always amazes me. I sugest getting a NEC handbook that offers more details and notes to help your understanding of the code. Also buying books and study materials from a well known auther. Check out some of the links on this site.
I passed my journey exam first try just by reading my code book. If you can aford it take an exam prep class; they run about $300 to $600 depending where you are. Heck, maybe your boss will pick up the tab?
In the meanwhile the folks around here are happy to any question you have.

 

[starbright28]

Well - i can understand your poirnt on if you start studying stuff that may not be legite. Bascially I can remember questions that I had on the test and now just working out problems from that. Also i have some stuff from college, my past 2 NEC Exam Prep classes and a Code Review class.

I have taken the exam prep classes 2 times before the last 2 tests. I have studying on my own each time. I don't know what's wrong and why i am not passing. This is my 4th time and frankily I am getting tired of studying for it.

I'll ask my questions i guess in this thread that I started... i basically sometimes looking for explanation on how to figure it out and where to look to make sure i find the answer. I don't want answers.

 

[starbright28]

questions that i am having a hard time with

questions that i am having a hard time with

Okay - so here are some items/questions that I am having a hard time with.

First how to you figure out the size of your equipment grounding conductor to run with your feeder wires to a panelboard? The enginner here seems to vary with the sizes for distance and panelboard size, but non are matching up to the chart that I am looking at (which I thought you use for sizing your grounding electrode conductor). Table 250.66

Here's what I am wondering.
Feeder 240 feet
using (1) 11/2" PVC conduit
running (4) #3 CU conductors (L1, L2, L3, N)
what size ground (equipment) will you need.

I am coming up with an #8.

 

[jtester]

Amanda

If you are really working with a feeder, you use 250.122, not 250.66. You're in the wrong section. If voltage drop is an issue, then you must increase the ground wire in a similar fashion to the phase wires. Otherwise the EGC size should be the same answer from everyone.

Jim T

 

[don_resqcapt19]

Amanda,
You need the rating of the OCPD to find the required EGC size for a feeder.
Don

 

[S'mise]

Amanda, the terminology cad really trip you up. Spend some tome in art.100.
But excellent guess! The trick to tests is to ignore irrelevant info and pick up on what they do tell you. Your example can not be specifically answered. You give distance but not load so voltage drop can not be calculated. The equiptment ground cant be calculated unless you know what the fuse size is (250.122)
so it depends what you are fusing. If you were given that on a test I would pick the #8 also, pick the closest answer with the info you have. All we know here is that the largest conductor can cary 100 amps (per 310.16) so I would guess that the minimum OCPD would be 100A. If the question said anything about specific devices, go to that section to make sure the proper OCPD is selected. They try to throw you of by adding irrelevant stuff but try to approach the questions methodically.

 

[starbright28]

oops - the question I posed is not actually a test question it is something that i wanted to double check on what the engineer specified. (bad ain't I)?

anyways the information I forget to give is that the panelboard is 125 Amps.

Here's what I am wondering.
Feeder 240 feet
using (1) 1 1/2" PVC conduit
running (4) #3 CU conductors (L1, L2, L3, N)

I never fully understood grounding and size of grounding conductor, and my guess it has been on a test and I've totally screwed that up. This is for a job we're doing and double checking items is what I typically do to ensure the drawings go out correctly.

He initally put no equipment ground because this is coming from a main disconnect in the public works building going in conduit udnerground to a salt storage building that has a panelboard mounted outside on it.

Thanks for the posts so far.

 

[Rockyd]

Amanda,

Here is my recommendation -

Book $59.00

Printed in full color, the 2005 Exam Prep book covers Theory, Code, and Calculations in great detail. Clear colorful graphics guide you step-by-step through all the material you?ll need to pass your exam the first time. This book contains hundreds of illustrations, examples, and practice questions covering all of these subjects including 36 practice quizzes. This book is intended to be used with the 2005 National Electrical Code.

Pages: 570
Graphics: 408
Includes all the questions contained in the NEC Exam Practice Questions Textbook
Calculations Practice Questions: 788
NEC Practice Questions: 2,400

Let me list the 12 chapters -

Unit 1- Elcectrical Math and Basic Electrical Formulas

Unit 2 - Electrical Circuits

Unit 3 - Understanding Alternating Current

Unit 4 - Motors and Transformers

Unit 5 - Raceway and Box Calculations

Unit 6 - Conductor Sizing and Protection Calculations

Unit 7 - Motor Calculations

Unit 8 - Voltage Drop Calculations

Unit 9 - Dwelling unit Calcualtions

Unit 10 - Multifamily Dwelling Calculations

Unit 11 - Commercial Calculations

Unit 12 - Delta/Delta and Delta/Wye Transformers

This link has the full Table of Contents...


Here is an example of the kinds of graphics that accompany Mike's explanations in his book...on page 203

To see a couple of pages of his book to see if it's for you, consider this link from chapter12...

If you use Mike's materials, it's a virtual guarantee that you'll pass the test(s). You can throw away hundreds of dollars with these exam groups, and "see what's on the actual test" or be secure in your knowledge after a trip though Mike holt's materials for $59. Without Mike's material's, don't know if I'd have passed the the Washington State Electical Administrator's exam back in 93,with an 86%.

The number is 1.888.632.2633 that's 1.888.NEC.CODE.

 

[S'mise]

hang in there

hang in there

I agree with Rockyd spend a few bucks and save alot of confusion. If you dont understand something read it again. It is much easier to learn to crawl before you try to run. That book will advance you and teach you not only what code is but the reasoning behind it.

That feeder questions is still very open ended. There are many variables that it makes it hard to know specifically you need. What type of panel and what is your calculated load? (so you can figure IR drop) Ambient temperature? Non-linear loads? Terminal ratings? ... the list goes on. Basically things are figured from the load and then work your way back to the supply side. As far as the equiptment ground goes you may not even need one, if the grounded conductor(N) ampacity is not less than 250.122 and can also cary the maximum unballanced load it can be used as an effive ground fault current path. (So the Neutral may need to be sized larger) We could zig-zag to code for days and perhaps just confuse you because one circumstance is usually different from the next. When you learning from a book you can understand the intent which goes a long way to understanding the rest.

 

[starbright28]

(don't you hate it when you get logged out and you had a nice response to your own message? That just happened with me)

Okay - Look like i need to really take a hard look at the grounding section of the code book.

The panelboard is located outside on the salt storage building. It is fed by underground conductors from the main sitribution panel in the public works builsing. these 2 buildings are not connected strucutrally.

the panelboard is 3 phase, 208/120v, 125 amps.

I still have the rest of the information in my previous posts.

I looked at T250.122 about the size of ground I need and I still get a #8.

The engineer also put on the redlines that we didn't need a ground because of 250.32 by using the neutral. But i don't understand why not with our application, and I thought it is always smart to run a ground anyways.

we woud still have a groudn that ties into the cement for bonding issues.

 

[don_resqcapt19]

Amanda,

The engineer also put on the redlines that we didn't need a ground because of 250.32 by using the neutral. But i don't understand why not with our application, and I thought it is always smart to run a ground anyways.

As long as there are no conductive paths other than the ungrounded conductor and the grounded conductor between the two buildings, the code does not require an EGC be run to the second building. See 250.32(B)(2). In this case the grounded conductor is bonded to the grounding electrode at the second building. If you have any other conductive paths, like water pipe, phone lines, or metallic conduit and EGC is required and the EGC, not the grounded conductor would be bonded to the grounding electrode at the second building. Under the proposed changes for the 2008 code, this installation would always require an EGC, but under the current rules either method is permitted.
Don

 

[S'mise]

grounded?

grounded?

The neutral is grounded and acts as the egc in this case, like Don said.
If there is a ground fault it will follow the neutral back to pop the breaker. But also make sure that gfci for equiptment is not on the common service (250.32(B)(2)) (we are still on the 02NEC here) The reason I asked what your load is going to be is because if this run is 250 feet and you are drawing 60 amps on that 125panel, you are already at 3% voltage drop with #3 wire. That would put you voltage down to about 202V how much drop you can tolerate? It depends on your load but it is better to avoid it. The code suggests not more than 3% on branch circuits or 5% total. But it is a violation to ignore 220.10 regardless. Remenber voltage goes down= Current goes up.
PS: I always copy what I just typed incase I get booted. I then just paste it back in. Works great for email too!

 

[electricdrill]

A guy i work with went to some of those classes and the instructor told him a bunch of wrong stuff like...your not to use annex C on the test.

 

[starbright28]

back to in regards of the calculations - voltage drop. I didn't even think to look at that. Like I said I'm questioning the engineer here. All the info I provided is what he picked out for this building.
But you're correct - why wouldn't we step up the wire size to accomodate the voltage drop.

to give you an explanation on how he figures things out. yesterday i had to get circuit numbers from him in regards to a couple of mechanical things added. he took right off the spec sheet the amps and volts and basically calculated them together to get watts. then he put the watts down on the panelboard. this was for a ERU for HVAC. ERU took place of Exhaust fans. To me here I am thinking watching him do this - is, does the 125% count for this (continouous load 3 hrs or more?) is that actually how you have been calculating everything on the panelboard? yikes, it makes me worried and to the point where - well how much of it is right shown?

I know electrician in the field won't exactly care about the actual load - they figure if he did the calculations, it is good. I know they (we) don't care about the watts and VA on the panelboard. But how to make him switch over without having examples, that would be nice.

As far as this equipment ground conductor - I'll go and show that there is non needed, but will take a look at voltage drop. The building has 3 - 350 watt metal halide lights, a receptacle, and an exhaust fan that is provided with the building. tell me the wires probably won't handle the load.

PS: I tired to copy the whole paragraph i wrote before in this and it didn't seem to copy and paste. not sure if i did it correctly???

 

[roger]

A guy i work with went to some of those classes and the instructor told him a bunch of wrong stuff like...your not to use annex C on the test.

I would say the instructor was correct. Most exams would want the answer to be from performing a calculation, not just looking at a table or chart.

Roger

 

[starbright28]

I have the loads of this panelboard that is being fed with (4) #3 conductors.

3 - 250 watt lighting fixtures, each on its own circuit. 250 watts each
1 - outdoor receptacle 180 watts
1 - power roof ventilator 180 watts

total VA: 1100.00
total watts: 1100.00
Panel power factor: 1.00
Power angle: 0.00
Total 3 phase current: 3.08

It's a Siemens panel. Outdoor.
Catalog #: W2442MB31350CU

Would the #3 copper conductors work?
Feeder length: 240 feet.
all conductors in (1) 1 1/2" conduit

 

[S'mise]

overKill

overKill

If that's all the is load is, voltage drop is not a concern at all.
BTW, use actual fixture rating if other than the lamp.
Figuring the lights at 125% I get 3.6A and a voltage drop of .37 volts.

Annexes should be used for reference only when your taking a test. And when doing VD questions use absolute K for 2/0 and larger wire.

Electricians should be at least aware if not concerned about actual load. That is, at least know the ampacities their dealing with.

Yes,125% is a calculation # for continuous load but its used for other things as well. A great way to learn is to jusk ask.

Wow, you even calculated the phaze angle!

 

[starbright28]

still learning

still learning

I was thinking you had to take the rating of the panel to do voltage drop.

What do you use for Amps?

I did the voltage drop as 1.732 (12.0) 150 (240) divided by the CM of a #3. I think using the wrong amps is where it got me.

Actually for our MN test they will give you K as a constant, and all you have to do is really memorize the equation. Sometimes you will need to know the resistance forumula.

Anyways - I asked the engineer too about this and he said no voltage drop. I guess thinking you have to size for your panel load - and using those amps (150) into the voltage drop equation, i guess i am dead wrong.

All those phase angles, power factor came right from the excel panelboards we use and they are set up by an equation. So don't give me credit all I did was copy down what i was seeing!

I'm learning more and more, and feeling stupid more too. I guess this is the "real world" equations, which is good so that I am exposed.

Thanks for the help. no new study questions at this time.