NEC Tips

This is for the EEs preparing for the next test. I recently receive some e-mails with very nice links and want to share them with you. I will post as soon as I get more...

NEC 310.15 - Ampacity

Also here is this:

310.4 Conductors in Parallel

By Mike Holt

Ungrounded and grounded neutral conductors sized 1/0 AWG and larger can be connected in parallel (i.e., electrically joined at both ends).

When conductors are run in parallel, the current must be evenly distributed between the individual parallel conductors. This is accomplished by ensuring that all ungrounded and grounded neutral conductors within a parallel set are identical. Each conductor of a parallel set must:

Be the same length.

Be made of the same conductor material (copper/aluminum).

Be the same size in circular mil area (minimum 1/0 AWG).

Use the same insulation material (like THHN).

Terminate in the same method (set screw versus compression).

In addition, raceways or cables containing parallel conductors must have the same physical characteristics and the same number of conductors in each raceway or cable. Conductors for one phase (ungrounded conductor) or the grounded neutral conductor, aren't required to have the same physical characteristics as those of another phase or grounded neutral conductor to achieve balance.

The equipment grounding (bonding) conductors for circuits in parallel must be identical to each other in length, material, size, insulation, and termination. In addition, each raceway (where required) must have an equipment grounding (bonding) conductor sized in accordance with 250.122. The minimum 1/0 AWG rule of 310.4 doesn't apply to equipment grounding (bonding) conductors [250.122(F)(1)].

When more than three current-carrying conductors are run together in a raceway longer than 24 inches, the ampacity adjustment factors of Table 310.15(B)(2)(a) must be applied. See 310.10 and 310.15 for details and examples.

Here is another good one on motor calculations per NEC for Overcurrent protection.

http://www.mikeholt.com/mojonewsarchive/EC..._1~20030303.htm

or this free NEC quiz:

http://www.mikeholt.com/codeQuizzes.php

RC

ee_4_pe said:

Here is another good one on motor calculations per NEC for Overcurrent protection.
http://www.mikeholt.com/mojonewsarchive/EC..._1~20030303.htm

Click to expand...

Thanks for posting, I feel much more confident!

dianevp said:

ee_4_pe said:

Here is another good one on motor calculations per NEC for Overcurrent protection.
http://www.mikeholt.com/mojonewsarchive/EC..._1~20030303.htm

Click to expand...

Thanks for posting, I feel much more confident!

Click to expand...

http://ecmweb.com/mag/electric_motor_calculations_part/

I confuse with answer from sample practice (Mike Holt) for the overload protection. Because his sample said "Deal element fuse" so the answer of 75A need to size down per (240.6A). How about the last example (same with Mike Holt) calculate for overload protection (14A*1.15=16.1A). Do we need to size down to 15A (correct answer??) If the question didn't say anything just like problem 510 in the NEES sample. It is just said "overload protection device" and the calculation is 74.5A (size down to 70A answer).

In the example D8 from NEC2008, the calculate the Feeder short circuit and ground fault protection, the answer is 190A, and they size down to 175A. When do we need to size up or size down the answer??

So we need to size down the answer when the question asking for overload protection (fuse or devices) or short ckt & ground fault protection??

Can someone help me to understand these??

Thanks,

Good stuff. Thanks.

In general, ECMWeb and Mike Holt's Forums have great articles and posts on almost everything NEC related. They also have great search functions on their sites so I spend a lot of time on both when researching topics for work. The EC&M articles are reviewed and approved before publication, but information you find in forums may not be correct. Make sure you do your own follow-up research on any code related comments that you read. I am not providing any links in this post, but a simple Google search will pull them up.

EC&M

For those of you who don't know, ECM is a resource full of Electrical Construction & Maintenance articles. They publish a hardcopy magazinie called EC&M and the firm I work at is one of their subscribers. I have found countless articles on there that have helped me throughout my fledgling career.

Mike Holt

Mike Holt has built a respected brand around his name including a large forum where electricians and engineers share their knowledge and experiences on various topics. There are a lot of master electricians that participate in the forums from various states.

Eng-Tips

Since we're talking about NEC tips here, another forum to look at is the Eng-Tips forum. There are also a lot of master electricians that participate in the forums here. Eng-Tips covers more than Electrical, but since this topic is about Electrical I will leave it at that.

Manufacturer's Websites

You can find white papers and technical documents on manufacturer's websites such as Square D, Eaton, and various other electrical equipment makers. Most of the time they reference NEC and other codes and are a good way to read about the important points of specific code topics.

This is a general post and I try not to link any specific pages because links do change and here are just so many good articles and posts throughout all of the above resources.

Best of luck on your PE exam.

Aside from agreeing with the last post, I recommend the following.

1. NEC Handbook - has explanations and example calculations.

2. Tom Henry's NEC Index - has a large index to the NEC

3. Ugly's Electrical Reference - this is very handy if you cross reference the tables in Ugly's to the actual tables in the NEC. For example, you can find ampacities a lot faster in Ugly's than flipping through the NEC - since the NEC Handbook is bulky.

SpacedOut31416 said:

1. NEC Handbook - has explanations and example calculations.
3. Ugly's Electrical Reference - this is very handy if you cross reference the tables in Ugly's to the actual tables in the NEC. For example, you can find ampacities a lot faster in Ugly's than flipping through the NEC - since the NEC Handbook is bulky.

Click to expand...

Seconded. These are my top two go-to sources day-to-day at work, and were among the few books I used in the test (the other was the Camara).

But: TAB THE HELL OUT OF THEM. Tab every section/table you use while working practice problems. The Ugly's isn't organized very well, and the NECH is just huge. You can get pre-printed tabs for the NEC if you want permanent and sturdy.

And of course, the standard "know your references" clause applies.

Good luck!

bethy said:

I confuse with answer from sample practice (Mike Holt) for the overload protection. Because his sample said "Deal element fuse" so the answer of 75A need to size down per (240.6A). How about the last example (same with Mike Holt) calculate for overload protection (14A*1.15=16.1A). Do we need to size down to 15A (correct answer??) If the question didn't say anything just like problem 510 in the NEES sample. It is just said "overload protection device" and the calculation is 74.5A (size down to 70A answer). In the example D8 from NEC2008, the calculate the Feeder short circuit and ground fault protection, the answer is 190A, and they size down to 175A. When do we need to size up or size down the answer?? So we need to size down the answer when the question asking for overload protection (fuse or devices) or short ckt & ground fault protection?? Can someone help me to understand these?? Thanks,

Click to expand...

-----------------------------------------------------------

Yes, you need to size down to 15A. For individual motor circuit, you need to size up fuse or breaker for an exception case as described in 430.52©(1) Exception No. 1 " Round the resulting number to next higher standard size (fuse or breaker) as listed in 240.6(A), if it doesn't correspond to a standard size".

Thanks,

jbachoua said:

QUOTE (dianevp @ Apr 5 2011, 12:19 PM) <{POST_SNAPBACK}>

QUOTE (ee_4_pe @ Oct 29 2007, 12:19 PM) <{POST_SNAPBACK}>

Here is another good one on motor calculations per NEC for Overcurrent protection. http://www.mikeholt.com/mojonewsarchive/EC..._1~20030303.htmThanks for posting, I feel much more confident!

http://ecmweb.com/mag/electric_motor_calculations_part/

Click to expand...

-----------------------------------

Mr. Mikeholt,

In your last example (ref to fig 7.11), You choose 14 AWG conductor for 20 amps and according to the table 14 AWG is justifiable. But on the same table ( * conductors) refers to consult 240.4(D) to ensure this conductor can carry required current. In this case, 14 AWG conductor capable for 15 A, so we need to select next higher size 12 AWG which is good for 20 A.

I am expecting your feedback or guidance from you or forum members.

Thanks,

Insaf said:

-----------------------------------

Mr. Mikeholt,

In your last example (ref to fig 7.11), You choose 14 AWG conductor for 20 amps and according to the table 14 AWG is justifiable. But on the same table ( * conductors) refers to consult 240.4(D) to ensure this conductor can carry required current. In this case, 14 AWG conductor capable for 15 A, so we need to select next higher size 12 AWG which is good for 20 A.

I am expecting your feedback or guidance from you or forum members.

Thanks,

Click to expand...

You should probably contact Mike Holt directly from his website. I don't believe he is an EB.com member nor does he read these forums.

very nice

Complex Imaginary has a very good drill book on the NEC. I only had time to work through a third of the book but as a result was well prepared for April 2014.

I would highly recommend Tom Henry's Key Word Index for any problem that deals with the NEC. It comes in to styles, depending on the codebook you have (plain or handbook) and changes year by year. Get this, and then any time you have to grab the NEC, grab the Key Word Index first. It not only lists the NEC article number, but the page number as well (assming you have the right index for the year and text of code book you have). It by far outdoes the poor index in the back of the NEC.

It really is a time saver and is really cheap.