Our county allows homeowners to test to acquire permits for "rough wiring" and "heavy-ups" (https://www.montgomerycountymd.gov/DPS/Process/combuild/homeowner-electrical.html).

I did electronics/electrics in school, so believe I have the basis for knowledge that would be required to take this test, and they provide the National Electrical code for reference during testing.

However was wondering if anyone else had undertaken this test, or similar in their area, and could advise some resources for passing this exam?

  • I'm in the same county and I've read about that but not taken the test. Commented Feb 7, 2019 at 20:02
  • 1
    To those who voted to close, I am not sure how asking about a resource for learning about a subject (books in the library was provided as such to date, which will be in circulation for years, if not centuries) fits with something that would become obsolete quickly.
    – user66001
    Commented Feb 8, 2019 at 14:22

1 Answer 1


Sorry, you don't. I also started in electronics... Very little of my experience was applicable to NEC code electrical.

Knowing how electrons are supposed to behave gives you a small edge. But you must throw out all your existing knowledge about "how to do things" and allow yourself to grasp a different paradigm and ultimately the reasons why. Code does nothing without a reason.

You will find the codebook to be useless. It's a book of law and is very poorly formatted to be a reference guide or learner. It says so, flat-out, in Article 100.

So, are you ready to answer questions like this:

You are wiring a receptacle circuit in 12 AWG wire. The circuit breaker and receptacles are rated for 75 degrees C. The cable is UF, which is rated for 90 degrees C. Do you use a breaker size of

  • 15 amps
  • 20 amps
  • 25 amps
  • 30 amps

20A. The stuff about degrees C was a red herring, to make you turn to table 310.15b16, which is what you'd do when under the gun and flipping through NEC at the exam.

You are running six circuits in 12AWG UF (90 degree C) cable which all pass through a conduit 22" long. What is the largest breaker you can use in these circuits?

  • 15A
  • 20A
  • 25A
  • 30A

20A. This situation comes perilously close to the 310.15b2a rule requiring a "50% derate off the wire's highest temperature column in 310.15b16, which is 30A at 90C" ... but the conduit is less than 24" so you dodge the rule.

You are wiring a new multi-wire branch circuit, featuring two hots and a shared neutral. You only have one space remaining in the panel. Which type of breaker is appropriate?

  • a duplex breaker
  • a quadplex breaker
  • a 2-pole breaker

A quadplex. A duplex is not appropriate for MWBC, and a 2-pole won't fit!

Select the minimum requirements for a Grounding Electrode System using ground rods:

  • one ground rod
  • two ground rods, or one if it passes the test in NEC 250.24.
  • two ground rods
  • one ground rod, encased in concrete

The last, 1 in concrete. I played a trick on you, this answer is affected by a local amendment!

The point

None of these things have anything to do with electronic design. Life is different on the other side of the wall-wart!

The solution

I say with sincerity, electronics guy to electronics guy, to hit the library and thumb through some books on residential electrical. Find one that speaks your language and devour it. You will find many things that seem unimportant, like the above. Then, browse a couple more and see what their takes are.

Then, spend a lot of time surfing this site, as it can backfill, expose you to common situatuons and give code refs, which books do not. Mostly read existing questions (we're not big fans of hypotheticals unless it's a really good question).

Hopefully the test won't ask questions inapplicable to residences, which is what most of NEC is.

Some actually involving design

In 120V/240V split phase, a multi-wire (shared neutral) branch circuit has both its hot wires breakered 20A, but no breaker on the neutral. Which condition causes the maximum (worst case) current that could possibly flow on the neutral?

  • 20A on both hots
  • 20A on one hot, 10A on the other
  • 20A on one hot, zero on the other

All the wires are in the same cable. Among the above choices, which one results in the least total wire heating in the cable?

Sadly, even these basic thinkers won't be on the exam.

  • Fascinating. Though I think they should have used principal instead of principle in the section requiring the concrete encased electrode. Commented Feb 8, 2019 at 2:13
  • Can't find any word starting with the letters prin, per what I assume manassehkatz is eluding to, but thanks Harper for such a detailed answer. If you're curious, I got 2 of the 4 questions you posed correct, and probably understated my understanding of electrics (I took those electronics courses in another country, so not sure what one knows/assumes US schools teach should apply to me). As I don't like wasting money...
    – user66001
    Commented Feb 8, 2019 at 13:35
  • ... I will take your advise and read up on electrician posts/find some books on the subject, instead of taking the test just yet. I would be interested if you could provide an answer, in your post above, to the question about maximum possible currently flowing along the neutral, and the least total wire heating, if you would please, so I can see if I am right also (might be helpful to others too).
    – user66001
    Commented Feb 8, 2019 at 13:37
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    My comment is referring to the Montgomery County amendments pdf that Harper linked. It is scanned so searching doesn't work well. But scroll down until you find the part about grounding and you'll see it. Commented Feb 8, 2019 at 14:45

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