Confused About Sizing Service Amperage

While going through some Test Prep questions, I got the following question (see below). I was under the impression that the size of the SEC would help determine service amperage, based especially, on the other options. Clearly, that is wrong. What am I missing? I don’t recall any information in the InterNACHI electrical courses telling us to size the Service Drop Wires.

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You’ve found a wrong answer marked as correct. One of many on the test.


Not sure I am understanding your question Matt. The size of the service drop is a good indicator of determining what the amperage should be. So the question above seems correct as the best answer provided.

Edit: I guess I stand corrected by Simon, but I would have answered as in the question. What is the correct or better answer?

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The service drop conductors are often sized smaller because they are exposed to air. Hence, if you use the service drop as the determining factor of the service size you’d be more wrong than right.

The service entrance conductors would be the best answer to the question.


As Simon stated the drop conductors are often much smaller than the service size because they are in free air and also they are not governed by the NEC. A service would be sized according to the NEC and the components of that service would begin at the service point which is after the drop. The correct answer as Thomas stated is the fourth answer.


I see now. Drop vs. Entrance wire (SEC.) Confused me too and as you pointed out, wrong answer marked right. :+1:

Credit goes to Simon… :wink:

I agree. :+1:

The more important question is why are there so many errors in the training material?


It’s about quantity, not quality up in here :man_shrugging:


Thanks guys. I’m glad to know I am not losing my mind. Now the bigger worry is, as Simon noted, one of many wrong answers.
It’s hard enough keeping all this stuff straight! :crazy_face:


That’s kind of sad. I always had high regard for this organization. Certainly they can afford to pay someone to review their material.

Maybe someone should let @bgromicko1 know to have it corrected.

His email is :wink:

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I tagged him so hopefully he’ll chime in :+1:

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The size of the service drop conductors is the LEAST reliable of the five choices. It is not at all a good indicator.

I have been told the training is validated by Master electricians.

That’s possible but we all make mistakes so there should be a better system of checking the accuracy of the questions and answers. Maybe using a larger pool of checkers would help.

I’m being a bit facetious, but I feel like the “size of the service entrance conduit” may be the LEAST reliable of the 5 sources. :rofl:

I reviewed the course material while I was at InterNACHI HQ teaching a few years ago. I found MANY errors. I gave Ben a marked up copy of the entire course with dozens of corrections. I don’t think anyone ever did anything with it. I recently went through some of the material for my continuing education hours. I found a disturbing number of errors.


The service drop wires are a very poor indicator, as they are often massively oversized. The most proper answer is the lesser of the drop, the entrance conductors, the meter socket, meter or the main breaker.

If you want any indication of this, many upgrades from 60A->100A or 200A service require no change to the drop. The drop is the responsibility of the power company anyway. There is zero reason the drop and the main capacity need be related.

It’s not the best answer.