Re: What are rules for double-tapping breakers
I commend you for being safety-conscious. It is a good question, and it does not have an easy answer. In fact, the only NEC article that I could find to back up your "calling this a defect" is going to come across (to your clients) as a bit "wishy-washy." The article is 110.3(B). It says,
Originally posted by tonype: I hope to get some clarification because occasionally an argument develops when I call this a defect. What other things should I be aware of?
If a breaker has two wires connected to it, and if the breaker was not listed for use with two wires, then it is a "defect," in the language of your profession. In our language, we would call it an "NEC violation."
Listed or labeled equipment shall be installed and used in accordance with any instructions in the listing or labeling.
On the other hand, if you see a breaker that is rated for two wires, and that has two wires, it will be tough for you (and even tough for an electrician) to tell if the load exceeds the rating of the breaker. You would have to have a list of everything that is connected to each wire, and have either the nameplate rating of each load or some other basis for determining the load. What Roger was referring to in his response to your Question #2 was that it is OK to load a 20 amp breaker to 20 amps, if the loads are not going to run "continuously." That term is defined as longer than 3 hours. So if you don't know the load, in detail, you can't reasonably call this a "defect."
Perhaps the best you can do is to cite the double-wire condition as something that you recommend be investigated by an electrician, since it is beyond your role to determine what is, and what is not, an NEC violation.
By the way, in our language, the words "tap" and "tapping" do not apply to the practice you are describing. I have heard this called "double-lugging a breaker," but not "double-tapping a breaker."
Charles E. Beck, P.E., Seattle
Comments based on 2014 NEC unless otherwise noted.