I recently cited a double tap (two ungrounded conductors terminating on one 20A breaker) in a service panel as a code violation, but when challanged on it, I can not find it in either the 1999 or the 2002 NEC. I fell like an idiot. Can someone help me out here?

110.3(B) or last sentence of 110.14(A)

rkidd,

Before citing "double taps" be sure that the breaker is not designed for 2 terminations.
The double tap was commonly cited when I was doing real eatate work. However, some designs such as the "pressure plate" type of termination (Square D uses this) allow 2 conductors of the same size to be terminated on the breaker.

This is one of those things that a lot of people in the trade assume is always a code violation. Not necessarily. It is completly dependent on whether or not the circuit breaker is listed for one or two wire. Many 15 and 20Amp circuit breakers are in fact listed to accomodate 2 wires. Reference the link below from the web site of Mike Holt (who probably has more credability than me
http://www.mikeholt.com/technical.php?id=nec/unformatted/Jan_ECM&type=u&title=NEC%20-%20Question/Answers%20(1-4-2K)

Thank you all for the speedy replys. With these three answers plus the ref. to the Mike Holt site, I get it. I was barking up the wrong tree thinking I would find something that would say only one branch circuit can be protected by one over current device. Thanks again. Ray