ECN Forum Forums Code Related Discussion NEC & other Code issues 10 ft tap rule

From what I get from the 10 foot tap rule is that if a sub-panel run in over 10 ft, you have to feed it - breaker protected. Am I wrong?
25ft tap rule? I'll have to check on that one. Any short explanations?

RE: 10 ft. Tap rule - (you should take a look at 240.21(B) for specifics)....IF the size of your tap conductor is rated at only 1/10 the size of the conductor you are tapping, then yes, you are limited to 10 ft.

However, if you increase the size of your tap conductor so it is sized at 1/3 the ampacity of the conductor you are tapping, then you can increase the distance to 25 ft. [see 240.21 (B)(2)].

If these tap conductors are running on the outside of the building, then you have unlimited length [see 240.21(B)(5)].

Dana- You need to look at that again- If you are in 240 the tap conductor relates to the device on the feeder. In fact conventional wisdom would have us relating to the device on a 10' tap. ie if the device were a 1200a switch the minumum size wire would have to be 120a. 25' tap relates to the "over current device" so if the 1200a switch had 800a fuses, we'd need to be 1/3 of the 800a.

When you go into Art. 430 for motors the taps change slightly.

yes - I was trying not to be too wordy or confusing. All conductor ratings have to be protected by a corresponding OCPD...these ratios to value 1/10, 1/3, etc. are detailed in 240.21(B).