Tap taptap12/7/2023 ![]() Remember: If there is a fault on the tap conductor, the overcurrent device protecting the upstream feeder is the device that must trip. The EGC for tap conductors is sized based on the upstream overcurrent device, protecting the feeder from which the tap is made. This sizing is often done incorrectly, resulting in an undersized conductor. The last element to address is probably the most often missed: sizing a wire-type equipment grounding conductor (EGC) or supply-side bonding jumper installed with the taps. If we were to ignore the rule and round up anyway, our tap conductor may be smaller than the minimum size necessary to trip the overcurrent device in the event of a fault. Section 240.21(B) and (C) clearly state the rules of Sec. With tap rules and transformer secondaries, DO NOT round up. Section 240.4 generally permits the overcurrent device protecting a conductor to be rounded up to the next higher standard overcurrent device, up to 800A, in the event the conductor does not correspond to a standard size as noted in Sec. Overload protection is provided at the termination of the tap, which is often a fusible switch in a main breaker-type panelboard that is not greater than the ampacity of the tap conductor. Now that we’ve addressed ground-fault and short-circuit protection, we are left with the final component of overload protection for the tap conductor. In short, the reason for the size - one-tenth on the 10-ft tap rule and one-third on the 25-ft tap rule - is that these limitations have been demonstrated as sufficient conductor size and length to carry enough current to open the upstream feeder overcurrent device providing the necessary ground-fault/short-circuit protection of the circuit in the event of a fault on the tap conductor. If the impedance of the feeder (and the potentially much smaller tap conductor) is too great, the feeder and its tap will not carry enough current with a fault on the tap conductors to open the overcurrent device upstream that protects both the feeder and the tap conductors. Where is the ground-fault short-circuit protection for the tap? The OCPD is protecting the feeder ahead of the tap. 2), the tap conductor may be as small as one-third the size of the overcurrent device protecting the feeder from which the tap is made. 1), the tap conductor may be as small as one-tenth the size of the overcurrent device protecting the feeder from which the tap is made. Why? The tap conductor is generally smaller than the feeder conductor from which it is tapped. The length of the tap, along with the size of the tap conductor, are major factors in determining the overall impedance of the tap conductor. So, what’s the deal with the distance limitation, and why is the distance important? In some cases, such as outdoor settings, taps are permitted in longer lengths. Tap rules in generalĮlectrical installers are typically involved with taps that are 10 ft or less in length or more than 10 ft but not exceeding 25 ft in length. This Section is where we find our tap rules that permit overload protection at the termination of the tap. The exception to this general rule of overcurrent protection at the point of supply is found in Sec. Section 240.21 requires that overcurrent protection shall be provided in each ungrounded conductor at the point the conductor receives its supply or generally at the starting point of the circuit. First and foremost, it’s important to recognize these rules do not apply to service conductors and other conductors that do not meet the definition of a feeder as outlined in Art. 240.21) continue to confuse many installers. Often used and frequently misapplied, the rules for tapping feeders (NEC Sec.
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