![]() ![]() Following the requirements of Table 430.72(B), we use Column C. Going down the left-hand column of Table 430.52 to AC polyphase motors and then across to the right to inverse-time breakers, which we had indicated we were going to use, we find a rating of 250 percent permitted. Our motor is a 10 horsepower, 208V, alternating current (AC) polyphase type with a full-load current of 30.8A, as determined from Table 430.250. Table 430.52 shows the percentage of full-load current permitted for the rating. Our reference here is to 430.52(C), which shows the rating of motor branch-circuit short circuit and ground-fault protection devices intended to protect the motor branch-circuit conductors. In the January 2013 Code FAQs, under “Sizing conductors and overcurrent protection,” you write, “30.8 × 2.5 = 61.6.” Either this is wrong or you meant to size to 2.0. Therefore, the minimum conductor size is 10 AWG and the overcurrent protection or branch-circuit rating is either 25 or 30A. Although Table 310.16 shows a 12 AWG conductor as having an ampacity of 25A, the asterisk directs us to Section 240.4(D), where we find that a 12 AWG conductor is limited to 20A for our purposes. Based on the previous computation, 18.75 × 1.25 = 23.4A. Section 422.13 requires a water heater with a capacity of less than 120 gallons to be supplied by a branch circuit that has a rating of not less than 125 percent of the nameplate rating of the water heater. The arrangement of the thermostat in the heater will only permit one 4,500W element to be connected at one time. What size branch circuit do I need for this heater? The nameplate rating is 4,500 watts (W) for each of two elements. ![]() I have a 40-gallon water heater in a single-family dwelling. ![]() Short-circuit and ground-fault currents rise rapidly and will open the motor branch-circuit overload protective devices before any damage could occur. The coil circuit current is small, and overload is not a problem. The motor control circuit conductors are protected from physical damage by the raceway in which they are enclosed. Using the panelboard housing as a conductor is not permitted.Įxplain how, when using Column “C” in Table 430.72(b), they say a 60-ampere (A) overcurrent device can protect a 12 AWG copper control circuit conductor? NEC 250.24(4) permits the grounding electrode conductor to be connected to the ground bus in the panelboard if there is a wire from the ground bus to the neutral bus. Questions can be sent to Answers are based on the 2011 NEC.Ĭonnecting the grounding electrode conductorĭoes the grounding electrode conductor have to be connected to the neutral bus, or can it be connected to the ground bus? If you have a problem related to the National Electrical Code (NEC), are experiencing difficulty in understanding a Code requirement, or are wondering why or if such a requirement exists, ask Charlie, and he will let the Code decide. ![]()
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