What is the maximum percent of unbalance load allowed for a feeder neutral with ungrounded feeder conductors in ranges, wall ovens, cooktops, and a clothes dryer?

What is the maximum percent of unbalance load allowed for a feeder neutral with ungrounded feeder conductors in ranges, wall ovens, cooktops, and a clothes dryer?

• A. 50%
• B. 90%
• C. 30%
• D. 70%

Answer: (D)

In a feeder that serves ungrounded two-hot conductors with a single shared neutral (a multiwire branch circuit), the neutral current is the difference between the currents on the two hot legs. Ranges, wall ovens, cooktops, and clothes dryers can have 120V loads inside that aren’t equally distributed between the legs, so some neutral current is expected. The NEC allows that unbalanced neutral current to be up to 70% of the ampacity of the feeder conductors. This limit protects the neutral from overheating while still letting you use a shared neutral efficiently. If more unbalance is anticipated, the neutral would need to be sized appropriately or provided with separate neutrals for certain loads. Therefore, the maximum percent of unbalance load allowed is 70%.

In a feeder that serves ungrounded two-hot conductors with a single shared neutral (a multiwire branch circuit), the neutral current is the difference between the currents on the two hot legs. Ranges, wall ovens, cooktops, and clothes dryers can have 120V loads inside that aren’t equally distributed between the legs, so some neutral current is expected. The NEC allows that unbalanced neutral current to be up to 70% of the ampacity of the feeder conductors. This limit protects the neutral from overheating while still letting you use a shared neutral efficiently. If more unbalance is anticipated, the neutral would need to be sized appropriately or provided with separate neutrals for certain loads. Therefore, the maximum percent of unbalance load allowed is 70%.