( 3 pole too but rarely a residential situation). Double pole breakers are required with a MWBC.Keep in mind there are a lot of Code requirements when adding new circuits. The installer would remove the 30A breaker and install a double pole 20A breaker and relabel the breaker to its corresponding loads. This is covered in the 2014 NEC 210.24 under the term tap conductors and it has very specific rules to follow.Īnother scenario is to take an unused 240/120 30A #10 4-wire ( two ungrounded hots + neutral + ground ) and turn it into a multi-wire branch circuit, MWBC for short. One common scenario is for a residence to have a 240/120 3-wire ( two ungrounded hots + 1 ground) unused range circuit feed two small 120V appliance circuits. The way I read your question was if an existing 240/120 was being unused, why is it not common to utilize it for two 120V branch circuits? Well, in fact it is common practice. There's no way to do it, besides a subpanel. Nope, the water heater's labeling and instructions require a 30A breaker. Okay, so hardwire both loads and use the 40A breaker. If hardwired loads provision more than 50% of circuit capacity, you can't have receptacles on that circuit. You can't put a 30A plug on a 40A breaker. That would require a 40A breaker, but now you have a problem. Let's say it doesn't require the 125% derate, so now you're putting 28.75 amps on one leg, and 31.75 amps on the other leg. In other words, the appliance uses all of the circuit's capacity, and is designed to do so. Code requires a 125% derate, which puts it at 28.75 amps, just enough to shimmy under the "30 amp" figure. Generally when you see a 2-pole 240V breaker dedicated to an appliance, the appliance is intentionally sized to use the entire circuit.
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