After a kitchen remodel, my 1650 W microwave was plugged into a dedicated outlet connected to a 120/240 v circuit breaker(not tandem). Another circuit with four kitchen outlets is connected to the same breaker. My question is whether either circuit will ever be exposed to the full potential 240 volts, or whether the circuits are necessarily limited to 120 volts because they are separate. After only a few days, the microwave plugged into the dedicated line died. I am wondering if this is because it was exposed to the higher voltage or some other reason. A label in the machine says it should never be used on a circuit with more than 120 volts. Do I need to get the electrician to make changes or did the microwave die of natural causes?
Electrical – What happens when two separate circuits are connected to a 120/240v breaker
circuit breakerelectricalkitchens
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It sounds like you may be mistaken as to how this is wired, or that perhaps I'm just not understanding your explanation. As others have mentioned, it's not possible to get 240 volts from a single pole in a 120/240V split phase system. Each tandem breaker provides 2 120 V circuits, this is true. However, if you measure between the terminals on a single tandem breaker, you'll get 0 volts. This is because the terminals are both powered from the same leg, and so are at the same voltage potential. If you measure from a terminal on the top tandem breaker to a terminal on the bottom one, then you'll measure 240 volts. This is because each breaker is connected to a different leg, which are each one half of a 240 volt circuit.
With all that said. For this setup to work, one appliance would have to be connected to both breaker. Something like this...
Notice that each appliance circuit has one wire connected to each of the tandem breakers. In this situation, you'd need a device like Speedy Petey shows.
Which ties the breaker handles together, to provide common trip characteristics.
Notice how the inner handles are tied together, and that the outer handles are also tied to each other. This way if either trip (or are turned off by the user), the entire circuit is shut off.
If this is wired the way you've explained, where the dryer is connected to the top tandem and the heater is connected to the bottom. Then there's some magic going on in those breakers.
It's referring to the electrical service supplying the house. Most homes in the US are supplied by a single phase service, which is often described as a 120/240 Volt system. If your house is supplied by a three phase system, it could be a 120/208 Volt system.
In both these cases you'll be able to install the equipment you have.
NEMA 14 devices are four wire grounding devices. Which means they'll require two ungrounded "hot" conductors (X,Y), one grounded "neutral" conductor (W), and one grounding conductor (G). When installed on a single phase 120/240 volt circuit, NEMA 14 devices can supply 120 and/or 240 volt loads. A NEMA 14-30 device is designed to supply 30 ampere equipment.
The circuit will require a 30 ampere double pole breaker, and four at least 10 AWG copper conductors. You'll connect one ungrounded "hot" conductor to each of the X and Y terminals. The grounded "neutral" conductor goes to the W terminal. And the grounding conductor connects to the G terminal.
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Best Answer
A two pole breaker can be used to create a multi-wire branch circuit. It should have a 3 wire cable with a bare ground. The two hot legs would have 240 volts between them and each will have 120 volts to the neutral.
If the neutral has a bad connection toward the origin of the circuit it is possible to get strange voltages as the loads are now in series with each other between the two hot legs. So you are splitting 240 volts between the loads if the neutral is disconnected. For instance, this could cause the microwave or other loads to have 180 volts while the other loads have 60 volts. This could cause damage to your appliances.
Have the voltage on the wiring checked and have it checked for bad connections before using it any more.
Good luck!