What Is a Double-Pole Circuit Breaker?

Double pole breakers feature two circuit breakers with one switch, and the main point is the single mechanical connection. A double-pole breaker feeds a 240-volt circuit and ensures that there is an opening of both hot wires, which is what differentiates an appliance that provides protection for the device with one that has half of the circuit still active.

Let us explain the working of double pole breakers where it is applicable and provide answers to the two questions that pop up each time when someone tries to use one of the two poles of the double pole breaker.

In brief, a double-pole circuit breaker provides connection to two busbars in the panel and delivers voltage of 240 volts across two terminals of its output. It trips both poles together owing to a common internal connecting link. Its applications include dryers, heaters, ranges, air conditioners, EV chargers, well pumps, and sub-distributors. You cannot use any of the poles independently and peddle a tandem breaker instead.

Where the 240 V Comes From

One unique aspect of the residential power supply in North America is that it consists of split phase. A center-tapped transformer provides two 120V wires that are 180 degrees out of phase. Each of these wires can be measured against the center tap, which acts as the neutral point, providing a voltage of 120V.

Increased current capacity is delivered through a single pole breaker connected to one of the wires, while the double pole breaker connects both the wires. The double pole breaker provides two terminals at 240V to the load.

The two machines follow the same design and function in a similar manner. They use a common trip bar and the same switch handle for operation.That assembly is visible in a two-pole miniature circuit breaker, including the internal link that makes the poles open together rather than in sequence.

Common Trip, and Why It Is Not Optional

Let’s say a 240 V dryer experiences a malfunction in one of its legs. If the circuit breaker stops only this leg of the dryer from functioning, the other leg remains in operation and the heating unit still receives 120 V power through the rest of the wiring. Therefore, anyone who touches the component of the dryer is in contact with a voltage-carrying wire that the breaker shows is switched off.

The common tripping function makes it impossible to get the above-mentioned condition. As soon as one leg of the circuit is turned off, the other leg is switched off as well, which means the circuit is completely off. Double-pole circuit breakers are made as one item, not as two single pole ones tied together, which is why almost all electricity inspectors disapprove of this approach.

Single-Pole, Double-Pole and Tandem

The single-pole device at the top of that table is the everyday item, and its construction is shown in this single-pole 32 to 63 A MCB. The confusion arises because a tandem and a double-pole are both wider than a single and both have two poles inside. Only one of them delivers 240 V.

Can You Use Just One Pole?

In terms of operation, one of the poles will be connected, while the other pole will be not in use, connecting a circuit to 120 volts. However, this is fundamentally wrong for three reasons.

First of all, the use of the device will take two positions instead of one, wasting space in an already crowded panel. The second pole is still connected to a powered busbar and has terminals under (the same) voltage, which creates a hazard for the next users. Finally, the circuit loses the main advantage of two-pole devices over single-pole devices, meaning that it gets none, as one pole wired left the second pole without any useful function.

Different models do exist, with two-pole devices having just one electrically active pole; however, these are official design products, rather than using two poles with one in the circuit. If you need to know whether a device switches the neutral or protects it, the marking on the front tells you, and our breaker FAQ explains the notation.

When a Double-Pole Breaker Is Required

Five home appliances consist of the majority of activity.

• Dryer and stove, rated 30 A and 40 to 50 A respectively with copper wire sizes of 10 AWG and 8 AWG.
• Hot water heater that is generally rated 30 A as the largest component in daily routine.
• The air conditioning or heat pump is designed to work under minimum possible electric load.
• Electric car charger unit rated from 40 to 60 A with continuous load of 32 to 48 A.
• Feeder to support subpanel installation with two-pole breaker rated at electric panel.

Subpanel case demonstrates the situation when making the right choice has most of the implications due to its impact on the rest of the devices. A 125 A two-pole device feeding a subpanel is a common arrangement, and the pole count, the rating and the breaking capacity all have to match the feeder and the available fault current.

Sizing and the Two Numbers on the Nameplate

Electrically operated equipment has a minimum circuit ampacity rating and also a maximum breaker size rating and both need looking separately. For example, a 3-ton air conditioner may show minimum circuit ampacity of 19.6 A and maximum breaker rating of 30 A. The wire size is selected according to the first value and the breaker size according to the second one. If a 20 A breaker is used based on the load of 19.6 A, nuisance tripping may happen and if a 40 A breaker is fitted based on perceived low rating of 30 A, the protection will be de-rated accordingly.

In all other cases the chain is load calculation – conductor ampacity – breaker size. The reason is that the breaker is made to protect the wire, so wire size is what decides the device used and not vice versa. For example, in the case of a 30 A device 10 AWG wire is needed, with 40 A making use of 8 AWG wire, while 50 A loads require 6 AWG wire.

With continuous load set to be 125% of running load current, this means that an electric vehicle charger with 40 A capacity will have a circuit of size 50 A, which is the reason why devices rated at 48 A and 40 A will work on 60 A and 50 A circuit breakers respectively.

GFCI and AFCI in Double-Pole Form

The 240 V outdoor or wet equipment does have 2 pole GFCI devices such as equipment for hot tubs, equipment for pools, outdoor air conditioning unit, and for some regions, 240 V plug sockets in garages. The cost for installation of such a device is fairly high and they are big in size as compare to the traditional counterparts which may create space issues in the panel.

The purpose of 2 pole AFCI is mostly to be installed in 240 V sub-circuits and feeder circuits where required. AFCI activation occurs mainly for 120 V circuits in homes, which leads to popularity of one pole AFCI device over the limited use of the two pole device.

The regulation specifying that the AFCI needs to be installed with any circuit does not affect the compliance of the regulation due to the fact that the new AFCI device can replace the old breaker. That is a conversation to have before the part is ordered, and our technical team will check the application rather than ship the cheapest equivalent.

FAQ

Why would I need a double pole breaker?

In situations where 240 V is required in case of the following devices to operate: a dryer, cooktops, hot water heating, air conditioning, electric vehicle charger, well pumping, or distribution board power supply. It has also a common trip functionality, as a result of which both conductors get de-energized simultaneously.

Can you use just one pole on a double pole breaker?

It will work, but it occupies space, has a functioning, unconnected pole, and does not provide any benefits compared to a single-pole setup. It cannot be considered a standard installation and it is not something a qualified electrical technician would intentionally fit.

Are all 240V breakers double pole?

In a residential panel, indeed. A circuit that works with 240 V is required to have two poles of electricity. A quad circuit has four poles; however, it still functions as a double-pole in itself.

What’s the difference between a single pole and a double pole circuit breaker?

A single circuit breaker includes a single pole, while a double circuit breaker involves two poles and thus gives twice the current.

References

• NEMA — Circuit Breaker Configurations and Ratings
• Cerrowire — Conductor Ampacity for 240 V Circuits
• This Old House — 240 V Appliance Circuits
• Bob Vila — Double-Pole Breaker Basics
• U.S. Department of Energy — Appliance and Load Planning

Conclusion

A double pole circuit breaker is a 240 volt breaker that has a common trip and each half is important. Make the size of the breaker appropriate for the conductor, circuit breaker panel series, and don’t subdivide the circuit to make 120 volt circuit breakers.

Send us the appliance rating plate or feeder size and we will verify the pole configuration, rating and breaking capacity in one step.