Simple question: what’s the difference between a single pole circuit breaker and a double pole? Is it as simple as 120V vs. 240V?
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yes
Furthermore, sometimes you have to disconnect two circuits at once -- for instance on a split wired receptacle. So you could use a two pole braker or just use a handle tie.
~Peter
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120v versus 240v. But also the two are mechanically connected in such a manner that if either trips it trips the other. Using two single-pole breakers instead of a purpose built two-pole breaker eliminates the assurance that both sides will trip even if you use a handle link between the two breakers.
Purpose built, purchases, or field manufactured links are not a substitute for a real two-pole breaker. They are only acceptable for multiwire branch circuit where no yoke has both circuits.
No.
A single pole breaker interrupts current in one conductor, a double pole breaker interrupts current in two conductors.
There are two typical uses. In one case one pole is on one phase and the other pole is on the opposite phase. Current flows through one breaker, through the circuit, and back through the other breaker. Since the current is wired to flow in series through both, and they are on opposite phases, the circuit is a 240 volt circuit. In the other common use, the breakers are also on opposite phases, but current flows out through each breaker and back through a neutral conductor. This arrangement produces two 120 volt circuits.
In the other common use, the breakers are also on opposite phases, but current flows out through each breaker and back through a neutral conductor. This arrangement produces two 120 volt circuits."
Waynel,
Could you give an example of this "common" use. i.e. why?
Jon
.....in some areas, this setup cheaply and quickly fills the requirement for" two or more 20A small appliance circuits ......."IMO,rather ,cheesy.. but accepted nonetheless
Edited 12/4/2005 7:30 am by maddog3
Edited 12/4/2005 7:33 am by maddog3
What he is describing is a multi-wire circuit.And as MD mentioned kitchen small appliance circuits are on.Another common application is where you are running in conduit or pulling multiple NM in an rewire application where they would be bundled. You can get 2 multiwire circuit, equivalent to 4 120 circuits, in one conduit or bundle (for 15 & 20 amp circuits). It they where run as individual circuits the wire size would have to be uprated due to derating requirements.However, technically a multi-wire circuit does not require a double pole breaker unless any one device has the hot from both legs (ie, a 240 receptacle or split 120 v one). Two single pole breakers can be used, but a double pole is good practice.
> In the other common use, the breakers are also on opposite phases, but current flows out through each breaker and back through a neutral conductor. This arrangement produces two 120 volt circuits.
Close. What the neutral carries is the difference between the current in the two hots. If this ever gets re-arranged by someone who doesn't know about it, the hots could both get put on the same leg, and the neutral would see the sum of the two currents. That can be dangerous. The neutral can potentially get twice the current it's rated to carry.
-- J.S.
I simplified my explanation based on the way the original question was asked.
Yes, the neutral does indeed carry the sum of the currents. If properly wired on opposite phases one current is positive and the other negative with respect to ground so when they are added the resulting current is the difference is absolute value, and they do partially cancel each other out.