I understand that double pole circuit breakers feed 240v (two120's) to water heaters, stoves, ect...
But, Im confused about the amperage marking on the middle tab; I see that most say 30A. Does that mean the each pole from that circuit breaker can handle up to 30A each pole? 30 + 30 = 60A total? or is the amps on each hot leg split into two; 15 amps each pole; 15 + 15 = 30A? I never worked with 240V circuits before, obviosly. I just need to install a small baseboard heater in my shop for the upcoming winters; it calls for a 20A 240v breaker.
Another quick question, but off topic: Why don't wire manufactures insulate the bare ground wire inside romex cables?
Overcurrent protection is placed on the hot side of a circuit, so with
120V circuits, there is only a single pole breaker for the single hot.
On a 240V circuit, you get 120 volts (relative to the neutral) per hot (from separate legs). The current that goes through one returns through the other. Overcurrent protection is needed on BOTH hots and must be rated the same because it is the SAME current that passes through both.
Since the voltage is doubled, even though the current is the same, the POWER that can be provided by the circuit is doubled.
A neutral conductor is only needed on a 240V circuit if there are loads that require only 120V on the circuit. In those cases, the neutral will carry the DIFFERENCE between the current in each hot. (e.g.: if one hot had a current of 10A and the other had 9A, the neutral would be carrying the 1A difference).
Why bother? There is really no safety issue as it only serves to bond metal chassis and boxes to ground. It will carry a current in fault situations, but no greater than the overcurrent protection on the circuit.
However, in the case of those ORANGE outlets, the ground pin on the receptacle is ISOLATED from the bare ground that the box is bonded by. A separate INSULATED ground conductor is needed to bond the ground pin to the grounding bus in the panel. Often the red conductor of a 3-wire cable is used for this purpose.
Depends on how it's wired, actually. A double-pole breaker can provide one
240V circuit, or two 120V circuits. In your example, a 30A double-pole breaker will provide one 30A circuit at 240V, or two 30A circuits at 120V.
Because it would be pointless to do so. The grounding wire is intended to insure that the metal frames of equipment (e.g. a washing machine) and exposed metal components of the premises wiring (e.g. conduits or receptacle boxes) are grounded and cannot become live. In other words -- it's connected to things that are not insulated anyway, and thus no purpose would be served by insulating it.
Ground Wires 'do not' carry current except under ground fault conditions. In that case, the breaker/fuse will break the circuit asap(by design).
A ground fault is a leak to ground. It may or may not pass through the grounding conductor.
Breakers trip on excessive current regardless of the path that it takes. GFCIs trip on an unbalance between the two wires that compose the active circuit.
It makes no difference how balanced or unbalanced you have the system, you will not be pulling more than 24,000W at least not for more than a few min before the main breaker trips.
It could well be less than that number if you max out one leg first. You need to have the system balanced to reach the 24,000W load, but the total amount of power available from the service is 24,000W no matter what.
If a hot comes in contact with a metal casing, that is grounded, it is called a ground fault. Following the NEC all grounded equipment conductors (the ground wire) have to have as lose impedance to electricy back to the source.
So using ohms law E=IR
E is electrical potencial, or Voltage I is current R is resistance.
Solve for I (current) results in I = E/R
substitute numbers for lowest norm voltage. I = 120 / ~0
*Note: Used 0 since a small house has almost 0 ohms back to the panel on the ground wires.
So calc Current, and you have an almost infinite amount of current, a short, and the breaker will open on this ground.
A normal breaker should open on any ground fault over thier set points. Meaning a 15 amp breaker should open on any ground faults over 15 amps, on over current protection. Ofcourse an almost infinite current, should trip the breaker on short circuit protection.
Your total load calc may be 200 A at 120 V, but you are still pulling 100 amps. You've got two 120 volt loads in series, that's all. You are STILl pulling 100 amps at 240 volts. Since the individual loads are in series/parallel, they share half teh voltage, so the total load calc comes out to 200 amps, but only 100 amps are flowing through the service. Really.
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