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
Each pole of a breaker, single, double or triple, provides the amperage
marked on the breaker. Double pole 20 amp gives you 20 amps on each legs or
20 amps @240 volts
I too, would like the ground wires to be insulated for my own safety
On Mon, 12 Jun 2006 07:09:40 -0400, "RBM" <rbm2(remove
Ground Wires 'do not' carry current except under ground fault
conditions. In that case, the breaker/fuse will break the circuit
So it normally carries 0 voltage, 0 current.
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.
hth, (please ignore spelling errors)
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
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.
"I really think Canada should get over to Iraq as quickly as possible"
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
Doug Miller (alphageek at milmac dot com)
On Mon, 12 Jun 2006 11:46:52 GMT, email@example.com (Doug Miller)
That's one thing people often do not understand. If you have a 100A
service and only use 120V items in the house, you can actually draw
200A. But if you have all 240V appliances, you can only use 100A. Of
course most homes have both, so that's where the mathematics comes
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
On Mon, 12 Jun 2006 08:34:35 -0500, snipped-for-privacy@UNLISTED.com wrote:
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.
Look at it this way: If I hang ten 12V lamps in series across a 120V
line, and each lamp is 120 watts, am I pulling a total of 100 amps?
I am not! I am drawing ten amps! Each lamp gets 12V at 10A. 100A
doesn't ever flow, anywhere in the circuit. But I'm still consuming
1200W: 120V at 10A, _NOT_ 12V at 100A. If the lamps were in
parallel, they would require 100A at 12V. But they're not. That's a
load calculation only.
An Edison circuit is just a 240 volt circuit with a grounded
center-tap. In theory, if loads are balanced, the neutral drops out
of the circuit, as the individial loads become a series-parallel
voltage divider network. Each load receives 120V at its rated =power=.
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