240v schematic diagram 3

[drogones12]

hi,

For a complete circuit, how does 2 hot legs supply a load with 240v without a neutral wire on the schematic diagram? Do electrons come in from one hot leg then go out the other hot leg? how does it apply in the resident home setting? all input will be greatly appreciated.

 

[davidbeach]

What purpose would a neutral serve if the load needs to 240V and you're supplying it with 240V?

 

[dpc]

This is ac. The electrons go nowhere very slowly. What matters is the voltage between the two conductors. A "hot" conductor is just one that is not grounded. The two "hot" conductors are NOT at the same voltage just because they are both called "hot".

 

[MikeHalloran]

It's AC; the voltage on each leg is constantly changing. When one leg is at +120V, the other leg is at -120V, relative to ground, because they both come from a center-tapped transformer on the pole outside the house. The center tap of that transformer is grounded.

Inside the house, within the fusebox, the two hot wires feed separate buses. The third, bare bus within the fusebox is where all the house's neutrals are tied together, and is the one point where the neutrals are also tied to a ground, usually a short bare wire attached to an actual metallic rod in the ground.

120V appliances connect to one of the hot wires and to the neutral bus. Within those appliances, electrons come in on the hot wire and leave on the neutral wire. Then they come in on the neutral wire and leave on the hot wire. Because the neutral is forced to (near) ground potential by the bus tie within the fuse box, it's only necessary to break the hot wire to render an appliance safe.

240V appliances connect to both hot wires. Electrons come in on one hot wire and leave on the other, just as you describe. Then the current turns around, and the cycle repeats. Because both hot wires are 'hot', not near ground potential, it is necessary to break both hot wires to render the appliance safe. That's why 240V breakers have two poles.

Safe, in the context noted above, is a relative term. If a circuit is damaged in such a way that a hot wire connects to the appliance frame, that's when the ground wires get involved, and force the frame voltage to near ground. This usually forces a breaker to open and remove the voltage from the hot wire.

All of the above applies to the USA, Canada, and some other places in the world. In Europe, there's no neutral wire at the appliance; everything is 240V, or at least not 120V.


The above is offered without warranty, and is my current misunderstanding of how USA house wiring works.



Mike Halloran
Pembroke Pines, FL, USA

 

[zeusfaber]

Minor correction to Mike's otherwise good explanation: In Europe, we don't do centre-tapped. You get a 230V ac live (± about 10V) and a neutral that is connected to earth at the supplier's transformer.

That means that you do still get a neutral at the appliance - but you don't get the same choice over voltages.

A.

 

[condern1]

The wiring required to get the 240 v would be 3wire conductor which is a black red and white wire with a ground. You will need to know the amp rating of what will be conneted to it for you to choose the right gauge wire. The probability will be that you will be using 12 gauge wire. You need to know what the wattages of the stuff your putting on the circuit to determine that.

 

[MacGyverS2000]

3-wire (red, black, and white + ground) is only required when switched circuits are involved... 240 in the home is quite easily had with standard 2-wire (black and white + ground).

Dan - Owner

http://www.Hi-TecDesigns.com

 

[MacGyverS2000]

Switched circuits OR two different 120V circuits... sorry, should have clarified.

Dan - Owner

http://www.Hi-TecDesigns.com