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#22935 - 03/07/03 10:10 PM 240 volt question
Eandrew Offline
Member

Registered: 05/24/02
Posts: 69
Loc: seattle, wa, usa
I was always told that in order to have a neutral you must have two hot wires and the neutral carrys the unbalance current between them.

So, a 120 v.receptacle does not technically have a neutral, but rather a grounded conductor because there is not unbalanced current.

Would a balanced 240 load even have use for a neutral conductor? Any examples on 240 loads with a neutral and those without a neutal. ? If you have two hots (on 240) do you have to have a neutral. Is it just like in 3phase motor loads where if its a balanced load then you dont need the neutral unless there is some sort of timer etc.

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#22936 - 03/07/03 10:43 PM Re: 240 volt question
elecbob Offline
Member

Registered: 08/23/02
Posts: 142
Loc: WA
A 240 volt load such as a baseboard heater or a water heater would not have a neutral(current carrying grounded conductor). But a 120/240 volt load such as a dryer or a range would require a neutral(current carrying grounded conductor).

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#22937 - 03/08/03 05:45 AM Re: 240 volt question
russ m Offline
Member

Registered: 02/22/03
Posts: 165
Loc: Burbank,IL,USA
Bob, Looks right to me.

210.4. Multiwire Branch Circuits.
(a) General. Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire branch circuit shall be
permitted to be considered as multiple circuits. All conductors shall originate from the same panelboard.

(c) Line-to-Neutral Load. Multiwire branch circuits shall supply only line-to-neutral loads.
Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.
Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

Eandrew:
As far as your first question.
I think it would be easier to say two 110v circuits shareing a grounded conductor makes the grounded conductor a neutral.
If your asking if it is a neutral, once one circuit breaks in a different direction, and no longer is split between the two circuits, I guess it is.
It could be treated diffrent once it breaks off, as far as useing the receptacles as a splice device.

Russ

[This message has been edited by russ m (edited 03-08-2003).]

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#22938 - 03/08/03 06:20 AM Re: 240 volt question
Len_B Offline
Member

Registered: 01/19/03
Posts: 56
Loc: New Hampshire
 Quote:
So, a 120 v.receptacle does not technically have a neutral, but rather a grounded conductor because there is not unbalanced current.


Technically it does have a neutral. The "neutral" is a center tap on a transformer or generator winding. A "neutral" does not have to be bonded to earth for the circuit to work from an electrical standpoint. Bonding to earth creates the "grounded" conductor. If you removed the bonding jumper the circuit would still work.
The bonding to earth(grounding) of the "neutral" is done/required by NEC to (equally) limit the phase potential(voltage) to earth, and to provide a safe low resistance return path(through other conductive parts bonded to the grounding system) for fault current.

 Quote:
Would a balanced 240 load even have use for a neutral conductor?
If you have two hots (on 240) do you have to have a neutral. Is it just like in 3phase motor loads where if its a balanced load then you dont need the neutral unless there is some sort of timer etc.


All 240 volt single phase loads would only use the two ungrounded phase conductors.
Two balanced 120 volt loads of 10 amps each on opposite phase legs would result in the voltage at this load midpoint(neutral) to be zero in respect to the transformer center(neutral) tap. Hence no current would flow in this "neutral". Whether a "neutral" is required depends upon the equipment and the circuit design.
Two 10 ohm 120 volt rated loads could be connected in series in a 240 volt circuit. These devices would not know that the neutral conductor was missing. This is essentially what happens in a multiwire branch circuit when the loads are perfectly balanced(the imbalance is zero, there is no voltage from the load midpoint to transformer center, so the neutral current is zero)

The examples above assume purely resistive loads.

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#22939 - 03/08/03 09:53 AM Re: 240 volt question
Eandrew Offline
Member

Registered: 05/24/02
Posts: 69
Loc: seattle, wa, usa
thanks very much for your replys. That questions been on my mind for some time. thanks again!

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