ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
twh 10
Admin 4
Recent Posts
Windows 10, who's upgraded?
by geoff in UK. 05/29/17 01:05 PM
How do you find a good employee?
by ElectricianBud. 05/27/17 10:58 AM
Recall notice: Bosch Solar panels
by ElectricianBud. 05/27/17 10:53 AM
Correct rotation, wrong sequence
by Potseal. 05/27/17 12:15 AM
Dryer, Range grounding from "Main" panel
by sparkync. 05/25/17 05:49 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
237,001 Are you busy
172,018 Re: Forum
164,894 Need opinion
Who's Online Now
0 registered members (), 46 guests, and 9 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#22935 - 03/08/03 02:10 AM 240 volt question  
Eandrew  Offline
Member
Joined: May 2002
Posts: 68
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.


Work Gear for Electricians and the Trades

#22936 - 03/08/03 02:43 AM Re: 240 volt question  
elecbob  Offline
Member
Joined: Aug 2002
Posts: 141
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).


#22937 - 03/08/03 09:45 AM Re: 240 volt question  
russ m  Offline
Member
Joined: Feb 2003
Posts: 169
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).]


#22938 - 03/08/03 10:20 AM Re: 240 volt question  
Len_B  Offline
Member
Joined: Jan 2003
Posts: 53
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.


#22939 - 03/08/03 01:53 PM Re: 240 volt question  
Eandrew  Offline
Member
Joined: May 2002
Posts: 68
seattle, wa, usa
thanks very much for your replys. That questions been on my mind for some time. thanks again!



Member Spotlight
Bill Addiss
Bill Addiss
NY, USA
Posts: 3,878
Joined: October 2000
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.010s Queries: 14 (0.002s) Memory: 0.7697 MB (Peak: 0.9054 MB) Zlib enabled. Server Time: 2017-05-30 07:15:33 UTC