ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
Recent Posts
VFD MotorFeeders
by gfretwell. 10/17/17 10:01 PM
What do you do?
by gfretwell. 10/17/17 01:08 AM
Good ol' copper pipe in the fuse holder trick
by HotLine1. 10/16/17 07:16 PM
Generator Cable Sizing
by HotLine1. 10/16/17 07:13 PM
Another generator question
by HotLine1. 10/16/17 07:02 PM
New in the Gallery:
Gallery Test
Popular Topics(Views)
241,352 Are you busy
177,303 Re: Forum
168,928 Need opinion
Who's Online Now
0 registered members (), 53 guests, and 10 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
renosteinke
renosteinke
Blue Collar Country
Posts: 5,316
Joined: January 2005
Show All Member Profiles 
Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.014s Queries: 14 (0.002s) Memory: 0.7695 MB (Peak: 0.9049 MB) Zlib enabled. Server Time: 2017-10-18 07:09:30 UTC