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#672 - 02/27/01 03:50 PM why doesn't a 240V circuit require a neutral?  
Boscodog  Offline
Member
Joined: Feb 2001
Posts: 13
Massachusetts
Hi guys! I'm not an electrician. I'm just a Joe homeowner who has developed an interest in wiring and I've got a question that I hope someone will help me with. All of the 'how to' books that I've read so far just state that a 240V single phase branch circuit doesn't use a neutral. Well, why is that? How does the current return? Thanks for your patience.


Work Gear for Electricians and the Trades

#673 - 02/27/01 05:59 PM Re: why doesn't a 240V circuit require a neutral?  
sparky66wv  Offline
Member
Joined: Nov 2000
Posts: 2,236
West Virginia
Boscodog,

First, technically, there is no neutral in a single phase system. The white (or natural grey) wire is called the "grounded conductor". This is not to be confused with the "ground" (green or bare wire) which is called the "equipment grounding conductor".

In a 120/240 Volt Single Phase system, the transformer secondary coil is "center tapped" to ground which defines the grounding conductor's voltage as "zero". The right and left extremes of the secondary coil are the taps for each 120 Volt leg. Voltage from either the right or left tap to the grounded center tap will be 120 Volts or thereabouts. But the voltage between the left and right taps are 240 Volts, not involving the grounded conductor at all.

Some circuits are considered 120/240 Volt. Your Dryer, Range, and the service for your house fit this description. These contain a grounded conductor as well as two hot conductors. This is to provide a grounded conductor for motors, timers and buzzers that operate at 120 Volts. Usually the heating element is the only 240 V draw on a dryer. Water heaters only require a "straight" 240 Volt circuit.

All circuits require equipment grounding conductors! (In residential, anyway...)

I'm kind of going out on a limb here...
Correct me if I'm wrong guys...

The current flows towards the load in both wires regardless of the type of circuit, straight 240V or a 120V to ground. The voltage alternates at 60 hertz, but the current flow still goes in one direction.

Okay, what about DC? The voltage may be - and + but the current still flows from both wires towards the load. The voltage gives the impression that the flow is circular, like a chain on a bike. This is not the case from what I am to understand.

I hope this makes it all clear as mud.

Please get yourself a copy of the National Electrical Code 1999 NFPA 70 if your serious in dabbling with electricity. It is not a "how to" manual, but you should make yourself familiar with it.

Other sources of info are here in the Electrical Contractor Network, and you can visit my site at http://www.kellyelectric.electrical-contractor.net for some tips for the homeowner.

Good luck and feel free to post questions anytime. If you have any doubts about something, don't hesitate to ask one of us here!


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

#674 - 02/27/01 06:06 PM Re: why doesn't a 240V circuit require a neutral?  
Mike  Offline
Member
Joined: Feb 2001
Posts: 62
Electrical current needs a path in order to work. A neutral provides a path in 120 volt circuits. Two hots, 240 volts, provide a path because the voltage/current alternates from positive to negative. The current flows toward the load during the positive cycle and flows away from the load during the negative cycle.

Quote
Originally posted by Boscodog:
Hi guys! I'm not an electrician. I'm just a Joe homeowner who has developed an interest in wiring and I've got a question that I hope someone will help me with. All of the 'how to' books that I've read so far just state that a 240V single phase branch circuit doesn't use a neutral. Well, why is that? How does the current return? Thanks for your patience.


#675 - 02/27/01 08:39 PM Re: why doesn't a 240V circuit require a neutral?  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
This item is very simple.

A single phase transformer, such as the ones commonly used for Residential areas, is nothing more than a 240 volt 2 wire secondary, with a center tap. Center tap is 1/2 of the winding. The center tap is where the "Neutral" conductor is connected [and is the first point of earth grounding]. This makes the secondary a 240/120 VAC 1 phase 3 wire system.

240 VAC circuits do not use the center tapped "Neutral", they only use the end terminations of the transformer's coil.

A 3 wire DC system works exactly the same way, except there is no transformer. The center tap is between two batteries [or cells] wired in series.

Center tapped secondaries can also be from split coil transformers. In this case, it is tapped imto the X2 - X3 jumper. It works exactly the same way.

There is an extensive discussion on this stuff in this forum, dating back around September, 2000. Look for an Archived thread named something like "How would you describe a neutral".

Note: The grounded common conductor on a 3 phase 4 wire Wye system doesn't always work the same as the 1 phase 3 wire grounded neutral conductor. It very rarely carries unbalanced current levels.


Scott.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#676 - 02/27/01 10:47 PM Re: why doesn't a 240V circuit require a neutral?  
Boscodog  Offline
Member
Joined: Feb 2001
Posts: 13
Massachusetts
Thanks to all for the prompt replies! I have to admit I still don't quite 'get' it, but I will ... some day ... 'cause I'm a plugger. [Linked Image] I'll be popping in every now and then. Thanks again. Later.


#677 - 02/28/01 10:03 AM Re: why doesn't a 240V circuit require a neutral?  
sparky66wv  Offline
Member
Joined: Nov 2000
Posts: 2,236
West Virginia
Quote
Originally posted by Mike:
Electrical current needs a path in order to work. A neutral provides a path in 120 volt circuits. Two hots, 240 volts, provide a path because the voltage/current alternates from positive to negative. The current flows toward the load during the positive cycle and flows away from the load during the negative cycle.



If current flowed in a circle, and went towards the line on the "neutral" side, we'd have very cheap electric bills indeed...This is NOT the case from what I am to understand... Please someone (Bill? Tom? Don?) exlain to me and others if this is true or not...Didn't I read this on this site somewhere having to do with common misconceptions about electricity?

Or am I just going nuts?


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

#678 - 02/28/01 10:24 AM Re: why doesn't a 240V circuit require a neutral?  
sparky66wv  Offline
Member
Joined: Nov 2000
Posts: 2,236
West Virginia
Here it is by God...

Go to http://licensedelectricians.net/ESF/Why%20Electricity%20is%20Impossible%20to%20Understand.htm#miscon

...mistaken belief that "electricity" travels one way, from source to
load, and at the same time it travels in a circle and returns to the source.

So which one is it? It can't do both...


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

#679 - 02/28/01 11:13 AM Re: why doesn't a 240V circuit require a neutral?  
Boscodog  Offline
Member
Joined: Feb 2001
Posts: 13
Massachusetts
No wonder I'm confused. I just read that stuff by Bill Beaty and discovered that I have just about every misconception known to man! My brain is feeling torqued right now. [Linked Image]


#680 - 02/28/01 01:22 PM Re: why doesn't a 240V circuit require a neutral?  
Mike  Offline
Member
Joined: Feb 2001
Posts: 62
Well!? Guess I throw-out most of what I learned in trade school about electical theory after reading Mr.Beatty's "misconceptions about electricity." [Linked Image]


#681 - 02/28/01 03:32 PM Re: why doesn't a 240V circuit require a neutral?  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,875
NY, USA
'66,

I think We need another thread for this one. I'm starting one titled How does Electricity flow?
http://electrical-contractor.net/ubb/Forum1/HTML/000103.html

Bill



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