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Re: [Amps] what is a 4 wire 240VAC service

To: amps@contesting.com
Subject: Re: [Amps] what is a 4 wire 240VAC service
From: Paul Decker <kg7hf@comcast.net>
Date: Mon, 4 Apr 2011 13:16:08 +0000 (UTC)
List-post: <amps@contesting.com">mailto:amps@contesting.com>

Great post Lee ! 



You could go one step further though.  I believe there is a case where the 
ground wire is used which you might provide some details on.  i.e.  think 
Grould Fault Circuit Interrupt. 



73, 

Paul (kg7hf) 









Date: Sun, 3 Apr 2011 16:12:46 -0500 
From: "Its from KE4VYN" <ke4vyn@msn.com> 
Subject: Re: [Amps] what is a 4 wire 240VAC service? 
To: <amps@contesting.com> 
Message-ID: <SNT104-DS59F11A820C6220713FAFE9EA00@phx.gbl> 
Content-Type: text/plain;        charset="Windows-1252" 



To understand how a 240/220 volt household circuit works you should first know 
a little bit about how a regular 120/110 volt circuit works. If you are at all 
familiar with residential electrical wiring then you probably already know that 
in most cases appliances, and fixtures connect to three wires: 


1) A black wire which is often known as the "hot" wire, which carries the 
current in to the fixture. 
2) A white wire called the neutral which completes the electrical circuit. 
3) A bare copper wire called the ground, the sole function of which is to 
enhance user safety. 

  

When the circuit is in use current is energized through the fixture by way of 
the "hot" wire and then to ground by way of the neutral, and unless something 
goes wrong the bare ground wire doesn't do anything except to remain ever 
vigilant in case of a problem. 

  

Now for 240/220 volt house current; Appliances that use straight 240 current 
also have three wires: 


1) A black wire which is often known as the "hot" wire, which carries the 
current in to the fixture. 
2) Another "hot" wire which may be blue, red or white (if it is white the code 
actually requires it to painted or otherwise marked one of the other colors, 
but often it is not) which also carries current in to the fixture. 
3) A bare copper wire called the ground, the sole function of which is to 
enhance user safety. 

  

That's it, no neutral. Now, if you are paying attention, then you are probably 
wondering "If there isn't a neutral wire then how is the circuit completed?" 
The answer is that when one hot wire is negative, then the other is positive, 
so the two hot wires complete the circuit together because they are "out of 
phase". This is why 240 volt circuits connect to double pole breakers that are 
essentially two single pole breakers tied together. In the main panel, every 
other breaker is out of phase with the adjoining breakers. So, in essence 240 
volt wiring is powered by 2 - 120 volt hot wires that are 180 degrees out of 
phase. 

  

I previously mentioned "straight" 240 volt appliances, but there is another 
class of 240 volt equipment; some appliances (such as clothes dryers and 
ranges) use 240 volt current to power their main function (drying clothes or 
cooking food) but use 120 volt current to power accessories such as the clock 
on your stove or the light inside the oven, or the digital readout on your 
dryer controls. That is why some 240 volt circuits have four wires: 


1) A black wire which is often known as the "hot" wire, which carries the 
current in to the fixture. 
2) Another "hot" wire which is red, which also carries current in to the 
fixture. 
3) A white wire called the neutral which completes the electrical circuit for 
the 120 volt accessories only. 
4) A bare copper wire called the ground, the sole function of which is to 
enhance user safety. 

  

At one time, the code allowed for one insulated wire to function as both ground 
and neutral in 120/240 volt combo circuits, but now all such circuits must use 
the 4 wire scheme. This is why your new dryer (or electric range) might have 4 
prongs on its plug and your old dryer receptacle only has 3 holes. 

In which case article 250.140 of the 2005 N.E.C. (National Electric Code) 
allows for the "pigtail" (the cord and plug assembly) to be changed to match 
the old 3 wire receptacle as long as certain conditions are met. The National 
Electric Code allows that, but your local code might not, so check first. 



73, 

Lee 

KE4VYN 



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