3 Prong Electrical outlet; basic understanding sought.

[ST]

I heard many times that the third bare grounded wire used in todays electrical outlet was added for safety purpose. <br /><br />Question 1: Can someone explain/elaborate how this safety is accomplished by adding the third wire? <br /><br />Question 2: I noticed that the neutral wire and this bare ground wire from the outlet were run in and connect to the neutral strip at the house electrical panel, and on to the Earth ground (or is it going back to the Utility Company?). Since both wires terminate at this same neutral strip, can they simply be connected together at the outlet?

 

[ndemge]

Re: 3 Prong Electrical outlet; basic understanding sought.

Taken from:<br /> http://electronics.howstuffworks.com/question110.htm <br /><br /><br />Let's say that a wire comes loose inside an ungrounded metal case, and the loose wire touches the metal case. If the loose wire is hot, then the metal case is now hot, and anyone who touches it will get a potentially fatal shock. With the case grounded, the electricity from the hot wire flows straight to ground, and this trips the fuse in the fuse box. Now the appliance won't work, but it won't kill you either. <br /><br />What happens if you cut off the ground prong or use a cheater plug so you can plug a three-prong appliance into a two-prong outlet? Nothing really -- the appliance will still operate. What you have done, however, is disable an important safety feature that protects you from electric shock if a wire comes loose.

 

[roscoe]

Re: 3 Prong Electrical outlet; basic understanding sought.

In addition to what NoelMG said, that loose "hot" wire will cause sparks, and a fire. If it grounds out and trips the breaker, the current stops and the sparks stop, usually before a fire can start.

 

[--GQ--]

Re: 3 Prong Electrical outlet; basic understanding sought.

Originally posted by ST:<br /> I heard many times that the third bare grounded wire used in todays electrical outlet was added for safety purpose. <br /><br />Question 1: Can someone explain/elaborate how this safety is accomplished by adding the third wire? <br /><br />Question 2: I noticed that the neutral wire and this bare ground wire from the outlet were run in and connect to the neutral strip at the house electrical panel, and on to the Earth ground (or is it going back to the Utility Company?). Since both wires terminate at this same neutral strip, can they simply be connected together at the outlet?

Answer # 1 <br />The bare wire connected to your outlet ground screw is to protect the person operating the equipment and not the equipment itself. It may also be green in color. Your power drill motor for example has metal (conductive) parts inside such as motor, gears, casing ect. which are bonded to the ground wire of the cord. When a short does occure, current will travel straight thru the ground wire back to the panel causing an overlaod beyond the breaker rating and will trip instantly. The drill motor may be a goner, but YOU will live to do it again. <br /><br />Note: A bare or green wire is a "GROUND" wire and not a "grounded" wire as you stated. A ground wire can only be bare or green and has no current carrying potiential. A "GROUNDED" wire is when a wire is intentionally grounded. This may also be your neutral (white) wire which has a current carrying potiential. These terminologies are very important in three phase applications.<br /><br />Answer # 2<br /><br />The main ground wire( usually bare #6 awg minimun incased in metal jacket) connects the main water line to the ground rod and to the neutral lug inside the panel. A neutral (white) wire also connects to the same lug and feeds up to the transformer on top the utility pole where it connects to a "GROUND" wire grounded at the base of the pole. Naturally the neutral and the ground wires are connected to the same point, but they are by no mean serve the same purpose. "Knock on wood", a neutral wire has a current carrying potiential where a "ground" wire does not and NO you can not connect them together at an outlet or any point where a load is to be served.<br /><br />Explaination: You and buddy "Joe" were to rewire your house. Buddy "Joe" had too much uncle "jack" cough medicine the previous night and only half-minded accidently jigs the neutral (white) wire while jabbing it to the studs. Fast forward....drywall, paint,finish plates, done. You turn the breakers on and everything works. Girlfriend "Jane" plugs in the vac., "honey we don't have power"! You open up the plug to find a hot but no neutral. Being the clever person that you are, you use the "ground" wire as a neutral. Girlfriend "Jane" turns vac. back on and off she goes. Meanwhile buddy "joe" opens the panel because he forgot to land the outdoor pool heater circuit. To access the screw behind it, he loosen the screw holding the "ground" wire circuit connecting to the vac. girlfriend "Jane" is using. Buddy "Joe" got a little jiggle. Girlfriend "jane" jump outside to find buddy "Joe" doing a jumping jack. You scratch your head.<br /><br />The "ground" wire is now a hot wire as long as the vac. switch in ON.<br /><br />Legal disclaimer: Names/events similiar to actual persons/situation is purely coincidental.

 

[ST]

Re: 3 Prong Electrical outlet; basic understanding sought.

NoelMG, roscoe and GQ,<br />Thanks to all of you guys for taking the time to answer the questions! <br /><br />GQ, your explanation with the characters Joe, Jane and me is quite hilarious; now I can say that I have a better understanding of why the ground wire is NOT to be connected to the neutral at the socket-even though they are electrically having the same potential.<br /><br /> This has always been bothering me; if they are having the same potential, why bother the expense/trouble to run another wire to the electrical panel? I knew there is an explanation to this; and your sample story above really explained of how an accident could happen if don't follow the code. I guess-for me-the key point is that the neutral is carrying the current, but not the green wire normaly-as you have stated above.<br /><br />Since the Neutral is buried at the base of the pole, I am correct to assume that the Earth (ground) is also being used to carry the electrons by the Power Utility companies?

 

[ndemge]

Re: 3 Prong Electrical outlet; basic understanding sought.

ST... I understand this better myself now.<br /><br />Now makes sense why subpanels need to have isolated ground/neutral, even though as stated, they go back to the same place.

 

[levittownnick]

Re: 3 Prong Electrical outlet; basic understanding sought.

The "GROUND" wire Must always be Green or Bare. This is so it is always positivitly identifiable. The "GroundED" wire is White which is a current carrying wire just as the (Hot) Black or Red are current carring wires.<br />Sometimes the White wire is used as a "Hot" or "Switched Hot" wire, therefore it cannot be counted on to be at or near ground potential. In older wiring the white wire can become darkened to the point that it is hard to tell the color. In other circumstances for whatever reason the hot and white get cross connected where the white is now Hot and the Black is return.<br />The Ground (Green or Bare) is never permitted to be switched. Some safety devices such as GFCI's switch both hot and neutral so that if the Hot and Neutral were crossed, when the safety tripped, it would be sure to open the hot wire.<br /><br />Consider what would happen if the white wire were used as a substitute Ground and at some point the white got crossed with the hot. When a grounded device was plugged into the outlet, the case of the "Grounded" device is now LIVE and there is no means for a GFCI to remove the Hot connection from the case. In an actual event this happened and a person was ELECTROCUTED. His family is without a father for his young children, and his wife is devistated.

 

[18rabbit]

Re: 3 Prong Electrical outlet; basic understanding sought.

If you look around your house you will see a pattern concerning appliances with two prongs and appliances with three prongs. Anything used in or near water (washing machines, water pumps, etc) has three prongs. Anything with a conductive (metal) cover or case (refrigerator, etc) has three prongs. Any ‘office’ equipment (computers, printers, shredders, etc) has three prongs. Home and shop appliances with nonconductive covers (plastic, rubber, etc) often have two prongs (vacuum cleaners, toasters, etc). Every once in a while you will find an appliance with a conductive cover that has two prongs (electric razors, etc). Those appliances have the cover isolated from the electrical/electronics inside; often the cover is screwed to a plastic chassis that holds everything together. So although it is conductive, the cover is isolated. Also, for appliances that are normally used in a bathroom, the cover is non-conductive or isolated, and a GFCI is on a two-prong plug (curling iron, blow dryer, etc).

 

[levittownnick]

Re: 3 Prong Electrical outlet; basic understanding sought.

This is a repeat of part of my previous post because I think it deserves the attention. If you don't like it please yell at me.<br /><br />The Ground (Green or Bare) is never permitted to be switched. Some safety devices such as GFCI's switch both hot and neutral so that if the Hot and Neutral were crossed, when the safety tripped, it would be sure to open the hot wire.<br /><br />Consider what would happen if the white wire were used as a substitute Ground and at some point the white got crossed with the hot. When a grounded device was plugged into the outlet, the case of the "Grounded" device is now LIVE and there is no means for a GFCI to remove the Hot connection from the case.<br /><br />In an actual event this happened and a person was ELECTROCUTED. His family is without a father for his young children, and his wife is devistated.

 

[tashasdaddy]

Re: 3 Prong Electrical outlet; basic understanding sought.

this subject has gotten so hot in Fla. with the use of pvc and other nonconductive material, we are now required to use 2 8ft grounding rods atlest 15 ft apart to ground our panels. no grounding to pipes. even phone and cable. all the news water and sewer supplies and plastic.

 

[Mark42]

Re: 3 Prong Electrical outlet; basic understanding sought.

I installed a "whole house" water filter in the water line before it split for hot/cold. Afterwards I was looking at it and realized that something was wrong. The copper pipe had a ground strap connecting it to a grounding rod outside. But I just cut the pipe and put in a plastic filter housing. That cut off the ground rod from the rest of the house!!! I guess everything still worked because of the ground going back to the utility pole from the service pannel. I added a jumper wire around the water filter anyway. <br /><br />Just something to think about when doing plumbing.