Question about grounded outlets

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  #1  
Old 09-05-07, 06:27 PM
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Question about grounded outlets

Hey all,
we just bought a house, and not all the three prong outlets in the house are truly grounded. We have a microwave and a treadmill that we'd like to be able to use in spots where we don't have access to a grounded outlet, and because of the way the wall is set up, it'd be extremely expensive to have it properly grounded. I know this is bad to do, but how bad is it? Are we just risking killing the appliances (which wouldn't matter much)? Or are we risking housefire, or electrocution? I know it's technically a no-no, but I wonder since they actually sell those cheesy three prong to two prong adaptors, maybe it's not a huge risk? Can anyone shed some light for me? Thanks!
 
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  #2  
Old 09-05-07, 09:49 PM
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Grounding protects you from electrocution and protects the structure from fire. With a grounded circuit, if a wire comes loose for whatever reason and contacts the metal case on say your microwave, washer, dryer, fridge the circuit breaker pops and power is cut off pretty quickly (even faster if you have a GFCI outlet installed). In an ungrounded circuit, if a wire comes loose and touches the case of your appliance, it turns the whole thing into one big conductor attached to power just sitting there until someone touches it.

Sounds like someone either did a remodel and added some but not all new circuits or replaced 2 prong outlets with 3 prong ones without adding a ground. When was the house built? Replacing the 2 prong outlets with ungrounded 3 prong outlets gives a false sense of security and is illegal (at least where I live...So Cal). A ground is needed to properly change these over to grounded outlets and that means running new wire (unless the existing wire is installed in metal conduit and boxes, which is unlikely) and installation of ground rods or properly attaching to the cold water line.

I'm sure the pros can give you more detail on exactly what's required if you should choose to do this but it's pretty involved. I would suggest checking all the outlets with an outlet tester and changing the improperly converted outlets back to 2 prong ones.
 
  #3  
Old 09-05-07, 10:30 PM
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Thanks for the advice. I'll figure out somewhere else for the microwave and treadmill to go. The house is about 35-40 years old.

One other question that came up today is this. When the house was inspected, I was told the basement outlets were grounded. When I plugged in my own tester today, it showed as being correct, except the red light flickered a little bit. Then today, when I plugged in my surge protector with my TV and everything connected to it, the "grounded" light on the surge protector failed to light. Could this be a simple problem, like the ground is coming loose inside the outlet?
 
  #4  
Old 09-06-07, 04:22 AM
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Do not use any devices that come with a three wire cord and plug on an ungrounded receptacle unless the receptacle is GFCI protected (and then do so with caution).

No ground and no GFCI protection is asking for trouble and extremely dangerous.

Devices like a microwave, a computer a plasma television (devices containing electronics) need a ground to function properly. They may function without one, but you do so at your own risk. Using a GFCI will not provide a ground.

Devices like major appliances (washers, dryers, refrigerators, etc.) need a ground for safety. With these devices, an ungrounded GFCI will provide safety, but not as much as a properly grounded receptacle.

I strongly suggest that you investigate (do it yourself or bring in an electrician) ALL the circuits in your house.

I recommend that you change any ungrounded receptacle to be two prong, or properly ground them, or at the least provide GFCI protection and use the "No Equipment Ground" sticker.

As for your basement receptacles, the problem could be a loose ground, or it could be an improperly grounded receptacle. The only way to tell is to investigate.
 
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Old 09-06-07, 07:15 AM
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Thanks for all the advice. I'll have my outlets checked out. One other question...regarding that basement outlet. Although the surge protector is three prong, everything that is plugged into it is only two prong. If I'm understanding correctly, that shouldn't be a danger to use, correct? Outside of the surge protector maybe not functioning as it actually should, I'm not risking fire or electrocution, etc, by having it in a non-grounded outlet, correct?
 
  #6  
Old 09-06-07, 07:33 AM
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It depends.

If the basement receptacle is improperly grounded, such as the ground connected to the neutral (often called a bootleg ground), then using the surge protector will present a danger. The metal case of the surge protector will be connected to the neutral, and the neutral wires carried current.

If the ground wire is intermittent then using the surge protector for two prong devices will not create an unsafe situation.
 
  #7  
Old 09-06-07, 12:45 PM
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I've posted this before somewhere, just can't find it now, so here goes again.....

I used to lived in a duplex built in the early 50s. All outlets were two prong. Only the kitchen was grounded properly to the metal box. Turns out, ALL wiring was grounded and all of the grounds were nipped off inside the boxes. As I watched an electrician replace a non-working outlet in the basement, he installed a three prong, grabbed hold of the ground with pliers, got enough to strip the end and pigtail a short ground to the receptable. Tested properly! Eventually, everytime we moved furniture for any reason in any room, I replaced the receptables in the same manner. By the time we sold, everything was three-prong grounded.

So I'd say check your wiring inside the boxes to see of there is a ground there that just needs to be connected.

Tom
 
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Old 09-06-07, 07:54 PM
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Around my area, most old wiring is only 2 prong, however, it is wired in BX (wires inside flexible metal armored cable). The armored cable of the BX is a ground , just like metal conduit. Now most houses in the area are wired with BX, so I usually don't fear seeing a two prong receptacle. First step is to take the faceplate off and see if the metal box is grounded and kinda peek in the back looking for armored cable entering the box. If its there, all you have to do is connect a ground wire from the box to the new three prong outlet and your good to go! If the box isn't grounded you have to throw a GFCI there in order to use a three prong device.
 
  #9  
Old 09-06-07, 08:04 PM
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Sorry to burst Striders bubble, but all BX cable sheath is not listed for use as a grounding conductor.

Due to the length of the jacket and the quality of the wrap the sheath can heat up and cause fires due to its' high resistance. It may not trip the breaker.
 
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Old 09-07-07, 11:00 AM
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What exactly is bx made out of? I know that stuff is alot heavier then MC.
 
  #11  
Old 09-07-07, 11:29 AM
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Type AC cable had steel sheathing when it started out. I believe you can get steel or aluminum now.
 
  #12  
Old 09-07-07, 12:45 PM
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"Old" B.X. which is steel , and has a larger "mass" than "new" B.X. , IF properly clamped amd connected to boxes and enclosure, is a better Ground-path than "new" B.X.

The "bonding strip " in new B.X. is NOT a Grounding Conductor- it's to prevent a No-Ground condition if there's a break in the armor.

Let's experiment --- Heat-energy = X # of watts watts = power

power in a circuit = the square of the current X the resistance of the circuit

Ex -- 10 amps thru 10 ohms = 10 X10 X10 = 1000 watts of power

Connect in series 2 ft of armor from "old" B.X. , 2ft of armor from "new" B.X. , and 2ft of "bonding-strip" . Connect these 3 elements across a welder with a 100 amp output.

Which of these 3 elements will melt first because of the heating effect according to our formula ? Which one do you think will melt last ?

Does the element with the most resistance produce the most heat ?
 
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