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ground question

4K views 30 replies 12 participants last post by  CowboyAndy 
#1 ·
my house has some old outlets with no ground. I want to know how dangerous this is and what I can do about it without tearing out my walls? I have recently had some power surges and the power company said their neutrals in the transformer were bad and replaced them. But I am still a little worried about my outlets.
 
#2 ·
most household appliances dont even have a 3 prong cord, so I would just install gfci receptacles if you do happen to need one somewhere... And unless your house is wired with knob and tube your boxes are grounded as long as the connections are tight all the way back to the panel.
 
#3 ·
most household appliances dont even have a 3 prong cord, so I would just install gfci receptacles if you do happen to need one somewhere... _-And unless your house is wired with knob and tube your boxes are grounded as long as the connections are tight all the way back to the panel.[/quote]

Chris, unless the OP house is wired in conduit, Greenfield, or romex that has a grounding conductor the boxes are not grounded. The best he can do in that case, without rewiring, is install GFCI receptacles.
 
#5 ·
there may or maynot be a ground present. at one time the ground would have been wrapped around the nonmetalic cable and clamped, or brought into the box and wrapped around the clamp screw. The best way to tell is with a tester.

OP take a cover plate off and test from hot side to metal box, if you have the same EXACT voltage as you do between hot and nuetral then adding a jumper in between the box and the ground screw on the new device would be exceptable, although splicing the exhisting ground to a pair of jumpers( one to the box and one to the device) would be better.

if there is no ground present or insufficient ground (wich may be another issue) then replacing the old "2 prong" device with a new "2 prong device is allowed.

you can also replace them with gfi's but this can be expensive and annoying.
if the devices look old and painted replacing them is a very good idea it also gives you a chance to vaccuum the dust and cob webs out of the box, just make sure your terminations are tight and the wire is wrapped all the way around the screw.


side note: I have seen the ground wires taken out of the box through the same entry the nm comes in through and landed on the outside of the box.

I reccomend a digital tester for this.

.
 
#8 ·
IMO yes.
Or use two prong receptacles.

A GFI installing in a situation like this will fool a surge strip into thinking there is a ground yet still be safe.
 
#12 ·
Most of the old BX I work with has no aluminum strip nor an equipment grounding conductor, so it is not an acceptable ground. The sheath will show a DC path on your ohm meter, but to AC current the spiral sheath is a high impedance path (inductance like a choke coil or transformer winding) which will fail to conduct enough current to operate the over current protection device. In addition, those spirals can then heat up like a heater element and cause a fire. Never use this BX for an equipment ground.
 
#14 ·
Don't forget to mark all ungrounded GFCI's as NO EQUIPMENT GROUND use the stickers that come with them and also do the same thing with any subsuquent recepticals down the line.:thumbsup:
 
#16 ·
While it is true that a GFCI will allow a 3-prong receptacle on a 2-wire circuit, some electronic equipment likes to have a real ground, bonded to the neutral at the service. I know that computers operating without a ground tend to crash more often on a "No Equipment Ground" circuit. Blue Screen of Death.

Inphase277
 
#17 ·
While it is true that a GFCI will allow a 3-prong receptacle on a 2-wire circuit, some electronic equipment likes to have a real ground, bonded to the neutral at the service. I know that computers operating without a ground tend to crash more often on a "No Equipment Ground" circuit. Blue Screen of Death.

Inphase277
But that doesn't automaticly mean that its going to happen. My computer was on an ungrounded cct for a few years, and never once had an issue with it.

Are there any "favorable" conditions to make this happen more in some cases and less in others?
 
#18 ·
No ground

CowboyAndy. It would depend on how well the power supply in the computer can filter out AC noise from other appliances like microwaves or old furnace motors, and static noise/charges on stuff like phone/ and cable lines. Newer switching power supplies are more dependable.
 
#19 ·
CowboyAndy. It would depend on how well the power supply in the computer can filter out AC noise from other appliances like microwaves or old furnace motors, and static noise/charges on stuff like phone/ and cable lines. Newer switching power supplies are more dependable.
Quick question about computers if anyone can answer this... is there any issue with having the vaccum plugged in to the same circuit (not same recep) as the computer?
 
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