Old house w/2-prong outlets ("grounding" question)

Reply

  #1  
Old 12-10-08, 02:41 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Received 0 Votes on 0 Posts
Question Old house w/2-prong outlets ("grounding" question)

To make a long story short..

I need to protect a couple of computers in my old house from surges/spikes...

After reading several prior threads on this forum, then I have discovered that surge protectors absolutely offer no protection whatsoever unless of course, the electrical outlet that it's plugged into is properly grounded..

Of course, I live in a house thats probably on the order of 50 - 60 years old and 2-prong wall outlets were prevalent at the time of construction..

So how do I check my wall outlets to see whether or not they are properly grounded?

Am I able to do this using a multi-meter (reads both AC & DC as well as Ohms)?....and if so, then what's the proper procedure for connecting my test leads and what are the physical objects/items that I should be connecting them to?

Thanks to all who reply!
 
Sponsored Links
  #2  
Old 12-10-08, 02:57 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
If you have two-prong receptacles in a 60 year old house then odds are strong that you don't have grounded circuits. You can check by taking the faceplate off the receptacle and peer into the box. If you don't see any bare copper wires in there, then you do not have any grounds.

The best solution is to install ground wires or new grounded circuit(s) to the location of the computers.

Another solution would be to replace one of the two-prong receptacles with a three-prong GFCI receptacle at the computer location. You can then use an induction choke based surge protector such as one sold by Brick Wall. These are much more expensive than the usual MOV based surge protectors, but they do not require a ground wire to protect equipment and provide a very high level of protection.
 
  #3  
Old 12-12-08, 12:13 AM
Member
Join Date: Mar 2007
Location: Norway
Posts: 282
Received 0 Votes on 0 Posts
Both economics, and another way of thinking safety long time ago are probably the reason for why ungrounded was common.

Using a standard telephone/data/power surge protection socket iwith no grounding will give some protection.
Voltage between live, and grounded will be limited.
Sinse you have no near by ground, the spike may not jum easily to the near by ground.

Touching that old cables may harm old insulation, and cause a need of rewiring it all.


I use the oldfashined way to do it, When I turn of the computer I turn off the powestrip, if it comes realy bad weather I unplug everything. Only once I have had problems, even with the cables unpluged, But it was a near by hit by lightning, it even started a fire, no surge protector could stop that.

dsk
 
  #4  
Old 12-12-08, 08:10 AM
Skapare's Avatar
Member
Join Date: Jun 2004
Location: USA
Posts: 198
Received 0 Votes on 0 Posts
Originally Posted by DixieH View Post
After reading several prior threads on this forum, then I have discovered that surge protectors absolutely offer no protection whatsoever unless of course, the electrical outlet that it's plugged into is properly grounded..
That's not true.

The kind of protection a power strip surge protector (a "point of use" protector) offers is voltage rise equalization. All interconnected appliances should be plugged into the same protector. All external wired connections (phone line, cable TV coax), should also be plugged into that same protector (so you would need one with those connections if it applies to your needs).

A surge can arrive at different voltages on different wires, and not always on all the wires. The MOVs inside the protector will conduct if the voltage exceeds a certain level (typically somewhere between 400 and 800 volts on peaks). This conduction causes the voltage level on all the wires to be the same, or nearly the same. The end result of a 2000 volt surge arriving at a protected appliance is that the voltage of every wire will rise to as much as 2000 volts.

It's not the voltage that kills (or destroys). It's the power dissipation, which is a product (in the mathematical sense) of the electrical current, and the voltage DROP (how much voltage difference exists at a particular pair of points, which itself is a function of current divided by impedance). By equalizing the voltage, you reduce the current, which reduces the power, which reduces the damage.

The voltage equalization needs to be done not only between the 2 or 3 power wires, but also between other wires. If the voltage on the phone line rises to 2000 volts, but the voltage on the power line does not, then you have as much as a 2000 volt (plus or minus the AC power voltage peak) DIFFERENCE somewhere between the modem and computer power supply unit, and a grave risk of damage.

If the voltage rises up to 2000 volts everywhere equally, that's not a big problem, as long as it does not rise too fast (and most surges do not rise too fast). To protect against very fast rises, a different kind of protection is needed (filtering).

If the ground wire is present from the circuit, and if the surge is not also arriving on the ground wire, the voltage equalizing can send some of the surge energy back over that ground wire, reducing the overall amount somewhat. This is not a substantial difference.

A ground wire provides a different kind of protection unrelated to surges. Computers need it because they are touched by users on a continuous basis during use. By comparison, a TV is not. The protection offered by the ground wire is to ensure that the case or frame of an appliance cannot become electrically energized from problems inside the appliance (such as a short between a hot wire and the frame).

Without a ground wire, the risk is the computer box could be charged up at 120 volts, and you could be shocked when touching the computer and something else that does form a ground path. The ground wire prevents the scenario by sinking that voltage to the ground level (which if the cause of the charge is a low impedance short, will trip a breaker or blow a fuse).

To get this kind of shock protection without a ground wire, you can use a GFCI device. This can be done in the wall receptacle (GFCI works without a ground wire) or via special power strips normally used for outside electrical work tools that include GFCI protection (and generally do not include surge protection so don't use them exclusively with a computer or other electronic appliances). The GFCI won't prevent the computer case from being charged to 120 volts. Instead, it shuts off the power if it senses that some of the current going out to the computer is not coming back over the wires it monitors.

If you use a UPS (uninterruptible power supply), this can complicate the use of GFCI. For best protection, the GFCI should be between the UPS and the computer (so you would need the outdoor tool strip protector). Some UPSes may refuse to power up if the supply circuit does not include a correct ground wire (and some can tell the difference between using a grounding adapter vs. a correctly bonded neutral at the breaker panel).
 
  #5  
Old 12-12-08, 08:27 AM
Skapare's Avatar
Member
Join Date: Jun 2004
Location: USA
Posts: 198
Received 0 Votes on 0 Posts
Originally Posted by d_s_k View Post
I use the oldfashined way to do it, When I turn of the computer I turn off the powestrip, if it comes realy bad weather I unplug everything. Only once I have had problems, even with the cables unpluged, But it was a near by hit by lightning, it even started a fire, no surge protector could stop that.
Faen, hvor mye lyn har dere i Norge?
 
  #6  
Old 12-12-08, 09:04 AM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Received 0 Votes on 0 Posts
Re:

Originally Posted by Skapare View Post
That's not true.

Without a ground wire, the risk is the computer box could be charged up at 120 volts, and you could be shocked when touching the computer and something else that does form a ground path. The ground wire prevents the scenario by sinking that voltage to the ground level (which if the cause of the charge is a low impedance short, will trip a breaker or blow a fuse).

To get this kind of shock protection without a ground wire, you can use a GFCI device. This can be done in the wall receptacle (GFCI works without a ground wire) or via special power strips normally used for outside electrical work tools that include GFCI protection (and generally do not include surge protection so don't use them exclusively with a computer or other electronic appliances). The GFCI won't prevent the computer case from being charged to 120 volts. Instead, it shuts off the power if it senses that some of the current going out to the computer is not coming back over the wires it monitors.

If you use a UPS (uninterruptible power supply), this can complicate the use of GFCI. For best protection, the GFCI should be between the UPS and the computer (so you would need the outdoor tool strip protector). Some UPSes may refuse to power up if the supply circuit does not include a correct ground wire (and some can tell the difference between using a grounding adapter vs. a correctly bonded neutral at the breaker panel).
Hey, thanks 'Skapare'...you're one smart cookie!

I'm still trying to interpret everything here, but I believe the jist of what you are saying is that the purpose of the ground wire is simply to provide an extra avenue for voltage dissipation to keep you from getting jolted when you grab the handle of the refrigerator door at just the wrong moment and that you actually can get some measure of protection from a surge protector with or without the ground wire in place...

And if I don't use UPS (which I don't, by the way), then I should just be able to put a GFCI outlet in place to imitate (but not replace) the protection that a ground wire would offer...

Is this correct??..

Again..a big thanks to all who have replied to this thread so far!
 
  #7  
Old 12-12-08, 10:00 AM
Skapare's Avatar
Member
Join Date: Jun 2004
Location: USA
Posts: 198
Received 0 Votes on 0 Posts
Originally Posted by DixieH View Post
I'm still trying to interpret everything here, but I believe the jist of what you are saying is that the purpose of the ground wire is simply to provide an extra avenue for voltage dissipation to keep you from getting jolted when you grab the handle of the refrigerator door at just the wrong moment and that you actually can get some measure of protection from a surge protector with or without the ground wire in place...
That's one of it's purposes ... the most important one.

Originally Posted by DixieH View Post
And if I don't use UPS (which I don't, by the way), then I should just be able to put a GFCI outlet in place to imitate (but not replace) the protection that a ground wire would offer...

Is this correct??..
Yes. NEC 406.3(D)(3)(b) will apply in this case.
 
  #8  
Old 12-17-08, 04:35 PM
Member
Join Date: Dec 2008
Posts: 2
Received 0 Votes on 0 Posts
Dixie

One more thing. I agree with whoever said you probably have ungrounded wiring in your 50-60 year old home if two-slot outlets were used. But you should check. I lived before in a 110 year old house with two-slot outlets and indeed, of course, all the (original) wiring was ungrounded. But I now live in a 50 year old house. Even though about one-third of the outlets are (or were, when we moved in) two-slot and the rest three, nevertheless the whole house is metal conduit wired, which means, as you probably know, that all outlet boxes (if metal) are grounded.

Anyway, since you are comfortable with a meter, there is an easy way to check. If your box turns out to be grounded, all you need to do is replace the outlet. With your meter on the appropriate AC range and the faceplate off the outlet, just put one probe into the narrow slot in the outlet and with the other one, contact the surface of the metal box (some scraping may be needed to get through oxidation.) If you see around the desired 120v, you should be good to go. Obviously, this is cheap and easy, if possible.

Good luck.
 
  #9  
Old 12-19-08, 10:51 AM
Member
Join Date: Dec 2008
Location: Boston
Posts: 2
Received 0 Votes on 0 Posts
One more thing to check

I too live in a 50 year old house that had 2 prong outlets, but what I found was that the wire used did have a ground. The ground wire was wrapped around the cable, and when it was inserted into the box, there is a clamp that is screwed down on the cable, grounding the box. What I did, after shutting off the power of course, was to unclamp it, and using needle nose pliers unwrap the ground and connect it directly to the new grounded outlet. It's a pain, but I know that all my outlets are now grounded properly. Verify by checking the ground connection at each box back to the panel. The advantage to doing this all at once is youget a map of the wiring route back to the panel. This can help if you want to expand a circut in the future.

Ken
 
  #10  
Old 12-19-08, 06:51 PM
Member
Join Date: Nov 2007
Location: (near) Boise, ID
Posts: 442
Received 0 Votes on 0 Posts
Originally Posted by KGR51 View Post
What I did, after shutting off the power of course, was to unclamp it, and using needle nose pliers unwrap the ground and connect it directly to the new grounded outlet.
If the boxes are metal and are grounded, I am guessing that you could use a self-grounding receptacle instead, which connects the ground on the receptacle to the box via a tab on one of the screws.
 
  #11  
Old 02-01-09, 03:37 PM
Member
Join Date: Feb 2009
Posts: 1
Received 0 Votes on 0 Posts
Originally Posted by KeyPine View Post
Dixie

One more thing. I agree with whoever said you probably have ungrounded wiring in your 50-60 year old home if two-slot outlets were used. But you should check. I lived before in a 110 year old house with two-slot outlets and indeed, of course, all the (original) wiring was ungrounded. But I now live in a 50 year old house. Even though about one-third of the outlets are (or were, when we moved in) two-slot and the rest three, nevertheless the whole house is metal conduit wired, which means, as you probably know, that all outlet boxes (if metal) are grounded.

Anyway, since you are comfortable with a meter, there is an easy way to check. If your box turns out to be grounded, all you need to do is replace the outlet. With your meter on the appropriate AC range and the faceplate off the outlet, just put one probe into the narrow slot in the outlet and with the other one, contact the surface of the metal box (some scraping may be needed to get through oxidation.) If you see around the desired 120v, you should be good to go. Obviously, this is cheap and easy, if possible.

Good luck.

I live in a house with two-socket outlets. I unscrewed the faceplate, unscrewed and pulled out the dual-outlet, the put one probe of my voltmeter in the outlet, one to the metal box. This read either 40v or 10v, depending on which socket I used (i.e. the left/larger or the right/smaller). Of course, if I put one probe each in the left and write sockets of the same outlet, I get 120 V (actually 117V).

Anyway, given this setup, can I buy a three-socket outlet and use the box as ground? I don't understand why I would get 40V or 10V when testing the metal outlet box - shouldn't it be 120V?

Thanks for your help!
 
  #12  
Old 02-01-09, 08:22 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,489
Received 32 Votes on 24 Posts
Anyway, given this setup, can I buy a three-socket outlet and use the box as ground?
Sorry, but the answer is no. If all you are attempting is a safer installation and don't "need" the ground as a reference point then you could install a "GFCI" receptacle. Most computers and many of the new televisions will require a true ground connection and if this is your intended use then you will have to install new wiring.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: