Ok for ground to be 5% lower voltage?


  #1  
Old 02-27-23, 07:06 PM
E
Member
Thread Starter
Join Date: Oct 2014
Posts: 646
Received 5 Upvotes on 5 Posts
Ok for ground to be 5% lower voltage?

So my wife moved her home office to the basement and I noticed that when I touched her computer case while shoeless I got a tingle, and there was a lot of static through her speakers so I checked the outlet and sure enough there was no ground wire. I looked at some near by junctions on that conduit and didnít find one, and rather than spend a lot of time trying to fish one in I decided to ground the outlet to the box since I knew somewhere it connected to a panel which I know is grounded.

But when I tested it to see if it was a ground, i got 212v vs the 222 phase to neutral. My first thought was that there was something wrong with our grounds (which in my country arenít tied to neutral in the home), but I checked some upstairs outlets I knew had ground wires and got no difference between ground and neutral so Im guessing it might be voltage drop from the steel conduit?

from a strictly practical point of view it solved the computer-case-shocking-people problem that I set out to resolve, but Iím curious, is that still considered a good ground path even though itís 4.5% off voltage wise and should I check something other than voltage with my multimeter?
 
  #2  
Old 02-27-23, 07:42 PM
C
Member
Join Date: May 2015
Location: USA
Posts: 3,087
Received 134 Upvotes on 110 Posts
That does indicate a poor or marginal ground path. Your multimeter passes very little current when measuring voltage but even with that very small current you have 10 volt drop. You could start by checking that the connectors that hold the boxes to the conduit are all tight. Metal conduit normally provides a good ground path, but that requires that the conduit connectors are be nice and tight (and if they are the type of connector that uses a screw to attach to the conduit, the screws have to completely screwed in so they get a good bite on the conduit).

At some point, the conduit has to be attached to ground. If the conduit runs all the way to your electrical panel, it will make a connection there, but if it doesn't run all the way to a panel, then there needs to be a ground wire connection to the conduit somewhere along its run.
 
  #3  
Old 02-27-23, 07:54 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 63,109
Received 3,610 Upvotes on 3,236 Posts
The meter represents a low resistance but other devices connected can cause a weak or poor ground to be seen. Something as simple as a loose connector screw could cause that.

I have had to pull a ground wire in some conduit systems in the past.
Especially with sound systems where a problem ground can be a disaster.
 
  #4  
Old 02-27-23, 11:05 PM
d_s_k's Avatar
Member
Join Date: Mar 2007
Location: Norway
Posts: 388
Received 19 Upvotes on 17 Posts
222V to neutral? What kind of supply system is that?

I live in Norway, and here we have mainly 2 different systems. At home I have around 127V to ground, but no Neutral wire, only 2 live wires with 230V between them, more modern systems here has 230V to ground and Neutral. Voltages exiting 48V is dangerous according to our regulations.
 
  #5  
Old 02-28-23, 04:54 AM
E
Member
Thread Starter
Join Date: Oct 2014
Posts: 646
Received 5 Upvotes on 5 Posts
Itís a nominally 220/380 supply system but in practice itís usually a few volts higher
 
d_s_k voted this post useful.
  #6  
Old 02-28-23, 02:44 PM
E
Member
Thread Starter
Join Date: Oct 2014
Posts: 646
Received 5 Upvotes on 5 Posts
What are the real world consequences of this being a poor/marginal ground? This isnít audiophile equipment, screwing in a ground wire to the box solved the computer case shocking people problem. Is this worth investing 2-3 hours of my weekend / evening time to pull a wire or do I declare it good enough for government work and call this problem solved?
 
  #7  
Old 02-28-23, 05:58 PM
C
Member
Join Date: May 2015
Location: USA
Posts: 3,087
Received 134 Upvotes on 110 Posts
Only you can answer that. The ground system is primarily a backup safety system intended to prevent a dangerous fault in a connected device from killing or injuring someone. When all the wiring on a circuit and all the devices connected to it are fault free, the ground pretty much does nothing. By not fixing it, you are betting that nothing ever connected there will have a dangerous fault. Frankly, I'm sure the odds are very much in that direction. But only you can decide if that's good enough.
 
  #8  
Old 02-28-23, 10:42 PM
d_s_k's Avatar
Member
Join Date: Mar 2007
Location: Norway
Posts: 388
Received 19 Upvotes on 17 Posts
It is hard to give a good answer, I still have ungrounded outlets in our house, and has never got that problem. As long as you are not in contact with any other things that may carry the current it is "safe" to touch a live wire, but a little bit moisture on the floor, or anything else that may carry the current it is a risk of life. Where I grew up we also had ungrounded outlets, and radiators, that was not a good combination. As a teenager I just used the radiator pipes as ground. In my first apartment it was a faulty transformer causing trouble. The refrigerator (connected to a grounded outlet) touched the kitchen water tube, and I got sooty marks on the refrigerator. I had 220 between both L and N to ground. And a gap of 50V between ground in outlet and water pipes.
 
  #9  
Old 03-31-23, 09:24 AM
A
Member
Join Date: Mar 2010
Location: USA
Posts: 4,422
Upvotes: 0
Received 261 Upvotes on 238 Posts
There is definitely something wrong when people get shocked when touching or using appliances, electronics, etc. (more than a momentary shock walking across the carpet on a cold day).

Either the house main electrical ground (grounding electrode system in the U.S.) is supposed to be tied to one of the current carrying conductors (giving that conductor the colloquial name of "neutral" in the U.S.) or it is not.

If neither current carrying conductor is grounded then both are considered to be "hot" and the voltage measured between either and ground is undefined and unpredictable. Then there may not be any touching of any exposed metal part to any wire or any metal part connected to that wire.

In the U.S., in 120/240 volt systems the "center" conductor (120 volts to either of the others) is supposed to be grounded.

If one of the two current carrying conductors is supposed to be grounded and you still measure more than a few volts difference between that conductor and ground then the grounding system is inadequate or defective.

Much of the time, hum or hiss in sound systems can be alleviated by running a separate ground wire among the various system components. Connect it to an in put jack shell or to a screw that penetrates to the metal chassis. Connect the far end of this wire to a known ground, here a water pipe or radiator will often do.
 

Last edited by AllanJ; 03-31-23 at 10:30 AM.
  #10  
Old 04-01-23, 08:58 AM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,090
Received 785 Upvotes on 665 Posts
Set your meter to Ohms and take a reading between neutral and ground. You will likely get something very close to zero.

Personally, I doubt this is an issue.
 
  #11  
Old 04-10-23, 05:30 PM
G
Member
Join Date: Sep 2009
Location: USA
Posts: 193
Received 11 Upvotes on 10 Posts
If you have a bad ground, It means if some device develops a short from hot to ground, the circuit breaker won't trip. Instead, all the grounded metallic surfaces becomes hot and are shock hazards. This problem must be fixed.
 
  #12  
Old 04-11-23, 09:01 PM
E
Member
Thread Starter
Join Date: Oct 2014
Posts: 646
Received 5 Upvotes on 5 Posts
Groundcurrent. Is that the case with a marginal ground as well? Because grounding it to the box in this case eliminated the problem of being shocked by the computer case. I assume that in case of aground fault the breaker would trip even faster if the difference in voltage was lower.

T.I., Iíll give this a try tomorrow and see what it says.
 
  #13  
Old 04-14-23, 04:34 AM
A
Member
Join Date: Mar 2010
Location: USA
Posts: 4,422
Upvotes: 0
Received 261 Upvotes on 238 Posts
(copied from another post) The equipment grounding conductor (may be in part or in whole metal conduit) needs to accomplish at least one of these things: (a) cause a ground fault to draw so much current as to trip the breaker, or (b) cause other series resistance in the (undesired) ground fault circuit (e.g. the portion of the computer's electronics between the hot supply conductor and the ground fault to the case) to have nearly all of the hot to ground voltage across it leaving near zero volts between the ground fault and the building ground. The "ground being 5% lower" or whatever means the EGC is inadequate, or marginal if you insist, either way there is an electrocution hazard.

A person might be killed with just 20 milliamps of current flowing through the middle of his body.
 
 

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