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Old 05-21-2019, 10:41 AM   #1
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Installing ground in home


I'm from the Philippines and our standard mains here is 220/240VAC. Since we had our home renovated, we decided to go ahead and have the proper grounding rods installed (grounding is very uncommon in our country).


So from the external electric meter, we have three wires coming into our main panel. Two hot 120V wires and a neutral. This means that our electrical outlets are a mix of 240V (two hot wires and ground) and 120V (one hot wire, neutral, and ground). I have a couple of concerns though:


1. I know that the neutral and ground bus bars should be bonded in the main service panel ONLY, and not on each of the sub-panels. Before I did the bonding, I measured the hot1-ground, hot2-ground, and neutral-ground voltages and was confused. The readings are:


hot1-ground -> around 220VAC
hot2-ground -> around 20VAC
neutral-ground -> around 100VAC


hot1-neutral and hot2-neutral are both 120VAC, so no issues there. But why is neutral-ground voltage 100VAC? I thought that's supposed to be close to 0VAC? If you bond that to the ground bus bar, won't it practically make the ground live? Sorry if I'm misinterpreting this.


2. Even though the bonding of the neutral-ground only happens in the main service panel, when you test the electrical outlets it would seem that the neutral and ground pins are shorted, correct? Because the subpanels get their neutral and ground wire feeds from the main service panel anyway. And that doesn't mean they're bonded but practically just means there is 0V potential difference between them. And all of the return current to the transformer will still go back to the main service panel neutral (because of high resistance in the main service panel ground path).
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Old 05-21-2019, 05:38 PM   #2
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Re: Installing ground in home


Quote:
Originally Posted by kevindd992002 View Post
I'm from the Philippines and our standard mains here is 220/240VAC. Since we had our home renovated, we decided to go ahead and have the proper grounding rods installed (grounding is very uncommon in our country).


So from the external electric meter, we have three wires coming into our main panel. Two hot 120V wires and a neutral. This means that our electrical outlets are a mix of 240V (two hot wires and ground) and 120V (one hot wire, neutral, and ground). I have a couple of concerns though:


1. I know that the neutral and ground bus bars should be bonded in the main service panel ONLY, and not on each of the sub-panels. Before I did the bonding, I measured the hot1-ground, hot2-ground, and neutral-ground voltages and was confused. The readings are:


hot1-ground -> around 220VAC
hot2-ground -> around 20VAC
neutral-ground -> around 100VAC


hot1-neutral and hot2-neutral are both 120VAC, so no issues there. But why is neutral-ground voltage 100VAC? I thought that's supposed to be close to 0VAC? If you bond that to the ground bus bar, won't it practically make the ground live? Sorry if I'm misinterpreting this.

I would try testing the neutral-ground wires again with all of the power off. If the reading on the neutral is different there may be an appliance or piece of equipment that is using the grounding conductor as a neutral. You can try to locate this by turning on the main breaker and then shut off each branch breaker one at a time until the reading changes. Here in the USA we have older electric clothes dryers and electric stoves that used the grounding conductor as a neutral. That gives a higher voltage reading between ground and neutral which some people refer to as phantom voltage.

If the neutral-ground reading does not change with your main circuit breaker off, you may be getting current from one of your neighbors. With your main breaker off put an ammeter on the grounding conductor to your new ground rods to confirm if it is carrying current. If this is the case, one of your neighbors may have a neutral problem.

Another possibility is that you have a neutral problem. With your main breaker on and some appliances and lights on, put an ammeter on the grounding conductor that goes to your ground rods. There should not be any current flow if everything is okay.


2. Even though the bonding of the neutral-ground only happens in the main service panel, when you test the electrical outlets it would seem that the neutral and ground pins are shorted, correct? Because the subpanels get their neutral and ground wire feeds from the main service panel anyway. And that doesn't mean they're bonded but practically just means there is 0V potential difference between them. And all of the return current to the transformer will still go back to the main service panel neutral (because of high resistance in the main service panel ground path).
When you use a voltmeter at an electrical outlet to test between hot and neutral, and hot and ground the readings will be almost if not the same.
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Old 05-21-2019, 06:52 PM   #3
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Ok. And from what I've been reading, the neutral-ground voltage in the main service panel will really read a significant amount of voltage if it is open (not grounded/bonded), correct? I forgot to mention that I measure the 100VAC while the grounding bus bar is NOT bonded to the neutral bus bar in the main service panel as I was in my testing phase. Is this correct?

Also, the hot-ground voltage should always be a little higher than hot-neutral if everything is wired correctly.

https://www.ecmweb.com/content/diagn...ems-receptacle
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Old 05-21-2019, 09:36 PM   #4
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Re: Installing ground in home


Before you bonded the incoming service neutral to your ground rod(s) and/or to your cold water pipe exiting underground, the voltage between neutral and ground in your house is technically undefined and indeterminate, and could measure any number of volts possibly varying as the day goes on.

The main purpose of bonding neutral to ground in your panel is so that in the event of a live wire touching the chassis or other exposed metal in a fixture or appliance, enough current will flow to immediately trip the breaker for that branch circuit. This helps prevent electrocution if a person should subsequently touch still energized exposed metal while also touching or standing on a somewhat conductive surface or item since the amount or current flowing needed to electrocute someone is very much smaller, less than a tenth of one ampere.

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Old 05-21-2019, 11:05 PM   #5
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Re: Installing ground in home


Ok, I was kinda expecting that answer. So there's nothing wrong with my setup.

What could be the cause of metal surfaces in the house electrocuting (a tingle) people when touched? I guesd a shorted neutral and ground on the sub panels or in any of the receptacles can cause that, right? Is there a way to test this with a DMM?

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Old 05-22-2019, 10:33 AM   #6
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Re: Installing ground in home


It may be that some of the answers to your questions may be found in the Philippine Electrical Code https://www.pdf-archive.com/2016/06/...rical-code.pdf

Warning, there may be a few problems in getting to this site!

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Old 05-22-2019, 11:15 AM   #7
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Re: Installing ground in home


Right, but it's still different when an experienced user shares his/her experience about these, you know.
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Old 05-22-2019, 06:30 PM   #8
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Re: Installing ground in home


Due to imperfect manufacturing a hot wire may have bee stretched too close to some sharp edge or crushed between other metal parts. The vibration (notable for something like a washing machine) causes the wire insulation to get cut and the inside of the wire touches the metal parts.
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Old 05-27-2019, 10:46 PM   #9
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Re: Installing ground in home


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Originally Posted by AllanJ View Post
Due to imperfect manufacturing a hot wire may have bee stretched too close to some sharp edge or crushed between other metal parts. The vibration (notable for something like a washing machine) causes the wire insulation to get cut and the inside of the wire touches the metal parts.

Makes sense. But if this happens, won't it trip the circuit breakers right away for me to notice that something's wrong?


Also, based on what I'm reading I can do a simple test to know if neutral and ground wires are reversed in a receptacle is by measuring the neutral-ground voltage which result should be greater than 0V (around 2-5V depending on the load). That load means any load connected to other receptacles and not necessarily the one I'm testing, right? Since all return current will travel go back to the same neutral wire path anyway.


Reference article: https://www.ecmweb.com/content/diagn...ems-receptacle
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Old 06-04-2019, 12:19 PM   #10
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Re: Installing ground in home


Anybody?
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Old 06-05-2019, 06:24 PM   #11
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Re: Installing ground in home


Quote:
Originally Posted by kevindd992002 View Post
Makes sense. But if this happens, won't it trip the circuit breakers right away for me to notice that something's wrong?

If the neutral conductor is shorted to the frame you could get a shock hazard without tripping the circuit breaker. This also would happen if the ground is being used as a neutral.




Also, based on what I'm reading I can do a simple test to know if neutral and ground wires are reversed in a receptacle is by measuring the neutral-ground voltage which result should be greater than 0V (around 2-5V depending on the load). That load means any load connected to other receptacles and not necessarily the one I'm testing, right? Since all return current will travel go back to the same neutral wire path anyway.


Reference article: https://www.ecmweb.com/content/diagn...ems-receptacle

Did you do the tests that I suggested?
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Old 06-05-2019, 06:39 PM   #12
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Re: Installing ground in home


We were actually able to determine that one of our AC units is causing the ground wire to be live but we're not yet sure if the AC unit itself (or the there was some short that was going on in the wires) is what's causing it. For now, we disconnected the grounding wire for that AC unit (as it was hard-wired) and all looks good.


What I'm trying to test now is all wirings are correct in such a way that there is no short between neutral and ground in the receptacles. I can actually try and do the ammeter test that you suggested. So just put an ammeter (I have a clamp meter) in the grounding conductor wire that's in the main service panel going to the ground rods while, say, a microwave is turned on, right? If the ammeter reads 0A then I'm sure that there is no short between neutral and ground?
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Old 06-06-2019, 08:02 AM   #13
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Re: Installing ground in home


Quote:
Originally Posted by kevindd992002 View Post
We were actually able to determine that one of our AC units is causing the ground wire to be live but we're not yet sure if the AC unit itself (or the there was some short that was going on in the wires) is what's causing it. For now, we disconnected the grounding wire for that AC unit (as it was hard-wired) and all looks good.


What I'm trying to test now is all wirings are correct in such a way that there is no short between neutral and ground in the receptacles. I can actually try and do the ammeter test that you suggested. So just put an ammeter (I have a clamp meter) in the grounding conductor wire that's in the main service panel going to the ground rods while, say, a microwave is turned on, right? If the ammeter reads 0A then I'm sure that there is no short between neutral and ground?
Your neutral and ground are bonded together at the main panel. If there is zero amps on the grounding conductor, it means that the grounding conductor is not being used as the return path back to the transformer which is the function of the neutral conductor.
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Old 06-06-2019, 08:20 AM   #14
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Right. So the grounding conductor where I need to measure the current at would be the wire that connects the ground bus bar of the main panel to the ground bus bar of obe of the subpanels, correct?

Is a microwave oven enough for this test? I would assume so.
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Old 06-06-2019, 01:06 PM   #15
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Re: Installing ground in home


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Originally Posted by kevindd992002 View Post
Right. So the grounding conductor where I need to measure the current at would be the wire that connects the ground bus bar of the main panel to the ground bus bar of obe of the subpanels, correct?

No, you need to measure the current on the wire going to the ground rod.

Is a microwave oven enough for this test? I would assume so.
Yes, you should see some measurable current from a microwave oven.
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