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04-23-2012, 08:31 PM   #1
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## utility neutral/neutral current question

this topic came up on another thread but its buried pretty deep. it is my understanding from several experienced posters that under normal circumstances all neutral current should flow back to the utility neutral, not the grounded plumbing or rods.

i am trying to figure out why. bear with this simplistic example.

100a service - 3 wires in - A (hot+), B (hot-) and N (neutral).
circuit 1 on A is using 12 amps
circuit 2 on B is using 7 amps
so a total of 5 neutral current amps have to go somewhere.

they could all flow back on N, but if bonded to N at the panel is a low resistence connection to say, copper water pipes, wouldnt some of the current flow there?

is the utility neutral supposed to be so low resistence that none of the current would flow to the grounds? if that is the case i need to call my utility ASAP because a considerable amount of current flows to my main ground.

where i am struggling is i dont see how a utility pole or transformer would be any lower resistance than miles of metal plumbing and since they are bonded together, the current can choose (i know wrong word but im not an electrican or an engineer) either path

04-23-2012, 09:23 PM   #2
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The current should flow back to the source, i.e. the transformer not to the earth. Even a fault on a grounding conductor flows back to the panel and then to the transformer through the grounded conductor(neutral) thus opening the OCPD.

 04-23-2012, 09:25 PM #3 Sparky   Join Date: Mar 2011 Location: Central Florida Posts: 706 Rewards Points: 510 While your grounds are bonded to neutral in your panel, they're not bonded to the Neutral of the transformer. so the current would have to travel through the earth, or water piping likely to your neighbors neutral, The utility neutral is the only place power should be returning to the source Last edited by Techy; 04-23-2012 at 09:28 PM.

 04-23-2012, 09:39 PM #4 Member     Join Date: Mar 2005 Location: Welland, Ontario Posts: 13,263 Rewards Points: 13,322 Blog Entries: 11 The POCO neutral connection is the lowest resistance path if it is in normal condition. If your connection has a high resistance connection then some or all of the current needs to find another path back to the POCO. If you have metal water lines in your town water supply then that current can flow out your water pipe, through the water main and into your neighbour;s water line and out his neutral connection.
 04-23-2012, 09:49 PM #5 Member     Join Date: Sep 2010 Location: Saint Louis, MO Posts: 324 Rewards Points: 252 its the "returning to transformer" bit i never got. I assumed current didnt really care as long as it got to earth. time to call the POCO i think. appreciate everyones thoughts on this Board. wish id known it was here when i started my project
04-23-2012, 09:52 PM   #6
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Quote:
 Originally Posted by kevinp22 its the "returning to transformer" bit i never got. I assumed current didnt really care as long as it got to earth. time to call the POCO i think. appreciate everyones thoughts on this Board. wish id known it was here when i started my project
Current does not try to return to the earth, only to its source.
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04-23-2012, 10:05 PM   #7
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Quote:
 Originally Posted by Techy While your grounds are bonded to neutral in your panel, they're not bonded to the Neutral of the transformer. so the current would have to travel through the earth, or water piping likely to your neighbors neutral, The utility neutral is the only place power should be returning to the source
This is wrong. The transformer neutral, your house neutral, and ground are all bonded together in your panel. The transformer neutral is bonded to the primary side neutral, which then runs back to power transformer at the substation. Of course this last part depends on your power company, the one I work for runs a wye configuration on the primary side. Some run delta on the primary side, so a neutral is not necessarily going to be present.

 04-23-2012, 10:10 PM #8 Member     Join Date: Sep 2010 Location: Saint Louis, MO Posts: 324 Rewards Points: 252 just for the heck of it, checked current flow right now 2.8 amps to water pipe ground 0.03 amps to ground rods 4.2 amps to utility neutral
04-23-2012, 10:12 PM   #9
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Quote:
 Originally Posted by chemman This is wrong. The transformer neutral, your house neutral, and ground are all bonded together in your panel.
Well, what is being said is if the transformer to panel neutral is open then the grounds are no longer bonded to the transformer; but there is a return path for current through the GEC, to earth, to the transformer ground, to the transformer neutral.

04-23-2012, 10:15 PM   #10
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Quote:
 Originally Posted by kevinp22 just for the heck of it, checked current flow right now 2.8 amps to water pipe ground 0.03 amps to ground rods 4.2 amps to utility neutral
Do you think your water main passes close to the transformer that services your house?

 04-23-2012, 10:43 PM #11 Member     Join Date: Sep 2010 Location: Saint Louis, MO Posts: 324 Rewards Points: 252 No ironically enough. I know for a fact (due to some work the water co was doing on my street) that the water main is on the other side of the street on the front side of my house. Water pipes enter on the front side. Poles/transformers are on the back side of the house. Service wires are old 2 AWG aluminum wires. Neutral has been spliced 3 times due to squrrels sharpening their teeth and breaking the metal (I am not making this up. last summer we had some tree work done that required a utility drop for one day so the power lines would not interfere with the tree company cranes. While my main wires were on the ground, I noticed the neutral in one place had maybe 6 of the 10 strands cut. Utility and tree people said it was from squirrels and the utility spliced it before reconnecting). The situtation with the current flowing to ground vs utility neutral was unchanged by that disonnect/reconnect so I guess the connection at the pole is not the issue. I am going to see if the POCO can check the connections on their side. There are 4 houses on the transformer - I am second closest house. Transformer looks ancient to me.
 04-24-2012, 12:42 AM #12 JOATMON     Join Date: Aug 2011 Location: S. California Posts: 11,404 Rewards Points: 1,964 Blog Entries: 2 I think I see your confusion.... The Earth connection is there to set the 'reference' for the neutral. In electricity, any voltage measurement is relative to 'something'. In our case, we have chosen 'Earth' as that reference....which in practical terms, is a good one... __________________ Even if you are on the right track, you will still get run over if you just sit there. My 2-Story Addition Build in Progress Link ... My Garage Build Link and My Jeep Build Link
 04-24-2012, 06:38 AM #13 Member   Join Date: Nov 2007 Location: Nashua, NH, USA Posts: 7,965 Rewards Points: 1,536 The purpose of grounding of the electrical system (using ground rods and water pipes) is to provide some lightning protection, although nothing of reasonable cost will protect against a direct lightning strike. Coincidentally the grounding electrodes in various places including at utility pole bases and at neighboring houses will complete a return path to the pole transformer via the earth for a small number of amperes should a neutral going to a house be broken. There exist distribution systems (primary lines, over 10 kv, from substation to pole transformer) using a single conductor on the pole (single wire earth return). This technique does not work well from pole transformer to house (secondary, 120/240 volt) because the number of volts dropped, given the resistance of the earth and the total current draw, is too great. __________________ The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit. Last edited by AllanJ; 04-24-2012 at 06:53 AM.
 04-24-2012, 06:43 AM #14 I=E/R     Join Date: May 2010 Location: Minnesota Posts: 2,052 Rewards Points: 1,000 Is the water pipe current yours or your neighbors? When you have a good reading of current on the water pipe ground, turn off your main breaker and see what happens. If the current disappears it is your current.
04-24-2012, 07:38 AM   #15
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In his other thread he said if he turns everything off the current goes to zero, so I think the problem is his.

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