JACK CARMAN
New member
Our client (for a public school) wants us to show calculations for what we are doing about "stray currents". We are not sure what is meant by stray currents, what we would do about them, and what would be the calculations?
STRAY CURRENTS
- Thread starter JACK CARMAN
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: STRAY CURRENTS
The short answer is that "Stray Current" is current flowing in the dirt under or around your facility from a source other than your facility. It should be noted that planet Earth is a fairly good conductor, and that utilities have been known to use the planet as a conductor.
But I cannot help with the "what do I do about it" or "how do I calculate it" questions. They are new questions to me.
Perhaps a utility representative could shed some light on this?
The short answer is that "Stray Current" is current flowing in the dirt under or around your facility from a source other than your facility. It should be noted that planet Earth is a fairly good conductor, and that utilities have been known to use the planet as a conductor.
But I cannot help with the "what do I do about it" or "how do I calculate it" questions. They are new questions to me.
Perhaps a utility representative could shed some light on this?
physis
Senior Member
Re: STRAY CURRENTS
If that is as specific as your client wants to be I would do very little and charge very much.
I don't know if they expect you understand their request or not but maybe they could elaborate.
Edit; And I might consider "any" current that exists somewhere it isn't intended to be to be "stray".
[ November 22, 2005, 06:25 PM: Message edited by: physis ]
If that is as specific as your client wants to be I would do very little and charge very much.
I don't know if they expect you understand their request or not but maybe they could elaborate.
Edit; And I might consider "any" current that exists somewhere it isn't intended to be to be "stray".
[ November 22, 2005, 06:25 PM: Message edited by: physis ]
Re: STRAY CURRENTS
"Stray Current" can mean many different things to different people. For the most part "stray current" means neutral current that is traveling in the earth due to the grounded neutral distribution system that is used in the US. There is not much that you can do about it, it is a fact of life. You may be able to show them that you have balanced the load across the phases in order to reduce neutral current to as low a value as is possible. That would not eliminate the current that is present from other customers on the same grid, but is the only thing over which you have any control. I think this is a case of some specifier having enough knowledge to make them dangerous. They probably read an article someplace about "stray current" and did not understand it, but they impressed their boss by throwing this requirement in the specifications. Ask them for a definition of what they mean by "stray current" and what remedial action they would like to see implemented and watch them sweat!
"Stray Current" can mean many different things to different people. For the most part "stray current" means neutral current that is traveling in the earth due to the grounded neutral distribution system that is used in the US. There is not much that you can do about it, it is a fact of life. You may be able to show them that you have balanced the load across the phases in order to reduce neutral current to as low a value as is possible. That would not eliminate the current that is present from other customers on the same grid, but is the only thing over which you have any control. I think this is a case of some specifier having enough knowledge to make them dangerous. They probably read an article someplace about "stray current" and did not understand it, but they impressed their boss by throwing this requirement in the specifications. Ask them for a definition of what they mean by "stray current" and what remedial action they would like to see implemented and watch them sweat!
bphgravity
Senior Member
- Location
- Florida
Re: STRAY CURRENTS
A good way to reduce "stray currents" is to not not take advantage of the code permitted reduction of the service grounded neutral conductor, and not worry so much about the total impedance of the service grounding system.
Higher resistance ground path + lower resistance neutral return path = less objectionable and stray currents flowing through the Earth.
A good way to reduce "stray currents" is to not not take advantage of the code permitted reduction of the service grounded neutral conductor, and not worry so much about the total impedance of the service grounding system.
Higher resistance ground path + lower resistance neutral return path = less objectionable and stray currents flowing through the Earth.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: STRAY CURRENTS
Are they worried about a shock hazard (like those that affect dairy cows) from currents flowing in the earth? Or, excessive EMF caused by "uncancelled" magnetic fields (like those found near service entrances)?
Are they worried about a shock hazard (like those that affect dairy cows) from currents flowing in the earth? Or, excessive EMF caused by "uncancelled" magnetic fields (like those found near service entrances)?
- Location
- Illinois
- Occupation
- retired electrician
Re: STRAY CURRENTS
There is really nothing that you can do about this as most of the neutral to earth voltage (NEV) is a result of the voltage drop on the utility primary neutral conductor.
Don
There is really nothing that you can do about this as most of the neutral to earth voltage (NEV) is a result of the voltage drop on the utility primary neutral conductor.
Don
Re: STRAY CURRENTS
This sounds like it might have come from an AV person complaining about objectionable noise in their audio equipment. I actually had an "expert" tell me to lift the grounds off of the receptacles feeding the podium where they plug their laptop into the sound system.
And of course I refused.
This sounds like it might have come from an AV person complaining about objectionable noise in their audio equipment. I actually had an "expert" tell me to lift the grounds off of the receptacles feeding the podium where they plug their laptop into the sound system.
And of course I refused.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: STRAY CURRENTS
Jack,
I like to keep discussions on the open forum, so I am reposting your PM here.
Maybe other members will have better information for you? Have you looked in the Power Quality forum?
Jack,
I like to keep discussions on the open forum, so I am reposting your PM here.
I have not enough data to convince me that these low level fields are as big of a general problem as some activists claim. I remember the uproar of the ELF project, in Northern Wisconsin and Upper Michigan, back in the late 70's. But I am not aware of any conclusive results from any study of that project.
Maybe other members will have better information for you? Have you looked in the Power Quality forum?
Re: STRAY CURRENTS
Magnetic fields are proportional to the current flowing, and the area enclosed by the current. The best way to keep the fields low is to minimize the area enclosed by the current at almost zero. For example, each hot wire is ran in the same conduit with the corresponding neutral wire. Every 3 phase feeder is ran with all 3 phases (and neutral if applicable) in the same conduit.
If you picture a current flowing to a light bulb, that current creates a magnetic field. The same current travels back to the source on the neutral wire. This creates an opposing magnetic field. The the hot and neutral are ran side by side, the two fields will cancel each other.
Magnetic fields are proportional to the current flowing, and the area enclosed by the current. The best way to keep the fields low is to minimize the area enclosed by the current at almost zero. For example, each hot wire is ran in the same conduit with the corresponding neutral wire. Every 3 phase feeder is ran with all 3 phases (and neutral if applicable) in the same conduit.
If you picture a current flowing to a light bulb, that current creates a magnetic field. The same current travels back to the source on the neutral wire. This creates an opposing magnetic field. The the hot and neutral are ran side by side, the two fields will cancel each other.
- Location
- Illinois
- Occupation
- retired electrician
Re: STRAY CURRENTS
The most common reason for an excessive magnetic field is a neutral to ground bond on the load side of the service disconnect.
Don
The most common reason for an excessive magnetic field is a neutral to ground bond on the load side of the service disconnect.
Don
Re: STRAY CURRENTS
I would take a minute to read Karl Riley's book "Tracing EMFs In Building Wiring & Grounding". It is inexpensive and very informative.
Tracing EMFs in Building Wiring & Grounding
-Ed
I would take a minute to read Karl Riley's book "Tracing EMFs In Building Wiring & Grounding". It is inexpensive and very informative.
Tracing EMFs in Building Wiring & Grounding
-Ed
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: STRAY CURRENTS
Karl Riley is one of our moderators and he literaly wrote the book.
For your use the video would be more usefull and you can use it to show your client.
Nearly all elevated EMF's are due to common wiring errors.
The book and video is available at www.magneticsciences.com
And you can send a PM to Karl Riley for more information.
Karl Riley is one of our moderators and he literaly wrote the book.
For your use the video would be more usefull and you can use it to show your client.
Nearly all elevated EMF's are due to common wiring errors.
The book and video is available at www.magneticsciences.com
And you can send a PM to Karl Riley for more information.
Re: STRAY CURRENTS
Hi Sam, I picked up Karl's 'Tracing EMFs' and I list his book as a must read. Karl reveals diagnostic methods and equipment he uses that reduce labor intensive search time in finding radiated EMI conditions that business industry pays big bucks to correct. It's been a while seeing your posts. Are you mellowing out or just super busy? rbj, Seattle
Hi Sam, I picked up Karl's 'Tracing EMFs' and I list his book as a must read. Karl reveals diagnostic methods and equipment he uses that reduce labor intensive search time in finding radiated EMI conditions that business industry pays big bucks to correct. It's been a while seeing your posts. Are you mellowing out or just super busy? rbj, Seattle
brian john
Senior Member
- Location
- Leesburg, VA
Re: STRAY CURRENTS
I have been involved in numerous neutral downstream grounds investigations. And there are two issues here, one is it related to an in-house issue or is it an off site issue.
Simple trouble shooting techniques utilizing a variety of amp meters and Multimeters can locate and isolate many of the sources. Typically, in house (office, schools, hospitals, data centers, ect) issues can pretty much be eliminated.
Some stray current issues related to adjacent customers on the same transformer can be located and limited. I.E. shared metal piping between structures ect.
In my experience I have only seen a few a few sites with stray current issues that we generated off site. These were resolved with dielectric couplings in the water lines.
I have been involved in numerous neutral downstream grounds investigations. And there are two issues here, one is it related to an in-house issue or is it an off site issue.
Simple trouble shooting techniques utilizing a variety of amp meters and Multimeters can locate and isolate many of the sources. Typically, in house (office, schools, hospitals, data centers, ect) issues can pretty much be eliminated.
Some stray current issues related to adjacent customers on the same transformer can be located and limited. I.E. shared metal piping between structures ect.
In my experience I have only seen a few a few sites with stray current issues that we generated off site. These were resolved with dielectric couplings in the water lines.
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