Creating a magnetic field near a pipe

[soaring]

I want to wrap no. 16 copper wire around 1" copper pipe to create a mag field. At 120v / 1 amp AC, how many turns will I need to get about 5 milligauss near the pipe?

 

[Baluncore]

I want to wrap no. 16 copper wire around 1" copper pipe to create a mag field.

Welcome to PF.
It will not work with AC because the copper pipe will be a short circuited secondary with your coil as the primary winding. The current in the copper will cancel most of the primary field.
What are you trying to do ? Why a copper pipe ?
Can you cut a slot up the pipe to prevent circular currents ?

 

[soaring]

The wire is coated so it doesn't conduct with the copper pipe. It's to be wrapped around the pipe then brought back in a straight line.

 

[berkeman]

The wire is coated so it doesn't conduct with the copper pipe. It's to be wrapped around the pipe then brought back in a straight line.

No, that's not what @Baluncore is talking about. When you make an AC B-field with a coil and some core material, you need to use a core material or configuration that will not look like a "shorted turn" inside the core (that cancels out the B-field).

That's why 50/60Hz transformers use laminated cores (with insulation varnish between the core laminations), and why higher frequency cores are made from ferrite materials (which are not very conducting).

If you look at your pipe and coil end-on, you would see a current flowing in the coil, say clockwise, and an induced current in the pipe counterclockwise. To prevent this counter-current flowing (and hence canceling out the total B-field inside the coil), you can cut a slot up the length of the pipe. From the end-on view, it would look like a small spot in the conductive pipe where there is no conductor, so no circular current will flow in the body of the pipe.

Does that make sense? Can you use a DC current instead to eliminate this back-EMF eddy current effect? Can you say more about why you want a B-field in/around this pipe?

 

[soaring]

I appreciate the responses from you guys. I'm out of my depth here. What I really want to do is counteract an already existing mag field coming from a water pipe. It's due to the neutrals not being able to handle the current so it goes into the water pipe. It causes one badass mag field that I want to overcome somehow. Any way I can wrap wire around that pipe to do it??

 

[berkeman]

It takes a loop of current (a complete circuit) to make the magnetic field. Are you saying that this is a ground fault current generated by some load? Is this in your house or workplace? What is the load that is generating the ground fault?

 

[soaring]

It's in the pipes in the neighborhood. Con Ed is too cheap to make the neutrals big enough, so the excess goes thru the pipes. I'm in a condo unit (4 units in one bldg) & have the mag field going thru a 1" copper pipe that goes right under my LR dining Rm floor. The field at floor level can go over 100 milligauss in the summertime. The easiest way to go would be a plastic coupler 10' outside the building. It's according to code, but the mensa candidates on the condo board wouldn't allow it.
I bought a transformer to knock down the current and was wondering if a coil around the pipe in the right direction would counter the flow?

 

[hutchphd]

That pipe would need to be carrying a lot of current to produce that field locally. How are you measuring the field? Why do you think your explanation of cause is correct? It may be something different.

 

[soaring]

Tested with a meter during the summer. (With a clamp meter around the pipe.) It was up to 10 or 11 amps sometimes, but only about half a volt. Con Ed measured it also. They said it was "safe". If you read enough about EMF's, you know they're full of it. I've read that they don't allow their own people to carry gauss meters.
Thank all of you who've replied so far. Much appreciated.

 

[anorlunda]

It's according to code,

I'm aware that many bizarre conventions apply in NYC unlike anyplace else in the world. But this one is hard to grasp. Can you give us more information when you say "It's according to code." What code? What does it say?

 

[berkeman]

Con Ed is too cheap to make the neutrals big enough, so the excess goes thru the pipes.

The Neutral wire and Hot wire will be the same AWG, since they are in the same Romex sheath. The Neutral circuit should not normally have a conduction path to the Ground wire inside the living spaces. What is the load that is dumping current into the ground connection? Neutral and Ground should only be tied at the breaker panel (per the National Electric Code, NEC) -- are there some uncertified electrical loads that also connect Neutral and Ground out at their position in the house/apartment wiring?

 

[soaring]

Putting a dielectric piece of (plastic) pipe in the copper line to stop the stray current from going through the water pipe is ok if it's 10' away from the building. That 10' allows the pipe to maintain its role as an electrical ground. That's according to the electric code from what I understand. Unfortunately its a mute point because the board won't allow it.
Also, the neutral is the same size as one of the positive leads into the house. So, the 240 breaks up into two 120's. But the same size neutral carries BOTH positives back to the transformer. This is in every unit. When there's a sh-t ton of current going thru the two positive wires, the neutral can't handle it, so it gets dumped to ground through the water pipes. Great for Con Ed's bottom line, sucks because it's creating a bloody magnetic field. - In NY your ground has to be connected to the water pipes.

 

[Tom.G]

Sounds like a Grounding problem in the building where the Neutral is open or disconnected somewhere, AND either a miswire or faulty equipment connected somewhere. Large electric motors and electric water heaters are prime suspects.

Your overall best approach would be to report it to the local Department of Building and Safety. They will see that it gets fixed.

In any case it needs to be fixed. It's a death trap if a plumber has to work on that pipe!

Tested with a meter during the summer. (With a clamp meter around the pipe.) It was up to 10 or 11 amps sometimes, but only about half a volt.

Half a Volt measured to where? What was the other meter lead connected to?

To track them down you need to shut off the circuit breakers until the measured current stops. If the current just changes at a particular breaker but does not go away, you have found ONE of the problems; keep going.

If no change in current is found then the problem is not connected to that breaker box. Find another breaker box to investigate.

If you are measuring the 10A current thru the electrical conduit, here is my take on it.

Same basic cause as current thru a water pipe. There may be a Grounding problem in the building where the Neutral is open or disconnected somewhere, AND either a miswire or faulty equipment connected somewhere. Again, a death trap if a plumber has to work on that pipe.

If you are measuring the 10A current thru the electrical conduit, here is my take on it.

goes right under my LR dining Rm floor. The field at floor level can go over 100 milligauss in the summertime.

Here is a situation I had that is somewhat like yours.

Back in the days before flat screen monitors, I had a CRT display for the computer. I was living in a first floor apartment with parking below.

In the early evening, when using the computer, the display would start wavering, moving around a little bit. Well, it wasn't the whole display moving, just what was displayed on it. Very annoying.

I complained to the manufacturer and they sent a replacement display.

OOPS! same problem.

So it is probably something here causing the problem.

Deeper investigation found that the electrical service for eight apartments ran in conduit in the garage, just below the floor, under the display. People would come home in the evening and start cooking on the electric stove, turning on lights and air conditioning, and so on.

Apparently the wires in the steel conduit were separated from each other a little bit so their magnetic fields did not fully cancel each other. The field must have been strong enough that some got thru the thin conduit wall and acted as magnetic deflection for my wiggly display!

I moved the monitor about 2 feet away and the problem disappeared.

Your problem is made worse by the conduit being non-magnetic Copper and not Steel, which can (partially) shield magnetic fields.
And in the Summer when air conditioners are running, much more current is flowing.

I'm pretty sure that the 10 or 11 Amps you measure with the clamp-on ammeter would be either an artifact of wire positioning in the conduit, or an overload effect within the meter. A clamp-on ammeter actually measures the magnetic field, not the current itself.

If all else fails:

• Try replacing the Copper conduit with a thick-wall steel one.
• Relocate (move) the electrical wiring (expensive)
• Find another place to live

Once more, your overall best approach would be to report it to the local Department of Building and Safety. They will see that it gets fixed.

Good Luck

Please let us know how this works out... we like to learn too!

Cheers,
Tom

p.s. Just to clear up a bit of confusion:

Also, the neutral is the same size as one of the positive leads into the house. So, the 240 breaks up into two 120's. But the same size neutral carries BOTH positives back to the transformer.

The two Hot wires carry AC that is out of phase with each other. When on is "+" the other is '-"; the polarity alternates this way at twice the line frequency of 60 or 50 Hz (cycles per second). They are connected to the ends of a secondary winding in the transformer out on the power pole.

The voltage between the two wires is 240V,
The Neutral wire is the center tap of the transformer winding, giving 120V between it and each Hot wire.

The end result is that the Neutral carries only the DIFFERENCE current used by each of the Hot wires. That's why the Neutral is the same size as the

 

[soaring]

To Tom G. and the rest of you folks -my sincere thanks.
About 4 years ago, we got a plumber to disconnect the water pipe outside the building for a few minutes and checked the magnetic field before and after it was disconnected. It did drop the mag field down close to zero right next to the pipe in my unit. Too bad the condo board shot down the fix of putting a dielectric coupling inline. Since Con Ed said it's safe, I doubt the building dept will do anything about it. I think my only choice is no. 3- to move. Unfortunately, my other half doesn't get how dangerous the mag field is and isn't as eager to look around for a better place.
I'm still thinking about wrapping that pipe (in my unit) with some insulated copper wire and running some current thru it. Do you think it can make any difference ?

 

[berkeman]

I don't think you've answered my question yet about what the load is that has its Neutral faulted to Earth Ground (sorry if I've missed it if you did answer that question). That would not be to code, and would be something that you could insist get fixed. Once you find the faulty load (whatever it is), talk to your local Building Department to get advice on actions that you can take.

 

[soaring]

I wish I knew what the load is and where it's coming from. The pipe outside the building is carrying this load. It may be coming from other buildings, or from one of the 4 units in my building. I've shut off all the breakers, one at a time in my unit with no change in the mag field. The unit next to mine tried the same while I was on the phone with her (at least she said so); again no change. The unit owner to the left of me is not very cooperative (to say the least). Maybe I should get in touch with the bldg dept to try to get some action.
Thanks again. You guys are great!

 

[berkeman]

Yeah, the Building Department would be good to contact. Keep us updated on what you find please.

 

[Averagesupernova]

https://www.physicsforums.com/threads/losing-neutral-in-the-utility-system.886787/
-
I started the above thread a few years ago because at the time there had been some confusion and misinformation concerning the neutral conductor in the utility system here in the USA. Thought it might serve a good review for those interested. It is a very common misconception that if there is ground current on a water pipe feeding a building that the fault has to be in that building. This is not necessarily so. Have fun...

 

[berkeman]

https://www.physicsforums.com/threads/losing-neutral-in-the-utility-system.886787/
-
I started the above thread a few years ago because at the time there had been some confusion and misinformation concerning the neutral conductor in the utility system here in the USA. Thought it might serve a good review for those interested. It is a very common misconception that if there is ground current on a water pipe feeding a building that the fault has to be in that building. This is not necessarily so. Have fun...

Interesting, thanks for the link back. So a missing Neutral connection at one panel can cause that ground current flow back to a neighbor's panel and their Neutral? Yikes. (BTW, the Mike Holt link is broken now)

The consequences of this have been discussed many times here on PF. Here is an example of what can happen.
http://forums.mikeholt.com/showthread.php?t=178779
If you live in a rural community with your own water system or your water supply comes in on plastic this sort of thing seems impossible. But the truth is that you could likely cut the neutral conductor completely off in the service panel and it is unlikely you would notice it if you live in a section of town that everything is well bonded with metal water supply pipe. The current that should be in your own neutral conductor is finding its way back to the transformer through your neighbors neutral. Scary to think that some hack electrician my neighbor may hire could cause problems in my own house. Messing with the neutral can certainly be more dangerous in the long run than being a little careless with one of the hot wires.

 

[Averagesupernova]

Hmmm. Bummer about the link being broken but yes, as described, the current that should be in the neutral can find its way back to the transformer in other ways. It is not uncommon for electricians or plumbers to do a quick check with a clamp on ammeter before disconnecting a pipe or ground wire for a repair that would involve such a thing. More than once a plumber has been surprised by sparks, etc. when a seemingly harmless water pipe is cut off.

 

[hutchphd]

Personally, I am more concerned about the currents than the magnetic fields.

1. If it really is a ground loop in the pipe the magnetic field should fall off roughly linearly with distance from the offending pipe
2. I personally am not aware of any evidence that a few milliGauss field causes any clinical issues and other appliances produce these kinds of fields routinely I believe

I don't mean to kick the hornet's nest, but is the magnetic field what we should worry about here??

?

 

[Baluncore]

I'm still thinking about wrapping that pipe (in my unit) with some insulated copper wire and running some current thru it. Do you think it can make any difference ?

The magnetic field is produced by the current flowing along the copper pipe. Winding a wire around the copper pipe will not correctly cancel that particular magnetic field geometry, to cancel the unwanted field you must run a wire parallel to the pipe, that will carry an equal and opposite current. That sounds simple, until you try to do it.

There are a couple of problems to solve.
The first is getting the return current from your current loop back to your generator without producing an equal and opposite field somewhere else.
The second is that you will need a sensor and feedback system to regulate your loop current. If the current stopped, a fixed cancellation current would keep generating the reverse field.

There are several other possibilities to contemplate.
1. Run another parallel metal strap some distance from the pipe, and bond that to the two ends of the pipe. The current will divide and take two paths. The fields will tend to cancel between the two. I imagine chicken wire unrolled and attached under the floor.
2. You might put a ground stake in the ground on the building side of your home and connect that to the pipe, in effect short circuiting the ground connection.
3. You might leave your current clamp meter, or a magnetic core around the copper pipe. That may inductively limit the current and send it to ground via some other water pipe. Why not harvest some of the energy available while you are at it, whoever has the neutral to ground fault will get a lower voltage.

 

[soaring]

Baluncore, thanks! I asked someone a while ago about a separate ground. They said it would require a very large wire going to it, since the copper pipe is a large conductor. They didn't think it would change things much. I may try a separate (empty) copper pipe at a distance from the first as you mentioned. If it doesn't work, or makes things worse, I'll just remove it.
hutchphd, also thanks. I'm way more concerned about the mag field! I've read about 5-6 books about EMF's. It's just anecdotal AFAIK, but anything over 1 milligauss can give a baby Leukemia within months. (Book - "Tracing EMF's" by Karl Riley has one tragic story). Experiments on humans show physiological effects on cells with less than a 1/2 milligauss field.
You guys saved me a lot of time from trying to wrap that wire around the pipe. And, I would have been right next to a large mag field the whole time. (I would only have done it in the spring or fall when the weather was best - no AC, or heating, to minimize the field.)
Thanks to all contributors to this post.