Shielding Magnetic Field From High Voltage Line

Is moving to another room out of the question?

No way. Room is fixed, line is there for another 5 years and two small babies to be protected. Epidemiological studies show cancer risk increase over 300 nT, you know.

If there is a hazard to living so close to power lines you can petition the power supplier to have them provide shielding for your home. I am not convinced there is a problem, there have been numerous studies into living next to power lines and most were inconclusive or showed no correlation to the power lines being a cancer causing stimulus.

What method did you use to determine the magnetic field in your home?

Drew K

I use Gigahertz solutions ME 3830 AC E / H measurement device.

About carcinogen agency of H field, there are different opinions for sure. But I think you are an American and Americans like to use statistics. So epidemiological studies show it which is "statistical" output. WHO stated H field as 2nd class carcinogen last year if I am not mistaken.

powerwatch.co.uk is a good web site with scientific approach for ones who are interested in this debate. I am not taking sides so do not come over me.

Regards, NKU

Nothing wrong with statistics, it is based on actual data. And it's better as well as more sound than theory.

But, It's how you use that data

Interesting point of view considering the EPRI study that was concluded in 1981 on this subject. (Not published for general public review.)

The conclusion clearly stated that the seratonin levels in lactating and pregnant women living within 300 feet of high voltage tranmission lines (100KV and above) are severely affected (decreased) causing an associative increase in depression in those exposed.

The study also stated that additional testing is needed in order to address "other" human health anomalies identified during the study.

Also; Consider that the average time of death of people working in close proximity to HV power lines and equipment is 67 years of age which is far below the national average.

I know for sure that the incidence of cancer among all of the people I have worked arround over the years that worked on HV power is alarmingly high compared to those that were not exposed.

I am not so sure that we are not being misled about many of these issues on the basis of negatively affecting the profits of large utility companies.

What other carcinogens were your hv friends working with? asbestos perhaps? solvents perhaps? did they smoke? drink?

Show me some definitive research that shows how being around hv (other than contact with) can hurt you...because there is a 118MW turbine just a handful of meters from my desk at work.

Drew K

I would just move.....

the United States Navy sheilds the critical rooms in their ships in Copper Mesh............ too bad your not a country.

Kris-Del offers a copper mesh hat.....from the're protecto hat line...

Will it get that nice blue green patina over time?

Since when a metallic mesh had acts as a shield for MAGNETIC FIELD ? ?

A metallic mesh had, as well as a conductive suit is a shield for ELECTRIC FIELD.

Do know and appreciate the difference between MAGNETIC and ELECTRIC FIELDS.

Copper mesh can work very well on magnetic fields. It all depends on the frequencies. It works for coaxial cable, no?

The woven outer braid of a coaxial cable is not a magnetic shield - it is an electric shield and form the return conductor.

It is surprising how may in this discussion do not know the difference between magnetic fields and electric field, but do enter the discussion.

Then pray tell, how does a magnetic shield work? Would you care to elaborate on the concept of skin depth? Maybe you can provide some illumination on self-inductance. I guess you have never heard about self-shielding. How about reflection losses? Absorption losses? Perhaps you can comment on how a low relative permeability material with high conductivity can block magnetic fields? This is going to be fun.

What was the saying that ends with, " . . . and to remove all doubt." ??

Please stick to the subject at hand . . . 50/60 Hz magnetic field.

Yes, you have removed all doubt.

To bring the portion more on track, this is what I was referring to.

http://www.bombshock.com/electronics/how-to-protect-yourself-from-electro-magnetic-pulse.html

It addresses better what my intent was to the op and its actually a pretty good read, tear it apart and over analyze it all you like.

It's so surprising that the U.S. Navy has next to absolutely nothing to point out its protection against foreign enemies. (Btw, I also said this with tongue in cheek and amused)

Depending upon its use, the woven outer layer of coax cable is more than likely for the purpose of sending any potential RF inference to ground. There is a separate distinction to be made, when you are considering ALL possible sources of "field contamination" between RF energy, and magnetic fields. But, that distinction is is lost on those who fail to comprehed, why the solutions to both problems look quite similar.

Do not know what your background is, but what started it, is when I said (with a tongue in cheek) the United States Navy uses it on their ships in critical command and control areas, and that is to protect it against a EMP during a nuclear blast.

Have you ever induced a electric field by using a magnetic field? Basically the same principal.

Than you deal with the electrical field.

Yes, you have just built an air core transformer. Not very efficient at power frequencies.

Where does the shielding come in?

Nothings perfect,

Why don't you talk to these guys, (http://www.navy.mil/) maybe you can Shed some light on them. I'm sure they would love to hear from you.

That's to protect the steel plate in their heads during lighting storms

How much for the hat? Does it come in unobtainium?

Depends on the style, whether you buy off the shelf, or we have one custom designed by our staff of overpaid designers...

DIY kit supplies....

PS: the unobtainium is currently unobtainable.....

it always is, when you ask a question like, How much for the hat? and not get response............

I can't afford it......

You pay a steep price for one of these beauties, . . . take it home, . . . and find out it does not shield your skull from magnetic field.

But is is a good shield for electric field from that 220 kV line nearby, . . .

I am curious...I have played with some strong magnets (1.4 tesla) and noticed that when I drop them through an aluminum tube they fall slowly (eddy current) but also if the aluminum is thick enough the pull of the magnet is much less when interacted with another magnet...it is like the aluminum blocks the pull.

I know that magnets act the same when dropped down a copper tube so I imagine the copper will have a similar blocking effect to putting the magnets together with copper inbetween.

How is this not shielding?

Drew K

It is. Copper and Aluminum are both conductors. Cu is magnetic and it requires a strong magnet to be that way. Al is not magnetic. Shielding is reducing the electric field in a confined space by using barriers that are either conductors or magnets. You are describing shielding if the metals are Cu and Al but I think Cu would be much better at the job. Thickness makes a difference. That's why the thicker Al had a higher effect.

Rose

But Steel is also a conductor...I need to learn a lot more about magnetism...

Drew K

Same here, except I pitted a SmCo magnet against a similarly-shaped and weighted bit of metal in a race down a 45-degree, 10 mm-thick aluminum plate, in order to demonstrate to our MIT interns, in practical terms, how moving magnetic fields induce currents in conductors. The magnet lost, predictably, thanks to eddy currents its field-in-motion induced in the aluminum panel which, in turn, opposed the magnet's motion. I shadowed that magnet from the other side of the panel with a probe and, predictably, measured a weaker field when the magnet was moving than when I stopped it with my hand. They had never heard of anyone doing this. MIT undergrads! What's the engineering world coming to!?

To olehwi:

Copper and aluminum are not magnetic in the sense that permanent magnets stick to them as they would to one's fridge, but the induced currents flowing inside conductors of any stripe due to external, varying magnetic fields are. Most definitely 'magnetic' indeed!

Both copper and aluminum also happen to be very good at shielding from electric fields, especially when used in a Faraday cage. The specific frequencies you wish to shield against will determine your material needs; whether non-ferrous, like Cu and Al, or ferromagnetic, such as mu-metal which is fabulously expensive but very good as a magnetic-shield material - up to a point.

If you're concerned only with high frequencies, aluminum foil works just fine. If low-to-DC frequencies, mu-metal is great, until becomes saturated, at which time it can no longer shield against any additional flux, essentially becoming 'transparent', if you will, to the excess field past that point.

You are correct in saying these metals are non-magnetic. They are non-magnetic. Not so for any currents flowing inside them, however! If you've got a current, you've got a magnetic field. Even air 'has' a magnetic field when lightning occasions to visit, and so you'd better wear that copper hat next time you're out golfing in a storm. And Keds. Lord knows lightning hates Keds. Abhors 'em so much it'll turn right around and go straight back to mama!

This would be far cheaper and a lot easier to apply to the walls than mumetal; it should provide some shielding:

Magnetic-Latex-Primer

There are other brands of magnetic paint besides this one, other colors, too, I think. Apply it to all of your walls, the ceiling and the floor, too, if possible, then paint over it with whatever color you want. If you're really worried about the windows, make some shutters painted with this paint too, to use at night over the windows.

Be aware that your cell phone reception may be poor after you've applied it.

This is a paint with magnetic pieces. Static magnetic materials may show some degree antimagnetic effect but this is too little to mention. It is more likely to have children's room with some eccentric magnetic property with this paint and not any other property else.

NKU

If the field is not too strong, that means you're far enough from the source so the field gradient is small (the field is similar everywhere nearby). It's a 60Hz (or 50Hz?) field, so you could create a canceling field by powering a coil from your AC line.

Helmholtz coils have predictable, nearly-constant, fields in their central region. Helmholtz coils are usual wound on a round form, to make a circular coil, but square coils work fine, and might be more fitting for wall and room dimensions. You could wind two large square loops and position them just outside your walls. Depending on the field's vector through your rooms, you might need a second set of coils at the floor and ceiling levels.

Did you say the transmission lines run parallel to your rooms? That should spare you the need for a 3rd pair of coils for the 3rd axis.

Variacs or Powerstats (brand names for adjustable autotransformers), are convenient for adjusting the fields in each coil to cancel the external field vector along the axis of the coil.

Would you also like to cancel or reduce the earth's magnetic field? You could add a DC current to do that.

CR4 Admin: Removed broken image links

Could you spend more time explaining your application and less mentioning 9/11. I don't even know if this is at a work place or in your home.

If at a work place (with children?) have you talked with your management or internal quality and safety department regarding the perceived risks backed up with data, or have you already and they have given you the go-ahead and budget and you are just trying to figure out the best way to implement the shielding.

Please provide more information.

Residential area/ Apartment / 7th floor.

The power line is 15 meter away. No possibility of removal for the next 5 years.

Target areas are bed rooms, priority on babies of 6 months and 2 years old. One bedroom with no windows will be preferred for babies and another room for parents. The latter has windows almost from ceiling to floor.

The line passes equidistant to the 7th floor. Presume to both bedrooms with the same conditions except that one has huge windows.

I have two mumetal options 0.02 mm and 0.2 mm. I try to fit a budget of 2 thousand USD at most.

SO more specific questions:

In plane wave applications, EM radiation bends around the edges and propagates in all directions. So I block every possible slit, cover 6 sides at the same time and use overlapping curtains or glass films for the windows and assure a very good continuous grounding. I have more than 200 applications in RF area but I do not have similar experience in H ELF.

Does M wave behave the same way? Do I need to block only one wall closest to power line or do I need to cover all three wall ( or more with ceiling and floor)?

I saw they paint the mumetals against corrosion so I will have a lot of civil works too.

Regards, NKU

Seriously! Focus on what is important! There are many other things out there in your part of the world that shorten life much more drastically than buying into some tin foil hat wearing luddite who is trying to scare you into believing in a boogey man when there is a real and present danger in the tobacco and pollutants surrounding you!

Don't believe I am just ranting, think on my words for what they are!

Drew K

Well said! I couldn't have said it better myself! I agree. Stay on what is important and not the silly things.

What you refer to is a property of the wave, and that property is dependent on the wave length. That wave length in your case is easily blocked by "mesh" of a kilometer or more in "hole" size! You do not have a problem there.

Look, the frequency of the signal you are trying to block is so low that you can't couple to it. YOU aren't big enough. Your body, if it is an antenna isn't even close to being 1/64 of a wave let alone the 1/4 wave length you need for "good" reception! And the baby? Even smaller!

The building itself and it's plumbing should be enough.

The T measurements you make are an average over time. What you are experiencing is a fraction of what you get just from space weather, running motors, microwave ovens, radios, TVs, power supplies etc. ALL operating at the SAME FREQUENCY.

YOU DO NOT HAVE ANY MORE OF A PROBLEM THAN YOU WOULD WITHOUT THE POWER LINES.

So how are you measuring this 500 nano Tesla field anyway?

Device ME3830 Gigahertz solutions. Parallel to ground ( it is a one D device).

The selenoid is also parallel to the ground. Other polarizations are rather low and negligible.

Dear Sir, I am not American but Indian, so neutral person. I am rather puzzled and shocked after going through whole debate. For my curiosity may I ask you few questions which I hope you would kindly reply:-

1. Since when this power line came to existence?. Before your residential building was constructed or after wards?.

2. What power company has to say about your problem, is it safe for you and your kids?.

3. What local authorities have to say about this problem?. If it is unsafe then why permissions are granted.

4.What health authorities have to comment about any health hazards?.

From some of the comments I understand that there is nothing to worry about. May be you are overprotective about your kids. Please do not get offended by my remark, just reply me with cool mind.

How long have you been living in this apartment next to these power lines? Were these power lines erected after you moved in? If they were already existing, why did you move in, in the first place? As mentioned before, I'd be more worried about the microwave oven, they can give you that nice warm feeling when you least expect it.

If you make a grid of 2'x2' from foil tape on the children's wall next to the power line, and you solder each joint. Then effectively bond to ground (earth). You will sleep well, knowing that you have your children sleeping in a protected zone. Don't worry about other exposure as the time in there room should be close to 1/2 their time in the home. I would use 2'' wide foil tape and a small amount of solder just to make continuity connection between over laps of tape.

Guys I give up...

In our "mideast" we are silly, we use huge transformers in our laptops so they emit mT range magnetic fields and we put our laptops right over our testicles and we further sleep like that so its exposure is much more, we do not have the ability of checking the academic searches on magnetic field effects (Swedish study 1960-1975; Wartheimer Leeper 1978; Nalia 2004; emf-portal.org ;Tubitak Black Sea Zone 300m range of power lines cancer doubles if not more and so on..); and we blow ourselves up if we are desperate (not exactly the same but similar to Oklahoma). So be it.

A father cares, no matter which nation he belongs too. A mother cares more, for she is a mother, it is her gift from God to care of and protect her offsprings.

Thanks for Phoenix911 for his tolerance, and thanks to all who tried to propose a solution instead of persuading me that I should not do it. I will surely do a combo solution even if it is for the placebo effect. Married ones would easily understand.

This is my last thread in this question adventure. Hope to meet you all soon with more adventures of Sinbad.

So what is your conclusion?. Just giving up does not solve the problem.Are you convinced now that your fear was just being extra cautious. Please do reply and do not just give up.

I actually understand where you are coming from, but this is a very expensive placebo just to keep someone else happy.

Good luck, but don't be surprised when you still measure the same nT values after all your work.

....your worried about your kids health and long term exposure - got it and the more power to you.

Back to basics

Magnetic fields are not 'groundable' however they are mostly re-directable or can be reduce thru basic loss in a material. Most importantly to remember is that we have an r^2 reduction with distance so:

#1. move further away from the power line, a little is a lot!

#2 any soft magnetic material is good (cheep cold rolled sheet metal) and can be put on wall. Some energy will be lost in the metal to align domains and the rest will be redistributed and lower the peak field seen without the sheet metal in place. Mu metal is great (does the same thing) but is really really expensive. Try to poor mans route first.

BTW the best advice I ever got from a pediatrician is worry about the big stuff like pools and car accidents and do what you can about the little stuff.

[serious_reply]

A better approach I think is to anchor your perspective in a well-grounded sense of proportion. As others here have already mentioned, 500 nT is nothing, magnetic-field-wise. Suffice it to say that your stressing over this is far more likely to prove damaging to your health than exposure to such a minute field. The magnetic fields your own body produces are of comparable strength and you've been exposed to those your entire life, yes?

[/serious_reply]

-----

(To certain friendly CR4 smart alecks whom I need not name [you know whom you are, you buggers] please insert "And so that's why people die, ay? Is that wot you're sayin'? Offed by their own itty-bitty magnetic fields, ay? Ay? Poor blighters! There outta be a law!" ) __________________________________________ .

Simply build a Farad cage in the room, ensuring the cages is properly earthed, then work inside the cage. A metal shed (hut) is what you will end up with. One Farad cage. If you only do certain walls the cage will not work and this means the ceiling needs to be done as well. Any openings will cancel out the cage.

The man is afraid of magnetic field from a power line . . . namely magnetic field of 50 Hz.

A Faraday cage does ZERO magnetic shielding at 50Hz.

A Faraday cage shields electric field at this low frequency.

We all like numbers........I quickly modeled a magnet in air next to a body of material. Then I added a piece of sheet metal ".018" between the body and the magnet. The magnetic field was attenuated by 1 decade. Remember you are probably only concerned about the sleeping position (10hrs per day?).The data indicated is a point in the body itself to the left.

Then I doubled the distance and it dropped another half a decade to ~ .5x10-6T. Regardless of the absolute the data scales.

Here is the results (FEMM) with and without sheet metal.

Again, throw up some lost cost sheetmetal, move to the other side of the room and measure....you might be surprised!

tommyb2:

This is interesting, thanks for your efforts....... what software did you use?

olehwi can you explian this?

The program FEMMdotinfo has been around for quite awhile and is a 2D FEA program that is quite powerful and amazingly free. It will also do electrostatics as well as thermal FEA meshing and analysis.

Note that it is cumbersome to use, but can import DXF files such that an actual representation of the hardware in question can be reviewed. In this case, I just sketched a simple model to look at scaling and what if scenarios. It took < 5 minutes.

Make sure you get the pdf manual and take a quick look at an example before even attempting to use it...it really is that cumbersome and you will quickly get frustrated.

Best of luck and take care.

Thermal FEA meshing ill look into that, thanks

This is obvious, but what does it have to do with shielding the magnetic field from a power line with a copper-wire-mesh hat?

I can assume that the "sheet metal" is some formulation of iron, quite magnetic and will shield the magnetic field from a magnet or a power line.

But how does the magnetic sheet metal "model" the performance of that "copper-wire-mesh hat? Your model - is not modeling.

Errr - funny group here?

OP wanted to know how to reduce B fields to give em peace of mind for his kid? Best response has been a berating of worry, don't use MRI, don't live life etc, kind of odd and disappointing?

Response to a quick quantitative sanity check on solution that can be implemented by OP vs kooky solutions with no data is "Your model - is not modeling". Not to start a flame war, but really, do you think your response is adding value?

Maybe you could supply some sort of support to your proposed solution of a copper wire mesh hat? You may also want to read up on E field vs B fields before responding. Most useful is to focus on OP question! However, I can help a little bit, copper mesh will not attenuate a B field, there is no bases for this approach.

All the best!

olehwi ponders: "This is obvious, but what does it have to do with shielding the magnetic field from a power line with a copper-wire-mesh hat?"

Crikey, mate! It's a bit of patently obvious tongue-in-cheek, that's what it is. Is this so completely non-obvious to you that it has to be painstakingly spelt-out in simple English?

uluaydin, the pooled results of quite a few studies in different countries may be found here. Also visit the links on that page for additional study results.

-e

mu-metal is a poor material for construction. Any rough

handling or shock will seriously degrade the relative permeability

and you will end up with an expensive sheet metal.