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Thread: High EMF Readings Outside Home

  1. #1
    Join Date
    Jul 2010
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    High EMF Readings Outside Home

    Could high EMF readings be due to problems with the incoming power line from the street, to our house, rather than internal wiring errors?
    What I did:
    1. Switch off main breaker. Wait 10 minutes, let any fields collapse.
    a. No difference in EMF readings. 2-4 ft. around panel area readings remain at about 100mG.
    2. Measure water pipe near service panel for current using clamp meter.
    a. 0.6 Amps
    3. With mains still off, disconnect #2 stranded GND wire running from service panel, to water pipe. Measure current and EMF.
    a. Current is 0.00 Amps, EMF stays same ~100mG.
    b. Touch GND wire to pipe. Current rises to 1.5 Amps. No voltage detected between pipe and GND wire.
    Measured EMF outside home from meter panel and along 130 foot driveway where incoming cable is buried. Weather is very wet and humid due to earlier thunderstorms. At ground level, EMF readings were >100 all along driveway, on surface of the street and at pole.
    The next morning, cooler and less humid, readings had dropped down to around 30mG all along driveway and street. Readings near the service panel had dropped from 100mG, to around 30mG.
    Thoughts?

  2. #2
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    What type of research do you do?

    What made you think to check for EMF?

    Describe where you live. Common water system with your neighbors?
    Rural, suburbs? Is there a transmission line close to the area? Have you been having electrical problems such as lights changing brightness?

    What type of amp meter are you using? What scale? Someone mentioned in another thread that a low amperage reading may not mean much on a meter with 100 Amp (or greater) full scale.

    Cooler, morning & less humid means that the total electrical load in the area has gone down and thus any EMF would be reduced.
    Tom
    TBLO

  3. #3
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    Smile Addressing Tom's Questions

    Hi Tom, addressing your questions as best I can:

    What type of research do you do?
    My research area is in molecular biology so that does not really factor into this discussion. I do however, understand a moderate level of electricity because of my hobby, ham radio.

    What made you think to check for EMF?
    I had read that EMF can aggravate diabetes and my son is a Type-1 diabetic. I first thought of checking for EMF because of our wireless router, computer screens, fluorescent light bulbs and the myriad small transformers in today’s electronics. I accidentally discovered that our problem is the electrical system and current on the water pipes, not lamp bulbs, routers or computer equipment or TVs. Those are not significant.

    Describe where you live.
    Older neighborhood. Homes built circa 1940 and upgraded. Ours was built in 1943, upgraded in 1960 with new wiring, a 200Amp panel and all-copper pipes. Many multi-wire circuits sharing a common neutral in the old part of the house, but still in good shape.

    Common water system with your neighbors?
    The city water- supply runs along the street with branches going left and right to each house along the street. The area is rural even though close to Wash. DC. There are no sidewalks and some of the people in the neighborhood still have wells and septic systems – we do not and no one on our street does anymore.

    Is there a transmission line close to the area?
    No. The only electrical supply is via std. telephone poles with transformers and drops to the houses.

    Have you been having electrical problems such as lights changing brightness?
    We have no problems with lights dimming or changing brightness. We have had many instances of transformers exploding after tree limbs break off and having electricity out for a day or two due to storms - happens often. I keep a generator on hand for those times.

    What type of amp meter are you using? What scale? Someone mentioned in another thread that a low amperage reading may not mean much on a meter with 100 Amp (or greater) full scale.
    I’m using a Sperry Clamp-on meter . Forty Amps is the lowest scale. Sperry’s website states that the meter has a resolution of 10milliamps. Ten milli amps is the minimal requirement according to the book “Tracing EMFs in Building Wiring and Grounding” that I bought from Mike Holt.
    I built an large addition to my home about 15 yrs. Ago, did most of the work myself including electrical and plumbing. So far, EMF readings in the addition do not exceed 1-1.5 mG, so I’m guessing the problem lies with the old wiring in the old portion of the house, objectionable current coming in from the neighbors through water pipes, or degradation of the power coming in underground, at about 4-5 deep, under the driveway. The underground service was put in in 1960. Somewhere I read that once the mains are shut off, any EMF still present must be coming from the neighbor’s house or the power line and not internal wiring. Don't know if this is true.

    Very recently, new Cable TV and new Phone cable was dug because the old cable had degraded. It is possible that during the dig under the street and close to the pole, the power cable was hit – the three cable types come awfully close together as they merge at the pole.

    Cooler, morning & less humid means that the total electrical load in the area has gone down and thus any EMF would be reduced.
    OK. Makes sense. But still leave the question of the EMF origin.

    I greatly appreciate your assist. Thanks.

  4. #4
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    100730-1310 EST

    George vonB:

    Generally in my house I am somewhere less that 5 milligauss. My meter and probe is only quantized to 5 mG. At the main panel, Sq D QO, I get in the range of 100 milligauss. Next to main water line 15 milligauss. 35 ft below my 3 phase delta primary lines meter reads 0, so less than 5 mG. 3 ft above my underground lines to house meter is 0. Next to rigid conduit into house about 15 mG.

    Using another voltmeter with the probe I am below 0.5 milligauss for the general background in the house.

    I do not know what to expect on a 3 phase Y with a good neutral. If the primary neutral is bad then with earth as the neutral conductor and where only a single phase on the primary is provided, then there is a large loop that will provide a moderately large external magnetic field.

    With the kind of signals you are measuring there is no decay time, maybe a few milliseconds. 10 minute wait is a waste of time.

    .

  5. #5
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    Quote Originally Posted by George vonB View Post
    Could high EMF readings be due to problems with the incoming power line from the street, to our house, rather than internal wiring errors?
    What I did:
    1. Switch off main breaker. Wait 10 minutes, let any fields collapse.
    a. No difference in EMF readings. 2-4 ft. around panel area readings remain at about 100mG.
    2. Measure water pipe near service panel for current using clamp meter.
    a. 0.6 Amps
    3. With mains still off, disconnect #2 stranded GND wire running from service panel, to water pipe. Measure current and EMF.
    a. Current is 0.00 Amps, EMF stays same ~100mG.
    b. Touch GND wire to pipe. Current rises to 1.5 Amps. No voltage detected between pipe and GND wire.
    Measured EMF outside home from meter panel and along 130 foot driveway where incoming cable is buried. Weather is very wet and humid due to earlier thunderstorms. At ground level, EMF readings were >100 all along driveway, on surface of the street and at pole.
    The next morning, cooler and less humid, readings had dropped down to around 30mG all along driveway and street. Readings near the service panel had dropped from 100mG, to around 30mG.
    Thoughts?
    I lost you when you said here "incoming cable was buried" - is it a power cable or another utility? your reply to ptonsparky said your power supply is "via std. telephone poles with transformers and drops to the houses".

    I am amazed at your EMF reading of 100mG. normally, I would find that reading when my EMF meter is beside an EMF source. even inside a substation, I would have to go near a transformer to get those readings.

    my take would be that the instrument is not accurate (a long shot, I know) or you are near buried power cables. buried power cables are closer to you than the ones hanging from overhead lines. the lower the voltage, the higher the magnetic field

    you mentioned the drop in EMF readings between your first reading (no time frame mentioned) and the 2nd reading that took place "next morning" that is "cooler and less humid". assuming that both readings took place in mornings, I would say the drop in power consumption due to the cooler morning will account for the lower EMF reading. which makes me (again) believe you are near buried power cables.

    here are some pictures on readings with an electric fan. the drop is EMF reading is due to the 12 inch difference in distance between the meter and the fan motor. the readings in the meter are in milliGauss

    the World Health organization (WHO) standard, which was also adopted here in the Philippines, is 833 milliGauss. even though 100 is a tad high, I believe that there is nothing to worry about.
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    Last edited by robbietan; 07-31-10 at 12:59 AM. Reason: additions
    NEC 1968 and 1948

  6. #6
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    100 mg is quite a bit. I would not be able to tell you if it should be of concern.

    As you can tell from robbietan's pictures the field around a motor drops rapidly as the distance increases.

    Not so with improperly wired circuits that do not have the conductors grouped together. I see places that have all the neutrals tied
    together in j-boxes even when they are associated with different circuits. Multiwire or not.

    Does the drive way parallel the underground service conductors? Is it concrete all 130'? I have in the past been able to locate a buried service with a MG meter but it was not very deep.

    Assuming you share a common metallic water pipe system with your neighbors, a faulty neutral at another location could become your problem. You could isolate your water pipes from the neighbors by having a plumber install an insulating section of plastic in the pipe feeding the house. He may not like the shock he gets as cuts out a section. Not really a joke as this can happen. It would have to be outside of the house.

    Your underground servce could be faulting but that eventually causes noticable problems in the house. CU would last longer than AL. You will have to coordinate with POCO and an Electrician with a megger to test it. Both ends of the service must be isolated.

    Try walking around the neighborhood with your meter and plot the pattern of readings. That should be right up your line of work.

    The answer to your original question is Yes.
    Tom
    TBLO

  7. #7
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    Perform zero sequence current measurements at your main panel with your clamp-on.It should read zero (all the time) and this will correlate to approx. zero mag field above your incoming driveway located cables.If the reading is not zero,it is time to call someone for help.
    May the force be with you

  8. #8
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    Quote Originally Posted by ghostbuster View Post
    Perform zero sequence current measurements at your main panel with your clamp-on.It should read zero (all the time) and this will correlate to approx. zero mag field above your incoming driveway located cables.If the reading is not zero,it is time to call someone for help.
    And unfortunately your average residential electrician may not be of much help unless you can provide direction. Most electrical testing companies have someone on staff that could address this issue.

    Typically we would do this with all possible loads on and with all loads off (two separate measurements)
    Perform zero sequence at the panel and any sub-panels (as noted by others)
    Measure current on the neutral ground bond jumper.
    Measure current on the incoming utility water pipe.
    Measure current on any grounding electrodes.

  9. #9
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    Generally for a residential service that has a common metallic water system within the community, you will have current flow on the bonded water line. Nothing you can do about it. Just make sure the bond is as close as possible to where the pipe enters the building.
    Tom
    TBLO

  10. #10
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    Quote Originally Posted by ptonsparky View Post
    Generally for a residential service that has a common metallic water system within the community, you will have current flow on the bonded water line. Nothing you can do about it. Just make sure the bond is as close as possible to where the pipe enters the building.
    We had 1 client with very high mag readings near all the bathroom copper piping.The utility was called and they cut all the wires at their pole except the neutral.There was 30 amps measured on this neutral wire going to the clients waterpiping with all power turned off to the house.The utility claimed they must have bad tx. grounding in this residential area and the clients waterpiping was providing the ground for this utility system.NOTE:The client had a 4 year old child with leukemia cancer and was very very concened.
    May the force be with you

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