The following is a report referencing an ELF magnetic survey began on 10/17/2000. I am leaving out the name of the person who requested the testing as well as the address where the testing was conducted. The testing was conducted in the state of Florida. The report mentions a floor plan but that was not provided to me, however the survey requestor remains at the address today. Additionally, for reasons well known to TIs, I will only include the initials of the professional who conducted the test although the full name is on the report. Nothing else has been redacted. REPORT ON MAGNETIC FIELD LEVELS AND SUGGESTED MITIGATION On 10/17/2000 I conducted a magnetic field survey of Villa H at 7PM, measuring at waist level, or 30 above floor level. The measurements are shown on the accompanying floor plan. The average of these measurements was 7.06 mG (milligauss). This was at waist level. A measurement at the floor above the source which runs through the villa parallel to te front measured 25 mG. These measurements were made at a time (7PM) which corresponds to 30% under the average peak of about 10.5 mG (maximum 20.88 mG) as recorded by an Emdex II data-logging triaxial gaussmeter worn by the survey requestor for 5 days from 8/25/00 to 8/30/00. The Emdex ll was provided by Cindy Sage Associates, a well known California EMF consulting firm. The Emdex was returned to them and downloaded to a computer to produce the graph. The measurements on the graph at 7PM agree with the 7 mG average level shown by our measurements. This magnetic field level in a residence would only occur in the upper part of the 99th percentile of homes nationwide, as shown by the 1,000 Home Study by EPRI (Electric Power Research Institute-supported by the electric utilities). This study, the Home Study, reported in the April/May 1993 issue of the EPRI Journal, showed an average (mean) of 0.5 mG for the thousand residences. At the high end, even at the 90th percentile, the mean was just 1.7 mG. In my 10-year experience as an EMF consultant for residences, schools and commercial buildings, a 7 mG mean is extreme. Looking at the floor plan with measurements, hat stands out to the experienced EMF consultant is the uniformity of the field within the entire villa. This is typical when an area is within a loop of field sources. The characteristics of the inside of a loop are uniformity. Following the magnetic field survey I used a field tracing instrument to discover the sources of the loop. I used the MSI Magstick, an instrument with a magnetic field sensor on the end feeding an amplifier into which earphones are plugged. One can easily trace strong magnetic fields buried underground with this instrument and quickly delineate the linear path. I found three strong linear field sources: One runs in the grassy area between the villas and the sidewalk. It started from a villa opposite the electrical master panel, ran parallel to the villas in a southerly direction, and then made a right angle turn to parallel the villas to the east. I did not follow it beyond this point. This field is from an electric current traveling most probably in a metallic water pipe, whether in the sprinkler system or water supply system. The second path parallels the rear of the villas, 6-8 feet out into the lawn. It begins at the electric meter panel. It is most likely coming from the underground electrical supply cables feeing the meter panel. The third path runs through the villa under the floor parallel with the others, in a path which runs directly under the threshold of the bedroom doorway. This is also the location of the villas electric breaker panel. The source is assumed to be the electric supply cable for all the villas in that row. After locating the source pathways, the next step was to discover the causes. High fields from linear sources are caused by net currents flowing in conductors. Net currents with their high magnetic fields result when one of the currents which runs in an electric cable has split off and some of it is shunted to a different path, typically a water pipe. When current from a conductor in a cable is diverted elsewhere, the magnetic fields of the different conductors no longer cancel each other and a net current field is created. Its strength is directly related to the number of amps of current which has been diverted to the water pipe. At the same time, the water pipe is now generating the exact same magnetic field. This gives the typical two paths associated with the shunting of neutral return current to a water pipe. (These divided currents reunite at the transformer source). Since in this case there were three paths, the task was to verify that the two paths were caused by neutral diversion from the main service panel, and to find where the third path was coming from. This was accomplished by taking a series of measurements at the main service panel with its cluster of meter panels supplying the various villas. This was done the next day at 2PM. This measurement protocol is described completely in my book. (I, Sandra McDonald am purposefully leaving out the name of the book although it is named in the report.) Please refer to the master panel diagram (the diagram was not included in the report I received from the survey requestor). The first measurement to be taken is of any net current from the supply conduits going to the main panel. To measure net current amperage one needs a special flexible amp probe which goes to a multimeter to read amperage. I used the AEMC Ampflex 300. Cables which have all currents running in them always measure zero net current. These cables measured 4.8 amps net current. This amperage would produce a magnetic field of 9.6 mG at one meter from the cable, which is in line with the measurements made. The next step is to see if the 4.8 amps, which represents shunted neutral current (missing from the cable) is detected in the grounding conductor which goes to the water pipe. This conductor was clearly visible going from the bottom of the panel to a clamp on a water spigot. Using a smaller clamp-on ammeter, 3.2 amps was measured going to the water system, which would account for the field measured in front of the villas in the grassy area. This leaves 1.6 amps of stray neutral to account for. We found this on three conduits feeding villas A, B and D. The amperage equaled 1.8 amps, strikingly close to the 1.6 amps we were looking for. (Neutral amperage fluctuates and unless one measures everything simultaneously, there will be some differences). These measurement verify the assumption that neutral current of about 4.8 amps (as of 2PM, 10/18) is being diverted to the water pipes, thus creating two strong net current sources which run in front and in back of the villas in the direction of Villa J. Next we need to discover the cause of the field source running under the floor of the villa. To do this we measure for net current in all the individual villa supply conduits. We see the apparent cause when we get to the conduit for Villa I. It measures 2.8 amps of net current. The most usual cause of net current on an individual subpanel supply cable is a illegal neutral-to-ground connection in the villa supplied. The most commonly found site for this neutral/ground connection is in the subpanel, where an uninformed electrician may have bonded the insulated neutral bus to the panel box, thus allowing neutral current to drain off to hatever grounding paths it may encounter, including the electrical conduit itself. This assumption was verified when we were given access to Villa I when the resident returned. hen we observed the subpanel, we found a glaring Code violation. A copper strap was connecting the insulated neutral bus with the panel box. This violates National Electrical Code (NEC) 250-24(a)(5) in the 1999 edition, or 250-61(b) in former editions. We measured the current on the strap and it measured 2.8 amps, thus explaining the 2.8 amps net we measured at the meter. It is possible or probable that this current does not return to the panel but continues in to Villa J and perhaps beyond. The question arises: why would an electrician make a connection so clearly prohibited by Code? One south Florida electrician I talked to in a condo near Ft. Lauderdale which had the identical illicit copper bonding strip in a subpanel told me that some of the older electricians have the attitude of thats just the way I do it, which then gets passed on to their apprentices. In any case, they dont understand the electrical reason for obeying this Code requirement. When the resident of Villa I calls in an electrician to disconnect (and preferably remove) this copper bonding strip, the magnetic field path going through the middle of the villa between I and the service panel hould disappear. However, it may come back in the future if all the subpanels in the villas have this same Code violation. Therefore, it is recommended to management to have an electrician check all the subpanels for a bond between neutral bus and panel box and remove them if found. Even with this field source eliminated the other two loop paths in front of and behind the villas will continue to produce a high field in the villas. Though grounding to a metal water pipe is required by Code, this shunting of neutral can be prevented within the Code. The most often recommended remedy is to have a plumber insert a plastic spacer or dielectric connection or union in the water pipe at least ten linear feet from the foundation of the building. linear means as measured along the water pipe. The ten feet is specified by Code as an adequate contact with soil to perform its function as a grounding electrode. This will stop the neutral current from flowing on this path and force it to flow in its intended conductor in the electric supply cable (called the service lateral). Before doing this, it is wise to call FPL to send a man out to check the neutral connections for that service. There are already indications tat there is a neutral impedance problem for the villas, or at least for Villa H. When the survey requestor reported to me that light bulbs dont last long there and appliances have been burning out, I checked the voltage in several outlets. It was 124.8 V. this is high, an indicates too high impedance in the neutral connections, either to her villa or to the supply neutral for all the villas. Power companies deal with this routinely and usually give it a high priority, as the voltage can go high enough in one hot leg to blow out appliances and low enough in the other hot leg to cause motors, such as in a vacuum cleaner to overheat an burn out. This check-up should be done before the plumber does his job. Once these remedial measures are taken, the average magnetic field levels in the villas should return to 0.5 mG or below. Name of consultant is signed and typed. Initials are KR. Instrumentation: Gaussmeter used, Bell 4090 triaxial gaussmeter, which has a typical accuracy of +/- 1%. Ammeters: AEMC AmpFlex, Tenma 72-555 clamp-on, Yokogawa CL-611. Tracer unit for buried conductors: MSI Magstick.
Posted on: Fri, 11 Jul 2014 23:21:31 +0000
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