I hope that this question is appropriate for this group. I was advised by a colleague that many of the group regular members were well-informed.
I have site that has a medium voltage powerline crossing it. I am engaged in a dispute with the power utility to get the line relocated. It would bolster my argument if I could show that the electromagnetic field (EMF) levels were above a certain level. I know the voltage level and current in amps of the line.
Does anybody know how to:
Calculate or estimate EMF at a given distance from the powerline with data described.
Or where I might find on the Web a site that contains table with precalculated EMF and electric field values for different line types. I think these are called wire codes in the trade but googling has produced little of use - I need at this stage expert or experienced recommendation!
Buy or hire an emf meter. I hired one as I was concerned about high levels in my house. I also walked across a local field with power wires across it, the readings at head height were off the scale. In my house my sons room had a bad area right where he slept.
I think I hired from healthy house. These people hire all sorts:
The meter and research on the net gave some suggested figures that were the maximum to be exposed to. I cannot remember the precise figures that I got, suffice it to say that the only household problem place was my son's room and this was caused by the water pipes under the floor acting as some form of radiating antenna, near which was a very high field.
I mention the power lines as an interesting show of the variations the meter would show.
The figures indoors where bad were hundreds of times less than below the power lines.
I am certain that for a court case it would need a calibrated machine with an expert witness, but I don't believe that is what the OP needs at present.
The problem is any figures will be based entirely on guesswork - there simply hasn't ever been any evidence that exposure to such fields causes any harm, and without such data any figures are meaningless.
I remember hearing a paper by an Oxford academic making this very point - probably about 8 years ago. Something to do with chemical free-radical generation at these lower levels.
I would like to see a certificate of calibration from an ACAS registered standards lab before I trusted a meter to tell me anything.
What is "bad" ? What is "off the scale" nV/m ? V/m If I remember the thrust of some of the recent "research" it is LOW fields that cause more problems (if they do) than High fields
I don't see how that could persuade them of anything.
Not reliably, there are a number of environmental effects to be considered and in any case the current flowing in the line will vary at different times of the day (and on different days). You will need to carry out field strength measurements. Avoid the toys that certain anti-power line groups hire out. Apart from their dubious calibration state they are marked in wholly unrealistic ways showing false "danger" levels to further their propaganda.
Trying to argue a health case is in any case almost certainly futile. The studies which will be relied upon by the power companies can be found at
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and none show any deleterious link between power lines and health. Trying to refute those will be somewhat difficult.
Where you'll probably get quite a range of opinions too!.
IMHO there is, like mobile phone radiation, a lot of research needing doing into these effects, but I suspect that its not going to make a lot of moolah for anyone so it isn't a real high priority as such.
I have heard of an anecdotal tale of a number of people who got various cancers who lived in a house near here that is directly under twin 33 KV overhead lines.
The current incumbent is a university biological researcher who seems unfazed by his surroundings, and likes the peace and quiet in his location, except for damp foggy nights when the wires hum and fizz quite a bit!......
If it is that important to you to get the power line relocated then have you tried asking the power company what they would charge to do the job?. (I am assuming you have been trying to get them to do it at their expense - sorry if I am wrong) Maybe if you were to pay, they would be happy to do it and it may be cheaper than taking the legal route. You say it is a "site" so I am guessing you have bought (cheap?) land where the line was already present. If so, I think you have no chance of getting them to move it at their cost.
I got the overhead lines into my house (only 240V) put underground. I dug the trench and they supplied/fitted the cable. It only cost me £125 - bargain - although medium voltage would undoubtedly cost a lot more but may still be a bargain if it makes your site a great one.
Costs nothing to find out. Let us all know what they say.
Just as a follow up I discovered a good resource that might be useful to others.
National Grid, the UK power infrastructure company, maintains a website about EMFs at
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. Amazingly, given the business that National Grid are in, it seems to be reasonable enough summary of the current debate about the potential dangers of EMFs, an explanation of EMFs and a wide range of links to interested parties including groups and people who clearly are not lackies or dupes of the electricity industry.
It is about the best resource that I've seen so far.
I`ll check that one out myself - but the point that all the nay-sayers forget about - if you want electric, cables are required - it doesn`t get around by telepathy.
I haven`t seen many of these activists wanting to get rid of all their electric and go back to using gas lamps.
As far as EMFs go, you also have to consider "self-inflicted" magnetic fields - of which many you will come into far closer contact with on a regular basis.
You can think of your own, but here are few to start you off...
...it would be easier to give a relevant answer if we knew what the motivation was (aesthetic, interference/EMC, EM exposure, (or ???) and whether it's the electric or magnetic field that you're interested in.
...it's easy enough to calculate for single phase (you need to know the wire separation, height and current) but harder for 3-phase (need to know the phase sequencing on the wires) and harder still for dual 3-phase - overall it's probably easier to measure. A 3-axis magnetometer will give you the magnetic field, the E-field can be estimated if you know the line voltage.
...typically between 5 and 100 microTesla except under fault conditions, e-field depends on line voltage and height. If your interest is driven by EM exposure considerations these levels are way below the exposure guidelines. If you want more info on this there are a variety of sites: World Health Organisation EMF Project site (loads of authoritative info), UK National Radiological Protection Board (recently published a review of research and concluded no proven risk), International Council for Non-Ionising Radiation Protection (ICNIRP) and so on. If you search on "EC recommendation 519" you'll find a huge amount of info. The bottom line is that there's been a phenomenal amount of research in this area and the only proven and acknowledged effects are nerve stimulation at low frequencies and thermal effects at higher frequencies. It's possible to find loads of sensational scare stories but there is NO independently replicated and peer-reviewed science that supports them (stands back and waits for tidal wave).
...if your motivation is interference or EMC - the only common equipment that's affected by this level of B field are CRT-based VDUs (anything above
0.5 to 1.0 microTesla will cause perceptible jitter. Very little is affected by LF e-fields but ground shift (especially after a line fault) may cause damage if you have multiple ground reference points.
Really. Well well. Fascinating what one learns on Usenet these days.
Maybe you can explain to us all how it is that a circuit - ring, star, or crop-circle ompholotic spiral - in which the currents 'out' and 'back' pass in opposite directions in conductors sharing the same outer jacket - gives rise to an Electro-Magnetik Feeled? (Hint: transformers and other things with Coils use jsut *one* of the con-duck-tours wrapped around the iron former).
If you're paranoid about electrickle fields, you'd do better to pay attention to the layout of your *lighting* circuits, in which the feed & return (that's live and neutral in your planet's English) are widely separated, as mentioned here in occasional discussions about interference with hearing-aid inductive pickups. There at least there's a mechanism to *produce* a detectable em field; how you then go from 'detectable' to 'brain and health scrambling' is another step, which might meet with a little scepticism. Still, Gallileo was also ridiculed in his time, wasn't he...
Not wanting to contradict you too much (don't want to say too much against the magic force as I earn my living from it), but this is only the case if the currents and their paths are precicely balanced. In a radial the current (except under certain fault conditions) will be balanced, but in a ring, the slightest difference in impedance between the two halves of the "live" ring and the two halves of the "neutral" ring could quite easily lead to (miniscule levels of) unbalance.
The fact that the cables are side-by-side, separated by at least 1 cable diameter doesn't help either. If they were twisted (as in flex or telephone or computer CAT5) the radiation problem would be lessened further, and coaxial cables - as generally used by the power companies for the last leg to your house these days - are the best of the lot, especially in a PME arrangement when the outer (neutral) is pretty firmly grounded. I'd expect to see very little field from such a wire.
Not that I'm an expert in EM fields, but I do have a background in audio where all the above measures (balancing, twisting, coaxial) are put to incredibly good effect in reducing problems from both radiated and induced radiation.
Good point about the lighting circuits - there was a discussion here very recently about that IIRC, and in particular with reference to hearing aid induction loop coils.
Err, I suspect Stefek was being somewhat ironic........
As I too spent all of my working life within the electricity supply industry, exposed to varying levels of EM radiation, let's just keep it in perspective, eh? The levels of radiation in yer average domestic scenario, or ideed, a 3ph lv overhead line, are infinitesimal compared to those encountered directly under a 400,000kv dual circuit, or within a primary or supergrid substation.
Thanks (genuinely) for making it clear what you meant: yes, if your ring has f'r example a well-made path to supply Live from both sides but a looseish connection in one of the Neutral legs, you're right that there'll be an imbalance in the currentses under such a fault condition. I thought you were suggesting that in a normal condition, a ring would inherently produce more of a field 'because there's a loop' than a radial would.
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