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#42225 - 09/16/04 09:10 PM EMF's  
gunther  Offline
Member
Joined: Sep 2003
Posts: 60
A lady in England that I am acquainted with has complained of headaches for a few years. She became suspicious of EMF's around her and bought a gauss meter. She says it goes way up the scale, especially when she uses equipment. According to her it is all over the house. She has had everything checked over by contractors and the utility and they haven't located any problems. I was just wondering if anyone was familiar with this area.
I have read that high EMF's can be caused by miswired circuitry such as combining neutrals from seperate circuits downstream. Not sure if they would have that problem in England, tho. I think its 230v, but is one leg grounded?
Another cause of high EMF's is bonding the neutral in a subpanel, according to some literature I read.


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#42226 - 09/16/04 11:16 PM Re: EMF's  
dereckbc  Offline
Member
Joined: Oct 2003
Posts: 156
Tulsa, OK
I am know expert, but here is what I know.

1. Source and return (phase and neutral)conductors not being paired and closely coupled. Does not allow magnetic cancellation.

2.Grounded circuit conductor (neutral) bonded downstream of service N-G bond.

3. Ring circuits used in UK. Her being in the UK, and Rings are common practice in UK, you would want to look into this one.

What is common to all situations is not running supply and return conductors together to obtain magnetic cancellation between the two.


#42227 - 09/16/04 11:34 PM Re: EMF's  
CJS  Offline
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Joined: Sep 2004
Posts: 35
Sanford,NC, USA
Good points by Derek.
In Europe, their services have just one hot leg which is 220V @ 50 hertz and a return. Their single phase is actually "single" phase (one hot). And so it is very important that everything has a dedicated neutral.

EMF is electro-motive force, or, voltage, right? You must be talking about eddy currents or very strong magnetic fields...
I also am not an engineer but the only thing I can think of is the same thing Derek mentioned last: One hot in a conduit with nothing to balance it out, or dangerous inbalances.


#42228 - 09/17/04 08:33 AM Re: EMF's  
winnie  Offline
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Joined: Sep 2003
Posts: 649
boston, ma
Caution: this particular field is littered with _tons_ of pseudoscience claptrap. At the present time, it is not good evidence to really understand what (if any) physiological problems can be caused by 'EMFs'.

For the purpose of discussing things with gunther's acquaintance, EMF is 'Electro Magnetic Field', and it is the low frequency (60 Hz) near field (close to the wires) magnetic field produced by current flow in power conductors. This use of 'EMF' should be differentiated from 'Electro Motive Force' or voltage. It is also distinct from Electro Magnetic Waves (light), in that this is the near field effect of the currents in the wires, and is stronger close up, but falls of more rapidly with distance than the far field stuff.

As I said, there is no good evidence for effects from these fields...but do a web search for 'Transcranial Magnetic Stimulation', and understand that there are _well known_ effects on the brain from magnetic fields that are 1000-10000 times larger than the ones that the EMF people are worried about. Given that very strong fields have significant effects, it is plausible that very weak fields have some difficult to detect effects.

Because we are talking about near field magnetic fields, the things to look for is area contained within current loops. The lower the current, or the lower the area of the current loop, the less energy stored in the magnetic field. Ideally all current should return on a parallel conductor that is quite close to the source conductor. The net current should be zero, and the magnetic fields of the two conductors should cancel.

Check for circuits where conductors at the same potential have been joined; current can flow to the load on one circuit, then flow from the load on the other circuit, introducing a very large loop area. (Note: I understand that we are talking about AC circuits, and that the current flows back and forth...) The join can either be on a phase conductor, or on the neutral conductor.

Check for neutral to ground faults. These won't trip a breaker (though they will trip a GFI), and can introduce significant currents through the grounded structure.

Check for circuits wired with separate phase and neutral conductors, as is the case with old 'knob and tube' wiring.

I believe that a ring circuit _operating normally_ can introduce significant loop current. The impedance at every splice would need to be exactly balanced hot and neutral to eliminate loop current.

-Jon


#42229 - 09/17/04 09:07 AM Re: EMF's  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Lights wired with individual conductors, i.e. not cabled and not in conduit, is another possible cause.


#42230 - 09/22/04 09:06 PM Re: EMF's  
gunther  Offline
Member
Joined: Sep 2003
Posts: 60
EMF is electro magnetic fields, think that's right. One thing was wondering about the wiring going to a switch. If the proximity of the neutral determines the cancellation of fields, should you then run a neutral to your switch?


#42231 - 09/22/04 09:13 PM Re: EMF's  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
gunther,
A hot and a switch leg provides the same effect as a hot and a neutral. The current is going in the opposite directions and the magnetic fields, for the most part, cancel each other out.
Don


Don(resqcapt19)


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