I have read a book on architecture that discussed various EM fields inside
One problem that was discussed was the use of single pole cord switches.
Apparently, after the lamp is switched off, the EM field continues on the
wire between the switch and the bulb.
Recently, I have searched for 2-pole cord switches and have not found any.
Anyone who plays guitar or has plugged an RCA plug into a HiFi has
seen the problem!
However, the problem is much larger than just "cord switches"!
Basically, a house is full of wires going to wall plugs and lighting
fixtures. The wall plugs usually are always on, and the lighting
fixtures are nearly as bad, given that the wires to the wall switch at
least are also always on. Table lamps and the like have an even worse
problem in that the cord is all over the floor and the "off" switch is
up at the bulb. This leaves all that cord ready to radiate various
The hum you hear in your guitar or when plugging a stereo signal line
is electrostatic. Which is to say 120v AC is being fed to the wires in
the walls which form one "plate" of a capacitor. If you happen to
touch a signal like in a stereo, your finger is conductive to a degree
and thus your whole body forms the other plate of the capacitor
feeding 60 Hz into the sound gear. This capacitance is small, but the
input voltage is high, and the stereo is amplifying with lots of
Architecturally speaking, a friend of mine built his house correctly
in this regard by having all AC lines switched in the basement
centrally. HE uses low voltage lines to wall switches which just
provide signal voltages to the remote switches controlling the AC
power. This way when the switch is OFF there is no connection to the
house wiring. However if you think that this means there are no EM
problems you'd be wrong. He has these lights on a dimmer and when the
kitchen fluorescent lights are on, the dimmer constantly adjusts
As it turns out all manner of interference can go up and down house
wires. And in his case if the various lights and plugs are ON, the
wiring is no different from standard wiring. RF interference can go up
and down the wires (which act as antennas) whether they are "on" or
"off". Double pole switches can break up the wires in to shorter
pieces which reduces pickup, but only if the switch is open.
As for cord switches, I'd expect a double pole one to do very little
given that most of the hum comes from the wall wiring not to mention
the big coil of cord on the floor behind the cord switch.
Thank you Benj for the great reply.
Yes, I'm aware of that. The book -Prescriptions for a Healthy House by Paula
Baker-LaPorte -has a chapter (16) on electricals. I was under the
impression that the two adjacent hot-neutral wires pretty much cancelled
out the fields, except very close to the wires. So if the switch is at the
end, just under the bulb, both wires have the same length and again, except
very close to the wires the EMF should be small. Or did I get this wrong?.
Wow! The player becomes electrical too :-(
When I buy a guitar, it will be acoustic :-)
That's a neat idea. It seems to me that Health Departments have kept out of
this field for far too long. I hate the thought of going back to
incandescent lamps and roll on LED lights.
That makes good wiring a very tricky process.
An electrician once wired a house for me and he pulled the wires to tight
through the studs etc that I often had trouble installing the outlets. Did
he know something that I didn't?
So, instead of looking for a 2-pole cord switch (Pass and Seymore don't make
them) if I just replace the lamp holder with one that has a switch, it won't
There are electric fields and there are magnetic fields. When current
is flowing through a wire, these are linked (Through Maxwell's
equations and Faraday's Laws).
When no current is flowing and there is a potential difference
(voltage), as an extension cord with nothing plugged into the outlet
end, there exists an electric field only. For several years now, low
cost (AC) voltage detectors which can sense this field and tell you if
a wire or outlet is energized, are available.
A double pole cord switch (if these exist) would theoretically isolate
the energized section and minimize the (electric) field to zero or
That being said, electric and magnetic fields are all around you
(depending on what country you live in at 50 or 60 Hz). They are in
your bathroom, in your kitchen, near your computer monitor, and your
electric heater/air conditioner. It is very difficult to isolate
yourself from these low-level fields. If you live near any kind of
overhead or underground power lines, you are most likely being bathed
in a constant low level field that surrounds the lines. It has been
this way since the late 19th century when the world became
A much larger issue of potential concern is near universal spread of
cellular phones (and their associated towers). These are 'always on'
in a sense, and operate in the same general band that your microwave
oven operates (although at much, much lower power).
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.