EMF from residential power lines

[MisterCMRR]

Hi, Bill.....thanks for your comments.

I was thinking more along the lines (no pun intended) about "hash" from computers, and who knows what else, being radiated from the wiring versus a electromagnetic field. Do your comments also apply for this situation?

Bri

Speaking very broadly, conducted emissions from an offending source (say a computer) don't get very far in premises AC wiring. I like to think of that wiring as a haphazard network of mis-terminated transmission lines, teeming with reflections and standing waves at frequencies over a few MHz (think about their electrical wavelengths). The folks who use the power-line for home automation know this first-hand! Some offending sources, such as the notorious cheap light dimmer, create a very wide spectrum of interference at at repetition rate twice the mains frequency. This means that the audible "buzz" isn't much of a clue as to whether the victim device is responding to an in-band audio frequency or the RF harmonics of the interference. A power-line "interference filter" wouldn't have much effect on the former but might cure the latter. Trying to pinpoint the route taken by the interference in these cases can be a real challenge!

 

[Brian Roth]

Once again, thank you Bill for your expertise. I may have picked up some mythology somewhere about AC mains wiring radiating less "noise" when encased in EMT or BX cable.

I know that in many locales commercial building construction permits requires AC wiring to be enclosed in metal "plumbing", but the building codes don't care about noise radiation from the wiring....they are concentrated on safety. In a way, that seems odd to me, since Romex is permitted in wooden house structures which are probably much more flammable than typical commercial structures. shrug

So. for a bottom line, does using EMT or BX for studio wiring provide NO benefit for studio installations? Besides meeting local building codes...

Thanks!

Bri

 

[Monte McGuire]

I recall years (decades?) ago a lot of drama from people living under power lines complaining about health issues. You can probably find medical studies in the literature researching and maybe quantifying that. AFAIK this is considered non ionizing radiation so harmless to humans.

My completely unfounded theory is that these kinds of HV power lines are maintained with herbicides to keep the underbrush from getting out of hand, and that the herbicides might be the actual cancer risk, not the E fields. It would certainly explain the correlation.

 

[abbey road d enfer]

Unless you ground that foil hat, it won't do anything about the electric field ...

If the aluminum foil hat is connected to the skin, everything under it will be equipotential. But anyway, with skin conductivity, it's already the case.

 

[MisterCMRR]

If the skin is considered conductive, how does the hat change the effect of the field on the person wearing it? The current flowing from head to toe wouldn't be affected at all. The whole point of a shield for electric fields is to divert the current away or around the victim (person or circuit). Just trying to follow the logic here ...

 

[abbey road d enfer]

So. for a bottom line, does using EMT or BX for studio wiring provide NO benefit for studio installations?

I would think the only benefit is when audio cables are run in the same conduit as mains cable (which shouldn't happen).

 

[deedee]

what about if you live in close proximity to a mobile phone mast ,
I'm hearing strong anecdotal evidence of increased rates of cancers in children and teens who lived in such locations all their life .

Anecdotal maybe, but I know not of any serious research to support this...or any mechanism by which exposure to such low levels of non-ionising low frequency radiation could cause cancer.

See also:

 

[ccaudle]

any mechanism by which exposure to such low levels of non-ionising low frequency radiation could cause cancer.

It is difficult to tease out confounding variables. At least around here, rich people do not put up with ugly power wires running over their property, so wealthy neighborhoods tend to be farther away, leaving the land under and near power lines for less expensive development. It is already well established that living in poverty results in a multitude of health problems that wealthier people either avoid or can effectively treat at an early stage, so in some cases close exposure to power lines is a proxy for being poor.

Locally there is a case getting attention where a neighborhood which was historically primarily minority and low income turns out to be sited not only in a relatively less attractive area, but on top of a former industrial operation which processed creosote impregnated wood, which left various contaminants in the soil and ground water, resulting in a noticeable increase in cancer cases in the immediate vicinity. If that had not come to light there would have been all sorts of correlations to poor health outcomes which in actuality were just secondary effects of getting shafted for being poor.