ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Ring circuits and EMF

The leakage current would mostly come from filters in the power supplies. The same should be true of HF ballast.

I'm not entirely sure about the 1mA. When Googled for leakage currents I got two results: A French site that claims it's about 2mA per computer and an
article on ePanorama which claims that it's typically less than 1mA.

The leakage current can vary considerably with the design of the filters.

It doesn't take very much capacitance line-to-ground to get a current of 1mA flowing:

About 0.014uF for a computer running on 230V at 50Hz, and around 0.022uF for a 120V 60Hz unit.

Is there any evidence that leakage currents dissappear and dissipate into the earth? Do they not make their way back to the transformer?

Karl

Yes, the leakage current would have to go back to the transformer. Thinking about our other current thread on different grounding methods, the leakage from the filter capacitors will get back to the transformer neutral:

1. In a TN-C-S (PME or American system) by way of the building EGCs, N-G bond, and supply neutral, along with any parallel paths created by pipework etc.; -or-

2. In a TN-S system, by way of the EGCs and the independent ground right back to the xfmr star-point; -or-

3. In a TT system through house EGCs and the actual earth itself by way of the local ground rod and the other ground rods on the network's neutral.

There's another quite strong source of EM fields in many British houses that we haven't touched upon yet: The lighting circuits.

These days, all cabling is (or should be) run so that current flows out and returns on adjacent conductors in a cable, thereby canceling the field as much as possible.

In the past, however, it wasn't unusual for lighting circuits to be wired with single-core cables where the phase and neutral could take quite different and widely separated routes around the house (I believe that some early knob-&-tube systems in the U.S. were wired similarly).

There are a large number of houses in my imediate neighborhood which were wired (or rewired) in the 1960s and use this method.

Although we have lighting circuits separate from those feeding general receptacles, there can still be a few amps flowing at some points -- Enough to generate a sizable EM field in the vicinity.

Yes, the knob and tube wiring I have seen is as you describe, with large loops of fields from small amperage. Though this method was abandoned in the 40s, there are a lot of buildings in some areas such as San Francisco which like to preserve older buildings where one finds this wiring still. It is legal to leave it or even add on to it, but not to install new.

It is interesting to consider that early house residents may have been exposed to higher EM fields even with minimum electrical usage than those in modern high-load houses which are wired according to present Code. An interesting study did show that cancer has risen following early electrification in areas previously not served. With knob and tube, the early users were getting a good dose of magnetic fields!

Karl

That may well be true.

To throw a monkey-wrench into the argument, however, I would add that in the radio/electronics field it seems as though some modern manufacturers could take a lesson from the past. Techniques which were once commonplace seem to have been forgotten.

Look in some equipment now and you'll find AC wiring from power transformers (both primary and secondary) running on separate conductors not particularly grouped.

In the old days, the effects of EM fields from such wiring were widely understood. Look at the way AC power was wired to the filaments in old tube equipment, for example, and you'll see a tightly twisted pair run close to the chassis (they didn't use the chassis as a return path, even though one side of the filament wiring was grounded to it).

Keeping the EM field from the filament wiring as low as possible was important when very low-level signals are being carried on adjacent wiring.

That's curious, since manufacturers have to meet standards for EMI emissions and protection.

Of course the effect on living space is small.

An electrician I know used to twist NM (Romex) conductors in house wiring to reduce magnetic fields, thus costing his customers much more in his labor. He did not realize that twisting has no effect on net currents, and is not needed when the wiring is correct.

Karl

Hey Welcome Karl!,
What an interesting topic you bring up.
EMF's have always been a thing that I have been worried about, with respect to the HV work that I do, however, I am always a fair distance away, using a Hotstick, but it kind of makes you wonder though, just how harmful are these things?.

Thanks for the welcome. I too wonder why I am standing in fields of 100+ mG clamping my ammeter around service conductors. I guess it is like a fireman: the fire is dangerous, but it is your job to go in.

About the actual dangers, it seems to affect young children most easily (leukemia). Statistics for adults (leukemia, brain tumours, Alzheimers, etc) are much weaker and have not convinced the community in general. Also, I would think it depends on whether one's family has a history of cancer. Mine have usually died of heart (and smoking).

Believe it or not, there have been literally thousands of studies on the biological effects of power frequency magnetic fields (and some on electric fields) in the last 15 years, and I mean thousands. So one has to read a journal such as microwavenews.com to keep up with it. And politics is highly involved in funding and also reporting of results.

I don't get into discussions about the health angle much any more since I discovered early on that most high fields in buildings are caused by Code violations. This lets me trace the error and get it fixed. Case closed.

Of course in the UK I would be a bit upset by Ring circuits and the separating of hot and neutral conductors in lighting circuits. Both woulod be Code violations here if installed today.

Karl