Residential Wiring Issues & High Magnetic Fields
PART 3: Tracking Down Unnecessarily Strong, Stray Magnetic Fields
Many people are concerned about the Low Frequency, Alternating Current, Magnetic Field Radiation (further referred to as Magnetic Fields or MF) that is emitted by our modern electrical system and the devices we use every day. The following blog tracks down what can cause residential wiring issues and high magnetic fields.
Although the potential health effects are in dispute, many Building Biologists, myself included, recommend being aware of the magnetic field situation in your home and taking steps to reduce your exposure where practicable, especially in sleeping areas, where 6-8 hours per day is spent in the same location.
In Part One I discussed knob and tube wiring and the potential problems and issues that may arise if your home still contains legacy knob and tube, including strong magnetic fields.
In Part Two, I discussed the benefits of modern wiring, especially Romex, BX or MC, and wiring inside conduit.
In this installment I would like to discuss one of the most common causes of stray, strong magnetic fields in buildings equipped with modern wiring:
Neutral to Ground Connectivity
To be more precise, the issue is really Neutral to Ground Connectivity in a subpanel, or anywhere in the wiring system other than then Main Service Entrance.
Let’s take a step back and discuss where the magnetic fields in our buildings are coming from.
Strong Magnetic Fields inside a home or building can be caused by many factors:
1) External Sources such as high voltage transmission lines or a large transformer.
2) Point Sources such as:
- Devices with large electric motors, such as fans, refrigerators, clothes washers and dryers.
- Devices that draw a large current load, such as electric heaters, electric stovetops, toasters and toaster ovens, microwave ovens, and air conditioners.
- Other point sources such as electronic dimmer switches, Red LED screens, and plug in transformers.
3) Legacy Knob and Tube Wiring (discussed in Part 1)
4) Improper bonding of the electrical system to the building plumbing
5) Neutral Current from the neighborhood electrical system (not connected to your own meter) running through the water or gas pipe system into the building electrical system through the plumbing bonding (to be discussed in detail in a future installment).
6) Wiring Errors in building equipped with modern wiring such as:
- Neutral to Neutral connectivity, especially in a junction box.
- Miswired 3-way switches, i.e. using 2-wire instead of 3-wire Romex.
- Neutral to ground connectivity anywhere in the electrical system EXCEPT in the main service entrance panel.
Most point sources emit a strong magnetic field, but, if well designed and properly wired, should only emit a strong field within a 3-5 foot “bubble” or zone of influence. I recommend being aware of the point sources in your home and keeping significant point sources away from sleeping areas, work and leisure areas, and any place where occupants congregate for any significant period of time.
Since point sources can be fairly easily identified and exposure controlled, this leaves the more insidious magnetic fields caused by internal building residential wiring issues. In modern wired buildings, i.e. those not equipped with legacy knob and tube, this is likely due to wiring errors within the electrical system. Finding these errors can be difficult and time consuming, but once fixed are a permanent solution and can significantly decrease the magnetic field exposure in a building. Many of these residential wiring issues cause the electrical system to be less efficient and waste electricity and are also electrical and building code violations and can cause excess heat and potential fire hazards, as well as possible shock/electrocution hazards.
Strong magnetic fields due to wiring errors are most often caused by an imbalance between the supply (hot) and return (neutral) current. Electricity is somewhat like water in that it always wants to take the path of least resistance to complete its circuit. When neutral current is given multiple paths, the current can split and a portion can return on each path, creating an imbalance along the intended circuit, leading to strong magnetic fields.
The most common wiring error I have observed both in my time as an electrician and as an environmental inspector is by far Neutral to Ground Connectivity.
In order to prevent multiple paths for return current, today’s residential electrical code requires that all ground connections, ground busses, neutrals and neutral busses be separated from each other in the entire electrical system EXCEPT at the main service entrance. This is intended to give the return neutral current ONE path back to the transformer and keep supply and return current balanced.
If strong magnetic fields are detected and a wiring error is suspected, I recommend isolating the circuit or circuits responsible and then trouble shooting those circuits.
If only one or two circuits seem to be responsible, trace the circuits and examine any junction boxes. If branches from multiple circuits share the same junction box, the neutrals may all be connected. If this is the case, an electrician should repair the connections appropriately, so that the neutrals are isolated and only connected to their proper circuit.
It may be that many or all of the circuits in a sub panel are suspect. This is likely, but not always, caused by the neutral and ground bus being connected in a subpanel. Sometimes the neutrals and grounds share the same bus. Other times the bonding screw is activated and bonding the neutral and ground bus together. Sometimes there is a bonding strap that connects the neutral and ground bus. If any of these cases are observed, it is code violation and should be repaired. Often the measured stray magnetic fields will be significantly reduced or disappear altogether.
Sometimes it appears there is a neutral to ground connection somewhere but no errors can be found in the building electrical system. This situation happened to me recently on an EMF trouble-shooting and repair job, and proved to be a particularly challenging and frustrating situation.
The electricians and I had spent some time and had already found and repaired a subpanel in which the neutral bus was bonded to the ground bus via a bonding strap. We were still seeing strong magnetic fields and the source appeared to be neutral to ground connectivity somewhere in the garage subpanel circuitry. After extensive inspection it appeared that every circuit and the subpanel itself was wired properly (and it was!). Still the stray magnetic fields persisted.
We tracked the issue to the electric clothes dryer, a 220-volt, 2-phase, appliance. We suspected the outlet was miss-wired, but alas, it too was correct. However, when the dryer was unplugged, mysteriously all the stray magnetic fields disappeared and no neutral to ground connectivity could be detected. BINGO! It appears that the problem was within the appliance itself!
Was the appliance defective? Was this a manufacturer’s defect? No, the issue was even simpler. 220 Volt supply outlets come in many shapes and sizes, and appliances are designed to be used with several different outlets. Normally, at least in the United States, the appliances do not come with power cords. At installation, the installer chooses the cord appropriate for the outlet and wires the cord to the appliance at the time of installation.
This particular neutral to ground connectivity issue was entirely due to the improper installation of the power cord on this 220 volt electric dryer!
Here is the gist of it. If a 3-wire outlet is to be used, the cord is connected to the dryer via the Hot 1, Hot 2, and Neutral connections. There is a strap that connects the ground and neutral in this setup. If a four-wire outlet is installed, the cord is attached to the dryer via the Hot 1, Hot 2, Neutral, AND Ground connectors on the dryer. If this setup is used, THE STRAP CONNECTING THE NEUTRAL AND GROUND CONNECTORS IN THE DRYER SHOULD BE REMOVED.
This was NOT done by the installer in our case, effectively connecting the ENTIRE Neutral Bus in the garage subpanel to ground, creating a plethora of stray magnetic field activity. The good news was that once we removed the gold bonding strap seen in the picture above, ALL neutral to ground connectivity disappeared and all of our strong, stray magnetic fields also dissipated.
Neutral to Ground connectivity faults should be high on the list when investigating an electrical system for residential wiring issues causing strong, stray magnetic fields. Be diligent in troubleshooting the entire electrical system for neutral to ground connectivity. But if you are sure that there are no wiring errors and are still detecting neutral to ground connectivity, check the appliances. Unplug anything plugged into the circuits in question one by one and check for N-G connectivity. You may be surprised to find the wiring error in an appliance. This particular problem may be more common than we know. Please comment if you have ever experienced similar wiring errors inside appliances or other electrical devices.