A Transformer Is Five Feet From My House. What Should I Measure?

October 30, 2026

Five feet is not a threshold, and it is not a verdict. It is a distance, and the question it raises is a good one: what is the 60 Hz magnetic field at the places in your home where you actually spend time, and is the transformer outside that wall part of the answer? The honest path is a small triaxial survey of the occupied spaces, with the utility’s help identifying the equipment, and with your own wiring checked before you blame the box. Here is how to run it.

First, Identify What You Are Looking At

The green cabinet on a concrete pad is a pad-mounted transformer, and the “five feet” in the title is a hypothetical distance to your exterior wall, not a utility rule and not a health threshold. Before measuring, get the facts about the equipment from a safe location:

• Ask the utility to identify it. A call or a written request to the serving utility will tell you what the equipment is, its voltage class, and its role in your service. Keep the response; it is the document that lets you separate the utility’s equipment from everything else.
• Keep your distance from the equipment. Never touch or open utility equipment, never obstruct access, never dig near it, and never enter restricted areas. Identification happens from public or your own property, from a safe position.
• Keep two questions separate. Service clearances and electrical access requirements are the utility’s rules, and they are about electrical safety. They are not exposure numbers, and a clearance distance is not a field measurement. Ask for the clearance information in writing, and treat it as its own file.

The Conceptual Map

Draw the chain, because the chain is where the answers live. A typical arrangement: the pad-mounted transformer, a buried feeder or service route running from it toward the house, your exterior wall, and the occupied space behind it, a bed or a desk. The U.S. National Institute of Environmental Health Sciences’ guide to electric power EMF is the plain-language reference for how these fields behave.

For context on the equipment itself: a pad-mounted transformer steps the distribution voltage down to the level your service uses, and it does so continuously, whatever the house is doing. It is always energized, but the field it contributes at your wall is a function of the current flowing through it at the moment you measure, which is why the time-of-day pattern in the next section belongs to the whole chain, not to the box alone.

Three physical facts explain why the distance in the title is not the whole story. First, a 60 Hz magnetic field scales with the current in the source, and the current in a service transformer follows the load on the circuit it serves. Second, conductor routing matters: the path the service conductors take, and how far apart the phases are, shapes the field pattern at the wall. Third, and most important for the measurement, low-frequency magnetic fields pass through ordinary walls, so the field inside the room is a combination of the transformer, the buried service route, and your own home wiring, and only an inside measurement at the occupied point can sort out how much each contributes. For the wider picture, including what to do when the lines are overhead, see our guide to living near power lines, and if you are buying rather than living in the house, our homebuyer checklist.

A Triaxial Survey You Can Run

The protocol is short, and the discipline is in the consistency:

1. Use a triaxial 60 Hz magnetic instrument. The field has a direction as well as a size, and measuring all three axes at each point is what lets you tell a directional source, like a nearby conductor, from a uniform background. Record in µT or mG, and note whether the meter reports peak or average, because a field that varies with the load will show a different peak from a different average, and the two are not interchangeable.
2. Measure at occupied height. The points that matter are the bed, the desk, and any other spot where someone sits or sleeps for a stretch, all at the height a person actually occupies. Add comparable interior reference points in quieter rooms, so you have a baseline for what the house already produces.
3. Take exterior readings only where access is permitted. If you can stand on public or your own property at the wall, a reading there helps locate the gradient. If you cannot, do not force it; the interior points carry the decision.
4. Record background, and repeat over time. Take readings at several times of day, or run longer logging, because the field follows the load. Note what is running in the house each time.
5. Check your own wiring before blaming the box. Before attributing a gradient at the wall to the transformer, investigate the obvious internal candidates: the service conductors entering the panel, large appliances on that circuit, and any wiring run along the wall in question. The internal sources are the ones you can actually change.

A Short Decision Tree

1. Ask the utility for written identification of the equipment and its site requirements. File the answer.
2. Measure the occupied spaces with the triaxial protocol above, at several times, with background and loads logged.
3. Decide on the gradient. If a repeatable local gradient appears at one occupied point, and it survives the internal-wiring check, then a layout change, moving the bed or the desk away from that wall, is the lever you actually control. If the readings at the occupied points are unremarkable and stable, the file closes: you have a documented answer, and the transformer stays where it is.

At every step, the safety rules are the same: never touch or open utility equipment, never obstruct access, never dig, and never enter restricted areas. The measurement is a quiet, patient activity, and the patience is the point.