Most electrical faults can wait until morning. This one cannot. Lights trading brightness across a building points at a lost neutral, and while it is happening it is destroying equipment and heating a connection you cannot see.
Most electrical faults can wait until morning. This one cannot.
If the lights in one part of a building get brighter at the same moment lights somewhere else go dim — and the two keep trading like that as things switch on and off — stop using the building’s power and get it looked at the same day. That symptom has a specific cause, and while it is happening it is quietly destroying equipment and heating up a connection somewhere you cannot see.
A normal 120/240 volt supply has two live legs and a neutral. Everything running at 120 volts — lights, receptacles, electronics — connects between one leg and that neutral. The neutral is the reference point that keeps each side at 120 volts, and it carries whatever difference exists between the load on one side and the load on the other.
If that neutral connection is lost or has gone high-resistance, the reference point stops being held. The two 120 volt sides end up effectively in series across the full 240 volts, and the voltage divides between them according to how much load is on each side.
That is why the symptom looks so strange. The side with less load on it floats up well above 120 volts. The side with more load on it drops well below. Turn something substantial on, and the split shifts — one side sags further, the other climbs. The lights are reporting the voltage faithfully; it is the voltage that is wrong.
The same thing happens on the 120/208 volt systems common in commercial buildings. The arithmetic differs, the behaviour does not.
The electronics are the tell. Lights dimming on their own is common and usually harmless. Lights dimming in one place while others brighten, plus electronics failing, is a different animal.
It is worth separating this from the ordinary version, because they get confused constantly.
Lights that dip briefly when a compressor, welder or large motor starts, then recover, are showing you inrush current and voltage drop. That is normal behaviour, it may be worth improving, and it is not an emergency. That situation is covered in why shop lights flicker when equipment starts.
The difference: ordinary dimming is a brief dip that recovers, affecting lights near the load. An open neutral produces a sustained see-saw, where one area goes up as another goes down, and it affects the whole building rather than one circuit.
Three reasons, and the first is the one people underestimate.
This is not a fault to monitor for a few days to see whether it settles.
Roughly from the street inward.
Whether it is utility side or your side often cannot be told from inside the building, which is why the free call goes first.
The diagnosis itself is usually quick, because the fault has a signature. Voltage measured from each leg to neutral, compared against leg to leg, while load is deliberately changed: on an open neutral the two readings move in opposite directions and still add up to roughly the full leg-to-leg voltage. That pattern is distinctive and it narrows the search immediately.
From there it is a matter of working along the path — terminations, bus connections, the meter base, the service — looking for the one that is not making proper contact, usually with heat damage to confirm it. Finding it is rarely the expensive part. The general approach is covered under electrical troubleshooting, and what a call like this typically involves is in what an electrical troubleshooting call costs.
Yes, and intermittent is normal for this fault early on. A connection that is failing makes contact some of the time and not at others, often depending on temperature or vibration. Intermittent means it is developing, not that it is minor.
No. Bulbs do not coordinate. If one area brightens at the same instant another dims, something upstream of both is changing, and bulbs cannot do that.
A cluster of power supply failures in one building over a short period is worth measuring rather than accepting. Equipment on the high side of an open neutral fails in exactly that pattern, and people usually replace several things before anyone checks the supply.
Then the fault is on your side of the meter, which narrows it considerably — service entrance, main panel terminations, or a shared neutral downstream. That is a straightforward search for an electrician once the utility has ruled themselves out.
Related but not the same. Losing one of the live legs usually means part of the building simply goes dead, and on three-phase equipment it causes its own set of problems — see phase loss on a motor. An open neutral leaves everything energised at the wrong voltage, which is why it does more damage before anyone works out what is happening.
Shut off what you can, call your utility if the whole building is affected, and call 403-872-8698. If it is after hours, say so — after-hours service is available at an additional charge and availability depends on what is already booked, but this is the kind of fault worth asking about rather than leaving overnight.
If it is not happening right now but you recognise the description from the past few weeks, send the details through the service request form along with a photo of your panel with the cover on.
Related work is covered under panels and equipment power and commercial electrical.
Grasse Electric serves Red Deer, Red Deer County, Blackfalds, Sylvan Lake, Penhold, Springbrook, Innisfail, Lacombe, Ponoka and Morningside.
Written by Todd Grasse, Red Seal Journeyman Electrician, Grasse Electric — Red Deer, Alberta. Published October 21, 2026.
Call for service, or send us the details and photos and we'll take a look.
