Flickering Lights:
Your heat pump starts and, for a split second, the kitchen lights dim. The dryer kicks in and the TV flickers. Almost everyone has seen it, and almost everyone thinks it’s harmless: “it’s just a little power dip.”
The dip, in fact, isn’t the real problem. The real problem is the rebound: the brief overvoltages that come with large appliances starting and stopping.
What everyone sees: the voltage dip
When a large appliance starts, it suddenly draws much more current than usual. The voltage in the house drops for a brief moment. This is called a voltage sag. The signs are easy to recognize:
- lights dim or flicker;
- an appliance seems to struggle or makes an unusual noise;
- an electronic device restarts for no reason.
The most common causes in a home: heat pump, air conditioner, fridge or freezer compressor, well pump, dryer, EV charger. The utility grid can cause them too, for example during switching operations or when power is restored after an outage.
What no one sees: the water-hammer effect
Think of a faucet shut off abruptly: the pipes bang. That’s called water hammer. Or think of a rubber band stretched and released: it doesn’t just return to its position, it overshoots before settling.
Electricity behaves in a similar way. Motors, compressors and transformers store energy in their coils while they run. When the current changes suddenly, especially when an appliance shuts off, but also at the end of its start-up, that energy is released all at once. The voltage then rebounds: for a very short instant, it rises above its normal 120 V before settling.
This rebound lasts a fraction of a second. The eye can’t see it, and an ordinary multimeter can’t measure it: you need a power quality analyzer. It can happen every time a large appliance starts or stops. In a home where the fridge, heat pump and dryer cycle several times a day, these events happen often.
Why it wears out your electronics
Almost everything in a modern home contains electronics: appliances, smart thermostats, TVs, computers, routers, alarm systems, heat pumps, EV chargers. Their components (power supplies, capacitors, circuit boards) are designed for a stable voltage.
Each rebound above normal voltage puts a small stress on them. A single one causes no visible damage. But it is generally recognized in the electrical protection industry that, repeated day after day, these stresses can accelerate component aging. The possible result: a dishwasher control board that fails after a few years, a thermostat that acts up, a TV that won’t turn on. People blame the appliance (“they don’t make them like they used to”), when the power supply may also be at fault.
That’s the difference between a dramatic surge, like lightning, and these small repeated surges: the first cause damage all at once, the second cause damage slowly over time.
When to call an electrician right away
A slight flicker when a large appliance starts is common. Some signs, however, call for a prompt inspection by a licensed electrician:
- lights flicker throughout the house, often or for no apparent reason;
- some rooms get brighter while others dim;
- a burning smell, a crackling sound or an electrical panel that is warm to the touch.
These signs can point to a loose connection, particularly on the neutral, which can cause significant overvoltages and a fire risk. In that case, the priority is to have the problem fixed at the source.
How to protect your home
A surge protector does not correct voltage dips. However, installed at the electrical panel, it limits the surges that pass through the panel and protects every circuit in the house at once, not just the devices plugged into a power bar. For the most sensitive electronics, it can be paired with point-of-use protection.
Not all surge protectors react as early. Their varistors (MOVs) redirect the surplus to ground when the voltage exceeds their threshold. Two values on the spec sheet help you compare:
- MCOV (Maximum Continuous Operating Voltage): the highest voltage the varistor can withstand continuously without acting. The closer it is to your home’s voltage, the earlier the varistor acts. A high MCOV lets small repeated rebounds through;
- VPR (Voltage Protection Rating): measured under UL 1449 and printed on the UL label, it indicates the voltage that reaches your devices during a surge. The lower, the better.
Armada’s Galeos surge protectors have an MCOV about 10% above the installation voltage: 130/275 V on a 120/240 V residential installation. Their VPR is 700/900 V (Series 2, 2+ and 3). Thanks to fuseless Power Pressure™ technology, they don’t silently disconnect and keep protecting. They are UL 1449 and CSA certified, made in Quebec, Canada, and backed by a 25-year warranty.
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Frequently asked questions
Why do my lights dim when the heat pump starts?
At start-up, the heat pump suddenly draws a lot of current, which briefly lowers the voltage in the house. This is a voltage sag.
Can a voltage dip damage my appliances?
The sag itself rarely causes damage. It’s mainly the brief overvoltages when large appliances start and stop that, repeated over time, can wear out electronics faster.
Is a power bar enough?
It only protects what’s plugged into it. Appliances, the heat pump and the panel itself remain exposed. A surge protector installed at the panel protects every circuit.
