Quick answer
A brownout is a period of lower-than-normal voltage on the power supply, often from grid stress or a deliberate utility voltage cut, that dims lights and strains motors without fully cutting power.
No single U.S. grid definition sets how low or how long. Utilities measure voltage against the ANSI C84.1 ranges, where Range A service voltage is within 5% of nominal 1.
Quick facts
The key facts about Brownout, with sources:
- What it is
- Sustained low voltage, not an outage 1
- ANSI C84.1 Range A service voltage
- ±5% of nominal (114 to 126 V on a 120 V base) 1
- ANSI C84.1 minimum utilization voltage
- 110 V (Range A), 106 V (Range B) on a 120 V base 3
- Deliberate utility cuts
- Voltage reduction, e.g. 5% or 8%, to prevent cascading failures 2
- Most at risk
- Motors and compressors 1
- Average U.S. interruptions, 2022
- About 5.5 hours per customer (outages, not brownouts) 4
Key takeaways
- A brownout is low voltage that lasts, not a brief flicker and not a full outage.
- Utilities aim to keep service voltage within ANSI C84.1 Range A, ±5% of nominal 1.
- Utilities sometimes lower voltage on purpose, by 5% or 8% for example, to protect a stressed grid 2.
- Motors in fridges, AC units and pumps are most at risk from low voltage.
- If only your home is dim, the cause may be a wiring or neutral fault; call the utility or an electrician.
What a brownout is
In a blackout the power is gone. In a brownout it is still on, but weak. Lights look dim or yellow, fans slow down and some electronics reset.
There is no single official U.S. definition with a set threshold. The term usually means voltage that stays below its normal range for seconds, minutes or hours. That is different from a sag, which engineers use for a dip lasting a fraction of a second, such as when a big motor starts.
The yardstick utilities use is ANSI C84.1, the national standard for service and utilization voltage. PG&E summarizes it: Range A service voltage is within ±5% of nominal 1.
A CPUC decision lists the minimums on a 120 V base: 114 V service and 110 V utilization for Range A, and 110 V and 106 V for Range B 3.
How brownouts happen
Grid stress. On very hot days, demand can push the grid close to its limits. Voltage drops along heavily loaded lines.
Deliberate voltage reduction. Utilities may lower voltage on purpose to reduce load and avoid wider failures. Con Edison's 2024 voltage specification describes 5% or 8% voltage reduction for a stressed network area, and notes customers may see lower voltage during it 2.
Local problems. A failing transformer, an overloaded line, or a loose connection can cause low voltage for a street or a single house.
Inside your home. Long, undersized circuits cause voltage drop. A loose neutral can make some rooms dim while others get too bright.
- If Neighbors see dim lights too
- Then Likely grid or utility issue; report it to your utility
- If Only your home, all circuits dim
- Then Possible service or utility connection problem; call the utility
- If Some rooms dim, others brighter
- Then Possible open or loose neutral; call the utility and an electrician now
- If One circuit dims when a big load starts
- Then Likely voltage drop on that circuit; an electrician can check it
Kinds of low-voltage events
| Event | How long | Typical cause |
|---|---|---|
| Voltage sag (dip) | A fraction of a second to a few seconds | Large motor starting, fault cleared elsewhere |
| Brownout | Minutes to hours | Grid stress, deliberate voltage reduction |
| Local undervoltage | Until repaired | Failing transformer, overloaded line, loose connection |
| Unbalanced voltage | Until repaired | Open or loose neutral |
| Outage | Minutes to days | Storms, equipment failure |
Worked example: what the ANSI ranges mean at your outlet
ANSI C84.1 minimums as stated in a California Public Utilities Commission decision, PG&E's ±5% summary, and Con Edison's example voltage reductions, all on a 120 V base 3 1 2.
| Condition | Rule | Voltage on a 120 V base |
|---|---|---|
| Nominal | n/a | 120 V |
| Range A service, low end | −5% | 114 V |
| Range A service, high end | +5% | 126 V |
| Utility voltage reduction, 5% | Con Edison example | 114 V |
| Utility voltage reduction, 8% | Con Edison example | About 110 V |
| Range A utilization, minimum | ANSI C84.1 via CPUC | 110 V |
| Range B service, minimum | ANSI C84.1 via CPUC | 110 V |
| Range B utilization, minimum | ANSI C84.1 via CPUC | 106 V |
The ±5% and voltage-reduction rows are our arithmetic on the published percentages. Actual limits depend on your utility's tariff and the voltage at the point of service. Range B conditions should be limited in extent, frequency and duration, and corrected within a reasonable time 1.
Where you notice a brownout
- Incandescent and some LED lights look dim or yellowish.
- Fans and motors run slower or hum.
- Air conditioners and refrigerators struggle to start.
- Microwaves take longer; electronics reboot.
- UPS units click over to battery.
Why a voltage cut can be the lesser evil
A deliberate brownout is a tool. Lowering voltage a few percent cuts demand across a whole area. That can keep a stressed network from failing outright, which Con Edison describes as preventing cascading failures 2.
For most homes, a short, mild voltage reduction is better than a blackout. The concern is when low voltage is deep or lasts a long time, or when it is a sign of a local fault.
Help the grid, help your equipment
When your utility issues a conservation alert, raising the thermostat a few degrees and delaying laundry or EV charging lowers demand. It also keeps your own motors from starting during the worst of the low voltage.
Why low voltage is hard on equipment
Many motors try to do the same work at lower voltage by drawing more current. More current means more heat in the windings. Compressors can struggle to start and may stall and restart. Over time this shortens their life.
PG&E notes that equipment may not work well outside Range B, and protective devices may operate 1. Electronics with switching power supplies cope better, but some reset or shut down.
Surge protectors do not help with low voltage. A UPS with voltage regulation can, for small electronics.
What drives the cost of brownout damage and fixes
We do not list prices. Damage costs depend on which equipment runs through the event: a stalled AC compressor is far costlier than a reset router. If the cause is in your home, the fix may be a loose connection, an overloaded circuit, or an undersized service that needs a panel upgrade.
If the cause is the utility's equipment, the utility repairs its side. Some utilities have claim processes for damage; ask yours. For backup options, see generator installation.
What to do during a brownout
- Check whether neighbors have dim lights too.
- Turn off or unplug large motor loads: AC, pool pumps, power tools.
- Unplug sensitive electronics, or run them from a UPS.
- Report it to your utility, especially if it lasts more than a few minutes.
- If only your home is affected, or some lights are brighter than normal, call the utility and an electrician.
- When voltage returns to normal, wait a few minutes before restarting large motors.
Preparing for brownouts
- Know where your main breaker and panel are, and label circuits.
- Put a UPS on computers and network gear.
- Ask an HVAC pro whether your AC has low-voltage protection.
- Reduce peak-hour loads when your utility asks for conservation.
- Have an electrician check connections at the meter and panel if dimming is frequent.
Warning signs to take seriously
- Lights dim and stay dim for more than a few minutes.
- Some lights brighten while others dim; this can mean a loose or open neutral 5.
- Appliances hum, stall or smell hot.
- Low voltage happens only in your home, not your neighbors'.
- Flickering that gets worse over days or weeks.
Bright and dim at once is urgent
If some lights get brighter while others dim, unplug electronics and large appliances and call your utility right away; this pattern points to a neutral fault that can destroy equipment and start fires. Do not open the meter or panel. If anything smells burnt, leave and call 911.
Standards that govern voltage
ANSI C84.1. The only national standard for utilization voltage. It sets Range A and Range B for service and utilization voltage. Its limits apply to sustained voltage, not momentary excursions 1.
Utility specifications and tariffs. Utilities set their own service voltage rules modeled on ANSI C84.1. Con Edison's EO-2096 (effective 30 August 2024) follows ANSI C84.1-2020 and allows voltage reduction during network stress 2.
State utility commissions. Regulate service quality, including voltage complaints. In California, utility Rule 2 already keeps most service voltage between 114 and 120 V under a conservation voltage reduction program, per a CPUC decision on emergency voltage reduction 3.
Reliability reporting. The EIA reports how long customers go without power; U.S. customers averaged about five and a half hours of interruptions in 2022 4. Brownouts are not counted as interruptions.
Brownout vs blackout vs surge
| Event | Voltage | Main risk | Response |
|---|---|---|---|
| Brownout | Low, lasting | Motors overheat | Shed motor loads; report it |
| Blackout | None | No power; food, heat, medical devices | Backup power |
| Power surge | Brief high spike | Electronics damage | Surge protection |
| Open neutral | Some high, some low | Equipment damage, fire | Call utility and electrician |
Brownout myths
- Myth A brownout is harmless because power stays on.
- Reality Low voltage can overheat motors and compressors.
- Myth Surge protectors protect against brownouts.
- Reality They clamp high spikes. They do nothing for low voltage.
- Myth Dim lights always mean a grid problem.
- Reality If only your home is affected, the cause may be your service or wiring.
- Myth Utilities never lower voltage on purpose.
- Reality Planned voltage reduction is a recognized tool for stressed networks 2.
Heat waves and grid stress
Brownouts track local grid conditions. Regions with long heat waves and heavy air-conditioning load see more grid strain in summer, and utilities there issue conservation alerts. Your utility and state commission set service voltage rules. Measure your own risk with outage history and backup needs.
What brownouts should change for you
If brownouts are common where you live, protect motors and electronics: a UPS for small electronics, and backup power sized with the generator sizing tool if outages follow.
If dimming is only in your home, do not wait. Call your utility first, then book an electrical inspection.
Questions about Brownout
What causes a brownout?
Brownouts come from grid stress on high-demand days, deliberate utility voltage reduction to protect the network, failing or overloaded local equipment, and sometimes problems at your own service. A loose neutral can also make some lights dim while others brighten.
Are brownouts bad for appliances?
Brownouts can be harmful, especially for motors and compressors in refrigerators, air conditioners and pumps. At low voltage, many motors draw more current and run hotter. Unplug or switch off large motor loads during a long brownout.
How long does a brownout last?
Brownout length varies. Some last a few minutes; deliberate voltage reductions during grid emergencies can last hours. A very short dip of a second or less is usually called a voltage sag, not a brownout.
What is the difference between a brownout and a blackout?
In a brownout the power stays on at reduced voltage, so lights dim. In a blackout power is lost completely. Brownouts mainly strain motors; blackouts stop everything until power returns or backup starts.
Why are my lights dim but the power is on?
Dimming lights could mean a brownout on the grid, a problem at your service connection, or a loose neutral. Check whether neighbors are affected. If only your home is dim, or some lights are brighter than usual, call your utility right away.
What voltage is considered a brownout?
There is no single official threshold. Utilities use ANSI C84.1: Range A service voltage within ±5% of nominal, about 114 to 126 volts on a 120-volt base. Sustained voltage below that range is what people usually mean by a brownout.
Should I unplug things during a brownout?
Yes, for large motors and sensitive electronics. Turn off air conditioners and pumps, and unplug computers and TVs if they are not on a UPS. Wait a few minutes after voltage returns before restarting big loads.
Can a surge protector protect against a brownout?
No. Surge protectors clamp brief high spikes. They do nothing for low voltage. A UPS with automatic voltage regulation can help small electronics; larger loads are best switched off.
Do utilities cause brownouts on purpose?
Sometimes. During severe grid stress, utilities may reduce voltage by a few percent across an area to lower demand and avoid wider failures. Con Edison's voltage specification describes 5% or 8% reductions for stressed networks.
Can a brownout damage my air conditioner?
Yes. An AC compressor that tries to start or run at low voltage draws more current and runs hotter, and it may stall and retry. Repeated events shorten its life. During a long brownout, switch the AC off at the thermostat and wait a few minutes after voltage returns before turning it back on.
Who should I call during a brownout?
Call your electric utility first, since most brownouts start on their side. If neighbors have normal power and only your home is dim, or lights are unevenly bright, call the utility and a licensed electrician.
Sources
- Pacific Gas and Electric Company, Voltage Tolerance Boundary (summary of ANSI C84.1), retrieved .
- Con Edison, EO-2096 Medium Voltage A.C. Service Voltage Limits (effective 30 August 2024), retrieved .
- California Public Utilities Commission, Interim Opinion on Emergency Voltage Reduction Measures (proposed decision, 2002), findings of fact, retrieved .
- U.S. EIA, Today in Energy: U.S. electricity customers averaged five and one-half hours of power interruptions in 2022, retrieved .
- Power Monitors Inc., Identifying Loose Neutrals (white paper), retrieved .
Expert review
Written by the HyreElectrical Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Voltage ranges from PG&E's ANSI C84.1 summary; voltage reduction practice from Con Edison EO-2096 (2024); interruption hours from EIA; loose-neutral symptoms from a Power Monitors white paper. The volt values in the example are our arithmetic on the published percentages. Read 10 October 2026.
Suggest a correction. We fix errors and say what changed.