The common causes
An electrician works through 5 conditions that all produce do my lights dim when an appliance starts.
- Motor inrush on a shared circuit: Well pumps, compressors and power tools draw a large starting current for a moment.
- Undersized or shared circuit: A heavy appliance sharing a circuit with lighting.
- Loose connection: A loose service, neutral or panel connection can cause voltage to swing as load changes.
- Service capacity: A service near its limit shows the strain when a large load starts.
- Utility-side condition: A supply problem outside the property, which is the utility's to resolve.
What to note before you call
For lights that dim when an appliance starts, 5 observations do most of the work.
- Whether one room dims or the entire house
- Which appliance triggers it
- Whether lights ever brighten unusually, which is more serious
- Whether neighbours see the same thing
- Any flicker, buzzing or burning smell
Reading the pattern of the dimming
How the lights dim tells an electrician where to look. If only lights on the same circuit as the appliance dip, the circuit is carrying a load it cannot supply without voltage sag, or a connection on it is loose. If lights all over the house dip, the problem sits upstream at the panel, the service conductors or the meter connection, or in the utility supply. If the lights sometimes get brighter as well as dimmer, that swing is the signature of a loose neutral, and it is the version that can damage electronics and should be treated as urgent.
The trigger matters too. A dip that lasts, or that a modest appliance causes, is not.
Vermont homes and dimming lights
Many older homes here still run on 60-amp or 100-amp services that were sized before electric ranges, dryers, heat pumps, EV chargers and well pumps became common. As loads have been added, the service has less room, and a large starting load shows it. Rural properties with long service drops and well pumps are especially prone to a visible dip at pump start.
The utility side is real as well. In Burlington the supplier is Burlington Electric Department, elsewhere in the region it is usually Green Mountain Power, and a supply problem at the transformer or the drop is the utility's to correct, not the homeowner's or an electrician's. Asking neighbors whether they see the same thing is a useful first test.
What the repair usually involves
Outcomes range from putting a heavy appliance on its own circuit, to repairing a loose connection at the panel or meter base, to a service upgrade where the load simply exceeds what the service can supply. A suspected neutral problem or a utility-side fault should be reported promptly. Because the cause decides the repair, get it identified and written down before authorizing anything large.
What happens next
For lights that dim when an appliance starts, the related service is panel and service upgrades.