Generator Voltage Drop: Cable Size and Distance

What voltage drop means

Voltage drop is the shortfall in voltage at the far end of a cable. An outlet on a generator produces voltage at its terminals, and the wire inside a cord resists the flow of current. Some of the voltage is spent pushing current through that resistance, so the appliance end measures lower than the generator end. The difference between the two ends is the drop.

The drop belongs to the cable and the current, not to the generator. Generator listings state the outlet types and a watt figure in the title, but they do not state the drop of a particular cord, because the cord is a separate purchase. The maker's manual is the place to read the recommended guidance for that unit.

Why cable length matters

A longer cable has more wire for the current to travel through, so it offers more resistance and a larger voltage drop. Two cords with the same gauge but different lengths do not deliver the same voltage at the far end. Length is the first figure to read on a cord label.

For shopping, the distance between the unit and the appliances is part of the decision. A generator that sits at the edge of a property needs a longer cord than one placed a few steps from a door, and the cord is an extra purchase. The Florida Division of Emergency Management tells people to use heavy-duty, outdoor-rated extension cords in good condition.

What gauge means on a cord

Gauge is the thickness of the wire inside the cord, printed on the cord as a number. A lower gauge number means a thicker wire. Thicker wire has less resistance, so it drops less voltage over the same distance than a thinner wire.

A higher gauge number means a thinner wire. Over the same distance it drops more voltage. Gauge does not describe quality; it describes a dimension, and the label on the cord states it. Two cords that look similar can carry different gauges, which is why the label matters more than the appearance.

What listings state about cords

Generator and power station listings state the product, not the cord. A generator listing shows the outlet types and a watt figure. A power station listing shows an AC outlet count and a continuous output in watts. Neither states how much of that voltage arrives at the far end of a particular extension cord.

A power station that uses an AC extension cord follows the same physics: a longer or thinner cord drops more voltage at the device end. The cord terms appear in two related articles: the extension cord length question and the extension cord gauge question.

Reading a cord label

A cord label states the gauge and the length, and often a watt figure for the cord's own capacity. The gauge and length together describe how much voltage the cord drops, and the watt figure describes the load the cord can carry. None of those figures is stated in the generator listing.

Compare the cord's watt figure with the watt figure you read on the appliance or device label. The U.S. Energy Information Administration's measuring electricity page explains watts in plain language and is linked in the sources below.

What to read before you choose a cord

Read the label on the cord for its gauge and length, read the appliance label for its watts, and read the generator manual for its cord guidance.

A cord that connects through the home's wiring is not a do-it-yourself decision. A licensed electrician, the maker, and the local permit office decide that connection.

The CPSC publishes generator guidance on its Generators and Engine-Driven Tools page, and the Florida Division of Emergency Management runs a generator safety page and a disaster supply checklist. Both pages are worth bookmarking. The Florida backup power guide puts generators and power stations side by side for the same home.

The National Weather Service hurricane preparation pages are a general storm-season resource, and the Florida Division of Emergency Management supplies a disaster supply kit checklist. Those pages describe the wider preparation picture; the cord decision itself starts with the manual and the cord label.

Shopping for placement in a Florida home

A house with a yard gives you space to place a portable generator and run a cord to the appliances. An apartment or condo is a different situation. The Florida Division of Emergency Management notes that apartment and condo living can be a place where generators are not needed and says to check with building management.

For a yard placement, compare 3,000 to 5,000 watt portable generators or large portable generators. For close neighbors, inverter generators are the models compared in the neighborhood guide. A battery power station usually sits near the device it powers, so the cord between them is short, and the drop over that short distance is smaller than over a long extension cord.

What to pick for your situation

Questions

Does voltage drop depend on the generator or the cord?

It depends on the cord and the current passing through it. The generator produces voltage at its outlets, and the cord loses some of that voltage through the resistance of the wire. A listing states the generator's outlets and watt figure, not the drop of a particular cord.

What does a lower gauge number mean on an extension cord?

A lower gauge number means a thicker wire. Thicker wire has less resistance, so over the same distance it loses less voltage than a thinner cord with a higher gauge number. The gauge is printed on the cord's label.

Where do I read what cord to use?

Read the generator manual, the label on the cord, and the Florida Division of Emergency Management's generator safety page, which says to use heavy-duty, outdoor-rated extension cords in good condition. The same page is linked in the sources below.

Do power stations have voltage drop too?

Any AC outlet loses some voltage over a long cord, including the AC outlets on a power station. A power station's AC output is stated in watts, and the cord between the station and the device follows the same wire resistance. The shortest cord that reaches the device is the one to compare.

What should I do if my cord will be long?

There is no list of correct lengths on this site. Compare the stated outlets and watt figures on the listings, read the cord label and the manual, and keep any connection into the home's wiring a decision for a licensed electrician and the local permit office.

How does the first watt figure in a generator title relate to the cord?

A generator title often shows a starting figure and a running figure, and the running figure is the continuous output the unit can carry. The cord does not change those figures. The cord's own label states how much load it can carry, and the appliance label states what the appliance needs.