A refrigerated container is not a refrigerator. It is an insulated box with a machine bolted to one end, and that machine needs electricity from somewhere. At the terminal it gets that from a plug. On a ship it gets it from the vessel. On the back of a truck between PortMiami and a cold storage facility in Medley, it gets it from a generator set – a genset – or it gets nothing.
For importers moving produce, seafood, pharmaceuticals or anything else temperature-controlled through South Florida, the genset is a small piece of equipment with outsized consequences. Here is how it actually works.
What a genset is and where it mounts
A genset is a diesel generator sized to run a reefer machine, typically producing around 15 to 20 kW at the voltage the reefer expects. There are two common configurations.
Clip-on gensets
A clip-on hangs on the front of the container itself, on the same end as the reefer unit. It is attached at the terminal or at a genset yard and travels with the box. Clip-ons are the more common arrangement for port drayage because they can be attached to any container and stay with it if the box is dropped at a facility that has no plug.
Undermount gensets
An undermount is permanently mounted under the chassis frame. It is faster to deploy because there is no attachment step – the driver hooks the chassis and plugs in the reefer cable. The tradeoff is that the power stays with the chassis, so if you drop the container and the driver leaves with the chassis, the box loses power.
For a live unload, undermount is usually more efficient. For a drop where the container will sit at a facility without a plug, a clip-on is the safer choice.
What it costs in South Florida
Genset charges are quoted as a daily rental plus fuel, and they are almost always a separate accessorial on top of the drayage rate. The rental covers the equipment and the attachment or detachment labor; fuel is billed at consumption or at a flat per-day allowance.
Rates move with diesel prices and with equipment availability, so a number published today is stale next quarter. What matters more than the headline number is the billing structure. Ask three questions before you accept a reefer quote:
- Is the genset billed per day or per move, and does a partial day count as a full day?
- Is fuel included, billed at cost, or billed at a fixed daily allowance?
- Who pays for genset days if the container sits at my facility waiting to unload?
That third question is where reefer costs quietly escalate. A container that lands on Friday and cannot be unloaded until Monday is three days of genset rental plus fuel on top of any chassis and per diem exposure. Our overview of drayage accessorial charges explains how these stack.
Temperature setpoints, and who is responsible for them
The setpoint comes from the shipper and travels on the booking and the bill of lading. The drayage carrier’s job is to confirm the reefer is running at the specified setpoint when it leaves the terminal, monitor it during the move, and deliver it at that setpoint.
What the drayage carrier cannot do is fix a load that was already out of temperature. If the container was discharged at the wrong setpoint, or the machine failed on the vessel, the damage is upstream. This is why the interchange inspection at the out-gate matters so much for reefers: the driver should record the setpoint, the supply and return air temperatures, and whether the machine is running on start-stop or continuous.
Insist that your carrier documents this. If a claim develops later, the out-gate reading is the dividing line between an ocean claim and a trucking claim.
The failures that actually happen
The genset runs out of fuel
The most common failure and the most preventable. A genset with a partially filled tank that sits over a weekend runs dry. If nobody is checking, the load warms for hours before anyone notices. Any carrier handling weekend reefer drops should have a fuel check built into the process.
The clip-on is not properly seated
A clip-on that is not fully latched can lose contact over rough pavement. The reefer alarms, the machine stops, and the display shows a power fault rather than a temperature fault – which is why drivers need to know the difference.
No genset was ordered at all
Booking a reefer move without specifying genset requirements is a real and frequent mistake. The container is ready, the truck arrives, and the box cannot legally or safely leave the plug. This is a dispatch failure, and it is why reefer bookings need a separate confirmation step.
The receiving facility has no plug
If you are dropping a loaded reefer at a warehouse that has no reefer receptacle, the genset has to stay with the container and keep running. That needs to be in the booking, not discovered at the gate.
Reducing genset exposure
The cheapest genset day is the one you do not need. Practical levers:
- Live unload instead of drop. If the cargo can be unloaded on arrival, the genset detaches the same day.
- Plug-equipped yard storage. If the container must wait, storing it where it can plug in eliminates genset rental and fuel entirely. Our yard storage facility is built for containers that need to sit somewhere secure between the terminal and the consignee.
- Schedule the receiving appointment before the vessel lands. Most genset overrun is a scheduling problem wearing a fuel-cost costume.
- Transload into a reefer trailer when the final delivery is far inland and the ocean container needs to go back empty.
If you are moving temperature-controlled freight through South Florida regularly, it is worth getting a drayage quote that prices the genset and the storage options together rather than as afterthoughts.
Frequently asked questions
How long can a reefer container hold temperature without power?
Far less than most people assume, and it varies with ambient temperature, cargo type, how the box is loaded and the insulation condition. In a South Florida summer, unpowered time should be treated as minutes rather than hours for sensitive cargo. Plan your moves so the container is never unpowered by design.
Do I need a genset if the container goes straight from the terminal to my dock?
For a short move with an immediate live unload, some shippers accept a brief unpowered run for less sensitive cargo. For anything with a strict temperature requirement, or where the unload is not guaranteed on arrival, a genset is the correct call. The cost of one genset day is trivial against the cost of a rejected load.
Who supplies the genset – the ocean carrier or the drayage carrier?
Either, depending on the port and the carrier. Some ocean carriers make gensets available through the terminal; many drayage carriers rent from a local genset pool. What matters is that it is confirmed in the booking, with the billing structure stated, before the container is dispatched.