Cab power and the reefer unit (2026)
The trailer unit has a fuel tank, a compressor, and a controller whose job is the load. The cab has starting batteries, maybe a house battery, and an inverter if someone installed one. Those are different machines. A cable that "should" be able to jump from one to the other is how people damage both. Do not run a homemade cable between them.
The photo is a Prime Inc Peterbilt with a refrigerated trailer near Spokane. The company name is in the photograph. It is not a recommendation, and it is not an electrical schematic.
What feeds the bunk
Use the Sleeper Cab Power Planner for the cab night: fridge, CPAP, fan, lights, laptop, and a heater only if you mean to run one. The inputs are the cab bank's amp-hours, voltage, and depth of discharge. They are not the reefer unit's horsepower and they are not its fuel level.
- A 12 volt fridge in the cab is a cab load. The fridge guide does not connect it to the trailer.
- A CPAP is a cab load. DC or inverter, as the CPAP note describes. The reefer does not know you are sleeping.
- Shore power, when the spot has a pedestal your cord matches, feeds the cab appliances the cord is plugged into. The shore-power guide covers 15 amp, TT-30, and 50 amp plugs that do not interchange. That pedestal is still not the reefer.
- A portable power station is its own box. Read its watt-hours. Do not assume the unit in the photo is wired to a trailer.
If a factory option really does let the cab use a dedicated alternator or a separate bank, the truck manual will say so. Follow that manual. Do not follow a forum sketch. Company trucks often forbid a new wire. Ask before you add one.
What the unit is busy doing
The refrigeration unit keeps the setpoint. Shutting it off to save fuel, to sleep, or to "borrow" the alternator is not a cab-power strategy. Cargo temperature belongs to the shipper's spec and the carrier's order. Alarms belong to the unit's instructions and the carrier's reefer desk. This page does not list codes and does not tell you to open the controller.
Noise from the unit is the sleeping note. Appointment pressure is the window note. Neither one moves watts into the bunk.
Swipe this table sideways. The page stays put, and the first column stays visible.
| System | Feeds | Does not feed |
|---|---|---|
| Cab batteries | Cranking, and the loads you sized in the planner | The trailer setpoint |
| Shore pedestal | The cord you matched to the plug | The reefer controller |
| Reefer unit | The cargo, on its own fuel and controls | Your CPAP, unless the truck manual documents a connection |
| Portable pack | Whatever you plugged into that pack | An infinite night |
The bunk has its own feed
Plan the bunk from the cab batteries, from shore power, or from a separate pack. Do not tap the refrigeration unit for a CPAP, a fridge, or a heater unless the truck manual says that wire exists. The unit is holding a setpoint. Borrowing it is how people end up with a warm load and a fuse they cannot name.
What the cab can feed, if the battery and the fuse allow it:
- A 12 V fridge. Read the amp label and put the hours on the fridge calculator.
- A CPAP on the cord the manual lists, or through an inverter sized at about 125 percent of the AC watts on the label. The CPAP note walks a night of numbers. The planner adds the fridge and the CPAP together.
- Phones and a laptop, which are small until you leave them on all night.
- A fan. A 1,500 W heater is not a fan. On a starting battery that also has to crank the truck, leave the heater for shore power.
Shore power means the plug in your hand matches the pedestal: a household 15 A, a TT-30, or a 50 A, and not a mix. Do not backfeed the inverter into the cord. Do not coil a loaded cord into a tight pile. If the pedestal is not there, you do not have shore power. Idling because you wish you did is a carrier and a local rule, not a default.
The reefer stays at the setpoint while you sleep beside it. The noise page is plugs, curtains, and leaving the controls alone. A team adds both people's loads. The shared power page is that sum. Two people do not get two batteries by hoping.
If you do not know the fuse, stop. A test light and a guess are how cabs burn. Ask the shop or read the manual for that truck. Skip a "reefer outlet" video that does not match your unit. Your manual wins.
| Feed | Use it for | Do not |
|---|---|---|
| Cab battery | Fridge, CPAP, fan, within the planner | A 1,500 W heater overnight on the starting bank |
| Shore power | Heat or anything large, matching plug | Backfeeding, or a coiled loaded cord |
| Separate pack | Whatever its label says | Assuming it equals the truck battery |
| Reefer unit | The cargo setpoint | A tap the manual does not show |
Conclusion
Size the bunk from the cab or from shore power. Leave the refrigeration unit on its own job. If the manual documents a real connection, use that. If it does not, there is no connection.
FAQ
Can I run a short cord from the reefer battery to the sleeper?
Not from this page. Unless the truck manual says that feed exists, treat the systems as separate. A homemade tap is how both sides get damaged.
Does a nose-mount reefer charge the truck batteries?
Do not assume it. Some installations are independent. Read the manual for the truck you are in.
The planner asks for amp-hours. Do I enter the reefer's fuel?
No. Enter the cab bank. Fuel in the reefer tank is not watt-hours in the sleeper.