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Generator Accessories

Generator Inlet Box vs Outlet Box: Differences and Picks

An inlet box brings generator power into the house through a transfer switch, and an outlet box sends power out to a device; this guide explains the difference.

Adrian Kessler
By Adrian Kessler · 8 min read
Generator Inlet Box vs Outlet Box: Differences and Picks
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A generator hums outside, the house stays dark, and the question is how the power gets in: that gap is the job a generator inlet box is built for, and generator inlet box vs outlet box comes down to direction, an inlet box brings generator power into the house, and an outlet box sends power out to a device. The sections below explain each box, how to choose between them, and the gear that handles the inlet side.

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The quick answer: generator inlet box vs outlet box

An inlet box is an inlet on the outside wall that takes generator power into the house through a transfer switch or panel. An outlet box is a receptacle that sends power out to a device plugged into it. If the generator must power the house during an outage, the inlet box is the part to buy; an outlet box cannot bring generator power into the house. The gear below covers the inlet side.

What an inlet box does

The listings describe the inlet box as an outdoor inlet that is hardwired through an outside wall directly to the transfer switch or panel, which removes the need for cords running through windows or doors. The Rophor listing says the box is designed to be installed outdoors in an open area where the generator is being used, and the RVMATE listing says the same, so the generator stays outside while the power comes in. The Rophor listing says the box is designed to be located outdoors where the generator is running to prevent carbon monoxide fumes from the generator from entering the house. The SURAIELEC listing says the box is designed for outdoor installation and is ideal for backup power during outages and severe weather. Our portable generator safety tips cover the same outdoor placement.

What an outlet box does

An outlet box holds a receptacle that supplies power to whatever plugs into it, such as a tool or an appliance on a circuit. It sends power out from the house wiring, the opposite direction from an inlet box. The listings here cover inlet boxes only, so no outlet box is scored in the gear section; the comparison below uses the inlet boxes in the listings and the outlet role described here.

How to choose between them

Choose by direction and by capacity. Direction decides the box: power into the house needs an inlet box, power out to a device needs an outlet box. Capacity decides the size: the listings here run 30 amp and 50 amp, with the 50 amp boxes at 12,000W and 12,500 Watts. Match the box to the generator cord: the RVMATE takes a NEMA L14-30P cord, and the SURAIELEC, RVINGPRO and Rophor boxes take NEMA SS2-50P cords. Our types of generator plugs guide explains the NEMA connectors. All listings here state an ETL certification, so certification does not separate them; the differences are capacity, the cord, and the extras such as a power indicator or a cord in the kit.

Box Amps Watts Certification
RVINGPRO 50A Inlet Box Kit 50 12,500 ETL stated
Rophor 50A Generator Inlet Box 50 12,500 ETL stated
SURAIELEC 50A Inlet Box 50 12,000 ETL stated
RVMATE 30A Generator Inlet Box 30 7,500 ETL stated

The table shows the split: the 50 amp boxes share the higher capacity, the RVMATE is the only 30 amp box, and all state an ETL certification. The RVINGPRO kit adds a 15 foot cord and an adapter, which the other boxes do not include.

Ways to keep an inlet box working

  • Keep the flip cover closed when the box is not working; the RVMATE listing says the flip cover can be closed to prevent moisture from entering the connector inlet.
  • The SURAIELEC listing says the 3R rainproof enclosure keeps out dust and humidity, and the Rophor listing says the spring cover closes when not in use to protect the inlet from the elements.
  • The RVMATE and Rophor listings claim 50% more wiring space than ordinary boxes, but neither listing names the ordinary box it is compared with, so treat that claim as marketing rather than a measured figure.
  • Check the power indicator before assuming the generator is connected; the RVMATE, RVINGPRO and Rophor listings each name a green indicator light.

The gear

The gear in this section handles the inlet side of the job: the boxes bring generator power into the house, the ETL listings cover certification, and the RVINGPRO kit adds the cord and adapter.

RVINGPRO 50A Inlet Box Kit. RVINGPRO lists the kit as a 50 amp generator inlet box and a 15 foot 50 amp generator cord, ETL listed, with a pre-drilled SS2-50P power box, a 14-50P to SS2-50R cord and an adapter. The cord is made of 100% copper conductor with a flame retardant coating and a PVC jacket, with a voltage of 125V/250V, a wire gauge of STW 6/3 + 8/1 AWG and a max wattage of 12,500 Watts. The box has 4 pre-drilled holes in 4 directions, left, right, bottom and rear, and the listing says the holes open with fingers within only 30s. The kit includes a 50 amp generator cord, a 50 amp generator inlet box, a 50A adapter plug, a cable tie and a storage bag, and a 90 day return service is stated. No warranty term is stated. It fits backup power where the box, cord and adapter arrive as a kit; buyers who already own a cord only need the inlet box.

Rophor 50A Generator Inlet Box. Rophor lists the box as a 50 amp generator power inlet box, NEMA SS2-50P, 125/250 volt and 12500 watts, ETL listed, for a 3 prong generator cord. The listing says the box is an outdoor electrical inlet, hardwired through an outside wall directly to the transfer switch or panel, which removes the need for cords running through windows or doors. The listing claims 50% more wiring space than ordinary boxes, with a removable front for easy placement and wiring, and a spring cover that closes when not in use. The listing spells anti-rust as Anty-rust and says the surface has anti-corrosive powder-coat paint. A green power indicator is stated, and the listing states dimensions of 6.1 by 4.1 by 3.1 inches. No warranty term is stated. It fits backup power where a 50 amp inlet with a stated wattage and an indicator matters; buyers who want a 30 amp box or a cord in the kit should look elsewhere.

SURAIELEC 50A Inlet Box. SURAIELEC lists the box as a 50 amp generator power inlet box, NEMA SS2-50P, 120/240V, with a 12,000W figure and compatible with 4-6 AWG wire. The listing says the 3R rainproof design and ETL certified receptacle provide enhanced safety and reliable outdoor performance, and the box is made from galvanized steel with a 3R rainproof enclosure. Six knockout holes allow multi-directional connections, with a detachable front panel for easy installation. The title calls the box an outdoor outlet receptacle, while the listing describes an inlet box. No dimensions, weight, warranty term or power indicator is stated. It fits backup power where a 50 amp inlet with a rainproof steel enclosure matters; buyers who want a wattage above 12,000W or a power indicator should look elsewhere.

RVMATE 30A Generator Inlet Box. RVMATE lists the box as a 30 amp generator inlet box, NEMA L14-30P, 125/250V and 3750/7500W, ETL listed, for a 4 prong generator cord. The pre-drilling design lets the wiring caps be removed and replaced without special tools, per the listing. The internal space is 50% larger than that of the ordinary power inlet box, per the listing, but no ordinary box is named. The box is constructed of steel with durable, anti-corrosive powder-coat paint, and a clear LED power indicator on the flip cover lights up when the power is connected. The title promises more water protection than the bullets, which describe a flip cover that closes to keep moisture out. No warranty term is stated. It fits smaller generators where a 30 amp inlet with an LED indicator matters; buyers who need a 50 amp inlet or a cord in the kit should look elsewhere.

FAQ: power away from the grid

What is a generator inlet box?

An inlet box is an inlet on the outside wall that takes generator power into the house through a transfer switch or panel, so no cords run through windows or doors.

What is the difference between an inlet box and an outlet box?

Direction: an inlet box brings generator power into the house, and an outlet box sends power out to a device. The Rophor listing says the inlet box is hardwired through an outside wall directly to the transfer switch or panel.

What amp inlet box fits a 50 amp generator cord?

The SURAIELEC, RVINGPRO and Rophor boxes are 50 amp and take NEMA SS2-50P cords, and the RVMATE is 30 amp with a NEMA L14-30P cord.

Can an inlet box be used outdoors?

The listings say yes: the RVMATE, SURAIELEC and Rophor boxes are designed for outdoor installation, with covers and ETL certification. Install the box outdoors in an open area where the generator is being used.

Do generator inlet boxes come with a cord?

Only the RVINGPRO kit in these listings includes a cord: a 15 foot 50 amp generator cord, a 50A adapter plug, a cable tie and a storage bag. The other boxes are the inlet box alone.

See the portable generator safety tips, the types of generator plugs guide, how to use a generator during a power outage and every generators guide. Also see our push button vs key start generator. Also see our 2000 watt vs 4000 watt generator. Also see our 6000 watt vs 8000 watt generator. Also see our l5-30 vs l14-30 generator plug. Also see our best carbon monoxide detector with digital display.

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