A generator interlock kit (or just interlock kit) is a device designed to allow safe powering of a home by a portable generator during a

power outage A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electrici ...

. It is a less-expensive alternative to purchasing and installing a dedicated

transfer switch A transfer switch is an electrical switch that switches a load between two sources. Some transfer switches are manual, in that an operator effects the transfer by throwing a switch, while others are automatic and trigger when they sense one of t ...

. The kit achieves the same function by adding an external interlock onto an existing breaker panel that allows the main breaker to be turned on ''or'' one designated load breaker to be turned on, but not both at the same time. The interlocked load breaker is repurposed as the "backfeed" breaker, and a generator is connected to it (wired directly or through a power inlet). Under normal conditions, the main breaker is on, accepting power from the external mains into the panel, and the backfeed breaker is off, isolating the generator. The external mains feeds the panel, but the panel cannot backfeed the generator.

Backfeeding Backfeeding is the flow of electric power in the direction reverse to that of the generally understood or typical flow of power. Depending on the source of the power, this reverse flow may be intentional or unintentional. If not prevented (in the ...

the generator should never be done, because it serves no purpose and risks damaging the generator. In generator mode, the backfeed breaker is on, accepting power from the generator into the panel, and the main breaker is off, isolating the external mains. The generator feeds the home by

backfeeding Backfeeding is the flow of electric power in the direction reverse to that of the generally understood or typical flow of power. Depending on the source of the power, this reverse flow may be intentional or unintentional. If not prevented (in the ...

the panel, but the panel cannot backfeed the external mains.

the external mains is unsafe and illegal, because it can potentially electrocute

lineworker A lineworker (lineman (American English), linesman (British English), powerline technician (PLT), or powerline worker) constructs and maintains the electric transmission and distribution facilities that deliver electrical energy to industrial, ...

s, start fires, and overload or damage the generator.

Installation and Operation

Early generator interlock kits consisted of two sliding steel or

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(depending on the brand) plates held together by three bolts and installed on the front cover of the home's

breaker panel A distribution board (also known as panelboard, breaker panel, electric panel, DB board or DB box) is a component of an electricity supply system that divides an electrical power feed into subsidiary circuits while providing a protective fuse ...

, however, some models made by

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(formerly Cutler-Hammer) and Siemens for panels manufactured by them install on the adjacent circuit breakers themselves and consist of a sliding arm for breakers installed back-to-back or a pivoting arm for breakers that are installed side-by-side or one above the other, these arrangements remain on the breakers even if the panel cover is removed as opposed to the mechanisms installed on the panel covers. When the main breaker is turned on, the plate or pivot arm blocks the generator backfeed

circuit breaker A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...

and allows the main

breaker Breaker may refer to: Objects * A breaking wave on water, or a "breaker", a shallow over which waves break * Circuit breaker, an electrical overload switch * Breaker (hydraulic), a percussion hammer attached to an excavator People * Breaker Mo ...

to remain on. Conversely, when the generator backfeed

is turned on, the main

is blocked and will remain off. The generator backfeed

is connected to a generator inlet installed (preferably) on the outside of the structure. A short cord connects the generator to the house inlet, usually through a

twistlock A twistlock or twist lock, together with matching corner castings, as defined in norms including ISO 1161:1984, form a standardized (rotating) connector system, for connecting and securing intermodal, and predominantly ISO-standard internatio ...

plug and socket.

Advantages

*Like a

, an interlock kit lets the generator energize the panel and all of its circuits (up to the load capacity of the generator); not just corded appliances. *An interlock kit does not require a separate

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to operate; it is installed directly on the home's

(provided it has an unused 2-pole breaker slot available). *A generator interlock kit (or a transfer switch), eliminates the need for

extension cord An extension cord (US), power extender, drop cord, or extension lead (UK) is a length of flexible electrical power cable (flex) with a plug on one end and one or more sockets on the other end (usually of the same type as the plug). The term usu ...

s to power appliances.

Disadvantages

*Even though many are tested by an independent lab to a UL standard, they do not carry the UL Listing mark. Without a UL Listing, some electrical inspectors will not allow the use of these interlock kits. *With kits installed on the electrical panel's cover, removing the cover could allow the generator backfeed breaker to be turned on while the main is on, potentially energizing

power line An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-p ...

s or overloading the generator, if the generator is connected. *In some applications, installing an interlock kit requires drilling holes in the panel cover; once it is installed, it cannot be removed. *Because the main breaker is shut off, homeowners have no way of knowing when utility power is restored, except by manually turning the generator's breaker off and the main breaker back on. However there is at least one product that will produce an audible alert indicating that utility power is restored. *Installing an interlock kit uses two or three spaces in the existing

Installation and Operation

Advantages

Disadvantages

See also

References

External links