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A '''generator interlock kit''' (or just '''interlock kit''') is a device designed to allow safe powering of a home by a [[engine-generator|portable generator]] during a [[power outage]]. It is a less-expensive alternative to purchasing and installing a dedicated [[transfer switch]]. 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).
{{Orphan|date=January 2013}}
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 [[backfeeding|backfeed]] the generator. [[Backfeeding]] the generator should never be done, because it serves no purpose and risks damaging the generator.
AIn '''generator interlockmode, kit'''the (orbackfeed justbreaker '''interlockis kit''')on, accepting power from the generator into the panel, and the main breaker is aoff, deviceisolating designedthe toexternal allowmains. safeThe generator feeds the home by [[backfeeding]] ofthe apanel, homebut throughthe apanel [[engine-generator|portablecannot generator]]backfeed duringthe external mains. [[power outageBackfeeding]]s, therebythe eliminatingexternal illegalmains and/oris unsafe [[engine-generator|generator]]and [[backfeeding]]illegal, situationsbecause thatit couldcan potentially [[electrocution|electrocute]] [[lineman (occupation)|power linemenlineworker]]s, start fires, and overload or destroydamage the generator.<ref>{{Cite web|url=http://www.nooutage.com/interlock_kits.htm|title=Panel Interlock Kit Kits - for safely connecting generator power without a transfer switch}}</ref>
==Installation and Operation==
AEarly generator interlock kitkits isconsisted of two sliding [[steel]] or [[plastic]] (depending on the brand) plates held together by three bolts and installed on the front cover of the home's [[distribution board|breaker panel]]., Ithowever, consistssome ofmodels twomade slidingby [[steelEaton Corporation|Eaton]] or(formerly Cutler-Hammer) and [[plasticSiemens]] (dependingfor panels manufactured by them install on the brand)adjacent platescircuit heldbreakers togetherthemselves and consist of a sliding arm for breakers installed back-to-back or a pivoting arm for breakers that are installed side-by-side threeor boltsone 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 movedthe downmain breaker is turned on, the plate or pivot arm blocks the generator backfeed [[circuit breaker]] and allows the main [[circuit breaker|breaker]] to remain on;. when moved upConversely, when the generator backfeed [[circuit breaker]] may beis turned on, but the main [[circuit breaker]] is blocked and will remain off. The generator backfeed [[circuit breaker]] 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 the use ofa [[Industrialindustrial and multiphase power plugs and sockets|twistlock]] plugs and [[AC power plugs and sockets|socketsplug and socket]].
==Advantages==
*UsingA angenerator interlock kit allows for all of(or a panel'stransfer circuits to be energizedswitch), up toeliminates the loadneed capacityfor of[[extension thecord]]s generator;to whereas using a generatorpower [[transferhome switchappliance|appliance]] only allows a few circuits to be operateds.<ref>{{cite web |url=http://www.interlockkit.com/ |title=Home |website=interlockkit.com}}</ref>
*Like a [[transfer switch]], 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 [[distribution board|panel]] to operate; it can beis installed directly on the home's [[distribution board|breaker panel]]. (provided it has an unused 2-pole breaker slot available).
*Interlock kits eliminate the need for [[extension cord]]s to power [[Home appliance|appliance]]s.
==Disadvantages==
*Even though many are tested by an independent lab to a UL standard, they do not carry the UL Listing mark.<ref>{{Cite web|url=http://www.nooutage.com/interlock_kits.htm|title=Panel Interlock Kit Kits - for safely connecting generator power without a transfer switch}}</ref> Without thata markUL someListing, localsome electrical inspectors will not allow the use of these interlock kits.
*RemovingWith kits installed on the [[distribution board|electrical panel's]] cover, removing the cover could allow the generator backfeed breaker to be turned on while the main is on,<ref>http{{Cite web|url=https://forums.mikeholt.com/showthread.php?t=113865&page=2|title = Wire resistance, temp, soil cond}}</ref> potentially energizing [[power line]]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.<ref>http{{Cite web|url=https://www.electriciantalk.com/f2/see-if-power-restored-interlock-kit-33891/|title = See if power is restored with interlock kit?}}</ref> However there is at least one product<ref>{{Cite web|url=http://www.nooutage.com/thp108.htm|title = THP108 PowerBACK - utility power return alert}}</ref> that will produce an audible alert indicating that utility power is restored.
*Installing an interlock kit requiresuses anywheretwo fromor 2 to 3three spaces in the existing [[distribution board|breaker panel]].
*[[ transferTransfer switch]] ▼*[[UL (safety organization)]] ▼
==References==
{{reflistReflist}}
==External links==
*[httphttps://www.ulinterlockkit.com/global/eng/pages/ ULGenerator Interlock Tech] Websitewebsite
*[httphttps://natramelecwww.ul.com/ National Ram ElectronicsUL] Websitewebsite
*[httphttps://www.nooutagenatramelec.com/ NoOutageNational Ram Electronics] Websitewebsite
*[http://www.geninterlocknooutage.com/ GenInterlock IncNoOutage] Websitewebsite
*[https://enstorageinc.com/best-inverter-generator-review/ Best Generator Guide]{{Dead link|date=August 2025 |bot=InternetArchiveBot |fix-attempted=yes }}
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▲*[[UL (safety organization)]]
[[Category:Electrical power control]]
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