Commercial holiday lighting installation field guide: load, GFCI, and the ladder

What a commercial holiday install is, and the two things that make or break it

A commercial holiday lighting installation is line-voltage lighting, fed at 120 volts, hung on rooflines, trees, columns, and entries for one season and then taken down and stored. It is not the low-voltage landscape system that runs at 12 volts off a transformer. The cord plugs into a wall receptacle at building voltage, so every connection, every run, and every receptacle is governed by the rules that apply to line-voltage outdoor power. The low-voltage path-lighting work is a separate trade with its own guide; cross over between the two and you will misjudge the load and the shock risk.

Two things decide whether the job goes well, and neither is the design. The first is electrical load. Daisy-chain too many strings on one run or hang too much on one circuit and you blow the in-plug fuse or trip the breaker, and a dark section of roof on a commercial site is a callback that same night. The second is the ladder. Falls from ladders and roofs are the injury that ends careers and bankrupts small lighting companies, and they happen on the easy houses as often as the hard ones.

Doing it right means a load and circuit plan before the truck loads, GFCI protection on the outdoor power, weather-rated connections kept off the ground, safe access planned for every elevation, and a product system built to install fast, control on a schedule, remove clean, and store labeled by site. The seasonal business runs on that last part. Cross-link the low-voltage lighting guide for path and accent work and the commercial maintenance guide for how a recurring route is run.

Why a commercial display is a professional job, not a DIY one

Scale is the first reason. A commercial roofline can run hundreds of feet, the trees are large, and the building has limited outdoor power in the wrong places. That combination forces real load planning and real access equipment, neither of which a property's own staff is set up to do safely on a December morning.

Safety is the second. The fall hazard does not scale down on a small building. A worker on a step too high or a ladder set at the wrong angle is one slip from a hospital bill that dwarfs the whole contract, and the property owner does not want that liability on their site. A licensed, insured crew with the right ladders and fall plan exists precisely to keep that risk off the owner's books.

The look is the third, and it is what gets the contract renewed. Even spacing, straight lines on the roofline, full even tree wraps, and bulbs all facing the same way read as professional from the road. A homeowner-grade job with sagging lines and gaps reads as cheap, and on a commercial property the look from the street is the marketing the owner is paying for.

The fourth reason is the money. Holiday lighting is recurring seasonal revenue. The same client buys the install, the in-season service, the removal, and the storage every year, and a good route compounds. That business model only works for a company set up to run it, which is the rest of this guide.

LED vs incandescent: LED is the standard now

LED is what a professional installs today, and the reason is wattage. An LED C9 bulb draws a fraction of a watt, where an incandescent C9 pulls around 5 to 7 watts. On a 25-bulb strand that is the difference between roughly 12 to 15 watts for LED and well over 100 watts for incandescent. Every number downstream follows from that gap: how many strings you can connect, how many circuits you need, and how much heat sits against the building.

The practical payoff is the series run. Because each LED string draws so little, the manufacturer often allows dozens of strings end to end where incandescent allowed only a handful before the fuse or the wire was at its limit. Long unbroken runs mean fewer power drops, fewer cords across the roof, and a cleaner job. LED also runs cool, which matters against dry roofing and stored in a box, and it holds up to the freeze-thaw and handling a seasonal product takes year after year.

The catch with LED is on the control side, covered later: LED draws so little that some are slow to register on a photocell, and the small leakage current in their drivers can nuisance-trip a GFCI if the strings are not designed for it. Buy commercial-grade LED rated for outdoor use and confirm the actual per-string wattage and the maximum series run on the manufacturer's tag. Those numbers, not a rule of thumb, drive the load plan.

Why holiday lights blow fuses and trip breakers

The number one technical failure on a holiday job is overloading, and it shows up two ways. You overload a single series run by connecting more strings end to end than the wire and the in-plug fuse can carry, and the fuse blows. Or you overload the branch circuit by plugging too much total load into receptacles on the same circuit, and the breaker trips. Both leave a dark display, and both are avoidable with a load count done before you hang anything.

Watts and amps are the whole game. Add up the wattage of everything on a run or a circuit, divide by 120 volts, and you have the amps. Compare that to the limit of the run, set by the manufacturer, and the limit of the circuit, set by its breaker. A blown fuse in the plug is the string protecting itself from a run that is too long. A tripped breaker is the building protecting itself from a circuit that is too full. Neither is a defect. Both are the system telling you the load math was wrong.

The trap on a commercial site is the shared circuit. The receptacle you plug into may already feed interior loads you cannot see, so the circuit is partly spent before your first string. Plan the load against the receptacle and against everything else on that circuit, and confirm the real circuit rating rather than assuming. The exact figures are set by the manufacturer's string ratings and the NEC as adopted locally, so verify against both and bring in a licensed electrician for anything touching the building's wiring.

Watts

Power a string or display draws; sum the watts on a run or circuit to find the load

Amps

Current the load pulls, found by dividing total watts by the supply voltage, commonly 120 V

In-plug fuse

The small fuse in the male plug of a light string that blows when the series run is overloaded

How many holiday lights can you run on one circuit?

You size the display to the circuit, not the other way around. A 15-amp 120-volt circuit has a theoretical ceiling near 1800 watts and a 20-amp circuit near 2400 watts, but holiday lighting runs for hours, so it is a continuous load. For continuous loads the common practice, following the NEC, is to hold to 80 percent of the breaker rating. That puts the working ceiling around 1440 watts on a 15-amp circuit and around 1920 watts on a 20-amp circuit.

Translate that to product with the per-string wattage from the tag. Low-wattage LED leaves a lot of room on one circuit, while incandescent fills a circuit fast, which is one more reason the trade went LED. The honest answer to how many lights fit is a wattage sum, not a string count: total the watts, divide by 120 for amps, and keep the result under 80 percent of the circuit.

The discipline that prevents callbacks is spreading the load. Do not run a large display off one receptacle just because it is closest. Identify the available circuits, divide the display across them, and keep notes on which run feeds from which receptacle so an in-season service call can find the problem fast. The exact ampacity and continuous-load rules are governed by the NEC as adopted by the AHJ, and any new circuit or panel work belongs to a licensed electrician.

How many strings of lights can you connect end to end?

Every light string has a maximum series connection, the number of strings you can plug end to end before the run is at its limit, and that number is printed on the manufacturer's tag. Exceed it and you blow the in-plug fuse, or worse, you overheat the wire feeding the far strings. The limit exists because the first string in the chain carries the current for every string behind it, so the load piles up toward the plug.

LED changed the count dramatically. Because an LED string draws so little, manufacturers commonly allow dozens of LED C9 strings in a single run where incandescent allowed only a few. A common manufacturer guide is to keep a single connected run at or below roughly 210 watts, though the NEC sets no per-run wattage limit, so the in-plug fuse and the product tag are the real authority, but treat that as a starting figure and use the limit on your specific product. The tag wins over any general number.

Read the tag and respect it, because the fuse is not a suggestion. The in-plug fuse is sized to protect that run, and bypassing it with a heavier fuse to make a longer chain work is how cords overheat. When a run needs to be longer than the limit allows, you do not push the chain; you bring power to a new point and start a fresh run. Carry the manufacturer's maximum series connection in your takeoff so the design respects it before the crew is on the roof guessing.

Do holiday lights need GFCI?

Outdoor holiday lighting plugs into outdoor power, and outdoor receptacles are required to be GFCI protected under the NEC, commonly cited at 210.8. A ground-fault circuit interrupter watches the current going out against the current coming back, and if a few milliamps go missing, the fault path is probably a person or wet ground, so it cuts power in a fraction of a second. On a wet roof in December, that protection is what stands between a nicked cord and a fatal shock.

If the receptacle is already GFCI protected, use it. If it is not, the fix is a GFCI-protected outdoor adapter or extension at the source, not skipping the protection. Bypassing or defeating a GFCI to stop nuisance trips is the worst call on the whole job, because it removes the one device that protects against the exact hazard outdoor lighting creates.

Nuisance tripping is real with LED, and the cause is the small leakage current in cheap LED drivers, which a sensitive GFCI reads as a fault. Buy LED strings marked GFCI compatible, keep connections dry and off the ground so moisture is not adding leakage, and split the display across more circuits so no single GFCI sees the combined leakage of the whole job. The GFCI requirement is set by the NEC as adopted by the AHJ, so confirm the local rule and leave any receptacle or circuit work to a licensed electrician.

Weather-rated connections and keeping them out of the wet

Every connection on the job lives outside through rain, snow, and freeze, so the connections, not the bulbs, are where the trouble starts. Use outdoor-rated cords and connectors, and keep every plug-to-plug junction up off the ground where water pools and ice forms. A connection sitting in a gutter or on the roof in a puddle is a GFCI trip and a corrosion failure waiting for the first thaw.

Make a drip loop at each connection. You let the cord hang below the joint so water runs down the cord and drips off the low point instead of tracking into the plug. It costs nothing and it stops the slow water intrusion that kills connections by mid-season. Where two cords meet in an exposed spot, a weatherproof cord cover or a wrap of the right outdoor tape keeps the junction sealed, but the cover is not a license to lay it in standing water.

Plan the cord routing the way you plan the lights. Cords should run where they are out of foot traffic, off sharp edges, and not pinched under a ladder foot or a roof hatch. A cord abraded against a metal edge all season is a ground fault in the making, and on a commercial site it is also a trip hazard the property owner will not tolerate. Route it once, route it clean, and the in-season service calls drop.

Where the power comes from, and not overloading the owner's panel

Before the design is final, find the power. Walk the building and note where the outdoor receptacles are, what they are rated, and what else is on those circuits. A large roofline on the far side of a building with one receptacle near it is a load problem you want to know about at the proposal, not on install day with the crew standing on the roof.

The building's electrical capacity is a hard constraint you do not control. A commercial display can add real load, and if the available circuits are already near their limit with the building's own equipment, your display tips them over and trips the breaker, sometimes the building's, which is a far bigger problem than a dark eave. Coordinate with the property's facilities staff or owner about which circuits you may use and how much headroom they have.

When the display needs more capacity than the existing receptacles can give, that is electrician work, not installer work. Adding a circuit, installing a new exterior receptacle, or tapping the panel must be done by a licensed electrician to the NEC as adopted locally and with the AHJ's permitting where required. Build the cost and the lead time of that electrical work into the proposal, because finding out in December that the building cannot power the design is the kind of surprise that loses the account.

Timers, photocells, and smart control

A display that the property staff has to switch on and off by hand will be wrong half the season, so put it on control. The simplest reliable choice is an outdoor photocell timer: the photocell turns the lights on at dusk automatically and adjusts as the days shorten, and the timer sets the off time, so the display follows the sun without anyone touching it.

Programmable and Wi-Fi smart plugs add precise schedules and remote control, which earns its keep on a route. From a phone you can confirm a site came on, change an off time for an event, or kill a circuit that is faulting without a truck roll. For a commercial property with set hours, a fixed schedule that turns on before dusk and off at a chosen hour often fits better than pure dusk-to-dawn.

Use zones. Put the roofline on one switched outlet and the trees or the entry on another, so the owner can run them on different schedules and so a fault on one zone does not take the whole site dark. One note on LED: a very low-draw LED display can sit below the threshold a photocell expects, so confirm the control is rated to switch the small LED load, and size the timer's amp rating to the connected watts.

C9, C7, mini, and specialty product

The product you reach for depends on the surface. C9 bulbs are the large, classic roofline bulb, spaced along the eave for the bold outline that reads from the street; C7 is the slightly smaller cousin used where a finer look or a lighter run is wanted. Both come as a bulk light line you cut to length and socket, which is how a pro fits a run to a specific roofline instead of fighting fixed-length sets.

Mini lights, almost always 5 mm wide-angle LED for professional work, are the choice for wrapping trees and railings, because the small bulb and tight spacing give an even glow and the low weight stays on the branch. Wreaths, garland, and lit decor fill out entries and light poles. Specialty product like permanent track lighting and pixel-controlled systems is a separate conversation, but the load and access rules in this guide still apply.

Buy commercial grade, not retail. Retail sets are built to a price for one or two seasons in a garage, with thinner wire, weaker sockets, and shorter series limits. Commercial product uses heavier gauge wire, sealed sockets, and is rated for the long series runs and the handling a route puts on it across many seasons. The cost difference is recovered the first time a commercial run survives the freeze that would have killed a retail set.

Hanging the roofline with clips, never staples or nails

Roofline lights go up with clips, full stop. You never drive a staple or a nail through a cord, and you never put a fastener through the roofing. A staple through a cord cuts the insulation and creates a ground fault and a shock and fire hazard on the spot, and a nail through a shingle or flashing creates a leak the property owner will be chasing long after the lights come down.

The clip is purpose-built to grip without damage. An all-in-one clip slides under a shingle tab or hooks over the gutter lip and holds the bulb, and the good ones handle C7, C9, mini, and icicle product so the crew carries one clip for the whole job. Many let the bulb rotate so you can face every bulb the same way down the run, which is the small detail that separates a clean job from a sloppy one.

Spacing and alignment are what the eye reads. Common practice is roughly 12 inches between clips on a gutter and around 15 inches on shingles, adjusted to land the bulb spacing evenly and keep the line straight. Pull the run taut so it follows the fascia without sag, and keep the bulbs on a consistent line. The fastening must hold through wind and ice all season and then release clean at removal, because a clip that fights you on the way down doubles the takedown labor that the season's profit depends on.

Wrapping trees: trunks, canopy, and the light count

Tree wraps eat product and labor, so the count and the method matter to the bid. The light-per-foot figure depends on the look the client buys: a denser wrap takes more string per foot than a light accent. A workable planning method is to divide the section height by your string spacing to get the number of wraps, then multiply by the circumference of what you are wrapping to get the footage. Measure the trees at takeoff so the truck carries the right footage instead of guessing on site.

Trunk and main-branch wraps are where the bold light lives. Wrap the trunk, then follow the major limbs out as far as the design calls for, keeping the spacing between passes consistent so the wrap reads even from a distance. On large trees, watch the weight: spacing the bulbs out, or using the lighter mini product, keeps the load off the branches so the wrap does not sag or pull free in wind.

Power the tree from the base and plan the run back to a protected source like any other circuit. A bank of wrapped trees can add up to real wattage, so it counts in the load plan the same as the roofline. The canopy and far branches are also the parts most exposed to wind and ice, so the attachment and the connection sealing get extra attention there.

Ground and stake displays

Ground-level product fills the spaces the roofline and trees do not reach: staked pathway lighting, lit figures, and inflatables at entries and along drives. The layout is a design call, but the electrical and the safety rules do not relax at ground level.

Two things bite here. Cords run across walkways and drives are a trip hazard and a damage point, so route them at the edges, under cover, or in a cord protector where they must cross, and keep the connections up out of the puddles and snowmelt that collect on the ground. And the load still counts: a row of inflatables with their own blowers and lights adds up fast on a circuit that may already be carrying the roofline.

The ladder and the roof: the injury that ends the season

Falls from ladders and roofs are the leading injury in holiday lighting, and they are not freak accidents. The CPSC and CDC track many thousands of holiday-decorating injuries every year, with ladder falls and roof falls leading the list. A single fall can mean a hospital stay, a workers' comp claim, and a lawsuit that closes a small lighting company. This is the hazard to be blunt about: the lights are not worth a life or a back.

Set the ladder right. The standard is the 4-to-1 ratio: the base sits one foot out from the wall for every four feet of height, which puts the ladder near a 75-degree angle. For roof access, the ladder extends about 3 feet above the edge so there is something to hold getting on and off, and it gets tied off or footed so it cannot kick out or slide. Maintain three points of contact climbing, never carry a load up that needs a free hand, and never stand on the top cap. An aluminum ladder near electrical work is its own hazard; keep it clear of live conductors.

Reduce the ladder time wherever the site allows it. Where the access exists, a scaffold, a lift, or a bucket truck takes a worker off a ladder for long roofline runs and is far safer than repositioning a ladder fifty times in the cold. Ladder and fall safety on the job is governed by OSHA, so confirm the requirements that apply to your work, and train the crew before the season, not on the first roof.

Working on the roof

Some rooflines cannot be reached from a ladder, so a worker is on the roof, and that changes the risk. A frosted or wet roof in lighting season has almost no traction, and a steep pitch turns a slip into a slide off the edge. Plan roof work for the conditions: get up before the frost burns off and it is the most dangerous, and stay off a roof that is iced or snow-covered until it clears.

Above a height threshold, fall protection is the rule, not a choice. This kind of work commonly falls under construction fall-protection standards, where work at roof edges typically calls for a personal fall arrest system, an anchor, and a harness, or another protective method. Treat steep, high, and slick roofs as the cases where the harness comes out every time.

The exact fall-protection trigger height and the acceptable methods are set by OSHA and vary with how the work is classified, so confirm what applies to your operation and the jurisdiction. The principle does not vary: a fall off a commercial roof is a fatal hazard, and the protection is cheap against the consequence.

Install timing and the weather window

The install window is the fall, before the hard freeze, and it is shorter than it looks. You want the displays up while the roofs are dry and walkable and the cords still flex, which in most of the country means starting well before Thanksgiving and finishing before the first real snow. Push the install into December and you are putting crews on icy roofs in the cold, which is slower, more dangerous, and harder on the product.

Cold makes everything worse on install day. Cord insulation stiffens and cracks if you flex it hard in deep cold, clips get brittle, and a worker in heavy gloves on a frosted ladder is the setup for the fall this guide keeps warning about. Sequence the route so the high, steep, and far sites get done early in the window while conditions are best, and leave the simple ground-level work for if the weather turns.

Build weather slack into the schedule. A season's worth of installs cannot all happen on the three good-weather days, so a route needs enough window and enough crews that a cold snap does not force a choice between a missed client and a crew on a dangerous roof. The weather risk is a planning problem you solve in October, not a surprise you eat in December.

The design, the proposal, and the takeoff

The design is where the job is won and where the cost is set. You walk the property, decide what gets lit, and turn that into a measured takeoff: the linear feet of roofline, the trees and their sizes, the entries, and the product type for each. Measure the rooflines and the tree circumferences for real rather than eyeballing, because the takeoff drives both the material order and the labor estimate, and a guess on a large roofline is a guess on the margin.

The proposal has to carry the electrical reality, not just the look. Note where the power is, whether the circuits have headroom, and whether the building needs an electrician to add capacity, because that cost and lead time belong in the price up front. A beautiful design the building cannot power is not a design; it is a change order waiting to happen.

Price the full season, because that is what you are actually selling. The number covers the install, the in-season service, the removal, the storage, and on a leased display the product itself amortized over its life. A bid that prices only the hang and forgets the takedown and storage labor is a bid that loses money on the back half of the season, which is exactly the part new installers underprice.

The seasonal recurring business model

Holiday lighting is a recurring seasonal business, and the recurring part is where the money is. The client buys a package every year: install, keep it lit, remove, and store. That is four billable steps per site per season, and a renewing client costs far less to win than a new one, so a route compounds in value as it grows and renews.

The first structural decision is lease versus buy. Under a lease model you own the product, the client rents the display for the season, and you handle install, service, removal, and storage, which keeps the product quality in your control and the client coming back year after year because you hold their lights. Under a buy model the client owns the product from year one and pays for it up front, which improves first-year cash flow but gives up some of the repeat lock-in. Most established companies lean toward leasing for the recurring revenue and the control, while buy fits a client who wants to own and a company short on storage.

A route this seasonal lives or dies on coordination, and that is where a field tool earns its place. FieldOS holds the site, the design and takeoff, the circuits and power notes, the product list, and the photos for each property, so the crew that installs, the tech who services, and the crew that removes are all working from the same record. The route schedule, the in-season service calls, and the storage labels all hang off that one source instead of a binder that lives in one person's truck.

Keeping it lit: in-season service

The season does not end at install; it ends at removal, and the months between are a service obligation. A run goes dark from a blown fuse or a connection that took on water, a storm pulls a section loose, or a GFCI trips and needs a reset. On a commercial site a dark display is visible to everyone, so the response window is short and the service is part of what the client is paying for.

Build the service into the model the way a maintenance route is built. Carry spare fuses, spare strings, and spare clips on every truck, and keep the per-site record of which run feeds from which circuit so a tech can find the dark section without re-tracing the whole building in the cold. The commercial maintenance guide covers how a recurring service route is run, and the same discipline applies here: scheduled checks beat waiting for the client to call.

Most in-season failures trace back to install shortcuts, which is the honest lesson. A connection left in a puddle, a run pushed past its series limit, a circuit loaded too full, a cord stapled instead of clipped. Do the install right and the service calls drop to weather and bad luck, which is the volume a profitable route can actually carry.

Removal, labeling, and storage

Removal and storage are where the seasonal business makes or loses its margin, and new installers underestimate both. The lights come down after the season, on the same kind of ladder and roof access that put them up, in colder and often worse weather. Rushing the takedown is where the second wave of falls happens and where product gets damaged by yanking instead of releasing the clips, so removal gets planned and crewed like the install, not treated as an afterthought.

Label and store by site. The reason the model is profitable in year two is that the product from a property comes down, gets coiled and bagged, and goes into storage tagged with that site, so next season it goes back up faster because it was cut and fit to that building already. A pile of tangled, unlabeled strings in a warehouse is a season's profit thrown away in re-sorting and re-cutting labor.

Track the inventory like the asset it is. On a leased model the product is yours and it is real money sitting in a warehouse, so you need to know what you own, what condition it is in, and what is committed to which site for next season. FieldOS keeps that inventory tied to the site record and the storage label, so the removal crew bags it under the right site and the next install crew pulls the right bins. The efficiency of remove-label-store-reuse is the whole reason a route renews at a profit instead of rebuilding from scratch every fall.

The failures that come back to bite you

The same short list of failures accounts for most callbacks and most injuries on holiday work, and every one is preventable at install.

Overloaded runs and circuits blow fuses and trip breakers, and they trace back to skipping the load count. No GFCI on the outdoor power, or a defeated GFCI, removes the shock protection the whole job is required to have. Ladder and roof falls come from poor access, the wrong angle, or working a slick roof without protection. Staples or nails through cords cut insulation and put holes in the roof, creating shock hazards and leaks at once. No labeling and storage system turns year two into a rebuild and eats the margin. And overloading the building's own electrical trips the property's circuits, which is a far bigger problem to the owner than a dark eave. Fix these at install and the season runs quiet.

What to document on every site

The site record is what makes year two fast and what lets a service tech fix a problem without re-tracing the whole building. Capture it at install while the crew is on site and the details are in front of them, not from memory in January.

Record the power sources and which run feeds from each, the circuit ratings and headroom, the product type and footage by area, the control devices and their schedules, the access method and any fall hazards, and the storage label the product goes back into. Photos of each elevation and each power drop are worth more than notes for the crew that comes back next season.

Common mistakes

• Overloading a circuit or a series run and blowing the in-plug fuse or tripping the breaker.
• Running outdoor lighting with no GFCI, or defeating a GFCI to stop nuisance trips.
• Falls from ladders and roofs from a bad angle, poor access, or working a slick roof without protection.
• Stapling or nailing through cords, cutting the insulation and creating shock and fire hazards.
• Driving fasteners through shingles or flashing and leaving the property with roof leaks.
• No labeling and storage system, so the product comes down tangled and year two is a rebuild.
• Overloading the building's own electrical and tripping the property's circuits.

Field checklist

Standards and references

The electrical rules come from the NEC, NFPA 70, as adopted and amended by the jurisdiction. GFCI protection for outdoor receptacles is required, commonly cited at 210.8, and the continuous-load practice of holding to 80 percent of the breaker rating shapes how much you put on a circuit. Use UL-listed product rated for outdoor use, and treat the manufacturer's tag as the authority on per-string wattage and the maximum series connection. The exact amps, run limits, and GFCI requirements are governed by the NEC, the product listing, and the AHJ, so verify against all three and bring in a licensed electrician for any work on the building's wiring, a new circuit, or a new receptacle.

Ladder and fall safety fall under OSHA. The 4-to-1 ladder ratio, the 3-foot extension above a roof edge, and fall protection above the applicable height threshold come from the OSHA standards for ladders and fall protection, and the trigger heights and acceptable methods depend on how the work is classified, so confirm what applies to your operation. The three things to get right above all: plan the load and put it on GFCI, get on and off the roof without a fall, and build the job to install, remove, and store so the route runs again next year. The AHJ has the final word on the local electrical and permitting requirements.

Units and terms

Holiday lighting borrows electrical terms and a few product names that are worth pinning down, because the same word can mean different things across a manufacturer sheet, an electrician's note, and a proposal.

Line voltage is the building's 120-volt supply the strings plug into, as opposed to the 12-volt low-voltage used for landscape path lighting. Load is the power a display draws, summed in watts and converted to amps at 120 volts. The maximum series run is the manufacturer's limit on how many strings you connect end to end. GFCI is the ground-fault device required on outdoor power. C9 and C7 are the large and slightly smaller roofline bulbs, and a photocell is the light sensor that switches the display on at dusk.

Line voltage

Building supply voltage, commonly 120 V, that holiday strings plug into; not the 12 V low-voltage landscape system

Load (watts / amps)

Power a display draws; sum the watts, divide by the supply voltage for amps to size against the circuit

Maximum series run

The manufacturer's limit on strings connected end to end before the run is overloaded and the fuse blows

GFCI

Ground-fault circuit interrupter; cuts power when current leaks to a fault path, required on outdoor receptacles

C9 / C7

The large classic roofline bulb (C9) and its slightly smaller version (C7), sold as bulk line cut to length

Photocell

Light sensor that turns the display on at dusk and off at dawn, adjusting as the days shorten

Related tools

Calculators and readiness checks for this work

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