How-To: Wiring Your Display

It goes without saying that electrical wiring is one of the most important elements to a successful light display. It's also one of the most critical things to get right because unbridled electricity is generally very unforgiving: one usually doesn't get a second chance as the very first mistake can be fatal to either you or someone else.

This is by no means a treatise in proper wiring technique -- this is left to the professionals or to those who have read about, understand and know how to perform proper and safe electrical wiring. Instead, this section is more conceptual in terms of thinking about wiring as it relates to your display because understanding a bit about electricity and electrical wiring infrastructure can help you be more efficient in designing your display and selecting the types and locations for various light control gear.

How much power do I need?

We'll start here because if you don't know this, you are literally shooting in the dark and are destined to blow a circuit breaker or fuse (if your home has fuses instead of breakers). Calculating your power requirement isn't really difficult if you have a design in mind and know what kind of lights you'll use and where you plan to hang them, and if you read the packaging for the kind of lights you'll be using.

The package will usually state the amount of electrical current (in amperes or "amps") the light string uses when fully on. Some may state this in watts instead of amps, but it's easy to mathematically convert watts into amps. But be sure that you calculate everything on the same basis, amps or watts. The two are NOT interchangeable. Some examples, and then we'll talk about the conversion math:

How do you convert watts into amps? The formula is really quite easy. Simply take the number of watts and divide it by the voltage used and you'll come up with an ampere equivalent. For example, if you have a 100-watt light bulb in a lamp in your house and your house uses 120 volt electricity, the equation is 100/120 = .83 amps. A 40-watt bulb would be 40/120 = .33 amps (about the same as a string of typical mini-lights!). So the formula is Watts/Volts=Amps.

What if the package doesn't specify amps or watts? You can probably make some assumptions based on like-kinds of lights, erring on the high side, of course, but purchasing a current measuring device is a much better and safer way to go. Units such as the Kill-A-Watt. (insert picture here) are tremendously useful and cost only about $20. They're indispensible for really determining what current draw one or more strings requires. Most DIY light enthusiasts would agree that a device such as the Kill-A-Watt is an essential piece of your light display equipment.

So what do I do with all these numbers? Add them up. Remember you can't add amps and watts together -- that's apples and oranges. The best way is to convert everything into amps and add them up. Let's say that your total comes to 35 amps of current. This would be the maximum current draw your lights would have if all of the lights are on simultaneously. Knowing the maximum current draw is extremely important. Now you're ready for the next step.

Determining Main Trunk Supply Lines

Your house has many electrical circuits that flow through a main power panel somewhere in your basement, garage, closet, laundry or workroom. In turn, this power panel is connected to the main power line that comes to the house from your local power company via the power pole outside (or a buried cable, if you're really lucky). The power panel is given a maximum amperage capacity, and common values are 100, 150 and 200 amps, depending on what was installed when your house was built. This large value is broken up into smaller values for each of the circuits in your house, such as 10, 15 and 20 amp circuits, so instead of one big 150-amp circuit and everything plugged into that, it's carved up into eight or ten other smaller-amperage circuits. This is for safety and convenience so that if one circuit becomes overloaded, your whole house doesn't go dark. Inside the power panel are either circuit breakers or fuses for each of the circuits that your house uses.

An industry guideline is that any individual circuit should only be utilized up to about 80% of it's maximum capacity. Therefore, a 15-amp circuit shouldn't be asked to provide more than about 12 amps of current. The 80% rule provides a safety margin to allow for power fluctuations as various electrical devices are turned on and off. Some lighting enthusiasts sometimes push the limit and edge very close to the maximum rating per circuit, and this practice is strongly discouraged. The margin is there for your safety. Blinky-flashy light displays aren't much fun after your house has burned down from an electrical fire caused by overloaded wiring. 'Nuf said.

In our example above, your total came to 35 amps. Dividing that by 12 amps/circuit, you would need three, 15-amp circuits to cover the 35-amp load. You could use other combinations of 10, 15 and 20 amp circuits and applying the 80% safety margin rule of course, to arrive at the number of circuits you'd need to accommodate 35 amps. But remember that your Christmas lights may not be the only things on those circuits! Interior lights and lamps, televisions, microwaves, coffee makers, etc. inside the house may be plugged in, too, so you'll also need to take them into account as to which circuits you decide to use.

Tip: In our example of 35 amps, remember that this was the maximum if all the lights were on simultaneously. If you never have more than 3/4 of your lights on at any one time, you might need only a more practical and usable total of perhaps 27 amps, about 75% of the maximum rating. Don't forget that your light sequencing software allows excellent selection of which lights are on at any one time, so if you're very careful sequencing your lights, you may be able to get by with fewer amps than the maximum. And remember that lower electrical usage won't be as costly, either. (True story: I know a guy who did just the above, but then forgot about it when he planned his grand finale -- which had all lights on. You can imagine what happened on his debut performance: the show was going along fine, and then at the very climax of the show when the music was about to hit the final chord and he attempted to turn them all on, <POOF> the whole show went dark and the music died. He'd blown the circuit breakers!)

Let's assume that you'll be using three circuits to power your lights. These circuits are the "main trunk supply lines" to your lights out in the yard and on the house. You will want to have three main extension cables to carry the electrical power out to the lights. But where should they go?

Determining Locations and Light Controller Types

Now that you know how many main trunk lines you have to bring power from the house out to the lights, you need to look at your planned display and figure out just where those main power cables will go. There's no right or wrong here, but here's a really good guideline: try to keep the main power cables as short as you realistically can. Why? Well, one really practical reason is that main power cables are generally expensive because they're big wires! They're not like your average 6-foot extension cord that you plug into the wall to light your Christmas tree!

Suggestions: Look at your display and try to divide it up into as many main areas as you have main trunk lines. Look for groups of lights. While not absolutely necessary, try to even it out as best you can. Consider whether cables need to run across steps, sidewalks or driveways (ouch - special considerations for these for safety) or how far away your furthest lights are, etc. You may want to have a group of trees lit way out in the corner of your yard, but logistically, if that creates a really long cabling problem, you may decide to move them closer if they're portable trees or perhaps light other trees or shrubs instead. Consider whether you want the main cables to be hidden from view and behind bushes or whether they can be safely strung across the yard. Remember that your display is at night and nobody will likely see the cables anyway, but during the day, outside cabling can become quite obvious -- especially those orange or yellow main trunk lines!

In any event, consider that the main trunk lines will go to main areas where the power will again be distributed from there to the lights themselves using smaller cables or to the lights controllers first and then the lights.

Why different controller types? Some light controllers have the capability to provide electrical power directly to the lights while other controllers work with external SSR devices only. An SSR is a "solid state relay" that actually does the turning on/off of the electrical power to the lights, but the SSR itself is controlled by various low-level pulses from a separate controller device. Example: if you have an electronic garage door opener, think of the remote control as the "controller" while the door opener/motor that mounted on the garage ceiling and plugged into an A/C outlet is the "SSR" that turns on the power and opens the door. While the end result of the two controller types is the same (lights turning on/off), the different wiring requirements of the two types is vastly different. On the controller with on-board electrical power for lights, the controller is plugged into power and multiple smaller extension cords go from the controller to the various strings of lights. On the controller that uses external SSRs, the controller AND all the SSRs are plugged into power and smaller signal control wires run from the controller to the SSRs to tell them when to turn on and off.

One type of controller isn't necessarily better than the other, but the different types provide for different power wiring configurations. If you have displays spread out all over your yard, it may be more convenient for you to mount an SSR on each display and run a single, long cable between each of the displays to provide electrical power and use a controller that uses the external SSRs because the low-power control cables (usually common cat5 network wiring) that connect each SSR to the controller may be less expensive than running thicker, more expensive electrical cables to each display from a controller that has on-board electrical power for the lights.

You'll have to do the math to figure out which is more convenient for you. What's important is that there are no wrong answers! Either method will work fine -- it's just that one method may be more convenient and/or less expensive than the other. But it's an important planning element because wire cabling has a cost, and some kinds of cable are more expensive than others. And generally speaking you'll likely discover that electrical power cables are much more expensive than cat5 network cabling.

Determining the Proper Cable Types to use

Wire cables come in many sizes (gauges) and many lengths. The larger the cable, the more electrical power it can carry and the more expensive it is to buy. Important point to remember: the larger the cable, the SMALLER the gauge number is. Therefore, a 10-gauge cable is actually BIGGER than a 14-gauge cable. You may be tempted to save a few dollars here and go with a smaller-gauge cable, but consider this: when you put a lot of electricity through a small cable, the cable gets hot. When the cable gets hot, the insulation around the cable can melt and catch fire. Got the picture? Bottom line: do not scrimp on your main trunk power cables. Buy good quality cables and they will last for a lifetime.

The second thing to know is that the longer the cable needs to be, the larger it should also be. If a 50-foot cable you have your eyes on will carry 12 amps of current but you need to go 100 feet, you should probably consider the next larger cable size for the 100-foot distance. Why? Because the cable wire itself has electrical "resistance" and longer cable runs of course have more total resistance than shorter runs, which leaves you with a somewhat similar situation as using a cable that's too small: it can heat up faster. Another problem that occurs with long cables is that the cable's own resistance causes a drop in the voltage over the length of the cable. Bigger cables actually have less resistance than smaller ones. It sounds backwards, but that's the electrical truth. There's a reason why the power lines you see strung along your local highway are so thick -- to carry a lot of electricity a long distance, they need to be really big.

Cat5 network wire: a 1000-foot spool of common, category 5 network cable runs about $50-$75 depending on your source and the quality of the cable. That's well less than ten cents per foot. It's available in a rainbow of colors, the most common of which are gray, tan, blue and white. Cat5 wire is generally used to carry the lighting control signals from the computer to the controllers. Cat5 wire is considered very low voltage/low current wire and the 8 wires that make up cat5 cable are quite thin, meaning that the cable is quite a bit more delicate than big, heavy electrical power cables. In fact, moving or bending a cat5 cable in sub-zero temperatures can actually break it, which would obviously create a problem in your light display. Cat5 cable should never be used to carry 120v A/C current -- the protective insulation on the internal wires is much too thin and running high voltages through it is just not safe. It's also not safe to try to run low voltage but very high amperage current through cat5 wire. For example, an arc welder's electrodes typically are at a rather low voltage but an extremely high amperage, and you've probably seen the sparks that happen when a welder is at work!

Common extension cables: common household extension cables that you can buy at the hardware store are often used outdoors because the size of the wires and the insulation surrounding them is adequate for carrying 120v A/C current relatively short distances -- typically less than 15 feet. And even though they're not specifically designed to be used outdoors, these cables generally hold up quite well, often for several seasons even in sub-zero temperatures. Common extension cables have been very successfully used to connect external SSRs to main trunk power, or for connecting strings of lights to controllers with on-board 120v A/C power. When familiar home-building centers periodically have sales on 6-foot cables, sometimes priced as low as $.70 each, DIY light enthusiasts generally buy them by the case!

SPT1 and SPT2 wire: this is often referred to as "lamp cord" and is about the same type of cable that is used to make common extension cables. SPT1 has less insulation and is slightly smaller than SPT2, and therefore cannot carry quite as much current. SPT1 is usually rated around 7 amps maximum while SPT2 is rated to carry about 12 amps. It's available in 250, 500 and 1000-foot spools, in colors (generally white, brown or dark green) and generally costs from 12 to 18 cents per foot. SPT wire is available at your local home building center or usually at lower prices over the Internet, but a heavy spool of wire can carry a hefty shipping charge so you have to do your homework before you buy it in bulk. Of course, SPT wire does not have connectors, so you need to factor in the cost of connectors on top of the wire (then you'll understand why DIY'ers buy the pre-made extension cables by the case!) However, you can't beat SPT wire for making custom length 120v A/C cables to run from your main trunk power out to controllers or displays in the yard.

Return to main page