Wood flooring experts who train contractors about sanding equipment see lots of strange things in their daily lives, from scary sanding techniques to the scariest of all: dangerous electrical hookup. Their stories are numerous; one trainer recalls a contractor who took the bare wires straight to the main lines feeding the box. The contractor had his helper turn the big machine on and off, on and off, until the wire melted to the main leads feeding the home. Essentially, they arc-welded the cable ends to the main leads in the box. The trainer stopped them and asked the contractor who taught him to do that. Not surprisingly, it was a familiar refrain to many in this industry: "My granddad did it that way, and he never had a problem." The job was an old home and had twist-out fuses; the next day an electrician installed a sub box with breakers and a three-wire plug.

Fortunately, what someone's grandfather or father did decades ago isn't acceptable on today's job site. You need to understand the safe way to hook up power and what the codes are for where you live. It isn't an exaggeration to say your life or someone else's could depend on it.

Cord Basics

Big machines run on 220 volts with an average range (depending on the machine) of about 210 to 235 volts. The cord is a 10/3 cable (10-gauge wire with three wires) with a white wire, black wire and green wire. When hooked up, the black wire and white wire are the hot leads, and the green wire is the ground (see "Cord Basics" sidebar). The hot leads (black and white) are the only wires that have voltage going through them during use. The green wire only has voltage if there is a short (or "fault"). Older homes have only 3-wire 220-volt outlets, and power boosters without 110-volt outlets are 3-wire.

Newer homes have 4-wire 220-volt outlets, and power boosters that have 110-volt outlets are 4-wire. A 10/4 cable has four wires: black, white, green and red. The black and red wires are the hot leads, the white wire is the neutral and the green is the ground.

The demands on a power cable change with the length of the cable: As the cable gets longer, the resistance increases and the voltage can drop, so the voltage should always be checked with a volt meter after each 100 feet of cable. Volt meters are cheap insurance (prices start as little as $10) to protect your machine from the wrong voltage, and they can also protect your health. Use them to check any wires sticking out from the walls on the job site—never assume that exposed wires aren't live. Unfortunately, wood flooring contractors have been badly hurt by accidentally walking into exposed wires while sanding.

RELATED: Safety Lessons from Real Wood Flooring Contractors

If you need to correct the voltage, a power booster can be placed in line, but keep in mind that most power boosters only increase or decrease the voltage by 10 percent. Power boosters have other advantages besides correcting voltage: they protect the sanding equipment against power spikes, they have a built-in volt meter, and some give you dedicated 110-volt outlets for your buffers and edgers so you don't trip the breakers in the house. You can buy standard boosters or have power boosters custom-built for your specific needs.

Cord Basics: The big machine cord is 3-wire; power boosters with 110-volt outlets are 4-wire. Older homes have 3-wire 220 outlets, while newer ones have 4-wire outlets.

Hooking Up

In some houses, there are 220-volt stoves, dryers and window AC units that—with the right pigtail—can be easily plugged into. In homes without that convenience, contractors must hire an electrician to install the correct outlet or they must find a power supply in the box. In some states, it is illegal for anyone but a licensed electrician to open the panel box. Many wood flooring companies include the power hookup by a licensed electrician as part of their job estimates, although others hook up the power themselves after being taught the correct method.

In some cases 220-volt power is not available. Sometimes the power source in the grid is simply not enough, and some older homes only have 110-volt power. In these cases, a generator may be necessary, but make sure it's big enough to run all the sanding equipment you need. In some areas of the country, there is no power in the house during new-home construction, so there is a common pole with electrical outlets for the contractors during construction. Never hook up power from a pole unless it's legal and specifically for that purpose.

Excluding those special situations, there are typically three ways to hook up your big machine:

1) Use pigtails into a 220-volt outlet.

If there are electric ranges, stoves or window AC units with 220-volt outlets in the home, an easy way to hook up is to create pigtails so you can plug right into the outlet. You'll need the correct male plug for the appliance outlet (there are different plug configurations for ranges and dryers and the 3-wire or 4-wire plugs). Put on the correct twist-lock plug for the outlet and connect to your power booster or into your machine lead.

The complication can be dealing with 3-wire versus 4-wire: for example, when you have a 4-wire power booster but you're in a house with only a 3-wire plug. Keep in mind that per code you must not tie the earth ground and neutral wire together in the leads (see the "4-Wire Code Compliance" sidebar on page 64). If you do not have a power need for 110 volts to be used on the cable, you can put on the correct plug but not hook up the neutral wire. Use the black wire and white wire as hot leads and the green as the ground.

2) Pay theelectrician.

Many contractors build the estimate including the price of an electrician doing the in-box hook-up or adding a 220-volt outlet next to the main panel. If it is a new home, you can work with the builder and request that a 220-volt, 4-wire outlet be installed as part of the new home. With existing homes, many contractors sell this as a safety concern for the homeowner: They can get the extra money because the homeowner has peace of mind knowing that it is done safely and correctly, and the correct plug is there if 220-volt power is needed again in the future. In the many homes that have twist-out fuses rather than breakers, this is a must.

3) Tie into the electrical panel

Tying into the electrical panel is illegal in many states. It is the hardest method and is one you must be trained to do. If you feel comfortable doing so, have been trained to do it and it's legal where you live, keep these things in mind:

• The power must be turned off before you tie in.

• Always use a volt meter to check the voltage of the leads.

• If the power box is set out and the knockouts can be removed easily, then remove the correct size, place the wire with the clamp or other strain relief on the cable and place the wires into the breaker. Once the job is completed, a plug or cap must be installed so the hole is covered.

• Make sure the cover of the box will close and cover the wires during operation. Letting the wires hang out with the cover open can be extremely dangerous.

• If the power box is set into the studs, it is difficult to tap out a knockout and feed the lead into the box. The drywall may need to be cut away and then replaced and repaired after the job is done.

• Make sure the wires are not just hanging free. A clamp around the wires or some other strain relief needs to be in place to prevent the wire from pulling loose and shorting out the box.

• The breaker size is important, because a breaker that is too large (such as 60 amps) will not trip when needed. If the breaker is too small, then it will trip too soon. Most of the big machines on today's market run well on a 20- to 30-amp breaker. The startup amp draw is high, but that is only for a brief moment; after that it drops to a safe level.

RELATED: Your Sanding Machines Don’t Look Like This, Do They?

Terrible Tricks

There are vast numbers of bad "tricks" that contractors use to avoid legitimate power hookup. For many years, contractors have been taught to use quick clips for direct hookup to the main leads in the box, but this is both illegal and unsafe— the weakest link in your hookup is the plugs or quick-disconnect clips. The weight of the cord can pull the clips out, shorting out the box, causing sparking and possibly a fire. Another trick is to use a booster to pull one 110-volt leg from one room and a 110-volt leg from another room. That does add up to 220 volts, but if only one of the breakers trip, there is still a hot lead feeding the big machine. Some contractors avoid having to deal with the correct plug configurations by simply stripping the wires and sticking them directly into the outlet—an incredibly dangerous practice with a high risk of electrocution.

The bottom line is: Be smart, be safe and follow the codes for your area. If you aren't sure about the right practices, ask an electrician. Don't put yourself, your workers or your customers at risk by taking chances with electrical hookup.

Sources for this article included: Frank Kroupa, NWFA; D. Wayne Lee, Clarke American Sanders; Eric Nolin, Palo Duro Companies; and Don Smithson, Golden State Flooring.


This pigtail for connecting the 3-wire to a 4-wire outlet might be illegal—it depends if the white and green wires are joined together inside the cord (joining them is illegal).
 If you're connecting your big machine (3-wire) to a 4-wire outlet, the easiest way is to use a power booster with a 4-wire connection.



4-Wire Code Compliance

What some people call the "new" code for the 4-wire hookup has been in place since the early '80s. What it says is simple: At no time can the earth ground and neutral wire be joined together. When they aren't joined and the earth ground is used for a fault, the short will be safely discharged.

However, if the white wire is joined to the green wire, then the short is sent back through the neutral wire.

If your power booster has four wires feeding into it, it is because of the 110-volt supply. If the white wire is not hooked up, the 110-volt outlets will not work. If you try to make the 110-outlets work without having the 4-wire in by making up a wire lead that bypasses the 4-wire in and joins the earth ground with the neutral, that is a violation of code.

See more on this topic: Wood Floor Sanding



Kim Wahlgren

Kim M. Wahlgren is the longtime editor of Wood Floor Business. Based in Madison, Wis., she manages the day-to-day operations of the WFB print magazine, website, E-News and social media. She holds degrees from the University of Wisconsin in journalism and Spanish. Away from the office, she’s busy enjoying her family, including two beautiful children, a sassy ex-racehorse, an extraordinarily silly black Labrador mutt and her husband, Brent, whom she met at … yes, wood flooring school.