October 1, 2007

Give Me Your Bond

Electricity, Grounding and Cable

By Jonathan L. Kramer, Esq.

Within the United States, nearly every state and most local governments have adopted the National Electrical Code, commonly referred to as the NEC and published by the National Fire Protection Association, as the local electrical code.

Articles 820 and 830 of the NEC deal with various cable drop issues. Included in these two Articles, at sections 820.40 and 830.40, are the requirements for "cable grounding" of the drop.

When is a ground not a ground?

Before discussing the NEC cable grounding requirements in detail, a few words of terminology are required.

When we talk about "drop grounding," in all but one situation (discussed later) we're really talking about "drop bonding." Drop bonding? Bonding to what? To answer that "what" question, first let's look at why we ground the cable drop ... oops! ... I mean, bond the cable drop.

There are typically at least three outside world powered or grounded cables connected to a subscriber's home. The first is the single or multiphase commercial electrical grid. The second is the legacy twisted-pair wireline telephone company. The third, of course, is the coaxial cable TV drop.

Each of the three systems comes together inside the subscriber premises at various points. Most commonly, the power and telephone systems "touch" each other at cordless phone base stations; and the cable TV and electrical systems "touch" each other at the set-top converter or at the subscriber's TV set or VCR.

Like water, like current

Wherever multiple systems touch, and where those systems are not at a common ground potential (i.e., they are not bonded), then electric current can flow. Electric current is something akin to water. It seeks a way to return to the ground point via the path of least resistance.

If the cable TV system drop is connected to a device such as a set-top box or a TV set that is also connected to the electrical system, and the cable TV shield is grounded to an independent ground rod while the electrical system is grounded to its own ground rod, current will seek the path of least resistance to ground. Depending on the least-resistant ground path, that current flow might be via the cable system, or it might be via the electrical system.

Our goal, and the requirement of the NEC, is to minimize the electrical potential between two different systems by connecting their ground returns together. We call the common "ground" return connection between two different systems a "bond." So when you talk about "grounding the drop," you should be thinking about bonding the drop!

Georg Simon Ohm's famous law first published in 1827 teaches us that voltage is the product of electric current flowing across a resistance.

When you increase the resistance between two points, or in our case two systems touching the same residence, for example by using independent ground rods, the voltage between those systems increases. When you decrease the resistance between the two systems by bonding them, you reduce the voltage difference between them.

The goal of bonding is that the two systems be at a common ground, resulting in no current flow or voltage difference between the systems.

Fuses and flames

Most subscribers don't care about Georg Ohm, but they do care about bonding, even if they don't know what it means or what it is. Why? Because they like to hook up equipment, themselves, and because they love their homes.

The NEC Handbook commentary for Section 820.40(D) also goes on to say:

"If an individual is the interface between the two systems and the bonding has not been done in accordance with the Code, the high-voltage surge could result in electric shock. More common, however, is burnout of the television tuner because this part is almost always an interface between the two systems. The tuner is connected to the power system ground through the grounded neutral of the power supply, even if the television itself is not provided with an equipment grounding conductor."

Simply put, if the cable drop and house electrical system are not bonded to be at the same ground potential, the subscriber may become a fuse.

I've said it before; I'll say it again: "Subscribers don't like to be fuses!"

In a relatively few number of cases over the years, most of which aren't burdened with substantial or reliable documentation, the lack of grounding has been suspected in structure fires. More commonly, heated drop and outlet cables have been detected and bonding resolved by installers and techs before flames have erupted. But taking a chance of finding that errant cable before it catches fire is like "Dirty Harry" Callahan saying, "... you've got to ask yourself a question: Do I feel lucky? Well, do ya, punk?"

How do I bond thee?

Having covered why's of grounding ... oops, bonding ... the cable TV drop to the electric ground, let's delve into the "hows" of it. Here, the NEC isn't going to be very helpful. Why? Because the NEC is a collection of minimum safety standards; it cannot begin to address the minutia of details that make up a typical cable TV installation.

Each cable TV drop installation is unique. To illustrate the point, let's look at the basic steps of an overhead install. Before performing any of the inside wiring work, the installer must walk the job to:

• Find the signal tap for the address
• Look for a legal grounding point, usually at or adjacent to the electrical service meter
• Select the route for the drop cable
• Find a suitable attachment point on the structure
• Figure out how to ensure the minimum clearance from power and telephone before and after the attachment point
• Determine the route the drop cable will take to the point of entry into the structure

Those six major decisions will require thoughtful analysis of dozens of component elements before the first cable is cut and the first connector is attached.

Most cable operators have standard practices guides for their employees to follow when installing drops. The SCTE also has a collection of installation resources available. These are good starting points for planning and performing a Code-compliant installation, including bonding.

Drive your own rod?

Having first run, and later inspected, cable systems for the past 30 years, I have heard many excuses for nongrounded drops. Some of the most common - and amusing - reasons have included:

• "Take a look: The cable TV drop hits the wrong side of the house."
• "The power ground rod is inside the wall. What do you want me to do? Crack open the wall?"
• "The customer doesn't want me to ground the drop."
• "I didn't have the parts to ground the drop when I did the install. I really, really, really intended to come back and finish the job!"
• "Grounding? What's that?"

While these may be laments commonly heard wafting through system ready-rooms around the country, the NEC Handbook 2 commentary for Section 820.40(D) makes it crystal-clear that none excuses the installer or tech from ensuring that the drop is bonded to Code. According to the NEC Handbook:

"The most common error made in grounding CATV systems is to connect the coaxial cable sheath to a ground rod driven by the CATV installer at a convenient location near the point of cable entry to the building, instead of bonding it to the electrical service grounding electrode system, service raceway, or other components that make up the grounding electrode system. A separate grounding electrode is permitted by the Code only if the building or structure has none of the grounding means described in 820.40(B)(1) or 820.40(B)(2), which is rare." (Emphasis added)

Of the excuses mentioned above, my favorite is, "The customer doesn't want me to ground the drop." Simply put, the subscriber doesn't get a vote as to whether the drop is going to be grounded. When adopted by the local government or required by the state, the NEC becomes the law, and that law must be obeyed at risk of a receiving a code violation. If the drop connects to the home, it must be grounded to the NEC code requirements (or the Code requirements adopted by the governing government agency).

But I have a really good reason not to ...

Under the NEC (and under most local ordinances), only the government code inspector can waive or modify the code requirements for a particular location, and only if certain conditions are met. NEC Article 90, at Section 90.4 sets out this authority and responsibility.

First the authority part:

"The authority having jurisdiction for enforcement of the Code has the responsibility for making interpretations of the rules, for deciding on the approval of equipment and materials, and for granting the special permission contemplated in a number of the rules."

But with the authority comes that pesky responsibility part:

"By special permission, the authority having jurisdiction may waive specific requirements in this Code or permit alternative methods where it is assured that equivalent objectives can be achieved by establishing and maintaining effective safety." (Emphasis added)

Now you understand why the "it's too hard to ground it right" excuse rarely gets any traction with government code inspectors.

Interestingly, some systems hold to the firm - if misguided - belief that an installation need only meet the NEC requirements if the subscriber's account is active. You won't find such an exception anywhere in the NEC, and frankly it's illogical. Current flow doesn't care about account status, and when it comes to safety code compliance, nether should you.


The author wishes to thanks Ronald Boyer and Steven C. Johnson of Time Warner Cable and Steve Allen of Kramer.Firm Inc. for their assistance in developing this article.


Jonathan L. Kramer is the head of the Kramer Telecom Law Firm.