Lightning Lessons From The Ground

As long-time listeners of the Mac Geek Gab podcast know, I am no stranger to the the damage that can be caused by lightning strikes. My home and office setup has suffered from no less than three since we moved here in 2005, and I’ve learned quite a bit about this the hard way. Here I’ll share what I’ve learned in hopes that you don’t have to learn it the same way I did!

I should start by stating that my home and office setup is not entirely common. My office is a completely separate building, with separate power and cable (TV/Internet) feeds from the pole on the street. Between the house and office the previous owner then buried two Category 5e (Ethernet) and two coaxial (cable TV) cables. These are of the “direct burial” type, meaning they don’t need to be (and as far as I know, aren’t) encased in any sort of conduit. I use one of the Cat 5e cables for a gigabit Ethernet connection between the house and office, and one coax for a TV connection. As you might guess, this creates its own set of complications.

I’ve always known that having an Uninterruptible Power Supply (UPS, a fancy surge protector with battery backup) was the right move, and indeed I have them on each piece of electronic equipment that I want protected. That’s all I had, at least until our first lightning strike left me unable to see the office network from the house (and vice versa). I quickly realized that though my AC power was protected by the UPS, the DC power that’s used to send signal through the Ethernet cable was NOT. When lightning charged the ground, that charged the buried Ethernet cable, and it found its quickest path back to “ground,” which meant going through my Ethernet switch to a connected device (since the switch itself isn’t grounded). The charge killed the Ethernet ports on the switch AND the device, then went to ground via the device. This means if I were to have a computer connected to the switch, it would fry the two ports on the switch AND the port on the computer. Yes, this is bad. It’s worse when this happens to the switches and devices on BOTH sides of the cable. The solution: protect your DC cables (coaxial, Ethernet, and telephone). And while most folks likely don’t have Ethernet cables coming in from outside your house, you do likely have coaxial and/or telephone cables coming in.

Two of my three damaging strikes here at the house have only impacted DC cabling. About 15 months ago I had a strike hit close enough to the house that AC power was compromised, too. All of my UPSs went into “overload” mode, shutting themselves down to protect connected devices. A few devices that weren’t plugged into a surge protector or UPS were completely fried and will never work again. The good news is that I believe that strike marked the last lesson I needed to learn about protecting my equipment in this particular setup, and though we’ve had a few strikes since then, I have suffered no more equipment damage. I want to share the sum of those lessons with you here.

Dave’s Lessons learned:

  • Surge protectors and UPSs DO work for their intended purposes. There’s no question about this. Use them to protect any electronic equipment you value.
  • Surge protectors only protect against spikes whereas a UPS will protect against much more common “brown-outs.” These happen when the power dips below acceptable levels and then comes right back. The battery in a UPS allows it to provide interim power so your devices don’t shut off and then quickly turn back on, potentially frying components with an immediate, unexpected return of power.
  • When buying a UPS, match it to your power requirements — you want the UPS to be able to provide at least 5 minutes of power to all connected devices. Typically this means not plugging in high-power-draw devices like laser printers. Use a surge protector for those instead.
  • Maintain your UPS batteries. After several years, they will likely fail and need to be replaced. You can then choose to replace just the battery or simply replace the enter UPS.
  • Look for all feeds in/out of house. AC power is usually only part of it. If you have a phone line or cable line (or network line, as I do) coming in, protect it using either the coax/ethernet/telephone protection built-in to your UPS or a standalone DC protection unit (like APC’s ProtectNet line of products).
  • When installing any equipment protection devices, make CERTAIN you connect them to ground. This means plugging all three wires into the wall (or using a 3-to-2 ground adapter AND CONNECTING THE GROUND WIRE). If you don’t ground it, your level of protection drops significantly. Remember, the surge will want to get to ground, so if you don’t connect the ground wire, the power will instead go through your equipment to get there.
  • For coaxial, Ethernet, or telephone, you’re likely safe enough if you simply cover the first point of entry. If your cable TV or phone enter the house and then go to a splitter, protect the line before it hits the splitter and, in theory, all the devices down the chain are connected. I alter this policy and add additional protection for any device that costs more than a few hundred dollars. US$25 worth of insurance is worth it to me, even if it’s overkill (or US$35 to protect coax on my televisions and/or TiVos).
  • Don’t plug a power strip into your UPS unit without first getting authorization from the UPS manufacturer. If you don’t follow this policy and you need to file a damaged-equipment claim, it will likely be denied. Most of the time the only equipment covered is that which plugs directly into the unit.


The above are the guidelines I’ve been following, in full, for the past 15 months and, as I said, I’ve suffered no lightning-related issues to any of my equipment (despite having plenty of nearby strikes in that time). Hopefully if you follow the same you’ll experience similar levels of protection. If you’ve got any of your own experiences or advice to share, let’s keep the conversation going in the comments below!