Static Electricity and DCC Decoders

Any electronic item using silicon chips (and that’s most these days) is susceptible to damage from Electrostatic Discharge (ESD), more commonly known as static electricity. It doesn’t take much to totally fry a chip; you won’t necessarily feel it or see a spark, and there won’t be any visible damage (unless you have an electron microscope). In fact, even as simple a device as an LED can be destroyed by static electricity.

Since DCC decoders are fairly sophisticated electronics, they’re more susceptible than most model railroad items to ESD damage, which can ruin a decoder, or just make it work oddly. Of course, many other things can make a new decoder not work properly, and decoders are built assuming they’ll be handled, so they don’t use the most sensitive components. It would be wrong to immediately assume ESD damage is the cause when one misbehaves. It could be, but poor wiring or mis-set CVs may be at fault. Still, taking a few precautions isn’t too hard, and may save you some cash and frustration.

Here’s my advice on how to work with DCC decoders and other exposed electronic components. I’ll be honest and admit I don’t always do all of this myself (but I usually try to). And to some extent it’s probably much more caution than is called for. But I really don’t want to deal with replacing failed components, even in those cases where the manufacturer provides a good warranty.

Kato ships their decoders in a hard plastic case with a small chunk of black conductive foam, and that’s the safest place to store a decoder. I leave it there until I need to touch it, and when I do pick it up, it’s by the edges to avoid touching metal parts. Kato USA unfortunately ships them in a small soft plastic envelope, similar to the way most other decoder manufacturers package their products, which isn’t quite as nice. Leave them in the envelope until needed.

First, find a way to get rid of any static charge that builds up. In an ideal world, both you and the work surface would be grounded through a high-resistance path, to allow any charge to slowly leak off. The “high resistance” part is important, as working on something that allows a static charge to move rapidly from a source through the item being worked on is very bad. A metal table is not a good surface, unless it’s insulated and only connected to ground through a mega-ohm resistor.

In a house, there are two main ways to connect to ground. First, grounded electrical outlets not only have a third “ground” pin (I’m assuming North American design), but the screw that holds the faceplate on the outlet is typically connected to ground within the outlet; a wire under the screw, touching unpainted metal, should be grounded. Second, in a house with metal water pipes, the cold water pipe is typically connected to ground.

Safety Note: Grounding yourself without a resistor isn’t bad from an ESD perspective, but it can be dangerous if you’re working around anything powered by wall current (like a soldering iron or DCC command station), as you don’t want a short-circuit through you to be the only path to ground. Use a wrist strap designed for ESD safety, or periodically touch grounded metal when you aren’t touching anything else, but don’t keep one hand on a cold-water pipe while working around electricity. That could be fatal.

A wrist strap that can be grounded is a very good idea (Google for “anti-static wrist strap”, without the quotes, to find dealers, or go to Radio Shack, which sells these for about $6, part 276-2397). Just clip it to a wire connected to a known good ground. These straps use resistors, so they don’t provide a ready path for a short circuit. If you don’t have a wrist strap, touching grounded metal immediately before working (after you sit down) should dissipate any static (note: touching metal that isn’t grounded, like the arm of a chair, won’t do much, but it could help drain a bit of ESD). As noted above, grounding yourself with a bare wire for the duration isn’t a good idea for personal safety reasons.

But don’t fall for the “wireless wrist strap” hoax. There’s a number of these on the market, either not stating how they work (it’s “wireless!”) or referencing an actual effect such as “corona discharge” that isn’t going to help for the kind of ESD of concern here. I’ve even seen them in reputable stores. A few people have taken these apart, and found a normal wrist strap, with no additional circuitry. Some even have the hole where the wire would connect covered with a sticker; those could never do anything. Some do include fine steel wool or wires (for the corona effect), but that’s not going to drain enough charge quickly enough to be useful (touching a chunk of ungrounded steel would do more). There are reports of increased component failures coming from factories that converted to use these things. Real wrist straps connect your skin to ground through a high-ohm resistor (to avoid the risk of shocks), and that’s what you need.

An ESD mat that can be grounded is helpful if you’re going to do a lot of installs, but they aren’t cheap (Google for “static dissipative work surface”, without the quotes, and you should find a number of specialist dealers who sell them). These, too, use high-resistance grounds, and often have snaps to which the wire from a wrist-strap can connect, so one ground line can serve both.

Next, set up your work area to avoid generating static electricity in the first place. Wood furniture on a wood floor is good. Avoid plastic tables and furniture, and rugs, if you can. Otherwise, consider working on a small piece of wood placed on the table, to insulate the things you’re working on from discharge through the table. You can put rubber feet on the piece of wood to protect the table top, or just rest it on a towel. Working in a very dry room is also bad (but very common in the winter, when most of us work on trains).

Clothing is important. Avoid wool, silk and polyester or other synthetics (cotton is good, as long as you don’t combine it with other fabrics). Avoid walking on carpet wearing socks. Don’t wear a sweater while working on electronics. Avoid petting your cat, too.

Lightweight plastic bags are a great source of static electricity (as are styrofoam packing peanuts), because they can rub together and generate a charge. Neither is a problem for shipping parts in good packaging (e.g., the Kato boxes or envelopes used by most decoder manufacturers), but you’re going to pick up a charge when you open the bag/box. Unpack any shipping boxes away from your work area if you can, and ground yourself and the plastic boxes containing the parts before opening any of those (for example, touch a metal faucet while holding the Kato box in your hand). Setting the Kato boxes down on a grounded ESD mat or holding them while putting on a wrist strap also works to dissipate any charge you and they picked up from the unpacking. Note: a heavier plastic bag, like the kind some decoders are sold in, could generate a charge if rubbed on something else, but is less of a risk than a lightweight bag that can fold in and rub against itself in multiple places.

Finally, avoid unnecessary handling of decoders or other exposed circuit boards. Even the ones wrapped in insulated tape should only be handled as much as is necessary, although the tape is good protection against ESD. Leave them in the box until you’re ready to work on them, then move them straight to where they’re going. If you’re going to solder directly to the circuit board, you can place it on some wood, otherwise leave it in the box and solder to wires separately until you need to pick it up. When you do handle a decoder, try to avoid touching metal components or even the black plastic “chips” on the board. Handle the board by the edges if you can.

All of the above may leave you afraid to touch anything. Keep in mind that a good wrist strap will eliminate most static electricity (as will periodic touching of grounded metal if you don’t have a strap). You can work on electronics in a bone-dry room, wearing a wool sweater over a silk shirt, as long as you and the work surface are properly grounded, although I wouldn’t recommend it. And with cotton clothing, wood tables, and sufficient humidity in the air, you’re likely safe even without grounding yourself. Take whatever precautions you can, and you’ll eliminate almost all risk of ESD damage.

The other common method of destroying decoders, typically caused by hooking up the wires wrong, isn’t ESD, it’s a short-circuit. That’s usually accompanied by smoke and a burning smell, and is rather obvious. Make sure the wiring is correct before applying power, and make sure bare metal isn’t touching the decoder board (unless it’s supposed to), before you put the train on a programming track or the railroad.