What is daisy chaining?

At my second job at Best Buy, we were taking out a display to make way for flashy new product that needed lots of space. That meant a new shelf layout, and new power strips. “No daisy chaining!” the manager bellowed as we plugged in the power strips. But what is daisy chaining? And is it always bad?

Daisy chaining means plugging one device into another, like tying together a garland from daisy flowers, rather than running wires all the way back to the original source. Daisy chains can be used for transmitting power, data, or both.

Why daisy chaining power strips is bad

why daisy chaining power strips is bad
This sight will make an electrician unhappy. There’s lots of exposed wire here, and if you use every outlet, you’ll probably overload the circuit and/or one of the power strips.

I’m pretty sure that store manager couldn’t tell anyone why daisy chaining power strips is bad. An electrician or a building inspector told some other manager at some point, and that word traveled down the line to him, then to us.

Electricians don’t like extension cords or power strips, and they hate daisy chains even more. The reason is because it makes it very easy to overload a circuit. If you chain a bunch of power strips together to give yourself unlimited outlets in a room, you can easily plug in more power than the wiring and/or the circuit was made to handle. I experienced this myself in college, when I was living in a drafty 100-year-old barn that was wired when having two light bulbs in a single room was a luxury. We had lots of weird rules about what you could plug in, where, and how, because we’d blown lots of fuses over the years. I may or may not have been involved in an incident involving a dorm fridge and a microwave taking out power on my floor and requiring a professional to fix some wiring.

Danger!

Exposed wires outside the wall are vulnerable to wearing out and causing shorts, and even fires. A chain of power strips causes lots of exposed wire. Worse yet, the person plugging those power strips together probably doesn’t know anything about what load those power strips are rated for. Each power strip becomes another point of potential failure, in addition to the circuit itself.

That’s why daisy chaining power strips is bad. One power strip in a room is almost always OK. If you live in an older house that doesn’t have enough outlets for today’s lifestyle, have an electrician add some outlets. It’s usually not as expensive as it sounds. It’s more expensive than a $6 power strip, but less expensive than the results if something goes wrong.

Daisy chaining in computers

what is daisy chaining
Commodore peripherals connected in a daisy chain to a single port on the back of the computer. This was by design, and worked fine. Except for cable management maybe.

Daisy chains aren’t always bad. In computers, they happen a lot, usually when connecting peripherals. Laptops usually don’t have enough USB ports for all the stuff we want to connect to them. So some peripherals have more ports on them. USB is designed to work that way, so there’s no danger. If it malfunctions, it’s because you don’t have enough current to power one of the peripherals, but plugging external power into whatever peripheral has a power port will fix that.

One case I can think of where daisy chaining with computers caused problems was in the 90s, with the parallel port. The parallel port was designed for printers, but over time we learned how to use it for other things. In the mid 90s, it wasn’t uncommon at all for people to buy a printer, a Zip drive, and a scanner, and plug them all into the same parallel port. But the parallel port was never designed for daisy chaining. Connecting two peripherals to it usually worked. Connecting three worked just often enough to convince people it was OK to do. But it wasn’t reliable. And when it didn’t work, there wasn’t much you could do.

USB and other examples

USB allows daisy chaining, partly because the situation with parallel ports showed people wanted it. Lots of other computer data standards used daisy chaining too. SCSI is one example. Atari’s SIO bus and Commodore’s IEC serial and IEEE-488 bus are another. Not only was daisy chaining fine in this instance, it was unavoidable. Commodore and Atari only gave you a single I/O port. In theory you could chain 25 devices to a Commodore if you had enough power outlets, and were willing to run the necessary utility software to prevent conflicts. But a more typical setup was a printer and one or two disk drives.

Daisy chaining in networking

Daisy chaining also happens in some implementations of Ethernet. So-called thin wire was the most common standard in the early 90s. It involved a daisy chain where each computer connects to the previous one in sequence. This was problematic because if you took a computer out of the middle of the chain, it split the network in two, so part of the network became unreachable for the rest. And if you didn’t crimp the cables with the proper tools, it could be unreliable. The network could split itself intermittently. Modern Ethernet with CAT5 wiring eliminates the daisy chains and the associated problems.

Daisy chaining isn’t bad when it involves a single computer, but chaining multiple computers wasn’t good for network uptime. That’s why we abandoned it in that instance.

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