Ferrules, Fuses, Wire Gauge, and DIN rail

[Richards]

I've received emails for years asking for tips on a few common practices, so, I thought I'd share some tips with the forum.

Ferrules. I'm asked whether I use ferrules, whether I dip the stranded wires in a solder pot, or whether I use the stranded wires bare. I use insulated ferrules. I always use ferrules. They're inexpensive from AutomationDirect or from FerrulesDirect. They're easy to use if you use a crimping tool. They protect you from having a stray strand of wire shorting something unintentionally. Note that code requires that you use a crimper designed for the ferrules that you use. That means that you cannot use pliers or other types of crimpers with ferrules without violating code. I use two different crimpers. One makes a hex crimp (six sides). A hex crimp works very well with curved or round terminal blocks. The other crimper makes a square crimp (four sides). A square crimp gives more surface area when used with spring-loaded terminal block and with any terminal that has flat surfaces (fuses, circuit breakers, Acorn terminal blocks, etc.)

Fuses (or circuit breakers)
I use either circuit breakers (usually D-curve) or Slo-Blo fuses. I use a master fuse to limit current going to the entire controller and I use additional fuses for each power supply. For instance, on my test bench, I use three circuit breakers; a master, a circuit breaker for the 24VDC power supply and a circuit breaker for the Teknic IPC-5 power supply. Because I have relatively light loads at the test bench and use only 120VAC single phase, I use a 10A master fuse. One thing that I always do is to connect the Line conductor to the top of the circuit breaker or fuse and the Load conductor to the bottom of the circuit breaker or fuse. That way, when I turn the circuit breaker OFF or open the fuse, I know which side of the fuse or break is live and which side is open. That helps when isolating problems in a live controller. You'll note that I use Midget 10x38mm size fuses (available from Home Depot). Many of the 3AG or 5x20mm fuses cannot handle 120VAC at high currents. Putting a 10A Slo-Blo fuse rated at 32V in a 120VAC line may work for a while, but it's not good practice.

Wire Gauge
If you want to start an argument with an electrician or an electrical engineer, just tell them what wire gauge you're using in your enclosure. Wire gauge charts give all kinds of numbers. For instance, 20 gauge wire on a chart that I use, tells me that for chassis wiring, 20 gauge wire can handle 11 amps! It also tells me that for transmission lines, 20 gauge wire can handle 1.5 amps. I use 20 gauge wire for all signal lines. Most signals only draw 10 milliamps. A few might draw 30-50 milliamps. 20 gauge wire is the largest size that fits orange ferrules. Orange ferrules are the largest size that comfortably fit the PLCs that I use. 20 gauge wire only costs $22.50 for 500 feet from AutomationDirect. 22 gauge wire costs $18.00 for 500 feet. 18 gauge wire costs $29.00 for 500 feet. I've used 24 gauge wire for signals with total success. If I didn't use PLCs, I would probably use 18 gauge wire for everything except power leads.

The wire gauge for AC depends on the total load of the control cabinet. If I plan to plug the controller into household wiring, I know that 14 gauge will carry all the current that house wiring normally provides, so I commonly use 14 gauge wire to the master fuse and 14 gauge wire from the master fuse to each power supply fuse. It's very important to always use a large enough gauge wire to handle the current allowed by the circuit breaker or fuse. A D-curve circuit breaker or a Slo-Blo fuse does not open fast enough to protect downstream devices, but if the wiring matches the breaker or fuse, you'll prevent a fire. As far as wire colors go, I use blue wire for +24VDC, white with a blue stripe for GND, gray for input signals, and orange for output signals. I use black wire for AC Line, white for AC neutral, and Green with a yellow stripe for earth. One thing that I always avoid is using the same color wire for AC that I use for DC. I know the difference between a 16 gauge wire and a 20 gauge wire, but when I'm talking with someone on the telephone, and have to tell him to check a 20 gauge black wire, I don't want to hear, "which wire is 20 gauge". It's much easier to tell him to check the white/blue wire going from terminal block xx to pin xx on device xx.

DIN rail
I like DIN rail. It allows me to use DIN rail mounted terminal block, DIN rail mounted power supplies, DIN rail mounted circuit breakers and fuses. With a little enginuity, mounting blocks can be created to DIN rail mount the Acorn, the relay board, the IPC-5 power supply and the Power4Hub. That means that replacing a device is easy. With DIN rail mounts, I don't have to remove the sub-panel from an enclosure to get to the screws on the back of the panel. Recently, I've started using angled stand-offs with the DIN rail. The stand-offs tilt the devices up or down, depending on how the stand-offs are mounted. They allow me to route wires under the DIN rail if devices are adjacent to each other. For example I connect a wire from the bottom of the master fuse to the top of a multi-conductor terminal block. I can use an 8-inch length of wire if I pass the wire under the DIN rail or I can use a 24-30 inch length of wire if I use the wiring trays. By wiring under the DIN rail, the wire does not cross over any other wires. It will not induce electrical interference into other wires in a wiring tray. It's simpler, easier, and less prone to cause a problem. Rectangular stand-offs are also available.

There you have it; some basic advice from an old man.

[GBCues]

Good Stuff Mike!
I appreciate the reference to FerrulesDirect - good prices on small (100) quantity ferrules in different sizes and colors.

[DrLocke]

Wise experienced advice. Or seriously OCD. LOL

[Black Forest]

good advice. Do you label your wires on each end also? I use a Dymo Rhino 6000 and label EVERYTHING. It helps me keep what little hair I have left! I either use shrink tube labels or flag type. I think my labeler is my most used tool.

[Richards]

I need a label maker and labels. I dug out an old Brother model portable label maker on my parts shelf that I tried years ago. It uses 1/2" label stock which is too large for wiring. You said you use the Dymo 6000 and heat shrink tubing. What is the part number for the tubing you use? Does it shrink to fit 22 gauge wires? If it does, it will be my next purchase.

[slodat]

I use a Brady BMP21 Plus label maker and their heat shrink labels. They do well down to 24awg or so. Very happy with it. I buy the label rolls on ebay for a good bit less than retail. Sometimes it takes patience to find the good deals though. My Dymo labelers, 5 in total, have all crapped out on me over the years. The Bradys seem to last longer.