I spoke with a customer on the phone that was having two problems. First is that their electric strike is only sometimes released when energized. Second, the Wiegand card reader does not reliably report a card number on the controller with every swipe. Being familiar with these issues after outfitting thousands of door installations, it's evident that the correct cable type may not have been used for the application.
We asked the installer..."What type of cable was used to wire these two devices to the controller?" Answer...CAT5 cable. We then asked, why didn't you use the correct cable types that were specified? "Because we had it on the truck, and it's all low voltage!" Wrong answer that can ruin an installation, especially considering that wire runs are most of the labor with door hardware installs. Why risk using the incorrect cable type only having to fix one of the most labor-intensive parts of the job later?
Cat 5 cable sure is inexpensive per foot. But it’s not for connecting strikes and maglocks to power supplies. There is not enough copper in the wire for that. It’s also not ideal for connecting a reader with Weigand or OSDP. Cat 5 is designed to carry “differential electrical signals.” Weigand is not a differential signal, and OSDP ideally requires a different data cable type. I see hack installation companies trying to use cheap CAT 5 data cable for everything. The excuse is, “It’s all low voltage. What does it matter?” That’s something a clueless installer would say.
What is a “differential signal”? Cat 5 cable has eight thin data wires twisted together into four pairs of wires. Just considering one pair of wires, a digital one, or zero is transmitted by the pair and measured on the receiving end as the DIFFERENCE of the voltage between the two wires. One wire in the pair will always be the same voltage but opposite in polarity to the other. This twist is done for shielding purposes.
If one wire in the pair is at +2 and the other is at -2V, this represents a “one” digital value. Should the voltages on the two wires switch to -2 and +2, this represents a “zero.” If the cable is in an electric field that introduces additional voltage to the pair of wires (lighting, power, other building system cables), both wires will raise to a higher voltage simultaneously since they are wrapped around each other. However, because we are only measuring the difference in voltage between the two wires to determine the signal value, the added offset voltage is negated. The offset voltage is electrical noise that gets discarded by the differential measurement.
Wiegand does not use two wires to transmit opposite polarity signals. It’s either 0 or 5 volts on individual wires, so this signal is not electrically compatible with Cat 5. Because of the nature of Wiegand signals, shielding in the cable is very important. Using Cat 5 for this connection, especially using the wires as individual conductors, will typically cause data errors. If you wanted to cheat and use Cat 5 wire for Wiegand, you could use both wires in a pair as one conductor for each Wiegand signal. The problem is that there is no electrical shielding, and you won’t have enough conductors to handle all the Wiegand connections required. That is unless you cheat again and put the two conductors of the reader power supply on one pair and use the remaining pairs as three conductors. Making these connections with super thin wire is difficult anyway, so why bother?
OSDP is a differential signal, but its shielding requirements and characteristic impedance differ. OSDP is mainly based on RS-485, which requires a shielded, single twisted pair cable. Cable designed for RS-485 usually has a more substantial shield and a larger gauge of a single twisted pair. Complicated to explain simply, but the impedance of a cable should be matched to the application. OSDP is based on RS-485, so the intrinsic impedance of the cable should be 120 Ohms. By matching impedance, the cable will conduct the data signals without reflection. Reflection is energy that is not sent through the cable and a phenomenon that could give you data errors. Cat 5 has an impedance of 100 Ohms, slightly mismatched. If you want to cheat and use a Cat 5 cable for OSDP, ensure it’s a “Cat 5e” cable with an additional shield layer not found in a standard Cat 5 cable. You might as well get the suitable cable type as it’s easier to connect and gives you better performance. Why risk more warranty service calls?
I have seen installations (with a DC power supply) with two pairs of Cat 5 connected for the positive power supply conductor and the other conductors used for the ground wire. Only a complete hack would do this. It’s far from ideal and is a dumb cheat. Even with multiple conductors bundled together, you still don’t have enough copper to do the job correctly with the higher currents involved, especially over a long wire run. The inductive loads of strikes require a high inrush current, and you have too much resistance per foot in Cat 5 cable to accommodate these current levels. Strikes may not release reliably every time due to the lack of current handling. Maglocks will have less holding performance. The wire may overheat. Maglocks may even have increased release times. Use a high-quality shielded 18 AWG two-conductor cable with a plenum (fire-rated) jacket for access control lock applications. This conductor size will handle most run lengths and provide solid lock performance.
In the course of doing many site physical security assessments over the years, I have run into security and facilities people whose experience with Maglocks has left them either big proponents of Maglock or big opponents to Maglocks, based on how good or bad their experiences with them were. I wonder how much of that satisfaction/dissatisfaction was due to faulty wiring?