During my last 4 years in Phoenix Contact, I attended several presentations on system cabling.  I had since learnt that system cabling is very easy to install, it not only eliminates installation errors, more importantly, it saves times and money for the customers. Nonetheless, I will not be surprised to know that more than half us are not aware that system cabling is not intended for every project.

Let me take this opportunity to share with you my findings.  I had put together an Excel spreadsheet, see below, to exhibit some of the facts and figures that I gathered.  Before I orientate you to the rows and columns, let us first recap the 2 current methods of wiring.

The traditional method of wiring is all about connecting the individual terminal block to the coupling relay or isolator and then finally to the I/O block in the PLC (Programmable Logic Controller), as below.

In contrast with this conventional method, the system method of wiring consists of mainly 3 components, namely the system adapter which connects directly to the I/O block in the PLC, a pre-assembled cable and lastly, a system termination board.  The marshaling terminal blocks are connected directly to the system termination board.  As a result, it effectively combines both the marshaling and interface panels together.  See below picture for further illustration.

On my upcoming calculations, I will be making a comparison between these two methods of wiring.  Also, to make it easier to understand, I will only focus on the areas as shown below and work on examples based on 32, 500, and 1,000 digital I/O points.

And now here is the explanation on the calculation spreadsheet which I have created:

ROI Calculation Worksheet:

ASSEMBLY COST: In this section, we will calculate the costs needed to terminate the cable(s).

• Traditional Method: Based on 32 I/O counts, we will need to cut, strip and terminate 64 points to the I/O block of the PLC. Over at the other end, we will terminate the 64 points to the coupling relays on the marshaling/ interface panel.  After which, we will connect the individual relay to the marshaling terminal block and thus bringing the total number of termination in the marshaling/ interface panel to 192 points.

• System Cabling Approach: Installer simply plugs the pre-assembled cable into the I/O block of the PLC and the termination board.

COMPONENTS COST: In this section, we will sum up the total components cost.  We will assume that the average cost of a terminal block is S$0.50/each, average cost of a 2 change over contact relay is S$7.00/each and average cost of a 32-channel termination board is S$550.00/each.

CABINET COST: In this section, we will assume that the average cost of a 42U cabinet is S$3,000/each and in a single cabinet, we can install a maximum total of 200 terminal blocks and 100 coupling relays.  If we just install the 32-channel termination boards, we can house a total of 5 boards.

ROI Calculation Worksheet #1:  Based on 32 I/O counts

ROI Calculation Worksheet #2:  Based on 500 I/O counts

ROI Calculation Worksheet #3:  Based on 1,000 I/O counts

From the above examples, we can conclude that traditional method of wiring is more cost effective when the I/O counts are less than 500.  When the I/O counts hit 500, customers may want to consider switching to system cabling as the price difference is merely $700 but it adds more value and innovation to their solutions.  The cost savings will become apparent when the I/O counts exceed 500.  So, the next time when you decide on the design of your cabinets, you may wish to weigh your options carefully.

Do write to me if you need me to put up a proposal for you!