Cable Numbering systems – who is right?

Cable numbering is very much on my mind these days as I re-design the way this is done in connectCAD. Seems like a good point to share some thoughts.

How to label cables is one those subjects where everyone has a different opinion. It’s arbitrary so that’s why people argue. But I think everyone would agree on one universal principle:

cable labels must be unique

Why? Because without unique cable labels you needs hours of time-consuming tests to distinguish cables that look identical.

How about using GUID’s this?

56DDEC82-8D92-44AA-93CE-EE3C5EF26ADA

we’d be safe in the knowledge that no other such id exists in the universe. But practically that would be hard to use. Imagine the size of the labels, or the task of trying to find such an id on the drawings of a large installation project.

So what  might one look for in a cable label?

Perhaps some information. How about the role of the cable in the system? or where it’s ends can be found? That would be helpful to an engineer on site and far easier to relate to the system drawings. So cable labeling falls into these two basic paradigms: location-based and function-based labeling or some mix of the two. Both have their merits so let’s take a look those.

Location-based labelling

This would be something like:    {building}{level}{rm}{bay}-{building}{level}{rm}{bay}-{serial}

{serial} is an incrementing number to distinguish the cases where more than one cable goes between two locations.

Location-based labeling is most useful for cabling infrastructure. i.e. cables that have cost a lot to install and would be re-used in the event of any changes. It makes it easy on site to see what cabling resources are available to meet the needs of system changes.

But labels of this form can get very long, and in the close confines of an equipment rack they can be very hard to read. Shorter cable runs within an apparatus room are not so much infrastructure as consumables. Little investment is needed to install them and most often it’s easier to make a new cable than to track down an old one for re-use. So in this case location-based labeling is less important, and we come to our next labeling paradigm.

Function-based labeling

Here labels tell you what the cable is doing in the system. What type of signal it is carrying. Which sockets on which devices it interconnects. Functional labeling is really useful during installation and commissioning as it let’s installers connect up hardware without the need to constantly refer back to plans. It gets you faster to a working result.

Making changes afterwards however can be more challenging. For consistency re-purposed cables must have new id’s applied in line with their new functions. This often does not happen and over time the installation diverges from it’s documentation.

Bearing in mind that there’s a case for both approaches engineers have often mixed the two: using shorter functional-based labels with apparatus rooms and cabinets, and longer location-based labels for cabling between rooms and buildings.

The perfect system

Is the one YOU use 🙂 right? It’s safe to say there will never be a perfect cable labeling system to fit all applications. The specifications are impossible to meet. The ideal labeling system would be:

a) universally unique
b) have codes no longer than 6 characters
c) human-readable, preferably using digits 0-9 for colour coding
d) convey location and function information

Well it can’t be done, so we end up with the debate that will flow on and on.

Here are some random thoughts before signing off.

If we sacrifice colour codes and let’s face it most people use a label printer these days, then we could use the whole of the range [0-9 A-Z] for numbering. Just like the airlines used three-letter airport designators. By encoding numbers into base 32 or base 36 you can get a lot more information into one digit. Don’t really know where I’m going with that one…

In connectCAD I’m thinking of a rule-based method of applying numbers. Each numbering system will comprise a set of match rules to be applied in order until one of them succeeds. When a rules conditions are met a number will be generated according to a format string so you can include and mix location, and function data to create the dream cable label.

Before you get goosebumps I’ll sign off.

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