How to specify cut-to-length cable

Original equipment manufacturers (OEMs), end users, and system integrators seeking to improve manufacturing and fabrication flexibility can purchase cut-to-length cables to save time and money.

By Jim Krebs December 3, 2019

Every automation system — whether on an original equipment manufacturer (OEM) skid, installed in a test lab, or built in the field — uses significant amounts of wire and cable. These conductors are placed into many types of functional service, mechanical operations and environmental conditions. Manufacturers and installers need the right cables on hand at the right time to do their work.

Designers often try to minimize the varieties of cable and wire types and colors required to simplify ordering and stocking and reduce waste. However, this is often a challenge, particularly for multi-conductor cables because they come in so many types.

Sometimes, consolidation efforts can end up costing more because certain cables may be over-specified with more conductors or increased size, all for the sake of reducing quantities of makes and models. Any amount of cable unused on the shelf, wasted during installation, or over-specified drives up raw material costs.

For these reasons, many manufacturers are shifting some or all cable needs to suppliers offering cut-to-length cables. Cut-to-length services can supply the exact cables needed for applications. It also gives end-users, system integrators, or machine builders the chance to test alternates, all while minimizing costs.

Determine cable type

Modern automated equipment uses cables for power, discrete and analog input/output (I/O) signals, and data/networking connections. These cables may be installed in raceway systems, open on the equipment, or arranged to accommodate motion for robotics and similar applications. Installations may be exposed to sunlight, water, washdown, chemicals or extreme hot or cold temperatures. Here are a few common categories of cables, generally arranged from largest in diameter to smallest:

Power tray cable
Variable frequency drive cable
Heavy duty flexible power cable
Flexible portable cord (service cord)
Continuous flexing motors supply cable
Flexible control cable
Continuous flexing control cable
Control and signal cable
Instrumentation cable
Sensor/actuator cable
Data cable (RS-232/422, RS-485)
Continuous flexing industrial Ethernet cable.

Each cable has characteristics making it suitable for its intended service (Figure 1). Sometimes the NFPA 70: National Electrical Code (NEC), which has many designations, may mandate certain cable types for applications. Other times, the work site may have requirements exceeding basic products that would otherwise be acceptable. On occasion, the matter can be confused by generic industry naming conventions and terminology.

When designers specify cables, they need to consider the construction, conductor materials, conductor ampacity, voltage loss due to impedance, insulation materials, shielding methods, voltage ratings, environmental ratings, conductor color codes and other factors. Communication cables, in particular, can have complex construction and technical details that must be specified (Figure 2).

Premium performance characteristics also may be desirable or required for an application. This is true for cables that flex or move in operation or are subjected to extreme temperatures. For instance, a basic cable will function as needed but can eventually fail. A premium performance cable incorporates improved materials and methods of construction so it can last longer in operation. Premium performance costs more initially but can deliver savings over time.

With many variables and products on the market it may be tough to choose the best fit. This variety also makes it hard for manufacturers or installers to adequately stock.

Cable business as usual

When it comes to using cables, the business-as-usual approach calls for keeping a stockroom full of any cable used in the past, just in case it is needed in the future. Most cable purchasers try to focus on a few cable type selections meeting most application needs and stock spools of those styles.

Even so, many have an inventory with multiple spools of abandoned or out-of-date cables on the shelf. To compound these issues, different designers may call for new and specific cables without checking what was available on the shelf.

With cut-to-length cable services, end users, machine builders, or system integrators can obtain what they need, when they need it. Prior to placing a order, verify:

Proper cable type availability
Delivery time
Pricing.

Those exploring cut-to-length cable services will want a supplier to stock the widest possible selection of cables. While certain cables may become a standard order, the cut-to-length route provides flexibility to change or improve selections over time, without waste.

One valid concern is time to delivery. Any cut-to-length supplier must demonstrate it has the means and methods in place to receive orders, make the necessary cuts, package the product, identify it, and ship it promptly.

If availability and delivery of cut-to-length cables can be assured, the final matter is cost. Buying bulk cable on the spool is always where the best price will be found, but only on a simple dollar per foot basis. Significant savings can be realized when users buy only what they need from a cut-to-length supplier, minimizing waste and stocking efforts.

Some suppliers recognize the shift toward cut-to-length services, and are tailoring work practices to meet customer demands. Users should watch out for suppliers that may impose excessive cut fees or inflated shipping charges, which make the cut-to-length approach less attractive.

Helping installers

In addition to addressing stocking and waste issues, cut-to-length cables also can help installation technicians in the factory or the field. Designers may know how to specify the cables, but they may not understand the geometry of the field installation and the lengths needed, so they rely on the installers.

The designers can specify the cables and the to/from targets of each. Installation technicians are well versed in routing and finishing the cables, so they can perform a take-off to determine the required length. The conventional next step would be checking stock, spooling off lengths, and ordering new or resupply cables as necessary.

With cut-to-length methods, technicians make the very same take-off but use it to order what they need and want. They can receive the resulting materials delivered within a day or two to the jobsite. This can represent a convenience for the field, especially when fast delivery times transform the cable suppliers into a virtual stockroom.

Making the cut, certification

When a cable supplier wants to offer cut-to-length services, they must take several important steps in facilities and procedures.

Establishing an online order-taking system makes it easy for users to choose needed cable types and lengths and makes the experience convenient. The cable supplier also must configure a work area at its facility with personnel trained to fulfill the orders. The work must be tracked to ensure quality.

One thing prospective cut-to-length cable customers may not know is Underwriters Laboratories (UL) requires traceability of a cable back to its manufacturer; surface printing on the cables alone isn’t enough to fulfill this requirement. A certified label must be affixed to the spool or cable shipping package from the manufacturer.

In the case where a cable is respooled into smaller quantities, such as when it is processed for cut-to-length, every spool must be provided with the original traceability information using special certification labels. This process is defined by UL as “Processed Wire – Respooled.”

A cut-to-length cable supplier should be certified as a re-spooler so it can apply UL labels to the product that has been processed during cutting operations. The label verifies that the original cable was UL-certified. The supplier also should track the master reels by lot number so it can provide a customer or the UL inspector with information about a particular cable, including manufacturing date.

Cut-to-length cables save time and money

For OEMs and field installers, the normal way of doing business often involves standardizing and buying in bulk. However, when many varieties of detailed products are necessary, this isn’t always the best approach. Electrical and control cables used for industrial equipment and installations come in many detailed configurations and therefore lend themselves to customer cut-to-length operations.

A supplier offering cut-to-length services can’t just send someone out to the warehouse with a pair of diagonal cutters, but must instead offer a comprehensive stock of cable, fair prices, and streamline online ordering and delivery methods. The supplier also should be UL- certified for cut-to-length operations. With all these pieces in place, customers may find that cut-to-length cables represent the best value for installations.

Jim Krebs is a technical marketing engineer at AutomationDirect. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media, cvavra@cfemedia.com.