How to Select a Cable Drag Chain: Fill, Bend Radius and Travel
A cable drag chain (also called a cable carrier or energy chain) guides power, signal and hose lines along a moving machine axis so they bend in a controlled way instead of rubbing, twisting or snagging. Most drag chain failures come from selection mistakes: a chain that is too full, a radius tighter than the cables can take, or a long travel run without support. This guide covers the decisions in the order to make them, with Murrplastik chains as examples.
1. List the cables and hoses first
Start with a complete list of everything that will run in the chain: power cables, motor and encoder cables, signal and bus cables, pneumatic and hydraulic hoses. For each line, note the outer diameter, weight per metre and the manufacturer's minimum bend radius for continuous flexing. The chain is sized around this list, not the other way round.
Use cables rated for continuous flexing in drag chains. Standard fixed-installation cables suffer core breakage after relatively few cycles, however well the chain is selected.
2. Fill factor and interior size
Cables must be able to move freely inside the chain. As the chain bends, cables on the inside and outside of the bend travel slightly different paths, and they need room to shift.
- Leave clearance around each round cable, commonly about 10% of its diameter, and more for hoses, which change length under pressure.
- Do not fill the cross-section completely. A practical guideline is to keep the total fill well below the full interior area, leaving room for movement and future additions.
- Do not stack cables on top of each other without separation; they rub and twist.
The interior height is set by the largest cable or hose; the interior width by the sum of all lines plus clearances and separators. For example, the Murrplastik MP 18.1 has an internal height of 18 mm and internal widths from 15 to 70 mm, while the MP 420 offers 42 mm internal height for large cable and hose packages.
3. Bend radius
The chain radius must be equal to or larger than the largest minimum bend radius among all the cables and hoses inside. Cable datasheets usually give this as a multiple of the outer diameter for dynamic use. If one stiff hose needs a large radius, it sets the radius for the whole chain, or it should be moved to a separate chain.
A larger radius than strictly necessary extends cable life but increases the installed height of the chain. Each series offers a set of radii, for example 18 to 58 mm on the MP 10.1 and 28 to 78 mm on the MP 18.1. Check the installed height for the chosen radius against the space available on the machine.
4. Travel length: unsupported or gliding
For short travels, the upper run of the chain is self-supporting: it spans from the fixed point to the moving end without sagging onto the lower run. The permissible unsupported length depends on the chain size and the weight of the cables, so check it in the chain data for your fill weight.
Beyond that length, the upper run rests on the lower run and slides on it. This gliding arrangement needs a guide channel to keep the chain aligned, and chains designed for it use gliding shoes to reduce wear. The MP 52.2 uses gliding shoes for longer service life. Maximum gliding travel varies widely by series: the MP14 is rated for gliding travel up to 12 m, the MP 45.1/2 up to 80 m and the MP 420 up to 150 m.
Vertical applications are rated separately for hanging and standing installations, and the standing limits are much shorter. Check both values if the axis moves vertically.
5. Chain length and fixed point
Mount the fixed end at the middle of the travel where possible. The chain then needs to cover only half the travel plus the bend. A common estimate is chain length = travel / 2 + π × bend radius + a small allowance for the end brackets. Moving the fixed point off-centre increases the chain length needed.
6. Open or closed chain
- Open chains with crossbars or frame bridges are lighter, cheaper and easy to fill. Frame bridges that open on one side, as on the MP 18.1, or a filling slot on the outside bend, as on the MP14, let you add or replace cables without removing the chain.
- Closed chains protect cables from hot chips, wood dust and debris on machine tools and woodworking machines. The MP 25G offers closed variants starting with a radius of 60 mm, and the MP 65 G opens on both the inside and outside bend for easier filling.
7. Separators and strain relief
Separators divide the interior into compartments so that cables lie side by side, power is kept apart from signal lines, and heavy lines do not crush light ones. Place heavy cables near the side bands and distribute weight evenly across the width. The MP 10.1 can be fitted with one to four chambers depending on width, and the MP 45.1/2 offers modular dividers and shelving.
Fix cables at both ends with strain relief, without clamping them inside the moving section. Many Murrplastik chain brackets include integrated strain relief.
8. Environment and noise
The Murrplastik chains above are made from black polyamide with a service temperature of -30 to 120 °C. For quiet automation cells, look for noise damping: the MP 45.1/2 soft-stop system reduces noise by up to 10 dB(A).
Quick selection checklist
- Full list of cables and hoses with diameters, weights and minimum bend radii.
- Interior height and width with clearances and separators.
- Chain radius at or above the largest cable minimum bend radius.
- Travel length, speed and orientation (horizontal, vertical hanging or standing).
- Unsupported or gliding, with guide channel if gliding.
- Open or closed, based on chips, dust and filling needs.
Drag chains from Rajdeep
Rajdeep Automation supplies Murrplastik drag chains across India, from light-duty chains for small axes to heavy-duty chains for long travels on cranes and gantries. See our cable management solutions for chains, cable entry systems and accessories.
Send your cable list, travel length, speed and mounting space through the enquiry form, and an application engineer will recommend a chain size and radius with the datasheet and price.