Cable Glands and Strain Relief: Keep Cable Loads Away from Power Supply Terminals
A power supply terminal should carry current, not the pulling force from an external cable. Select a cable gland for the cable jacket and enclosure entry, then design the internal support so that installation, vibration and servicing do not tug on the terminal connection. A tidy bundle alone does not demonstrate effective strain relief.
For equipment builders, this is a mechanical interface decision as well as an electrical one. The gland, cable jacket, internal clamps and power supply terminals each have a different job. Ordering them as a coordinated assembly avoids discovering at final wiring that the cable fits the hole but is not properly retained.
Start at the cabinet wall, not at the terminal screw
A cable gland usually forms the cable entry into the equipment enclosure. Its clamping range must suit the actual cable outside diameter, while its thread and sealing arrangement must suit the enclosure opening. The individual conductor cross-section is not the same dimension as the jacket diameter. Confirm the permitted cable diameter, clamping range and protection requirements in the selected gland’s documentation.
A gland can provide strain relief when selected and assembled for that duty; it is not merely a decorative sleeve. Check the particular gland’s instructions rather than assuming that every fitting with the same thread has identical retention, sealing or environmental performance. A reducing insert, different jacket material or cable near the edge of the permitted range may change the selection.
Give each part of the cable path a clear job
| Interface | What it must achieve | What to establish before ordering |
|---|---|---|
| Enclosure entry | Retain the intended cable and provide the specified entry protection | Cable diameter, jacket compatibility, thread, wall thickness and sealing method |
| Internal cable support | Prevent cable movement from loading the terminal connection | Clamp position, supporting structure, service movement and cable bend requirements |
| Power supply terminal | Make the intended electrical connection | Accepted conductor preparation, connection rating and manufacturer’s tightening instructions |
| Service access | Allow inspection or replacement without straining adjacent wiring | Tool access, controlled slack and a repeatable cable route |
Do not add a universal tightening torque or pull-test value to the drawing. Those acceptance values belong to the selected gland, terminal and equipment design. A cable tie used to organize conductors is not automatically a qualified substitute for a strain-relief clamp.
Use the LRH-150-12 as a chassis-mounted example
را WEHO LRH-150 family illustrates why the enclosure and power supply must remain separate design items. The referenced LRH-150-12 is a vented, low-profile metal supply measuring 159 × 97 × 30 mm. Its source label states a 300–450 VAC input and a 12 V, 12.5 A output. It is not a universal-input unit and must not be selected for a supply outside that input window.
The terminal arrangement is L1, L2, protective earth, two negative output positions and two positive output positions. The drawing identifies bottom M3 mounting provisions. A gland belongs in the equipment’s designed cable entry, not in a newly drilled hole in this power supply case. The supply’s screw terminals and transparent terminal cover do not replace enclosure-level cable retention.
Lay out the supply, gland and clamps together. Keep its ventilation openings clear, leave access to the terminal cover, and route wiring without pressing it against sharp sheet-metal edges. Fixing details and conductor preparation still require the delivered product’s instructions; the photograph is not a wiring acceptance document.
Separate external pulling forces from the final connection
Consider what happens when an installer draws cable through the entry or when a technician opens a service panel. If the external cable moves, that movement should be controlled at the intended retaining hardware, not transferred directly into a short, tight conductor at the supply terminal. Support the cable jacket where the clamp is intended to grip it, then provide the required transition to individual conductors.
Leave enough controlled slack for the planned service operation, without draping a loose loop across ventilation slots or allowing it to rub on a moving part. Follow the cable manufacturer’s bend-radius guidance. Cable routing should also preserve the separation and insulation provisions specified by the equipment’s electrical design; an attractive photograph cannot establish those requirements.
Review the assembly before energizing it
A useful mechanical inspection is performed while the equipment is isolated. Check that the gland is secured to the enclosure, its seals and locknut are installed as specified, and the clamp actually grips the intended jacket rather than a loose sleeve. Verify that the cable route remains stable through the intended service movement. Then check that the final electrical terminations can be made without pulling the conductors taut.
Record the actual gland part number, cable diameter and clamp arrangement on the equipment drawing. If a cable supplier changes the jacket diameter, revisit the gland selection instead of assuming that the conductor size guarantees the same fit. Have the responsible qualified person define and perform any required retention or electrical tests; the visual inspection is only one part of acceptance.
Frequently asked questions
Does the correct gland thread guarantee a correct cable fit?
No. Thread size describes the enclosure interface; the gland’s specified clamping range must separately cover the actual cable jacket diameter. Check both before buying.
Can the terminal screws serve as strain relief?
No. Design the cable support to keep pulling and twisting loads away from the electrical termination. The terminal connection must be assembled according to its own instructions, not tightened harder to compensate for an unsupported cable.
Does an IP-rated gland make a vented supply waterproof?
No. The entry component’s rating does not establish the protection of the complete enclosure, and it does not change the vented power supply into a sealed product.
Send the cable and enclosure details with the power supply enquiry
For a practical review, provide the input voltage, output load, actual cable outside diameters, enclosure entry drawing, service movement and environmental conditions. Include a photo or sketch showing the gland-to-terminal route. Contact WEHO to confirm the power supply model and mounting information, while the equipment designer and gland supplier confirm the cable-entry and retention requirements.
