Because a flat crown pinches the sheath, and the damage is usually invisible.

Deforming the sheath reduces insulation thickness at that point.

Compressing the conductor changes its electrical characteristics.

On data and coaxial cable, crushing alters the geometry the cable depends on and degrades performance without breaking anything.

A network cable can pass a continuity test and still fail at speed because of a staple.

Shaped and insulated crowns exist specifically to hold without a pinch point.

A polymer saddle spreads the load and separates the metal crown from the sheath.

Spreading load is the mechanical function and is what prevents crushing.

Separation is the electrical function, keeping a metal fastener off the cable's insulation.

The saddle also grips the cable slightly, which reduces movement and chafing.

Polymer choice affects temperature range and fire behaviour, which matters in some installations.

Plastic-bodied cable clips take the same idea further and dominate domestic wiring in many markets.

To match the cable, not approximately clear it - too narrow pinches and too wide lets it move.

A crown that grips too tightly damages the sheath immediately.

A crown much larger than the cable lets it shift under the staple, which chafes the sheath over time.

Flat cables and round cables need different crown profiles as well as different widths.

Manufacturers list clips and staples by cable size or type rather than by dimension alone.

Where several cable sizes are run, several clip sizes are needed.

Not with a staple sized for one - the outer cables get crushed.

A crown bridging a bundle bears on the outermost cables and concentrates load on them.

Bundles need a cleat, tie or clip designed for the bundle diameter.

Bundling also has electrical consequences, since grouped cables run hotter and may need derating.

Wiring regulations frequently have rules about grouping and support of bundles.

Where several cables follow one route, containment such as trunking or tray is usually the right answer.

Yes - spacing, permitted methods and fire performance are all regulated in most markets.

Support spacing is specified so cables do not sag or strain their terminations.

Permitted fixing methods differ by cable type and by installation environment.

Many jurisdictions now require supports that do not fail in fire, so cables do not fall and obstruct escape routes when plastic clips melt.

Those rules differ by market and by cable type, and they are the governing specification.

The applicable wiring rules should be identified before the fixing method is chosen.

They are the most sensitive - crushing changes the cable geometry that the performance depends on.

Twisted pair and coaxial cables rely on consistent conductor spacing and dielectric geometry.

A staple that deforms the cable changes impedance at that point.

The result is reflection and signal loss rather than an obvious failure.

Structured cabling standards commonly prohibit staples and specify clips or hook and loop supports instead.

Minimum bend radius is a related rule that fixings must respect.

By hand or with a purpose-made cable tacker with depth control - a general staple gun will crush the cable.

Cable tackers are designed so the staple stops at the correct depth over the cable.

General staple guns drive flush, which is the wrong depth for a cable.

Hand driving with a hammer works and requires care on the final blow.

Insulated staples are more forgiving than bare ones but can still be overdriven.

If a staple has been overdriven, the cable should be inspected rather than assumed.