The first minute of use does most of the damage

Everything below about cold starts and warm-up comes from what actually happens rather than from what is supposed to.

Why starting is the hard part

Lubricant drains from bearing surfaces while a machine stands, so the first movement happens with a thinner film than normal. Electrical machines draw a large inrush current at switch-on, which heats windings and stresses contacts and protection.

Temperatures across a machine are uneven at start, so parts expand at different rates and clearances are momentarily wrong. Control systems are calibrated for steady operation and behave less precisely during the transition to it. The combined effect is that a disproportionate share of a machine's lifetime wear happens in its first minute of each use.

Lubrication before load

Hydrodynamic bearings rely on motion to generate the film that separates surfaces, so the film does not exist until rotation begins. Applying full load before that film has formed produces metal-to-metal contact, which is the most damaging condition a bearing meets. This is why many machines specify a period of light running before load, and why that instruction is not a formality.

Compared like for like, cold lubricant is thicker and reaches distant surfaces more slowly, which extends the vulnerable period considerably. Grease-lubricated components have their own version of this, since grease must be worked before it releases oil where it is needed.

Electrical inrush and what it stresses

Motors draw several times their running current while accelerating, and that current appears as heat in the windings. Repeated starting in quick succession compounds the heating, since the machine has not dissipated the previous start.

Heating elements and lamps present a low resistance when cold, which produces a similar inrush at every switch-on. Power supplies charge their input capacitors at switch-on, drawing a brief but very large current. This is why many machines specify a minimum interval between starts, and why ignoring it shortens motor life.

Thermal shock in anything that heats

Rapid heating creates temperature differences within a component, and those differences create stress because material expands unevenly. Glass, ceramic and coated cookware are particularly vulnerable, since their materials tolerate compression far better than tension.

In the small print, heating elements and their supports cycle through the largest temperature swing of any part in an appliance. Joints between materials with different expansion rates fatigue with each cycle, which is why cycle count matters more than hours.

Preheating gradually where the design allows reduces these gradients and costs nothing but time.

Cold, batteries and fluids

Battery chemistry slows in cold, reducing available current and making a pack appear more depleted than it is. Charging some chemistries below freezing causes permanent damage, which is why well-designed chargers refuse to do it. Fluids thicken in cold, so pumps and hydraulic systems work harder and deliver less until they warm.

Judged against the category, condensation forms when a cold item is brought into a warm room, and switching it on before it has equalised risks electrical damage. Allowing equipment to reach room temperature before use is a habit that costs a few minutes and prevents a category of failure.

Manufacturer figures are measured under conditions the manufacturer chose.

Habits that reduce start-up wear

Allow a brief unloaded period before applying full load to anything with bearings, gears or hydraulics. Avoid repeated rapid restarts, and respect any minimum interval between starts that the manual specifies for the machine.

After the warranty ends, let equipment equalise to room temperature after being stored or transported somewhere cold, and give condensation time to disperse. Preheat gradually where a machine allows it, particularly anything involving glass, ceramic or coatings. Where a machine is used briefly and often, consider whether fewer longer sessions would reduce the number of starts.

The takeaway

Give anything mechanical a moment before you load it, and count starts rather than hours.

Buy for the failure you can live with, not the feature you will use twice.