Your personal safety should be your top priority when using any power tool. While there are specific guidelines for safe operation in the manufacturer-supplied users' manuals for electric lawnmowers, many terms may be unclear or open to interpretation. There may also be questions as to why the guidelines recommend certain methods and discount others. Clarification will dispel any doubts or fears.
The users' manuals for electric lawnmowers warn to never use the mower in wet or damp grass or during a rain. Using any electric device in the rain will be hazardous to the device and may cause serious personal injury. That should be a foregone conclusion. Always heed the safety warnings supplied by the manufacturer. The terms open to interpretation are "wet" and "damp."
How Wet Is Wet?
To determine if your lawn is too wet to cut, simply walk across a reasonably flat expanse. If your footprints are easily spotted and the grass doesn't spring back quickly, it's too wet. You will likely notice that your toes are wet as well. Heavily shaded areas will require even more drying time. While on your "test walk," keep an eye out for any objects you don't want under your mower, such as toys, rocks or garden hoses. Aside from the obvious danger of mixing water and electricity, there are good reasons to never cut wet grass with any type mower.
Cut the Grass or Manicure the Lawn?
Wet grass gets compacted easily as it did underfoot on your "test walk." This is readily apparent by the ruts left behind by the wheels of the mower and the clumps of clippings piled up hither, tither and yon. A job like that looks bad at the time and worse in a day or two when the compacted ruts spring back and you have a yard full of miniature mohawks. No mower works well in wet grass as wet clippings adhere to the underside of the mower deck, adversely affecting air flow. The air flow created by the blade and the deck is a major contributor to a smooth finish.
Now or Never
So wait until your test walk reveals light moisture, such as a drop or two on each shoe. In high humidity climates, you might get completely dry test results only in late afternoon when the temperature climbs. In every situation, call upon your good judgment. If you enjoy having an appealing yard, it's called gardening, but if you despise the chores, it's yard work. Be a gardener. The sense of accomplishment is fulfilling, and you add to the pleasure and value of your home.