From a combination of legal and practical hurdles, an employee is rarely liable financially for anything but wilful damage.
Legally, a duty to take reasonable care of goods exists, but reasonable care isn't synonymous with the absence of damage to the goods, and the standard of reasonable care to which an employee will be held is low and basically amounts to not doing anything deliberate to damage the goods.
The reason this policy exists is twofold.
Firstly, employees are often in charge of goods whose value is completely disproportionate to the employee's own resources, and the courts are unwilling to get involved in an overall arrangement which essentially consists of employers handing out valuable and delicate goods to paupers, and then trying to squeeze those paupers dry when something accidentally goes wrong.
Secondly, the employer has relatively arbitrary power to compel expensive goods to be handled and used in circumstances where risks are obviously non-zero, including in circumstances where it may make overall sense for the employer to take the risk (given the value of the work done, and the potential to pool many risks), but it wouldn't make sense for the employee to take that risk. The employee usually isn't in a position to evaluate and manage the risk, or to decide whether to accept the risk. For this reason, courts don't tend to consider the employee as the appropriate party to bear the risk.
Practically, an employer may have considerable difficulty proving the circumstances in which damage occurred - often, the only evidence may be from the employee who the employer is alleging caused the damage.
Conclusion
In terms of a direct answer to the question, no, employees are certainly not liable for "wear and tear".
But employees are also not generally liable for any accidental damage, even if it isn't wear and tear. Whatever the employer gets back, is what it is.
It would be for a judge to decide whether particular circumstances fell below the standard of the employee's duty to take reasonable care of the employer's goods, but that is a very low standard.