Question
Will the severing  of a large root on the 30 yr old Spruce damage the tree.

Answer
It will depend on if that was the only root severed. If the roots was cut digging a hole and this was the only one I would thing there would be little damage to the whole root system. In the very least you might loose one limb but I would not expect any damage to show up.

Now if a trench was dug through the root system if could cause damage. IF more then 30 % of the roots were cut then I would expect some dieback of the foliage. If you think of the area of the roots under the tree as a pie and you draw a line across the pie shape where the trench was cut and the cut piece is more than 30% then you may have damage to the crown of the tree.

With out knowing any more details this is about all I can answer.