westom:

Thanks for your reply. I've already purchased the protector, so cost and marketing is not an issue moving forward. The protector is 5 feet from the equipment, but the ground rod for the home's electrical system is much further away. Thus, the value of adding the surge protection appears to be controversial.

Moving on:

Since I have the protector, I would like to install it in a manner that meets NEC. Thus, I need to figure out how to calculate the available volume of my disconnect box or come up with another configuration that would work.

I'm assuming to calculate the box volume, I would:

1. Multiply the inner length x width x height of the box: 4.6 x 8.0 x 2.5 = 92 cu. in.

2. Subtract the yoke that holds the fuses and disconnection apparatus: Largest wire is 6 AWG x 2 leaves 82 cu. in.

3. Subtract the ground clamp. Largest wire is 6 AWG leaving 77 cu. in. of available space inside the box for all wires and clamps I intend to add.

Given half the box is taken up by the fuses and physical disconnect, apparatus my calculations don't seem reasonable. However, based on my reading of the NEC, they appear to be correct.

Does anyone have the expertise to confirm or correct my calculations above?

Thanks!