Versions:

MC: 1.10.2
Forge: 12.18.3.2254
CompatLayer: 1.10-0.2.5
Not Enough Wands: 1.5.4
Extra Utils 2: 1.10.2-1.3.3

Reproduction:

https://puu.sh/vbqgw/894a702f59.jpg
That was on a server I play on. I did reproduce it in a "Single Player" world to get the crash below. The only 2 important blocks are the Mechanical User and the Powercell. Moving wand works fine in a player's hand on a Powercell. Mechanical User has no problem placing Powercells

Crash Report:

https://gist.github.com/Alex-hawks/1138a8a6e1c0cda991109c1cac460a36

Thank you for taking the time to create this issue, as we're no longer supporting versions below 1.12, I'm going to go ahead and close it but if this bug seems to continue over to newer versions, please do report it again so we can investigate the issue further.