Find 3d distance between 2 sets of points

[SB5]

Hi,

I'd like to find the 3d distance between all points in two point feature classes. One is 12 000 building points, the other 22 000 point locations of a construction machine (along a line), constructing many km of tunnel. My aim is to be able to select the building points within x meters when the construction machine is at a specific location. How can I do this without running Near 3d several thousand times?

I am using arcgis 10.3 with basic license. I am not very familiar with scripting.

[DanPatterson_Retired]

Thanks Xander... looking for distractions between marking

[SB5]

I just realised that what I had done was to change the fields from lines 12 and 13, I thought I had to specify them myself. That's what happens when a code rookie tries to overcompensate I guess. I will try again over the weekend, will most likely work as a charm. Thanks for taking the time to guide me.