AutoDesk makes a version of AutoCAD that you can download to your mobile device.
It is fully featured. It is powerful. It works great on an iPad Pro.
Even if you don’t use CAD software often, you might find it handy for opening CAD files (.DWG, for example).
You can download it here:
http://www.autodesk.com/products/autocad-360/overview
It’s free for 30 days, then requires a monthly fee afterwards: $4.99.
There is an electrical companion that you can also download: AutoCAD Electrical:
http://www.autodesk.com/products/autocad-electrical/overview
Try them both for free. You might be surprised how well it works on a mobile device.