I plug my 530 into my mac as I want to download a route but it "disconnects" in about three seconds

faragherm Does the Edge remain charging if you plug it into a wall outlet using the same cable? 

Yes 

It’s helpful if you describe what troubleshooting steps you’ve already tried to narrow down the possible causes.

eg

Has it connected before on the Mac?

Confirm that a data cable was used and not a charge only one.

Using different cables

Directly connecting to the Mac instead for through a hub etc.

I have connected successfully previously but recently it connects and then disconnects in a 3 seconds.

I can nt plug in directly to the Mac book pro as it does have standard USB connections - only USB C - so I have to use a Hub.

I have used many different Cables.

It sounds like it could either be the dongle/adapter or a setting limiting the connection to the dock. I would suggest reaching out to Apple. Link. What Can I Do if My Computer Doesn’t Have a USB Port?