Cable confusion - connecting second monitor to iMac 2019

[Jack Hennety]

Just got myself a second monitor to use as an extended desktop with my 2019 27” iMac. Monitor is a Philips 258B6QUEB.

Having never done this before, I thought it looked straightforward enough - connect one of the iMac’s USB-C ports to the new monitor’s USB-C port with a USB-C to USB-C cable. Because the USB-C to USB-C cable that came with the new monitor is ridiculously short, I used the cable that came with my iPad Pro 2018 instead.

However, the Philips monitor doesn’t like it - no signal detected. That cable works fine if I connect the iMac to the iPad Pro, so the cable’s not a write off. But the iMac and the monitor only see each other if I use the cable that came with the monitor.

So I’m going to get another USB-C to USB-C cable, of a decent length. Here’s the question! Will any old USB-C to USB-C cable be ok, or do I need that says it supports something in particular eg. Thunderbolt 3?

Thanks...

 

[priitv8]

You will need a Thunderbolt 3 cable. It will look exactly like a USB-C cable.
USB-C is a mess from the compatibility and capability standpoint.
You will need to know if the cable in your hands is just a charging cable, a USB 2 cable, a USB 3 cable (in 2 flavours) or a TB3 cable.
EDIT: now looking at that monitor, you'll have to figure out which communication channel does it use for image transfer: USB3.1, DisplayPort or Thunderbolt. It is not evident from the specs.
iMac supports only TB or DP for video.

 

[dwig]

...
So I’m going to get another USB-C to USB-C cable, of a decent length. Here’s the question! Will any old USB-C to USB-C cable be ok, or do I need that says it supports something in particular eg. Thunderbolt 3?

Thanks...

"...any old USB-C to USB-C cable" may or may not work, as you've found out.

The USB-C cable that ships with the new iPPs is designed to be a charging cable of reasonable length and modest weight (and cost). In order to do this, the cable only supports USB2.0 data and thus doesn't support USB-3.x data or the DisplayPort-AltMode needed for connecting a monitor.

You need a cable that specifically states that it supports DP-AltMode displays. Generally, any that support TB3 will and any that support USB 3.1gen1 or gen2 will also. These, expecially the TB3 cables, will generally be somewhat limited in length compared to the charge/USB2 cables.