Can IP cameras be daisy chained ?

We first note the below consumption and source capabilities:

1.  A Wired IP camera typically uses 6W of power max. Depending on Camera's IR range, night time power requirement shoots up by 1.5W (20m range), 2W(30m range),  4W (50m range) and  ~7W (80m IR range). This gives us a wide PD range of 6W-13W.
2. An 802.3af port can supply 12.95W of power to the PD, while 802.3at (PoE+) can supply 25.5W of power to the PD. 
3. A USB wireless camera (10m IR) uses about 0.5A max
4. A USB power brick can supply 2.4A Charging current at max, with 1A/2A the common Charger/DC-UPS output current ranges
5. An IP camera using H.265+ encoding uses no more than 1 mbps per megapixel bandwidth while recording the FOV.
6. A Cat5e cable can provide 100mbps bandwidth per wired port (most wired IP cameras are 10/100 mbps only)

Therefore it tell us that in some cases the power of wired links exceeds the camera (PD) drain by a factor of 2 (802.3af) or 4 (802.3at). And for data, its much more than that 4. Therefore, conceptually its seems attractive that 2-4 cameras can be daisy chained or run of ONE PoE/PoE+ port, saving potentially significant amounts of cabling effort. For USB links also, similar ratios come into the realm of possibility. 

For wired cameras could become more attractive as 802.3bt switches start appearing on the market, which will supply 60W and 90W power levels on a per port basis. And if power is sourced locally (via AC-DC SMPS adapter), we could potentially daisy chain many more devices

On the usability side often more than 1 cameras are mounted on poles or cameras in one place (close proximity) in opposite directions or even 3 cameras on one site, creating potentially useful use cases. even otherwise in some cases home-run wiring involvers more cabling effort & cost than daisy chaining.

However we should note that most Wired IP cameras DO NOT support daisy-chaining by supporting downstream PoE extension or even pure *data ports, neither do wireless IP Cameras support USB out to connect a second camera. But this may be beginning to change:

The popular Wyze cam (Version 2) now allows USB out and allows chaining of upto 3 indoor wireless cameras, with an advisory to use only short daisy chaining USB cables (we will discuss this a bit later)

And Vivotek is doing the same  with wired cameras by including a 2-port switch and POE extender onboard the camera device.

So maybe more of such daisy chaining  features will start appearing in both wired and wireless camera models from more OEMs in the future. Maybe.

Till that happens, we still may have some options: Involving Bus powered (passive) USB hubs (1x2, 1x3, 1x4) or USB-A-Female-to USB-A-Female splitter cables for wireless cameras and PoE extenders (1x2, 1x4):

These are strictly not daisy chaining type of equipment, but they shift the home run point to an IP camera location and especially useful for installing cameras in close proximity (like fixed focus cameras in multiple directions, with a small PTZ at same location to aid live monitoring). Availability and pricing may be of some concern though as not many brand offer such solution. The only drawback of this design approach is that you can reset all 2-4 connected cameras together using power cycling method and not each one individually (they can be restarted only via graceful software reboot methods).

For USB powered wireless, things a more tricky as extremely low voltage tolerance levels are involved unlike 802.3af/at/bt standard. Refer this URL for USB power details. Here we summarize key points:

USB contact Resistance = 30 milli-Ohm

No. of contacts = 4 // 2 for positive wire, 2 for -ive wire

USB cable resistance (20 AWG wire or best cable) = 33.3  milli-Ohm / meter

We assume 10m as longest cable distance for wireless IP cameras (small installations) , rather than 100m or more (big installations).

So USB cable resistance for 10m cable (10x2x33.3) + 30x4 = 786 Milli-Ohm

Potential drop across a 10m cable link = (786/1000)*(Peak-Current on Home-run) = 0.726 *2= 1.572V

For 1m cable, the drop becomes (1x2x33.3 + 30x4)/1000 * 2 = 0.3732

USB spec requires USB voltage to be 5V +/- 5% or only a 0.25V voltage drop is permissible.  So its clear , we can't use long cables to daisy chain and only 1m  maximum can work, that too if charger outputs a bit higher voltage (such as 5.2-5.4V).  This limits overall usability.  Its safe to say that cluster 2-3 cameras can be used in a single location (or close proximity) at maximum. You may just daisy chain power cable instead and put multiple DC-DC UPS at each camera location rather than trying to use one DC-DC UPS to serve multiple cameras at distant locations

Longer passive USB cables can however be used for 1 camera (0.5A max current) as voltage drop will reduce significantly [its 0.363V for one 10m(30ft) cable serving one camera drawing 0.5A max].

- Suman Kumar Luthra @ APRC-P3 Telecom Sub-Committee