Sharing - pole , 9 way 12v box

[jhartleycaw 0]

Evening all,

 

I have been given the unenviable task for refreshing some domes at work.

 

To save having to rewire, we are going to use the existing wiring, which is a BNC coax and a strange cable which seems to be 2 twisted pairs(or even 4 core) and a shield/ground. Looks to be slightly beefier than cat5 cores.

 

Each dome needs a 12v feed for the actual camera, and a 12v feed for the heater/fan, 750ma for the cam, and 1a for the heater/fan, as far as I can work out.

 

My idea was to run +- for the RS485 on 2 of the cores, and then +12v down each of the 2 remaining ones, sharing the - across 2 outputs off the 9 way with the shield/ground. 4 cams, use 8 of the outputs. 1 +12v feed for the cam, 1 for the heater. Or just twist 2 cores together, and split them at the other end.

 

Will this work, or a recipe for disaster? Not sure how bridging the - will affect the PTC fuses.

 

Backup plan is run cat5 to each camera, and triple up 6 of the cores for power and use the remaining 2 for signal, but as I said, want to avoid time in the ceiling chucking cable!

 

Thanks

 

James

[aibudo 0]

What is the maximum footage from the DVR and cameras? What is the size of 2 pair cable wires? If within the acceptable loss of DC, then just use 1 pair for the camera power and the other pair for the heater/fan.

 

If I understood what you were asking.

 

Dennis

[jhartleycaw 0]

Hi, thanks for the reply, in answer to your questions:

 

DVR to each camera is max 10-15m

 

I'm not sure on the size of the cable, only that it is belden branded and has 4 cores and a shield.

 

I would give a pair for each, but I want to use one pair for signal(RS485) so only leaves 2 cores and the shield.

 

So basically wondering if I could use 1 core for power, 1 core for heater, and then share the shield between them. Effectively using 2 channels of the 9, 1 core to each plus and then split the shield to each minus. Would this blow the protection or share 2.2 amps between the feeds(assuming each channel is 1.1amp rated). I think I am assuming the minus is common across the 9 channels, which is more then likely wrong! It is one of those lockable boxes, with a 12v psu at the bottom and 9 fused channels.

 

Does that make sense?

 

Thanks again

 

James