Voltage Drop on Cat 5 cable

[Hoof Hearted 0]

Having successfully installed an 8 camera system at home, I'm looking at installing a CCTV System around the factory where I work. At home I used Cat5 cable to take the signal and power. But the longest cable run was only 20 metres. At work, some of the cable runs will be up to 60 metres. Am I likely to have problems with voltage drop over such a long cable run?

 

Ian

[bpzle 0]

You'll always have voltage drop, with any cable you choose...

 

How much is dependent on the setup you have.

 

1. Are you using 12vDC or 24vAC?

 

2. What exactly will the CAT5 be carrying? Power & video; Power, video & audio; Power, video, & PTZ control?

 

3. In the CAT5, what pairs do you intend to use and for what?

 

4. The cameras that you are using, how much power do they require? AKA amps?

[Soundy 1]

Up to 60m, if you use 24VAC, you shouldn't have a problem, except maybe if you want to run a PTZ. Remember that for any given power rating, 12V requires twice the current of 24V, and thus will see greater voltage loss over distance - 6W, for example, is 500mA at 12V, 250mA at 24V.

 

Here are a couple of calculators that should help:

 

http://www.netkrom.com/voltage_loss_over_cat5_calculator.html

http://www.nvt.com/content.php?func=distcalc

[Hoof Hearted 0]

Thanks for the replies. I'm probably going to be using 12v, but the good news is that there wont be any PTZ. So I can use 3 pairs for the power supply and one for the video.

 

I looked at a couple of the cameras I am considering. They consume 1.8W which is 1.5A at 12v

 

I'll take a look at those calculators. Thanks again

 

Ian

[Soundy 1]

Actually, 1.8W at 12V is only 0.15A (150mA).

[empak 0]

If you are using an eight channel 12 volt power supply, you can adjust the output voltage on the fuse board, If I am using 12 volt and running power on the same cat5 cable you can adjust the output power a bit higher than 13 volts, check voltage at camera side and adjust accordingly, you can also use all four pairs : ie blue/blue white : video, brown orange green for 12volt + and brown white, orange white, green white for 12 volt -, you can also use cat6e 23 awg wire if you are worried about too much voltage drop.

 

[Soundy 1]

If you are using an eight channel 12 volt power supply, you can adjust the output voltage on the fuse board,

 

This is true only of SOME power supplies...

[Numb-nuts 1]

The simplest way to avoid voltage drop is to supply the power to the camera locally.

Obviously this is not always possible. As for the video signals, I would risk using passive

baluns and if by some chance you get difficulties, you can always replace the baluns with

active baluns.

 

A word of caution. If you are supplying local power to each camera, you may encounter

ground loops due to the varying earth potential of different mains circuits.

So far touch wood, I have never encountered this but have read of these problems

here numerous times.

[Soundy 1]

The other problem with local power for the cameras is that it spreads out your system management, instead of keeping all critical components in one central, easy-to-access location. You probably don't want the transformers visible, so that usually means finding somewhere to hide them... which often means somewhere with limited accessibility. Not fun if you need to troubleshoot power issues later.

 

It's one thing, too, if this is your home setup... but for a customer, show a little consideration for the next guy who comes along to service the system, and will have to spend hours trying to figure out where the #*^%#* you powered the%&^(@!! cameras from, you stupid #%#*^&$@(!!!!!

 

Central power greatly simplifies troubleshooting: check the camera end for voltage... if it's not there, check the power can... if it IS there, you know the problem is somewhere in the wire.

[bpzle 0]

If you are supplying local power to each camera....

 

Actually I've been recommended by an electronics engineer that this is probably best "solution" to ground loops... albeit a dirty one...

 

If you have issues using a traditional 12v distributed PSU, take the problem devices and power them locally or SEPERATELY. That's the exact opposite of what you're recommending???

[Soundy 1]

I don't think it's "local" power, so much as separated power, that addresses the ground loops. A transformer provides physical isolation between the line voltage and the stepped-down voltage, which also isolates the camera's power ground from the other cameras's power and video grounds... whereas in a power can, all cameras share a common power ground.

 

The first time I ran into bad ground-loop issues with Cat5 and baluns, simply disconnecting each camera from the power can and putting it on its own transformer cleared things up perfectly. The transformers were all "central", right beside the DVR, plugged into the same power bar.

[ssmith10pn 0]

Wrong thread

[MarcoZandrini 0]

Remember that the PoE standard allows only up to about 15 watts of power via cat5e.

[Soundy 1]

802.3af is 15.4W max... which is actually plenty for most fixed cameras, even with IR; at 12V, that gives you over 1.25A.

 

The newer 802.3at-2009 spec (aka "PoE+") lists up to 25.5W, or well over 2A at 12V.

[Numb-nuts 1]

If you are using an eight channel 12 volt power supply, you can adjust the output voltage on the fuse board, If I am using 12 volt and running power on the same cat5 cable you can adjust the output power a bit higher than 13 volts, check voltage at camera side and adjust accordingly, you can also use all four pairs : ie blue/blue white : video, brown orange green for 12volt + and brown white, orange white, green white for 12 volt -, you can also use cat6e 23 awg wire if you are worried about too much voltage drop.

 

 

Reading this surprised me as your colour convention for cat5 is exactly the one I use