Guest grahamc Posted May 12, 2006 Share Posted May 12, 2006 Is it necessary too use baluns for video signal down a twisted pair of cat5 utp cable over a distance of about 30 meters? Also, if I send 24V AC to power the camera down 2 pairs of twisted wires, does it matter how I connect them? ie. one side of the supply thru' one pair and the other side thru' the other, or both phases through each pair? The supply is rated 1amp..is it ok to send through the cat5 or will it melt! Any help much appreciated. Link to comment Share on other sites More sharing options...
ian.cant Posted May 12, 2006 Share Posted May 12, 2006 Is it necessary too use baluns for video signal down a twisted pair of cat5 utp cable over a distance of about 30 meters?You would no doubt get a picture but for the sake of a pair of baluns i would use them, theyre cheap enough Also, if I send 24V AC to power the camera down 2 pairs of twisted wires, does it matter how I connect them? ie. one side of the supply thru' one pair and the other side thru' the other, or both phases through each pair? The supply is rated 1amp..is it ok to send through the cat5 or will it melt! it wont matter, just use a pair, if the run is more than 30 mtrs though i would consider doubleing up on a couple of pairs. It will only melt the cable if you put high currents through it which will melt the camera also! Any help much appreciated. Link to comment Share on other sites More sharing options...
Guest Posted May 12, 2006 Share Posted May 12, 2006 it wont matter, just use a pair, if the run is more than 30 mtrs though i would consider doubleing up on a couple of pairs. I would ensure that each pair has one side of the power connected to it, rather than using a pair for each IYSWIM, keeps inteference down within the cable. It will only melt the cable if you put high currents through it which will melt the camera also! How so? Surely the camera would only melt if it was faulty. If the cable was carrying high currents then the chances are the load would be using the current, probably by design, so wouldn't melt. You can't 'send' currents down a cable and 'overdrive' something. And can we please use the quote feature properly, this 'colours in the middle' makes it hard work to reply to anyone. Link to comment Share on other sites More sharing options...
Alexg Posted May 12, 2006 Share Posted May 12, 2006 A current is what something draws, not something you can send!! A cable will only be carrying a current of say 2 amps if the device connected to it is drawing it! If you have a 4 amp PSU connected to a length of cable with no device on the end, the cable wont have a 4amp load on it untill you connect a device to it, if the device you connect to it draws 2 amps then thats all the current that will be going down the cable. Link to comment Share on other sites More sharing options...
Rich Posted May 12, 2006 Share Posted May 12, 2006 Another thing, if you are using a power supply that can supply enough current to melt the cable then its probably over rated or supplying all the equipment on the system, this is why each individual supply to each piece of equipment should have a seperate correctly rated fuse inline. Link to comment Share on other sites More sharing options...
dynamic Posted May 12, 2006 Share Posted May 12, 2006 Hi Graham, Cat5 is usually derated to 350mA to avoid overheating, and you should make sure that it's either fused or current limited to a safe level unless you're happy to have the house burn down. Also, don't forget that you have about 9 ohms per 100 metre (each way, making 18ohm/100m round trip), so don't expect to get out the same voltage as you put in. Have you considered using PoE (Power over Ethernet) equipment? Link to comment Share on other sites More sharing options...
arfur mo Posted May 12, 2006 Share Posted May 12, 2006 another thing, if you are using a power supply that can supply enough current to melt the cable then its probably over rated or supplying all the equipment on the system, this is why each individual supply to each piece of equipment should have a seperate correctly rated fuse inline. hi Rich, people can use a fuse block (Maplins/RS/LJD) with each leg fused at say 500ma. that way you know which cable has 'eaten all the pie's'. only one camera fails and the other camera's remain working. what seems to be in need of a little more illumination, the fuse protects the cable not the device, so if a problem occurs the cable is protected by a fuse from overload and thus possble burn out/fire. the fuse will still offer protection to the device too. this is very wise and recommended, as a short could occure say at the point of connection at the far end of the cable, or cable damaged by ground works/rodents etc. so a device's fuse would be of no use in that scenario, the less experienced engineers need to be aware of the sound reason's to fuse at the source. i only reinforced this because the times i see a fuse in the local j/b and a 6amp in the psu, i assume because if you blow the local fuse, it saves walking back to the psu to replace it. regs alan If you think education is difficult, try being stupid!!!! Link to comment Share on other sites More sharing options...
Gopher Posted May 12, 2006 Share Posted May 12, 2006 Personally I wouldn't risk putting power down cat5 cable, unless there was absolutly no other way to do it, at 350mA per strand, that's not gonna power much + there is the interferance aspect of it all. I've wired up 24ac cat5e domes and put a seperate cable in for the power - belden does the job nicely. If the camera has a buillt in balun to take it to cat 5 then over say 30m you'd probably still have enough to recover a picture going straight to co-ax just flip the pair over so the cable that is your video signal - connect this to the sheath, and the scr to the core - don't ask why it works like this, most just do (or the ones I've done do). if your going co-ax->cat5->co-ax no crossover needed. As for the distance since it's <200m you can get away with a passive balun if you have to use one this just does the same job as connecting them together, it just looks neater.. I know that passive is rated longer but I always err derate things a great deal, never trust the spec full till I've Tested it.. Hope that helps ya a lot. Intruder / CCTV / Access Control Technical Support Personal Subscriber to the "K.I.S.S" principle, that's Keep It Simple Stupid, are you? Link to comment Share on other sites More sharing options...
Rich Posted May 12, 2006 Share Posted May 12, 2006 hi Rich, people can use a fuse block (Maplins/RS/LJD) with each leg fused at say 500ma. that way you know which cable has 'eaten all the pie's'. only one camera fails and the other camera's remain working.what seems to be in need of a little more illumination, the fuse protects the cable not the device, so if a problem occurs the cable is protected by a fuse from overload and thus possble burn out/fire. the fuse will still offer protection to the device too. this is very wise and recommended, as a short could occure say at the point of connection at the far end of the cable, or cable damaged by ground works/rodents etc. so a device's fuse would be of no use in that scenario, the less experienced engineers need to be aware of the sound reason's to fuse at the source. i only reinforced this because the times i see a fuse in the local j/b and a 6amp in the psu, i assume because if you blow the local fuse, it saves walking back to the psu to replace it. regs alan I thought that is what I said, I refer to the likes of dantech PSU's that have a fused distribution board. Of course the cable should be protected from the psu with a fuse, not at the equipment. Link to comment Share on other sites More sharing options...
arfur mo Posted May 13, 2006 Share Posted May 13, 2006 I thought that is what I said, I refer to the likes of dantech PSU's that have a fused distribution board. Of course the cable should be protected from the psu with a fuse, not at the equipment. hi Rich, as usual all your advice is very good. i'd say most i meet from a non technical background believe the fuse is to protect the appliance, we know its for the cable. i wanted to reinforce good practice with the clear theory behind it in the public area. many who look in here are diy, and it's not always clear to them why take the precautions we do without thinking anything more of it. i hope i did not cause any offence, if i did it was not intended mate. regs alan If you think education is difficult, try being stupid!!!! Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.