Grounding question

[RinkRat 0]

Hey folks... nice place you have here. Hope ya'll can answer what I assume will be a pretty straight forward question for most of you.

 

I'm going to be doing a self install, 7or 8 24v cameras, using an Altronix power supply. DVR will be a Geovision system I've built myself. Question needing an answer concerns the cameras. Was going to run 18/2 power wire until I noticed a groung screw on the cameras. Should I be running 18/3 and grounding the cams? Do I have to ground them? If so, will the Altronix power supply have a place to ground all cameras to or is there someplace else I should be looking to ground to.

 

Thanks in advance for any response guys(gals).

[rory 0]

I havent seen any 24VAC cameras with a ground screw, besides the one that is on the dual 12VDC and 24VAC, in other words there should only be 2 screws, using 24VAC it does not matter what screw you use for which wire. If you are using 12VDC then the black to the ground and red to the 12V.

[RinkRat 0]

Hey rory, thx for the repy.

 

Camera in question is the Panasonic WV-BP144, link is here

 

http://www.panasonic.com/business/security/cameras_lenses.asp

 

It's under fixed b/w cameras... bottom of page. Operating instructions show 1 wire to ground, 2 to power.

[rory 0]

Oh yeah, thats just ig you want to ground it also, not found on all cameras. You could ground it to something right near the camera, or run an extra wire back to the Power Box and use the same ground that the Power Supply is using I guess. ALtronix normally comes with a ground also

 

ROry

[Cooperman 0]

You have to gound (earth) 24v AC cameras in our neighbourhood.

 

One thought Rory, if you are grounding an AC camera 'locally', their is a small risk on some installations, particularly on larger sites, that you could end up with earth loop problems. Wherever possible, it is preferable to use 3 core cable back to a common point.

 

Just a suggestion.

[rory 0]

Ok, must be a Uk thing, but its good to know

 

With our 3rd world power we have here, even using a LC or UPS doesnt help, let alone grounding, I've seen UPS's & LC's come out unscaved while the PC's were fried...Just FYI, our power goes off every week, for numerous hours due to failed electric products, just last week we were off for 10 hours in my area. Basically the gov bought cheap products from South America and they fail all the time so our power goes off all the time.

 

Do they have RG59 Siamese cable with 3 power wires??

[Cooperman 0]

Rory,

Ever thought of getting a wind generator

 

Given that the power situation is as bad as you say, don't your customers insist on back up supplies? I would imagine that in retail outlets, there would be quite a high risk of looting stock.

 

I can't say I've ever come across a coax + 3 cores, but then 24v AC isn't that popular over here. 12v DC is far more widely used.

[rory 0]

yes everyone has back up. But they only last so long, normally our power can be off all day, only those that can afford it also have generators.

 

 

The biggest problem though are the low voltage spikes.

 

On that note, im going to do some experimenting with a car battery and an altronix multi output supply, as we have used them with alarm panels during the long hurricane outages.

[Cooperman 0]

If you use 12v DC cameras, then obviously back up supplies are relatively easy. In the past, I've used small groups of 24Ah sealed batteries (usually 3 or 4) for complete system 'back up'.

 

Then if you need to change low batteries during back up operation, they can be replaced one at a time, without taking down the whole system.

They're generally more stable than a car battery which is designed to release a large amount of energy for 'starter' cranking.

Sealed cells are much better suited to constant drain applications.

 

For individiual camera back up, you could perhaps use smaller 9Ah trickle charged cells located close to the camera (simple relay changeover when the mains supply goes off). A bit more expensive, but very reliable.

 

It obviously all depends on the wiring layout, and the size of system.

 

If you're having problems with spikes, have you tried using suppressors / capacitors to smooth them out?

[rory 0]

yes Voltage Regulators, still doesnt help when power goes out.

[rikky 0]

Cooperman,

 

I wouldn't call the earth loop problem 'small'. In fact whenever different groundings are being used image distortion is for sure.

 

Has anyone tried those ground loop UTP baluns?

[Cooperman 0]

rikky,

 

The thing about 'earth loop hum' is it can be as sublime as a very slight interference in part of the picture, to a total scramble with no perceived sync., and therefore no visible picture.

 

It all depends on the difference in earth potential.

 

The worst ones are when it happens at different times of the day, or even changes over a period of time (dry / wet ground can create variable earthing in some remote locations).

 

The ideal situation is when you can predict that it is likely to be a risk, and then design around it. Unfortunately, that takes experience, and even that can't guarantee success everytime.

 

For those who haven't been caught out by earth loop ... I envy you.