When you install a CCTV system, you sometimes end up with these horrible lines across the screen.
Typically the first thing you do is return the camera as it must be faulty, only to find it works fine in the shop or that the replacement does the same thing.
The typical cause of this is an earth loop, where a voltage difference has occurred at one end of the coax cable to the opposite end, with respect to earth.
They can appear as different patterns on the screen or even cause a DVR not to record due to distorted synchronisation pulses. Following are some of the visual effects you may see.
There is no point in blaming anyone for these as they are unpredictable as to when they will occur but are more common where the security camera is installed in a location that has a different earthing point to the DVR or monitor. For example a camera pole is not earthed to the same point as a building where the DVR is. In fact you can get earth loops in many other applications including data as corruptions and audio as a buzz.
There are several practices that will reduce the chances of getting an earth loop but none will prevent them.
- Insulate the camera from the bracketThis involves removing all electrical connection between the cameras metal case and the mounting bracket but is only required if the bracket is on a conductive surface such as a pole or tin.
- When installing the coax cable, ensure there are no nicks in the insulation caused by dragging it over sharp edges or friction burns.
- Where possible, join the earth of both ends together. This is costly as you will need to run extra copper earth cable to each camera.
- Install fibre optic connections to the remote cameras. This can be expensive but does offer other advantages. You have also prevented lightning strikes from going through your entire system, destroying everything. You can put multiple cameras on one fibre.
Having done at least points 1 & 2 above as a part of the normal installation, should you still get an earth loop you can install a device called an earth loop isolator and the problem will magically go away.
These devices are available in various forms including rack mount, DIN mount, surge protected but a good one to keep in the tool kit is this in-line ground loop isolator, which is inserted between the DVR input and the coax going to the camera.
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Option C and D are quite time consuming and expensive. I will go for an earth loop isolator.
Im the perfect world every CCTV installer would have a couple of earth loop isolators in the tool kit as it is such an easy fix to a problem that can appear at any time.
Reality is most technicians have no idea what an earth loop is.
Generally I try to use 24 VAC equipment so no earth is needed and ground loops are quite rare. I a ground loop occurs I go for option A. If there are still ground loops, I will use ground loop isolators.
Hi Norman,
I am working on a site now that has 2 monitoring locations at opposite ends of the building. The nature of the building requires a VERY consistent earthing rail and has copper strips that link every room.
Despite this, we have a earth lop to the 2 farther monitors.
I am yet to install the isolation transformers – Mondays job – but am quite surprised to see the earth loop in this CCTV system.
It goes to show – they can appear anywhere
If the Isolator doesn’t work check to see if the camera is on the same electrical phase I think this is only relevant if they are mains cameras.
I remember have this problem in a plant hire shop that was using a 3 phase mains supply the cameras and VCR were on different phase’s.
isolation transformers were tried but had no effect.
Hi Richard
I have not encountered different phases causing earth loop problems in CCTV myself.
However it does definatally mess up the synchronisation or sequential switchers and matrix switches.
Not such an issue now with IP cameras.