A number of considerations need to be made when designing a cctv
system. Power requirements, distance, cabling to name a few...
Single Versus Multiple Port
If you are running a single camera, or maybe 2 camera security
system, it is probably more cost effective to purchase a single power
supply adapter for each camera. Up to 4 single camera supplies off of a
power strip may work when you are designing this type of system, but
neatness may count for something as well. A single power supply box
offers an effective, attractive solution for multiple camera power.
To fuse or not to Fuse
- DC or AC CCTV Power
CCTV and security systems have until the last 10 years been
primarily 24VAC. Advent of smaller, more compact and covert cameras has
resulted in an increasing number of 12 volt DC installations. Both are
lightly regulated (low voltage) for construction allowing flexible
securty and surveillance installations, and each has its advantages.
- 12VDC requires a smaller footprint for a camera because it does not
require a built in rectifier. though originally adopted for covert
camera applications, it became popular for larger C/CS cameras as it
lessened the manufacturing costs. 12vDC is NOT good for long cable runs
however, and some 12V DC power supply boxes are more costly than their
24V AC counterparts. Also, for some time the 12V DC powered camera was
shunned by many professionals because it was hard to get "in phase" when
installed in a Multiplexed video system. Current Digital video recording
has all but eliminated this problem.
- 24VAC Power supplies are often simple transformers distributed into
multiple ports, or used singly. Advantage is cost in multiple port
systems because of reduced components. 24VAC power performs better over
long runs with less need for heavy gauged wire runs. Most, but not all
outdoor housings which have blowers and heater, require 24VAC. The power
consumption is better handled with 24VAC as well.
- Often, mixed systems exist where both types of cameras are used.
Newer12V DC camera addtions to established 24VAC systems can be
accomodated with the use of power converters. These are simple devices
which regulate a 24VAC voltage to 12V DC. Sometimes the 24VAC to 12VDC
power converter is used when sending power over a distance to a 12VDC
camera. If you need to use these power adapters, allow overhead on the
current rating. IE: 400ma required for a 12V camera could use an 800ma
ac to dc converter. This would ensure the camera does not overload the
converter avoiding potential converter failure.
A typical multi camera security system utilizes a mulitport power
supply, with either glass fused, or ptc (circuit breaker) overload
protection. Fuses are usually preferred, but in many cases the PTC types
allow automatic reset of the fuse once power is removed and restored.
This can eliminate the need to have fuses laying about, and can still be
cost effective. The downside of the PTC design for cctv power is that
they can take too long to react, and may not offer adequate protection
as a properly rated fuse. Also, there are occasions where a PTC will
fail permanently resulting in the loss of a port, which may require
replacement of the entire unit If all ports are occupied). We recommend
using fuses, but if a PTC is preferred, then design your cctv power so
that you have extra ports available.