Source: https://www.hdmi.org/spec21sub/cablepower

For example, a camera that has a rated power consumption of 6W (6 Watts) will draw approx. 500mA @ 12V or 250mA @ 24V (W / V = A) – And this is before we factor in the voltage drop caused by cable gauge / length of run / termination resistance, etc. Assuming that we stick with industry best practice which recommends that you do not connect more than 70-80% of the rated load of the power supply, in this example, in order to power 16 of these cameras, you would require a 10A /12Vdc power supply or a 5A /24Vac power supply.

There’s a difference between 12Vdc & 24Vac Supplies (apart from the obvious):

Due to manufacturing complexity, DC supplies can be up to 3 times more expensive than an equivalent AC supply for any given current rating i.e. a 12Vdc 5A supply can be up to 3 x more costly than a 24Vac 5A. In the example above, if we select 12Vdc over 24Vac, we will need a supply that is up to 6 x more expensive (twice the current rating + 3 x more expensive to manufacture).

12Vdc Regulated Supplies:

There are a couple of other things that need consideration – first is that good quality 12Vdc power supplies are designed to deliver a constant (regulated) 12Vdc. You should be able to measure this from no load (nothing connected) through to full load (the power supply rating – eg 2.5A, 5A, 10A) So, cable run induced voltage drop aside, the connected devices should always have a constant (12V) DC voltage supplied to them, regardless of input mains voltage (240V) – note that the mains supply voltage can vary both up and down depending upon location, cabling infrastructure, local load and time of day.

24Vac Supplies:

24Vac supplies on the other hand have no internal voltage regulation, in fact the only time that you will be able to measure approximately 24Vac on the output of these supplies is if two factors are met:

1) The incoming mains is 240V (not 215V or 260V, etc. – as it can sometimes be in certain areas)

AND

2) The connected load is close to (or at) the maximum rating of the transformer (eg 2A load on a 2A power supply, 9.9A load on a 10A supply, etc.)

If output load remains stable but the incoming mains voltage varies up or down, the output voltage will track up and down proportionately:

eg: 230Vac In > 23Vac Out / 255Vac In > 25.5Vac Out

Likewise, (assuming that incoming mains is 240Vac) – if a 24Vac 10A power supply has a connected load of 1.5A (as can sometimes be the case where an installer specifies a 10A supply to cater for future system expansion), then the output voltage can be anywhere between (say) 26V and 28V – depending on transformer quality and design. Now, if the incoming mains rises to (say) 255V from 240V, then output voltage could be over 30Vac – potentially leading to longterm connected equipment damage.

Depending upon the installation requirements, 24Vac power is generally more flexible when it comes to medium to long cable runs – Ohm’s Law tells us that for a given equipment current draw and cable length, the voltage drop over the distance will be similar for 12Vdc or 24Vac – however, if the calculated voltage drop is (say) 2.5V, then the camera connected will probably work satisfactorily on 24Vac, but may not start at all on 12Vdc (24V-2.5V = 21.5V ~ usually within the operating parameters of most cameras, while 12V – 2.5V = 9.5V ~ probably below the minimum operating voltage of most cameras)

The Bottom Line:

While there are a couple of exceptions, if mains voltage is reasonably stable and your cameras can accept either 12Vdc or 24Vac, then 24Vac power is generally the way to go – for both performance and cost effectiveness.

In CCTV camera systems, the distance how far you can run the security cameras depends how far you can run the power cables. There are length limits for both the coax video cable and the power cable. In this article, we will discuss the differences between 12V DC and 24V AC power sources in security camera systems.

Traditionally, CCTV security cameras were 24V AC, but around 2005 the 12V DC cameras started to become popular due to their low cost. Nowadays the majority of HD analog security cameras (such as HD-TVI, HD-CVI, AHD, CVBS) require 12V DC power supply.

The analog security cameras use siamese coaxial cable which, a pair of wires consisting of coaxial cable 75OHMs and 2/18 gauge power wire. However, there are security cameras that take dual voltage 24V AC and 12V DC.

Using a 24V AC power supply and 18/2 gauge the power can run up to 750 feet without any current drop. Using 12V DC power supply the cable can run up to 300 feet at max.

A security camera’s power consumption is usually referred to in milliamps (mA). Usually, the camera’s power consumption is generally around 200-400mA. Things like mechanical filters, infrared IR LEDs, and internal heaters will increase this number and eventually it gets closer to 1-1.5 Amps.

Trying to power a 1.2A camera with 12V DC over a long distance is unfeasible as there will be too much total resistance in the long cable run that adds up to a substantial voltage drop resulting in camera failure.

A common problem attributed to voltage drop is where the security camera works fine when there is low consumption but at night, when the IR LEDs turn on, it stops working completely. Problems can also include hum bars, video distortion, and other symptoms which are often mistaken as a bad camera

Nowadays most of the CCTV and HD over coax cameras use 12V DC. They usually come with an individual 12V DC power supply or can use a multi-camera power supply box. Many higher end commercial grade cameras come in dual voltage, which allows installers to use a 12V DC or 24V AC power supply accordingly to the installation job

The power cable and the power supply (12V DC/24V AC)

It’s possible to run power longer distances if you use thicker gauge cable. For example if you increase the size of the power cable to 16 gauge instead of 18, you can run the 12V DC 380 feet with less than 10% power drop. You can run the 24 V AC up to 1,100 feet.

So the thicker the cable, the less the power drop and the farther the power can be transmitted. However, the good cables can get expensive, you need to analyse the project and find out the right balance between the cost and equipment.

When you plan your video surveillance system, there is a maximum amount of distance you can run your power cable to the security cameras. In this blog, we will elaborate more about the difference between using 24vac power supply for camera vs 12 VDC.

The majority of analog security cameras (TVI,CVI,AHD,CVBS) require 12vdc power. The analog security cameras use siamese coaxial cable a pair of wires consisting of coaxial cable 75OHMs and 2/18 gauge power wire. However, there is analog security that takes dual voltage 24VAC and 12VDC.

For commercial security camera installs it is recommended to use dual voltage analog security cameras. Installers will not have to face any issues of voltage drop that happen from using 12VDC. Using a 24VAC power supply and 18/2 gauge the power can run up to 750 feet without any current drop. However, using 12v dc power supply the cable can run up to 250 feet at max, third of the distance that can be run by using 24VAC.

Regular security camera draws between 0.5 to 1.5 amperes. Pan tilt Zoom cameras require more ampere to run the PTZ motor, ranging from 2-5 amperes.

Thicker Power Cable

Eighteen gauge wire is the most popular power cable for security cameras. Thicker power wire can be utilized to run further distances. The price of thicker wire might not be as feasible as buying a security camera that takes dual voltage and using a 24VAC instead.

The first thing to do is to determine how far the farthest camera from the power source is. If the cable run is less than 250 feet than you can use 12v dc power supply. IF you are running longer runs you might need to consider buying dual voltage cameras, buying thicker wires or higher ampere power supply.