# How to properly calculate a power supply unit for multiple analog cameras

We have acquired four Intervision-xp-964ec analog cameras for a company. They were without power supply units, just devices.

The cases of cameras says: 12V (max 420mA).

We tested them with a laboratory power supply unit, they are fine.

Now we would like to connect them at different places, maybe even outdoors. The most obvious way is to purchase four 12V 1A power supply units and connect them to 220V power network, but an electrician stated that having 220V cables running outside is not the safest, and he would like to avoid it.

It was suggested that I should order a single power supply unit, which has to be installed indoors and then all four cameras should be connected to it by long wires (up to 150m maximum, I think.)

From school, I remember that if you connect devices in parallel then they shall have the same voltage, but the current (measured in amperes) will be divided. I suggested that in this case it may be fine to order a 12V 4A power supply, but the electrician warned that there may be some losses in the cables during transport.

Which power supply should I order to effectively distribute power to four devices each of which may consume 12V 420 mA and they may be located at maximal distance of 150m away from the general power supply unit?

The distance may be different, a camera may be placed right in couple meters away from the power supply, or it may be located at 100m-150m away from it.

• This sounds like electrician naivety or BS: But an electrician stated that having 220V cables running outside is not the safest Nov 2, 2021 at 10:51
• That's what I was told and I have to deal with that. Nov 2, 2021 at 10:59
• Sure running mains outdoors may not be the safest thing but it can be done. Power supplies need to be rated for outdoors use as well, unless they can be indoors right near the camera. Running 12V at 5W for 150 meters also may not sound like a good idea. You need outdoors rated cable, thick enough wiring to not have too much voltage loss, which you don't even know how much you can have. You might also need fuses so that a short at the camera end does not melt the wires if power supply can push a lot of amps. More hassle than four separate supplies. Anyway, this is a product usage question. Nov 2, 2021 at 12:44
• Mains voltage wires are run outside all the time, they just put them in an appropriate metal or plastic conduit pipe. Nov 2, 2021 at 14:39
• If you have each device located 150m away and run separate power lines to each one, you would need at least 8AWG wire for each (2mOhm/m) to stay under a 1V drop. The total run of 300m would still drop 0.9V. Can't even guarantee the cameras will work with an 11.1V input. You could, theoretically, get a 48V power supply, and run 48V to 4 DC/DC converters at the point of load and convert to 12V for the cameras from there. Nov 2, 2021 at 15:27