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dragonash
04-11-2009, 12:29 AM
Ok, hers the deal.

My parents have a security system in their place of business. The system no longer works and the reason being....and this was stated by the installer "The wires reversed polarity"

that doesnt make sense to me. I know about outlets being reversed, but thats human error.

I think this guy is BS'ing everyone and I KNOW he is overcharging them. Good thing my parents never listen to me ~_~


Anyway, they have a standard standalone DVR security system with a powersupply (like these http://www.securitycameraworld.com/accessories-Power-Supplies.asp)

However, electricity is not my area, so it's possible he might know something i dont.
I tend not to trust him when he was blaming the network I setup for the reason as to why remote access to the cameras didnt work. (he happened to setup the wrong port on the DVR system itself) Thats just some reasoning for not trusting him... that and the price AND the fact that he took back the powersupply without me seeing it.

I wonder if he even grounded it!!
Anyway.... can wires (yes, just wires) get reversed polarity and blow out the powersupply?

Saboteur
04-11-2009, 12:45 AM
Perhaps today's XKCD was more than just fiction!

http://imgs.xkcd.com/comics/urgent_mission.png (http://xkcd.com/567/)

The alt-text of the pic reads:

Sure, we could stop dictators and pandemics, but we could also make the signs on every damn diagram make sense.

Wes
04-11-2009, 01:26 AM
Those security systems run on 12V DC, sometimes with a battery backup inside. In order to "reverse polarity", someone has to open up the box and somehow using the red wire connect to the negative and the black wire connect to positive. That could burn out the power supply or the circuit board.

Freightliner
04-11-2009, 05:02 AM
Yes Wes, that's true, but it would do it in a flash, not over a period of time.

If you are talking about the wall socket that the PS is plugged into, that's a yes and no answer. If the "polarity" of the 120v receptacle is reversed, it may or may not work depending on what it is. A vacuum cleaner would work, SOME electronics would not, depends on how well the company that made whatever you are plugging into the wall. The wall socket has a "hot" wire and a "Neutral" wire and the Ground. Notice the wall plug has one slot longer than the other? that's so you can not reverse the plug, or the device you are plugging into it. This is to protect not only the device but you as well.

Could something get damaged from a spike if it is reversed, yes, it can also get damaged from a spike if it is wired correctly.

A stand alone power supply will often alert you by audio or a light or both if the polarity of the wall socket is not correct and will not work from the get-go. And there is no way the wires inside the PS could be reversed unless someone just replaced the battery and screwed that up big time.

No. if you hook up a device that requires power, 12VDC from this control box you linked, it just simply will not work. The only way you could damage the box would be to have the positive and negative wires touch each other, another words a "short" but that should blow the control fuse and not damage anything.

Wes
04-11-2009, 10:20 AM
No, for the security system, the power supply is simply a power supply. Reversing the wire in the 120 side won't do a thing.

Ninjahedge
04-11-2009, 01:07 PM
That does not make 100% sense when we are talking 120V AC current coming from the wall. The polarity cycles sinusoidally. Only after conversion will it be DC and be a major problem....


But I have never really heard of anyone having a huge problem with flipping the plug....

I do remember there being some problems with unidirectional circuitry and hooking it up "backwards" in regards to electrical potential....but nothing like this.

BTW, him talking about the wires magically "reversing polarity" is BS, but are you hearing that directly from him, or through your parents? If your parents are not familiar with electronics, word of mouth can get pretty interesting!

dragonash
04-11-2009, 09:50 PM
yeah, i figured the guy was bsing my folks.

there was a fire at their place of business over a year ago and coincidently, the cameras went out. They dont know if it was because of the fire or not. Maybe the water from the hoses....but still.. it didnt make sense. The guy TOOK the evidence (the powersupply) and I suspect was trying to milk them for new parts.

Little did he know that myt parents are lazy and didnt care lol. Now that i heard they want to enter another "deal" with him for a newer system, I told them to stop.

I know he is overcharging them an easy 5x the amount for the standalone dvr system. And I am betting that all the wires are working perfectly. The cameras just have 2 wires coming out from them.

1 coax cable that has a special termination to attach to the dvr system
1 wire that terminates to the power supply (the red and black wire)