Grounding - Elk and Altronix Aux Power Supply

[SteveInNorCal]

The Installation Manual is very clear about not grounding the M1 Gold in numerous sections:
 
Page 4, Notes
"3. This terminal (formerly earth gnd) not used. Do not connect any neg terminals to ground."
 
Page 7, RS-485 Connector Note
"This terminal (formerly earth ground) is no longer used. Do not connect this or any neg. terminals to earth ground."
 
Page 11, Earth Grounding
"Tests have determined that the best results against lightning and transients are obtained by isolating the control from ground. Do NOT connect any of the terminals, especially the Neg. terminals to earth ground."
 
However, when I get to page 67, Appendix F - Regulatory Agency Statements, the instructions regarding auxiliary power supplies say: "Connect Negatives of both supplies together," i.e. jumper from the Elk M1 G ground on the RS-485 data bus to the negative on the  auxiliary power supply.
 
The AC supply to my Altronix auxiliary power supply is grounded, but I'm not sure if the -12 VDC on the Altronix is grounded. Consequently, I'm not sure if I have ground passing through to the Elk -12 VDC.
 
Everything is operating fine. Do I need to worry about a possible grounding of the Elk -12 VDC through the Altronix PS?
 

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[CORT]

You are discussing two different matters: AC ground on one hand and 0 volt DC on the other.  The point is that you want the power supply of the M1 to be at the same relative 0VDC as the accessory power supply.  To accomplish this, connect a wire between the negative (or 0 volt) DC terminal of your accessory (Altronix) power supply and the negative DC terminal of the power supply feeding the M1.  Please ask if you have more questions.

 

[mikefamig]

To add to what CORT said above -
 
You need to distinguish between earth ground and "common" reference on the Elk 12vdc power supply.
 
The M1 has it's own 12vdc power supply and voltages measured on the M1 are measured in reference to a common "-" point in the 12vdc circuit. This "common" may or may not be connected to earth ground.
 
Your 120vac source in your house is an earth grounded system. In the 120 AC outlet there are 3 conductors, line, neutral and ground. Your power transformer also has 3 plugs - line, neutral and ground which are connected to the 120vac system when you plug it into the AC outlet. So the 120vac to 16vac power transformer is earth grounded. This is not only correct but required by code.
 
Now think about the two wires between the power converter and the M1. This is 16vac and one wire is line and the other neutral. This has to be true for the ac current to flow. There is no third earth ground wire. In an AC system the neutral and ground wires ARE connected together at the load center so technically the neutral wire is eventually connected to earth but this is not what elk is referring to.
 
After connecting the 16vac to the M1 control,the control steps the 16vac down to ~12vdc to supply the security system and accessories. This is the power supply or circuit that Elk wants you to isolate from earth ground.
 
To make a long story not get longer, you do not want the "-" common reference on the M1 12vdc control connected to earth ground. As long as you use the Elk branded power transformer and don't make any connections from the control to ground then you are good.
 
I'm not an electrician and I did my best to explain this as I understand it but you guys can feel free to correct me if I'm wrong. It wouldn't be the first time and we all know that you can't believe everything you read on the internet.
 
Mike.
 
EDIT:
 
When you have an auxiliary power supply you do want to connect the "-" common of that second supply to the "-" common of the M1 control power supply.

 

[Del91574]

To simplify and clarify a couple of errors:

Altronix's AC portion is connected earth ground (bonded to the electrical ground for the house)
 
Elk is only made common to the DC voltage portion of the Altronix and electrically is floating to earth ground (no connection)

You make the Elk and Altronix's DC negative common by bonding the two which eliminates any potential voltage differences. Not really necessary all the time, but should be done as a "best practice" and absolutely necessary if powering anything on the data bus.
 
The COM or - DC terminal has ZERO potential voltage to earth ground.

 

[SteveInNorCal]

Thanks, everybody. I have the 12 VDC Neg on the Elk RS-485 bus connected to the Altronix 12 VDC Neg terminal per instructions. The Altronix 120 VAC side is connected to Hot, Neutral, and Ground. The Elk transformer is plugged into H, N & G, but provides 16 VAC Hot and Neutral to the M1 Gold unit. I am good to go.

 

[mikefamig]

While we're on the topic of the power supply, I have a question.
 
I have a p212s  auxiliary power supply in my system and I have the common connected between the power supply on the control and the p212s. When I look at the status screen in elkrp the voltages reported on the zones connected to the control are 7.3vdc v and the voltage on the zones connected to the p212s are 7.3vdc but the voltage of the supevisory zone on the p212s is 7.0vdc.
 
It doesn't seem like a problem but does anyone know why there is a voltage drop on that one zone?
 
Mike.

 

[Del91574]

I just looked at my 212s' and I'm running at 7.1V
 
It's a pseudo point driven from the supply itself to supervise the unit, not a physical connection per se and the system responds based on the 3 states of the zone as to what is going on at the unit. The 212 has basically the input/output section of a KP built into it, so it's not an actual representation of system voltages on an input.

I'd say you're looking at manufacturing tolerances of +/- 5% which is pretty tight for most resistors.