Circuit card grounding

[PaulD]

Installation for my HAI Omni Pro II emphasized the need to ground the board but I was cautioned to NOT ground it via the ground in a normal 120v outlet. Apparently creates potential probles for ground loops and alternative electrical paths between components which can damage circuit boards. As a result, I ran a seperate ground wire to a new ground rod and everything appears to be OK. I am moving into a new house and will need to repeat the grounding process and I am curious if there is any reason I cannot run a ground wire straight to the same ground rod that my electrical service is using (but not thru the house outlet wiring).

To someone not familiar with the technical aspects (aka...me) of common vs seperate ground rods, it appears that it should not make a difference since the ground rods all all in the same earth. If there is a difference, that impies that there should me some amount of seperation between the rods otherwise you could insert rods right next to each other and create the equivalent of a single rod.

 

[mdesmarais]

Apparently creates potential probles for ground loops and alternative electrical paths between components which can damage circuit boards.

I would think this would be why you WOULDN'T do it. . . only reason I can think of for not using the wall gnd would be lightning protection, or concern that the ground is not a high quality one. I'm very curious to see what answers you get!

Markd

 

[Sandpiper]

As a result, I ran a seperate ground wire to a new ground rod and everything appears to be OK.

Having a separate unbonded ground rod is against code. If you must have second rod, it must be bonded (connected to the first with a #6 AWG wire).

There is no reason not to connect to the electrical ground rod. All grounds in the house is suppose to come back to this single ground point. The main reason for having only one is to prevent damage through the grounds during a lightning strike. Basically, lightning can produce a large voltage difference between the two ground rods, causing your ground wires and anything attached to them to fry. By having a single ground point, any voltage created will be the same throughout the house and no current will flow.

Now, where should you ground.......or should you ground at all? Opinions on this differ all over the place. In my opinion, no one has done enough testing to prove what is the best way. Many alarm panel vendors recommend NOT to ground. Many recommend to ground at the nearest outlet. I have heard that some recommend a separate ground to the ground rod. If it were me, I would ground to the nearest outlet, if the vendor recommended it. Otherwise I'd leave it ungrounded. Code does not require a Class II alarm system to be grounded.

Only one other recommendation. Many times lightning will get to the alarm system through the telephone wiring. I have experienced this many times. I recommend installing a surge protector in front of the alarm system. The ELK 950 does a very nice job. Link here. Follow the vendors instructions when installing.

 

[Sandpiper]

Out of curiosity, I looked up the OMNI II installation instructions. This is what it said:

Ground the controller’s “Earth Ground” terminal to a cold
water pipe or to a 4-foot ground rod to preserve its built-in
transient protection. Grounding method must be in accordance
with the National Electric Code, ANSI/NFPA 70.

They sure leave out a lot of detail. No mention that the 4 foot rod is against code....only 8 foot rods are allowed. No mention that the rod must be bonded to the electrical rod. I would say this is bad advice.

If the gound rods are bonded anyway, why have a separate rod. Just ground to the nearest outlet.

 

[PaulD]

The advice I was given said that grounding directly to a ground rod was the only acceptable means. Other methods such as thru a electrical outlet would void the Omni warentee but I cannot find anything in writing to verify that. The reason given was that a surge might seek a ground via an alternate path which could be via a different circuit card and fry the wire or electronics along the way. In any case, I am using a seperate ground wire that goes straight to the 8 ft ground rod that is used by the electrical system.

 

[Sandpiper]

The reason given was that a surge might seek a ground via an alternate path which could be via a different circuit card and fry the wire or electronics along the way. In any case, I am using a seperate ground wire that goes straight to the 8 ft ground rod that is used by the electrical system.

I hate when that happens. I think I'll run a separate ground wire for my TV, DVD player, microwave, computer, clocks, audio amp, printer, stove............. they all have circuit cards and are right in the way of those surges.