residential grounding questions

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  #1  
Old 01-29-11, 04:41 PM
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residential grounding questions

Two questions on residential grounding. I tried to use the forum search but was having trouble, so apologies in advance if this was buried on page 3 or 4..

1. I'm installing an equipment rack (relay rack) in my basement for home structured wiring equipment (routers, coaxial splitters, patch panels, etc.). Since there will be powered equipment in the rack, does the rack need to be grounded or bonded to electrical ground?

2. A friend was showing me around their new townhome the other day. When she showed me the utility area, I noticed that there was a wire (I assumed ground) bonded to her water pipe near the water service entrance to the house. Although her home plumbing appears to be copper, the service entrance does not (it was some sort of rubberized piping). Is bonding to the plumbing only allowed if the entrance is also copper, or is the grounding just a "localized" system (i.e. not earth ground).

Thanks in advance. Both questions are relevant to Virginia (Fairfax County to be specific).
 
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Old 01-29-11, 05:02 PM
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Welcome to the forums! The equipment you will be installing will be grounded, so when you bolt them to the rack, the bond is continuous if they are in a metal case. Your friend didn't have a proper bonding to the water pipe if it was plastic or other than metal in the ground. It was worthless. It needs to be grounded back to the panel. If the rack is just something to sit the routers on, like a shelf, then bonding the rack would not be necessary, as it would just be a "shelf unit", and not integral to the equipment.
No problem with the question, as I don't think it has come up before, or not recently, anyway. Others will have their comments, so don't take mine and engrave them just yet. Many good ideas on the forum.
 
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Old 01-29-11, 05:10 PM
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Larry gave you some good info about the grounding of the racks etc.

That may have been a bond wire to the plumbing. Without seeing the whole picture it would be hard to tell.
 
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Old 01-29-11, 05:34 PM
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Thanks for the info, gents!

Regarding the plumbing/ground/bond...it just struck me as odd. I recommended she have an electrician check it out just to be on the safe side. Considering some of the diy-hackery electrical I've seen it was better for her to be safe than crispy. It was in a quite obvious place so I'd hope that her house inspector at least saw it during the walkthrough...but you never know.
 
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Old 01-30-11, 08:42 AM
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In data centers and wire centers, there is a master ground bar (MGB). Depending on the size of the facility, this bar can be a foot long, or three feet long. Often there is more than one, but they are always jumpered in a bus arrangement or with massive conductors.

Commonly, the building ground is in the center of the bar. That conductor provides a direct path to local ground.

One end of the bar is regarded as the "quiet" side, so grounds for electronics relay racks are connected there, from "noisiest" to "quietest". For example, you would have your most sensitive and critical electronics connected farthest out on the bar. Closer to the center you would have less sensitive stuff.

The other end of the bar is "noisy", with AC power ground near the center and UPSs toward the outside.

The idea is that the more frequent transients and fault currents stay as far as practical from the most sensitive equipment.

This is not usually directly relevant to what you do at home, but it's good to keep in mind as you set up your grounding and bonding at home.
 
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Old 01-30-11, 09:28 AM
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Great Info!!

That was some great info. Learned some stuff i never knew. Thanks
 
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Old 01-30-11, 03:39 PM
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Thanks for more great info. Slightly stupid question - how is a residential ground typically provided? Is it a true "earth ground", or just bonded to a ground bus back at the main panel? (referencing post-1984 construction) Thanks!
 
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Old 01-30-11, 05:04 PM
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I think in 1984 either a ground rod or cold water pipe ground was compliant. Today a ground rod and a cold water pipe ground where the water service enters the building is required.
 
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Old 01-31-11, 09:03 AM
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Originally Posted by squib View Post
bonded to her water pipe near the water service entrance to the house. Although her home plumbing appears to be copper, the service entrance does not (it was some sort of rubberized piping).
Even when the water service is plastic pipe, the electrical ground still must be bonded to the portion of the water system which is metal. It just means that your friend's house also must have some other type of grounding electrodes as the plastic pipe does not count as it would in a house with copper water service. Legal electrodes include ground rods, ground rings, Ufer (foundation rebar bond), and a few other things that probably don't apply. If this townhouse is part of a larger building or multi-unit structure it is possible the earth ground is provided at the central electrical panel(s).
 
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