Proper grounding of service panel

Old 01-03-15, 02:54 PM
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Proper grounding of service panel

I have a question about properly grounding my service panel. The existing 125V service panel didn't have any grounding bar inside the panel. Most of the house is just 2-wire in metal conduit without a ground wire, but the metal conduit is bonded to the water and gas pipes. The previous owner replaced a couple of the service lines from the panel to junction boxes with NM 2-wire, and connected the ground wire to the service panels neutral bar.

I'm doing a kitchen and bathroom remodel and updating all electrical to those rooms. I will eventually get to the rest of the house, but need to get a proper grounding system for the current work.

As I mentioned the existing metal electrical conduit has been bonded to the water and gas pipes. As far as I can tell, due to the age of the house, there is no grounding system besides the metal conduit being bonded to the water pipes. The water pipe is metal and extends more than 10' into the earth.

I'd like to install a grounding rod, but this is January in MN and the ground is frozen solid. If I add a ground bar in the panel, and bond that to the water pipe on the service side of the water meter, will that be sufficient gounding assuming the resistance test is sufficient? Or is a grounding rod (or two) a necessity?
Old 01-03-15, 04:41 PM
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Welcome to the forums.

If that is your main panel, with a main breaker, then the grounding goes to there. I'm guessing you meant 125Amp service panel ?

You should have a piece of #4 wire.... can be bare or thwn green connected from the combination ground/neutral bar to the cold water service at the point where it comes in the house. There should be a jumper using that same wire across the water meter.

Depending on the age of the service..... ground bars weren't originally required. You can install one and connect it to the combo ground/neutral bar of the panel with bare or green #6 thwn wire.

Electrical conduits should not be connected or grounded to gas pipes. The conduits are supposed to connect to the panel and pick up ground there.
Old 01-04-15, 06:39 AM
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The grounding electrode conductor from the main* panel neutral bus to the water pipe needs to be a continuous run (i.e. the #4. copper wire), not a hodgepodge of metal items such as conduit, junction boxes, and perhaps sections of #4 wire.

If your grounding electrode system from panel neutral bus to water pipe is already in place (may be grandfathered) then actually bringing it up to today's code includes adding a ground rod, with #6 (maximum ever required from ground rods) copper GEC to some point on the pre-existing GES. If you should add more ground rods, say, for radio or TV antennas, these must become part of the GES with #6 copper wire to so bond them.

In the main panel the ground bus bar and neutral bus bar are one and the same, except that if there aren't enough holes, an additional bus bar, jumpered to the first or both making good contact with the panel back, may be used for the equipment grounding conductors (ground wires) of some of the branch circuits.

Gas plumbing needs to be bonded to the GES. One method is running a copper wire (#4 for 125 amp service, it's called a bonding jumper, not a GEC) from a gas pipe to the GEC for the water pipe, although a gas pipe exiting the house underground does not count as a grounding electrode. The purpose is to bond the gas plumbing to the electrical system ground, not vice versa, although it is true that if A is bonded to B then B is bonded to A.

* The panel or box where the first main (master) disconnect is, which disconnect might be the 125 amp top breaker of your load center panel, or which might be a breaker set or switch assembly in a box with nothing else in it.

Last edited by AllanJ; 01-04-15 at 07:08 AM.
Old 01-04-15, 07:09 AM
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Your electrical system is grounded from the transformer not from the water pipe/service.
Your service is grounded by the Grounded Conductor, otherwise known as the Neutral. The steel box of the service is bonded to the neutral via a strap or screw. You can add ground bars if you need more space in the panel, but you do not need a jumper as Allen posted. The attachment screws are good enough.

The conduit is also grounded if it is EMT because it is attached to the grounded metal can of the service.. FMC or "Greenfield" is not listed for grounding unless the conduit is less then 6' and the circuit is 20 amps or less.

A ground rod does nothing for a ground and is for high voltage events such as lightning strikes.

Based on the age of your home everything may be grandfathered in. At one time bonding to the closest water pipe was SOP. Now it is required to be where the water pipe enters the house. The size of the conductors feeding the panel based on table 250.66.
Old 01-04-15, 11:19 AM
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The size of the conductors feeding the panel based on table 250.66.
Yes!! The size of the GEC is not determined by the rating of the main breaker amperage, but by the size of the largest ungrounded service entrance conductor. Generally, a #6 copper GEC to the water service is all that is required for a typical 125 amp service.

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