[roycemek]

I'm relocating and putting a new 400A meter main / service entrance (Milbank M400 feeding 2 200A subpanels) on the side of the new garage I'm building and I wanted to find out some information on what and how many grounds are needed? I've read for my area a ground connection is needed to the cold water pipes within 5 feet where it enters the main dwelling. What other grounds are needed aside from this one. Do I need to also drive in a ground rod? What exactly is a ufer ground and will that be needed where we are digging for the new footings?

Two other questions, a little of topic but, if I am to use the Milbank M400 400A meter main is it OK to pair it up with 2 Square D 42 sircuit subpanels or will I need to use Milbank subpanels since that is what the main service entrance is? The layout for the new electrical service is the meter main / service entrance is located at the rear of the property on the side of a detached garage and the proposed house subpanel is located approximately 60 feet away. Will either of the subpanels require an additional 200A breaker (The Milbank M400 will have 2 - 200A breakers already)?

Thank you for any and all your help.

Best regards,
Royce M

[tkrussell]

My answers are in bold to your questions:


How many grounds are needed?
As many as needed to achieve 25 ohms or less. The lower ohms the better.


Ground connection is needed to the cold water pipes within 5 feet where it enters the main dwelling.

This means no farther than five feet away from the building entrance, and, of course must be a metal water system. This is typical for utility suppled water, and if it exists, must be the main grounding electrode.Also, if you do have a metered water utility, the meter needs to be jumped with the ground wire. This means to connect the ground wire twice once on each side of the meter. The will allow the water meter to be serviced by the utility workers and not worry about breaking the ground path. many utility workers have been shocked from normal or abnormal ground fault currents flowing in the ground wire.

What other grounds are needed aside from this one. Do I need to also drive in a ground rod?

If a water system electrode exists, it will be considered as the primary electrode, and must be supplemented with any other type of grounding electrode, typically a ground rod, or more than one, to achieve 25 ohms or less. If more than one rod is needed, each rod must be a minimum of 6 feet away from any other rod.


What exactly is a ufer ground and will that be needed where we are digging for the new footings?

A ufer ground will connect to the reinforcing bar in a poured concrete foundation, which will use the surface contact of the concrete to earth as an electrode. This can be used as a secondary electrode if desired, along with the water ground and rods, but cannot be used alone.

If I am to use the Milbank M400 400A meter main is it OK to pair it up with 2 Square D 42 circuit subpanels or will I need to use Milbank subpanels since that is what the main service entrance is?

No , you do not need to use a Milbank panel, you can mix brands of equipment, which is done on almost every service out there. not all manufacturers make all the equipment necessary.


Will either of the subpanels require an additional 200A breaker (The Milbank M400 will have 2 - 200A breakers already)?

No, neither of the panels will require a main breaker since the required main breakers will be located at the service entrance meter location. The panels may have a "main" breaker in them if desired.

Since the main breakers will now be remote from the panels, be sure to use a four wire system from the mains to the panels, the fourth wire being a separate equipment ground to each panel. At each panel, keep the neutral insulate and isolated from the equipment ground.

You should check with your local inspector for any special codes or requirements on grounding. Soil conditions vary greatly and many areas already know the quality of grounding and may have certain requirements.

[roycemek]

Thank you TK for the info. I didn't really think about the jumper at the water meter but now that you mention it, it makes good sense.

Just a few more questions on the ufer ground. A couple guys have mentioned to me that when installing the ufer ground they would get a 25ft long piece of continuous copper and tie that into the rebar in the footing and use that. Others have mentioned to not waste any money on the copper and user the rebar directly which comes only in 20ft continuous pieces. And another website lists to not use copper at all as the ufer ground because of the way it would interact with the steel when tied to the steel rebar. What is your opinion on the ufer ground and how to install it? If I'm installing a flush mount meter main can the ufer ground stub up come up vertically through the footings so that it remains within the wall or does it need to be external to the footings and outside the wall?

This might be a dumb question but how do you measure resistance on a ground (25ohms or less)? I know how to measure resistance across two electrodes with a multimeter but in the case of the main grounds one side is the ground and the other goes to where?

Thank you TK I really appreciate all your help.

Best regards,
Royce M

[tkrussell]

Ufer grounding electrodes is a regional issue. We do not use this method very often in New England, with exception to large commercial or industrial buildings.

Connect it with a copper wire as long or as short as necessary to hit the rebar, assuming the rebar is all connected through out the foundation.

The connector needs to be rated for direct bury, and any coating on the rebar needs to be removed, and the copper cannot come in contact with the steel and the rebar. For these reasons Ufer grounding can be difficult, and many times become ineffective.

The best connection is a CadWeld connection, where the metals are literally welding together by a special process. This method is not for DIY'ers, due to the special costly molds that are needed.

A connection to the utility water ,and supplemental ground rods is usually enough.

Measuring the resistance of a grounding electrode once was a mystical science using what is called "3 point" or "4 point" ohm meters, until recently with the invention of a relatively new ground resistance meter which clamps around the main grounding electrode conductor, similar to an Amp Probe.
To review some of the instruments available, visit a popular manufacturer, AEMC

Measuring grounding resistance cannot be done with a multi-meter. And the instruments I have shown cost several thousand dollars. A quality electrical contractor may have at least one of these instruments, however due to the cost, and lack of knowledge and/or concern many will not have these.

If a contractor cannot be found in your area with any type of ground resistance meter, look for an electrical testing firm associated with NETA ,Tegg, or some other 3rd party testing agency.

[roycemek]

Thanks TK. The ufer ground seems more involved than I thought.

Regarding the utility water ground connection, I was told that it must be connected a max of 5 feet from where it enters the main dwelling. I've gotten a couple difference responses regarding my particular situation for where this needs to be and maybe you can help me understand this a little better.

Basically what I have is the main dwelling at the front of the property and a detached garage at the rear of the property. The main water meter sits on the street in front of the main dwelling and from it a 1" copper line runs to the house. At the front of the house the 1" main copper line is T'd at which point one end feeds the house and the other goes directly through the center of the house (via the crawl space) exits the house at the rear and goes down into a trench to eventually come up again at the front of the garage and into it to feed the bathrooms within. My question is, can I connect the main cold water ground at a point directly in front of the garage or do I have to run conduit all the way to the front of the house and connect to the water line there? The meter main I'm putting in is mounted directly above the entrance where the water enters the garage so having the ground there would be very convenient.

Thanks,
Royce M

[tkrussell]

You can connect to the water line outside of the home at any point, as far as the National code is concerned. Check with the local water utility and electrical inspector just to be sure of any local issues.

The "5 foot max" inside is intended to not allow a connection to a metal water line as an grounding electrode beyond 5 feet away from the point on entry into the building to eliminate the possibility of encountering a fitting that will prevent continuity.

Check with your water utility, they may be taking care of jumping out the meter, since it will be located outside the home, and they probably are responsible for it, and it is not practical for the electrical installer to jump the meter out.

Since the water line will be close to the detached garage, any panel there will need a grounding electrode, grounding only the equipment ground bar, since the neutral will be insulated and isolated, connecting to the water may be convenient for that building also.

Re-reading your question, just to be sure there is clear understanding, the grounding electrode conductor must start from the enclosure that contains the main service disconnect switch, and go directly to a grounding electrode. You cannot just come from any panel that happens to be close to the water.