Grounding a sub pannel

Do whatever you want. If you burn the house down you can start over.

A good question...you might want to check with a professional in your area.

Here grounding of the neutral conductor is only allowed at the main service disconnect. The subfed panel is grounded through the grounding conductor that runs back to the "main" panel and the bonding screw in the sub fed panel that bonds the neutral conductor to the ground bus must be removed.

An extra set of ground rods at the two buildings could also generate a "ground loop" current.

Will be interested in hearing the opinions/experiences/practices of others in the group.

Fred

There needs to be one system ground at the service entrance. Sub feeders to subpanels need a grounding conductor that runs back to the system ground. They should not have their own ground rod. Under certain circumstances (metal conduit or raceways), the raceway may serve as this grounding conductor. If non metallic feeder cable or conduit is used, a separate grounding conductor must be provided from the sub panel ground bus back to the system ground at the service entrance.

| I am doing th electrical on my brothers new house.... here is the question? | the main pannel is a 400 amp pannel and then a set of 200 amp breaker to the | house from the 200 amp breakers 65 feet to a disconect and then 65 feet more | to the 200 amp sub pannel .....

Your wording for this is not clear to be 100% certain I can visualize exactly what the situation is.

Is the 400 amp panel in the same house as the sub panels?

Which of these is true:

1. There is only 1 200 amp subpanel and some branch circuits originate in the 400 amp panel.

1. There are 2 (or more) 200 amp subpanels, but also some branch circuits originate in the 400 amp panel.

2. There are 2 (or more) 200 amp subpanels, and NO branch circuits originate in the 400 amp panel.

Are both 65 feet sections of feeder inside the house? Or is one or more of them outside (maybe between buildings)?

A pictoral diagram would help. Another method to better describe things is to sequentially list the components encountered in exactly the order starting at the service feeder coming from the utility presumably going to a meter first.

| the question is does he need to run a ground wire or ground the pannel with | a ground rod and both a ground rod and a 4 gauge ground wire | and is 4 X 4 ott and a 2 ott aluminum wire large enough to do this | project....

The general description is this. There needs to be a bonding point that bonds the neutral and the grounding wire (EGC) somewhere between the meter for the service entrance and the first disconnect (which could be the main in a main breaker panel if that is the first box the service feed goes to after the meter). That bonding point is also connected to the grounding electrodes (I recommend always at least 2 electrodes, even if the quality of the electrodes meets the requirements that allow 1).

From the bonding point all feeds and branch circuits must carry a grounding wire (EGC) that is separate from the neutral (some circuits may not have a neutral, but would still have the grounding wire). Subpanels in a separate building must have the grounding wire connected to grounding and MUST NOT bond the neutral to the grounding wire (and therefore must have separate bus bars for ground and neutral with the neutral bus bar insulated from the matallic enclosure). I recommend even the main panel be wired with this practice (separate bus bars, neutral insulated) even though it would not be required if it contains the bonding point.

If you have a separate disconnect between the main panel and the meter, then the bonding point must be in that disconnect and the main panel must be wired like a subpanel.

Under certain circumstances that I don't know much about, you may ground and bond two (maybe more, I don't know) parallel main panels together. I believe they must be close to each other for this to be allowed. It's done a lot so I presume it is allowed, but I don't know the details. But it also seems you are not taking this approach, anyway (I wouldn't).

If the construction involves metallic conduit or metal armored/clad cable, and specific branch circuits will be used for life support equipment, computers, or sensitive media electronics, I recommend including in these circuits an "isolated ground" wire, which is a separate grounding wire not used to grounding the metallic points that the primary grounding wire would be doing, and use "isolated ground" type receptacles, with these branch circuits originating from the main panel even if that means a long branch circuit run. That "isolated ground" wire will usually be a green wire with a yellow stripe to identify it apart from the main grounding wire. Such a circuit should also be available at the point where Cable TV and telephone wiring enter the house (which should be very close to the main electrical entrance for common grounding).

I also recommend any "3 wire" circuits (dual voltage), which are usually found serving kitchen ranges and laundry clothes dryers, also be fed directly from the main panel (regardless of the conduit/cable type).

I recommend not using any shared neutral circuits. But if you are already committed with some, I recommend these originate from the main panel.

Assuming this is a 208/120 volt 3 - phase 4 -wire grounded system (your description is a little lacking )

On pulling in an equipment grounding conductor - if you are using metal pipe or if there is any metal conductive paths from the house to the sub panel then you are required to pull in the grounding wire sized per NEC Table 250.122 and bond this conductor to a suitable grounding electrode at the second building. If there are no conductive paths then you can bond the neutral to a grounding electrode conductor and to the grounding electrodes like a service. A grounding wire of size No.

On using 3 - 4/0 ungrounded conductors and a 2/0 neutral. The neutral has to be sized to carry the unbalanced loads or must be sized the same as the ungrounded conductors if the majority of the load is nonlinear like electrical discharge lighting and computers. The general rule is to not down size the neutral if you do not know what the loads are going to be. For residential work, downsizing the neutral one or two sizes is common and allowed.

These are general considerations and do not take into account all code rules that may apply. You should hire a professional.

I dont want to burn it down that is why i am asking for help .... if you do not want to help shut up