Grounding requirements for a sub-panel

[Nardie]

I am installing a new sub-panel fed from my main house panel. The new sub-panel is a 240V/125A panel without a main breaker, and the neutral and ground bus are connected. I plan on using 2 #2/0 with a #4 neutral and #4 ground. The cable will be direct buried, so no conduit. Do I need to install a ground rod for the new sub-panel, or make sure the neutral and ground bus in the new sub-panel is not connected. I want to avoid having a parallel path to ground thus creating circulating currents. I have looked at article 250.32, and I'm a little confused. Exhibit 250.18 shows no ground rod with the neutral and ground bus separate. Exhibit 250.19 shows a main circuit breaker with an isolated neutral and ground bus with a ground rod. So what should I do. Thanks for the help.

 

[ActionDave]

I am installing a new sub-panel fed from my main house panel. The new sub-panel is a 240V/125A panel without a main breaker, and the neutral and ground bus are connected. I plan on using 2 #2/0 with a #4 neutral and #4 ground.......

Why? If you are going to re bond the neutral what do you need an EGG for? And if are on any code cycle past 2005 the set up you have is illegal.

 

[Ponchik]

Why 2/0? is it for voltage drop?

If the subpanel is in a detached structure then you will need a disconnect and a grounding electrode.

If the subpanel is in the same house structure (2nd floor, garage...) then you do not need the grounding electrode.

For both installations you do need to keep the Neutral and the grounding conductor separated from each other.

 

[Smart $]

There is little point in telling us what wire size(s) you are going to use unless you back it up with your calculated load, maximum calculated unbalanced neutral current, feeder breaker rating, and panelboard rating.

Additionally, you did not state whether or not this subpanel is in the same or detached building or structure. If detached, you need a disconnect as 'edward' noted and a grounding electrode system as required by 250.50, which may require more than one electrode.

The neutral and the grounding system conductors must remain isolated in new installations.

 

[Nardie]

The new sub-panel is installed in a detached structure. The new panel has the ground and neutral bus connected. I didn't drive a ground rod, since I installed a ECG from the main panel. When you say the sub-panel should have a disconnect, it is connected to a to a circuit breaker at the main panel. So is this adequate.

 

[Smart $]

The new sub-panel is installed in a detached structure. The new panel has the ground and neutral bus connected. I didn't drive a ground rod, since I installed a ECG from the main panel. When you say the sub-panel should have a disconnect, it is connected to a to a circuit breaker at the main panel. So is this adequate.

Neutral and ground do not get [re-]bonded. A GES per 250.50 is required for a detached building. If there are no existing qualifying electrodes, you may as well drive and connect two rods (to the EGC, not the neutral)... and the GEC(s) wiil connect in the disconnect located on the outside or nearest the point of entrance. The subpanel can serve as the disconnect if it has a main breaker and located as required. See 225.31 and -.32.

 

[ramsy]

..The subpanel can serve as the disconnect if it has a main breaker and located as required. See 225.31 and -.32.

Does a Main Lug 6/12 circuit sub-panel comply with 225.33(A) disconnect if only full size breakers are installed?

 

[GoldDigger]

It might qualify if there are no more than six breakers.
That is an option for a service disconnect, but it may or may not apply to a feeder disconnect.

Sent from my XT1585 using Tapatalk

 

[ramsy]

It might qualify if there are no more than six breakers.
That is an option for a service disconnect, but it may or may not apply to a feeder disconnect.

I believe 225.33(B) answers my question.

If twin breakers are later added to a main lug sub-panel, "handle ties" can bring operations back to 6.

The service section 225.33(A) refers to 225.30, which includes feeders on the load side.