Grounding at a new location

ldiorio · August 2017

i have a roof solar system in operation now and am going to add 6 new panels at a ground setup

combiner box will be at the panel location
do i need to drive a grd rod and /or run a ground wire back to my E-panel

lou

jonr · August 2017

I would do both.

BB. · August 2017

Local ground to local earth ground rod for lighting path.

6 awg cable from remote ground to home ground, IF you have common power wiring going between. Such ac solar panels to home charger and or ac power from home to remote shed. This is to provide a safety ground to trip breakers and fuses to prevent shocks.

Bill

jonr · August 2017

The ground wire from rod to rod also limits differences in ground potential during a close lightning hit. So less chance of the flow jumping onto your other cables and destroying equipment.

Wbuffetjr1 · August 2017

Sorry for the layman question here, just wanting to clarify....

I drove a ground rod at the panels and connected that to the combiner box with 6awg copper. I then connected the combiner box to the epanel with 6awg copper. The epanel is connected to it's own ground rod with 6awg copper. I did NOT connect the two ground rods together. It sounds like I need to reconfigure??

BB. · August 2017

In my humble opinion. For lightning protection, lightning will only follow the 6 awg for 10-20 feet or so. Beyond that, the earth has a lower impedance (that is the "AC version of resistance). If your distance is longer than that for lightning ground--It really does not matter if the ground rods are connected or not (although, it is probably better. Normally the 6 AWG (or heavier) ground wire is uninstalled and direct buried--That makes for an overall better lightning ground).

For the other grounding reason. This is to provide a short circuit return between the array/out buildings and the main solar power system (DC/AC power). For example, if you had 120 VAC from home to an outlet on the solar array metal frame and there was a short between hot and the array frame, there would not be enough current to trip the breaker/AC supply back at the power building. And somebody could get electrocuted (25 Ohms are higher DC resistance is normal between earth and the ground rod. 120v/25ohms=4.8a which is not enough to trip a typical 15 amp minimum breaker). A short could electrify the metal array structure and somebody could get a bad shock between the metal frame and wet grass or well casing (for example).

Since it sounds like you do not have AC power at the array, there is still the possibility that a solar panel + lead could get grounded at the array and cause a similar issue and a 6 awg between the ground rods would short out the current and the combiner box fuse/breaker could trip in that case if there is a 6 awg tie between the two grounds and you have the battery negative grounded at the power shed/home. Would I dig up a trenched cable run to do this grounding (or re-trench)--Boy, that is a tough one to answer.

One thing that you did not talk about was how lightning prone your area is... If you do get lots of lightning, you should consider installing DC and AC surge suppressors. These shunt the lightning energy from the electrical wiring to the local ground rod. One "set" at the combiner box, another where the DC panel lines enter the home (assuming combiner box is at array and a second power entry at home), and another on the AC output of your inverter/main AC power panel. Midnite makes some very interesting suppressors.

https://www.solar-electric.com/catalogsearch/result/?q=surge+supressor

-Bill

jonr · August 2017

> For lightning protection, lightning will only follow the 6 awg for 10-20 feet or so.

I see sources stating that some worthwhile lightning effectiveness of a buried ground bonding wire extends to ~150 feet. Buried ground radials on towers are limited to ~75 feet, but that's because it becomes more cost effect just to add more (ie, there is diminishing effectiveness but not none).

From a lightning standpoint, it's better to have things like solar panels and well pumps located closer to the house. And if you have to run power to your shop 300' away, consider disconnecting the power when you aren't using it.

Wbuffetjr1 · August 2017

Bill we are at 10,000' in Colorado. Not a ton of lightening but when it is there it always seems close! The panels are ~120' from the solar shed. Solar shed is 30-40' from the cabin. No AC at the panels. I have one midnight surge suppressor installed at the combiner box and two at the epanel (one for AC and one for DC). Sounds like I need to connect the two ground rods.

I have the solar temporarily wired into the cabin via the old generator connection. I ran out of time to get it finalized this trip. The cabin has it's own AC panel and ground rod. Does that ground rod need to be connected to the epanel ground rod as well? Thanks for all the help!

jonr · August 2017

Yes, all ground rods or equivalent should be bonded together.

westbranch · August 2017

I believe there is one poster here that has a long run to his PV s > 200 ft, and his line is in pipe all the way back to the cabin... then he has used a Dryer plug to connect to his house, also way UP in the mountains... the 'cord' is > 10 feet so when he disconnects, he minimizes the possibility of lightning jumping 10 feet through air to the house wiring..

Grounding at a new location

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