Grounding across 3 panels?

[RichardJ]

Could anyone please comment on the following grounding situation?

There is 1 Main Service Panel and 1 Overflow Subpanel in the same building, and 1 Subpanel in a detached garage.

The Main Panel has its Neutral bar and Ground bar bonded to each other and to the case.
The Overflow SubPanel is directly under the Main panel in the same building, it has its Neutral bar isolated in plastic mounts, and its Ground bar bonded to the case.
The Detached Garage Subpanel also has its Neutral bar isolated in plastic mounts, and its Ground bar bonded to the case.

The connections between the three panels are with 8/3 wire: Red/Black/White/Bare-Copper.

A 40amp 2-pole breaker in the Main Panel is connecting the 2 hot Red and Black wires to the Hot bar lugs on the Overflow Subpanel. The White wire is connected to both panel's Neutral bars, the Bare Copper wire is connected to both panel's Ground bars.

A 40amp 2-pole breaker in the Overflow Subpanel is connecting the 2 hot Red and Black wires through 30 feet of buried conduit to the Hot bar lugs on the Detached Garage Subpanel. The White wire is connected to both panel's Neutral bars, the Bare Copper wire is connected to both panel's ground bars.

First question: Most importantly, is this configuration electrically safe? What dangers are there?

Second question: Is this code compliant? The garage was built in the 1960s, would it be grandfathered under older code?

Any comments greatly appreciated.

 

[iwire]

What about this concerns you?

 

[George Stolz]

It's like reading Stephen King, but nothing happens. It scares the heck out of me.

 

[RichardJ]

I was concerned about the lack of two grounding rods buried 8' deep and 6' apart, bridged with an unbroken run of min 6awg wire, connected to the Ground bar in the Detached Garage Subpanel. Is there a danger to not having this? Since the structure is from the 1960s, is the configuration described in the first post code compliant by grandfathering?

If grounding rods are added, should the Neutral bar and Ground bar in the panel then be bonded together?

Should the Detached Garage Subpanel be fed into a 2-pole 40amp breaker instead of fed into the Subpanel's Hot bar lugs, so there is a Main Breaker to shut off the Subpanel locally since its a detached structure?

Is this also compliant because of code grandfathering from the 1960s?

 

[iwire]

I was concerned about the lack of two grounding rods buried 8' deep and 6' apart, bridged with an unbroken run of min 6awg wire, connected to the Ground bar in the Detached Garage Subpanel.

Well you provided a laundy list of what you have but you did not tell us what you did not have.

OK code wise a detached structure supplied by a feeder needs a grounding electrode system.

It does not have to be two rods, it could be other electrodes.

If a rod is used you can either prove 25 ohms or less to ground from it or you must add another electrode.

The wire between the rods does not have to be unbroken, only the wire from the panel to the first rod must be continuous or spliced with irreversible connections.

Is it unsafe how it is now? I do not believe so, but it sounds like an NEC violation.

If grounding rods are added, should the Neutral bar and Ground bar in the panel then be bonded together?

Absolutely not. Never bond the same neutral to ground more than once.

Should the Detached Garage Subpanel be fed into a 2-pole 40amp breaker instead of fed into the Subpanel's Hot bar lugs, so there is a Main Breaker to shut off the Subpanel locally since its a detached structure?

Your terminology makes it tough, but a detached structure is required to have a disconnecting means either outside the structure or inside the structure closest to the point the conductors enter.

Is this also compliant because of code grandfathering from the 1960s?

I do not know if it was compliant or not at that time.

 

[RichardJ]

Thanks for your reply.

The disconnecting means on the detached structure can then be brought up to code by feeding that Subpanel through another 40amp 2-pole breaker acting as a Main Breaker, rather than how it is currently fed through the Subpanel's Hot bar lugs?

Do you happen to know what year the NEC began requiring the grounding rod or other electrode requirement? Currently this detached structure has none. The Detached Garage Subpanel receives its ground from the Bare-Copper wire in the 8/3 cable running 30' from the main structure in underground conduit. The Bare-Copper wire is coming from the Ground bar in the Overflow Subpanel which in turn comes from the Ground bar of the Main Panel.

Is this configuration dangerous? Up to what year would this have been code compliant?

 

[petersonra]

Thanks for your reply.

The disconnecting means on the detached structure can then be brought up to code by feeding that Subpanel through another 40amp 2-pole breaker acting as a Main Breaker, rather than how it is currently fed through the Subpanel's Hot bar lugs?

Do you happen to know what year the NEC began requiring the grounding rod or other electrode requirement? Currently this detached structure has none. The Detached Garage Subpanel receives its ground from the Bare-Copper wire in the 8/3 cable running 30' from the main structure in underground conduit. The Bare-Copper wire is coming from the Ground bar in the Overflow Subpanel which in turn comes from the Ground bar of the Main Panel.

Is this configuration dangerous? Up to what year would this have been code compliant?

As a practical matter, I am not convinced that the lack of a grounding electrode at the detached structure necessarily creates a hazardous condition. It is however, a code requirement.

Just curious. How detached is the garage? Can you nail a 2x4 between the two to make it a single structure?