Electrical Question

[fxdlryan]

I'm having problems with my builder and building inspector with electrical in my new detached 2 car garage. My house has 2 each 200 amp panels, one of those panels feeds a 100amp subpanel in the detached garage. The building inspector is demanding two separate grounding rods for the new structure (detached garage). Everything I've heard recently, including from my builder is that this creates a floating ground situation and that it should not be done. The building inspector is quoting NEC 250-32, AC, '99 page 86. I don't have a copy of the NEC and the excerpts I find on-line still don't lead me to a very clear answer. Since he's quoting the NEC, I'm guessing this isn't some County requirement. Anyone know the official answer?

 

[twostory]

The building inspector is demanding two separate grounding rods for the new structure (detached garage).

Anyone know the official answer?

Just do what the inspector says to do.

I drove 2 ground rods for my detached garage, which is fairly normal for the US.

Bottom line, this is a cheap, easy request the inspector wants, so why try to fight it?

 

[cw_racefan]

I have 2 ground rods (in series) at my garage, in addition to a ground running from the main to the sub. Note that the ground and the neutral in the sub must be separate bus bars. BTW, I have the exact (down to the 2 200 amp mains, and 100 amp sub) same setup as you. I know this is code in my area, though don't remember which year NEC they follow.

 

[fxdlryan]

Just do what the inspector says to do.

I drove 2 ground rods for my detached garage, which is fairly normal for the US.

Bottom line, this is a cheap, easy request the inspector wants, so why try to fight it?

I'm not trying to fight it, I've heard for years that having grounding rods off of main panels and a sub panel can create a floating ground situation. I'm just curious and I'm asking for enlightenment. My builder actually bought the ground rods and wire already and has them here after the first inspection failed. His thought was the inspector failed it thinking it was a main panel and not realizing it was a subpanel. Looks like they will be installing the ground rods tomorrow. Was the floating ground thing a myth that has been debunked in favor of safer ground rods for every structure or what?

 

[Aceman]

Anyone know the official answer?

The inspector gave the official answer to you? He quoted it chapter and verse. Detached buildings need a grounding electrode. Since it sounds like you didn't stub up a concrete encased electrode(rebar), you'll have to drive two rods instead.

You may be confusing the terminology, in a subpanel you float the neutral with a 4-wire feed.

 

[PAToyota]

The building inspector is quoting NEC 250-32, AC, '99 page 86.

I know this is code in my area, though don't remember which year NEC they follow.

Those are the magic words... Even though there are newer codes out that have changed the requirements, a municipality needs to adopt them as part of their building code. So if you have an area that hasn't adopted them yet you have to build to the older code.

 

[Stuart in MN]

I have a copy of the 1999 NEC. Article 250-32 requires grounding electrodes (ground rods) at each separate structure, but it also requires that all ground rods at all structures be bonded together - you didn't mention that part in your post, but I assume it's what the inspector wants (and it is the right thing to do; if all ground rods are bonded together there's no issue with floating grounds.)

 

[fxdlryan]

I have a copy of the 1999 NEC. Article 250-32 requires grounding electrodes (ground rods) at each separate structure, but it also requires that all ground rods at all structures be bonded together - you didn't mention that part in your post, but I assume it's what the inspector wants (and it is the right thing to do; if all ground rods are bonded together there's no issue with floating grounds.)

The rejection notice made no mention of bonding all ground rods together. If they have to be bonded together, I think that's where things will get tricky. Connecting the two new ground rods and the old ones will require digging up a fair amount of concrete and asphalt, , but it's just one more delay in a long list of delays.

 

[twostory]

Was the floating ground thing a myth that has been debunked in favor of safer ground rods for every structure or what?

This web site can probably answer your questions. It discusses the many ways to wire a detached building, depending on the amp service. It also contains many color drawings.

http://www.selfhelpandmore.com/homewiringusa/2002/accessory/detgarage/index.htm

The ground rods are connected using an unbroken wire to your garage's sub panel. The neutral wiring in your detached garage is NOT connected to the ground in the detached garage. The neutral is only connected to ground at the main service panel (back at your house.)

 

[JohnK007]

Twostory,
What a great website!! Haven't read through it all yet but what little I did read was very easy and understandable. Thanks for the link!

 

[kbs2244]

I am a little light on this, but I think the "floating ground" refers to a set up where you do not hav the netural routed back to the panel but are depending on the rods only for the ground.
In other words, if you only ran the 2 hot wires out to the garage, without third netrual tied back to the ground at the meter, your garage would be "floating."
What the inspector is wanting is a back up grounding in case something goes wrong on the netural wire going back to the panel. If it gets loose or cut, at least you still have grounding in the garage.
Tie them all together and you will be well grounded.

 

[fxdlryan]

TwoStory,

Thanks for the website, I feel somewhat enlightened now. I'll feel better when I get home and look at everything in both panels and see exactly how things are wired up. I wasn't looking to lock horns with the inspector, just to clarify for my own knowledge and not get lit up like a Christmas tree some day, .

You never know who's in the right. A few weeks ago, the inspector was going to fail outside gas line because the gauge was marked in 1/2 psi increments, not 1/10 psi increments, luckily I was there and placed a quick call to the guy who did my gas work. He laughed and said, "Inside is low pressure, you use 1/10 psi gauge there, outside is high pressure, you use 1/2 pound there, is the inspector still there?" Five seconds later the inspector says to him on the phone, "I'm gonna let you slide this time." He put his rejection sticker away and pulled out an approval sticker. In that situation, I still don't know who was right, but being there and placing a phone call meant the difference between a Rejection and Approval sticker.