moved sub panel entrance, reuse old ground?

[rvcoaster]

have a detached garage, approx 700' square and 70' from main house. original sub panel in garage is decent (100A main lug, lots of room for breakers maybe 24?) but the feed from main panel to sub panel was horribly wrong (10/3 UF buried 12" under grass). voltage swing leg to leg was 85V/150V when starting larger tools - unusable setup.

i ripped all that out and ran 75' of conduit 27" deep, pulled (3) #4 and (1) #6 THHN from house (SER from main panel to house exit). voltage is quite nice (swing is around 0.1V now). main panel has 60A breaker feeding subpanel.

one of my more bewildering issues (for me) is this: i moved the sub panel in the garage to a different wall to create a straight shot conduit run - if i had ran conduit to where the panel was originally it would have taken 350' instead of 250' (big house) and i would have killed 12 trees digging the trench. a straight shot killed no trees and knocked off 100' however the ufer ground hookup is still where it always was. right now i have no garage building ground (i do have ground run to main panel) and i dont know if its better to run a new ground where the panel entrance is now or run a #6 50' through the wall and somehow legally tap the ufer to the panel.

i'm out in the boonies. my electrician said dont hook up a building ground out here but i lay awake at night worrying. the advice (unofficial) i have gotten locally is to run two 8' rods 6' apart where the panel is now and dont use the existing ground but i tell you what - the ground is intolerable to get through. its like cement; the trench digger struggled and gasped going through this stuff, and there are large rocks down there. i am not seeing two ground rods going much past 12" before massive issues crop up.

can i hook up the original ground by running #6 50' through the walls? i know NEC wants a contiguous run but allows certain connections.

 

[sberry]

It probably isnt worth losing sleep over but you need to hook up some sort of ground, if you have uffer why not use it, run the wire.

 

[Charles (in GA)]

I would set the two ground rods and forget about it. Not worth 50 ft of #6 copper.

Charles

 

[mtne]

50' of #6 might be worth it if the ground is that hard and you don't have a big hammer drill with a cup to drive them.....

 

[Charles (in GA)]

If you do run the wire, it as you mentioned, must be continuous and if you have to splice it, it must be done in an approved manner, most likely by exothermic welding. You can get a kit do exothermic welding at most electrical supply houses.

Charles

 

[Charles (in GA)]

A reminder about Ufer grounds. If you put insulation sheets, or plastic sheet under your slab, you DO NOT have a Ufer ground.................

250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1).... snip .....
(2).... snip .....
(3) Concrete-Encased Electrode. A concrete-encased
electrode shall consist of at least 6.0 m (20 ft) of either
(1) or (2):
(1) One or more bare or zinc galvanized or other electrically
conductive coated steel reinforcing bars or rods of
not less than 13 mm (1⁄2 in.) in diameter, installed in
one continuous 6.0 m (20 ft) length, or if in multiple
pieces connected together by the usual steel tie wires,
exothermic welding, welding, or other effective means
to create a 6.0 m (20 ft) or greater length; or
(2) Bare copper conductor not smaller than 4 AWG
Metallic components shall be encased by at least
50 mm (2 in.) of concrete and shall be located horizontally
within that portion of a concrete foundation or footing
that is in direct contact with the earth or within
vertical foundations or structural components or members
that are in direct contact with the earth. If multiple
concrete-encased electrodes are present at a building or
structure, it shall be permissible to bond only one into
the grounding electrode system.

Informational Note: Concrete installed with insulation, vapor
barriers, films or similar items separating the concrete
from the earth is not considered to be in “direct contact”
with the earth.

 

[oleguy]

the ufer is supposed to be at bottom of footing.not supposed to have vapor barrier there.

 

[kngelv]

If you have a problem with rocks you can dig a trench 8' in length and 30" deep. Lay the ground rod in this. If you want two ground rods then dig two trenches with the requisite distance between them and connect them with a ground conductor. This is required if your house does not have a two ground rod installation. If it does then by code you are not required to drive a ground rod at the garage as long as you have a conductor at your garage panel connected to the house grounding system. However some cities do require one and some do it for piece of mind. Hope this helps.

James

 

[awdblazer]

what about a ground plate? we can use them here in canada
just a thought

 

[rvcoaster]

this does all help, thank you. i still havent decided what to do yet, i guess my first step is to make sure i do have a prior decent grounding system in place rather than a hack job.

this place has gone both ways;some work has been exquisite and some has been just awful. for example the shingles, soffits, drip edge was done to the nines but LB was used as junction box, and conduit from said LB trailed off into thin air. i've found buried NM in the yard (i ripped it all out). the subpanel wiring was beautiful but had the wrong feeder. the garage door openers were installed well but no one had adjusted them until i did so the whole framework was binding when the doors closed. i could go on and on.

 

[rabidsquirrel]

As long as the conduit body has enough volume, it can be used as a splice box.

 

[Charles (in GA)]

As long as the conduit body has enough volume, it can be used as a splice box.

Provided the manufacturer has marked the cubic inch capacity on the conduit body, and the installer has left at least 6 inches of free conductor from the point where the wire enters the body

Charles

 

[Charles (in GA)]

the ufer is supposed to be at bottom of footing.not supposed to have vapor barrier there.

On monolith pours, I've seen the vapor barrier run down thru the footer and up the sides to the forms. Not saying its right or wrong, just that I've seen it done.

Charles