Ben, There is a way if the ledge is solid and true. Twice I have done the following with ledge at 18” to 24” below grade. Excavate down to ledge, drill down into the ledge and you will determine the suitability of the following method. Drill for a pattern of many rebar penetrations in to the ledge. Drill to a reasonable depth (as deep into the ledge as you are able) in my case it was based on our drilling tool and bit length capabilities. We used a large sono tube. 42” as a recall, both of these jobs were over 12 years ago and my recall on the exact size may be off. Determine the best adhesive product to use in your drilled holes for the rebar, again my memory fails as to what we used based on recommendation from a local civil engineer. The sono tube height above grade was determined to be 2’ for one TPM12 and 3.5’ above grade for a TPM16. Depth down to the ledge determines how high above grade you need the concrete footing/base. Use rebar lengths that will end a few inches below the finished surface. For grounding you can coil up ground wire and lay it on the surface of the ledge before your concrete pour. I ran the ground wire through a short length of 1/2” or 3/4” PVC conduit, to protect the copper ground wire where it comes out of the concrete. Place the conduit coming out of the concrete with the ground wire just to the side of where the mounting plate base for the TPM will be and fill the PVC conduit with a good caulk sealer to keep air and water out of this hole as a nexus of concrete, and air will corrode the copper. The TPM’s for those two jobs were made of 8” SCHD 80 steel, we had a large plate welded to the bottom with 4 vertical side supports on the pipe up about a foot. Place the appropriate sized anchor bolts in the concrete pour to match your TPM base. Both of these TPM’s have worked out well over the years. Local conditions will determine the suitability of this method.
Sent from my iPhone > On Jun 23, 2021, at 6:39 PM, Ben's Solar and Battery <b...@mcfeeters.net> > wrote: > > Hi Wrenches, > > We typically use SunModo ground mounts with ground screws which we can put > just about anywhere as our screw guy has a rock drill. > We have one customer who is dead set on a top of pole mount array and will > not settle for a typical ground mount with multiple posts. > There is shallow ledge all over her property and we feel that digging > multiple large holes to find one spot where we might be able to get deep > enough would be a waste of time and resources. We have called an underground > locator who uses ground penetrating radar and he scanned a few spots, but was > unable to give us a good location based on soil types. > What are you guys doing in this situation? Are there any alternatives, such > as a pole mount with large base and ground screws? > I hate saying it can't be done! > > Thanks! > Ben > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org > _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org
