Friday, July 9, 2010
Electrical services in rammed earth
In one of the recent posts I pointed out the electrical conduit in the concrete foundation. Now, with the wall forms in place, the next step is to mount outlet and switch boxes against the face of the forms in the specified locations. The boxes are heavy gauge sheet metal, strong enough to resist deformation during ramming. They are also deep so that the conduits can enter the boxes far enough into the wall to allow space for the rammer heads between the conduit and the wall face. Purchased from an electrical supply house (not Home Depot), they are called "Deep Masonry Boxes" (DMB) ; singles for outlets and single switches, doubles, triples, or quads for multiple switches.
One of the principal challenges, besides getting the lay-out right in the first place, is securing the boxes tightly enough against the form face that they stay square when being rammed around. We've worked out a system, through trial and error, that seems to work quite well. Two people working together make this job much easier.
First, we cut wooden "locator blocks" the exact dimension of the inside of the DMB. (The blocks must be cut on a slight bevel on all four sides so that they will extract from the boxes once rammed.) Secure the blocks to the form face in the precise locations for the outlet or switch. The way to do this is first screw them from inside the form with 2" screws. Then, from the outside of the forms and using the tips of the protruding screws as your indication of where the block is, have your helper screw the block from his side, this time with 1-1/4" screws. Now, inside the form, take out the 2" screws and feed tie wire through the back of the DMB and through the two small holes made by the 2" screws. Have your helper pull and twist the wires so that the box is around the block and tight against the forms. Use a short stick or cut-off conduit between the twisted wire and the form so you can cut the wire once the wall is rammed.
After all the boxes are secured against the forms, the next step is completing the connections to the conduits that extend from the foundation. I don't have photos of that yet, but I'll try to cover it later. We're through work for this week. Khyber and I have meetings relating to an upcoming project on Monday and Tuesday, so look for the next post on Wednesday. Edward will have all of the soil blended and water conditioned. Rigo will finish buttoning up the forms and set the catwalk. We'll try to ram on Thursday.
The photos in this post show Jack preparing the boxes with terminal adaptors and grounding pigtails plus one photo from inside the formwork where three boxes are in place against the form face and the other photo of the tie wire and conduit cut-off holding the boxes tight.