Saturday, December 14, 2013

How We Installed a new 480 Volt Electrical Service

Installation progression clockwise from top right.

Have you ever seen a 480 volt, three phase arc flash?

I haven't, and I don't really want to either.  Luckily there was no risk of an arc flash during this project because the power circuit can only be completed by the electrical company, after the final inspection.  I found a youtube video of an arc flash, but there was nothing but safe operating procedure during the installation of a new 480 volt service.

The most important skill of constructing a new service is the installation of anchor bolts in the concrete.  Uni struts, service panels, trans-sockets, gutters, and rigid conduit are all held in place by concrete anchors.  With the correct hammer drill, the installation is quick and the result is robust.  The anchor bolts hold thousands of pounds of equipment in place, and allow the force to be transferred into the concrete and down to the ground.

Top left: drilling into the concrete; Top right & bottom left: hammering the bolts into the wall; Bottom right: the disconnect mounted with anchor bolts.
Clockwise from bottom left: coring holes into the concrete wall, installing nipples through the wall and into the service panel, hanging strut above the service panel, applying red fire caulk around the nipple, and bolting a junction box to the wall.
Coring through the concrete wall allowed for the threaded nipples to connect the outside panels and conduit to the inside panel and conduit.  The gap between the nipples and the concrete wall is filled with expanding spray foam, and fire caulk.

Left: Ninety degree Left Back electrical fitting, Right: the rigid four inch conduit with exposed threads.
The conduit from the gutter, or horizontal enclosure, to the ninety degree turn through the wall is four inch rigid conduit.  This conduit screws into the electrical fittings, but given the coarse threading, some threads are left exposed.  Of course exposed threads will rust quickly, so grey spray paint is applied to all threads.

Left: The finished interior service panel, Right: The exterior tans-socket.

The electrical drawings.

While we finished the installation with great results, and the final inspector said he liked what he saw, there were some bumps along the way.  The first snag arose when the electrical drawings were marked by the city in red, as if the old service needed to be removed.  The intention was not to remove anything, but simply add a new supply for an electric motor.  A call to the city cleared up the confusion, but each service must be labeled so that firefighters understand there is more than one supply to the building.

Left: The original, inadequate, neutral kit.  Bottom Right: Stepped back neutral lug.  Top Right: Correct neutral kit.

The second issue was a hardware incompatibility.  The larger of the two outside panels was supplied with an inadequate neutral kit.  600 volt wire is larger in diameter than 500 volt wire, but the neutral kits were designed for the smaller size.  Instead a stepped back neutral lug was ordered from the supply company, but these didn't work either because the large diameter wire couldn't make the sharp turn necessary to terminate.  We finally used a side by side lug that easily terminated the neutral wire.

Left: I am drilling a hole for the eye bolt anchor.  Top Right: Eye Bolt anchor above rigid conduit.  Bottom Right: Eye bolt anchor above the weather heads.

We didn't forget the eye bolt anchor to support the heavy conductors from the power company supply line.  A cable will travel from the eye bolt to the wooden pole, and the conductors will be supported by something other than the weather heads.  I drilled a hole, inserted the eye bolt through the wall, and tightened the nut on the inside with a square washer to distribute the force of the heavy electrical conductors.  A little silver silicone around the eye bolt will prevent any water infiltration.

Of course the project was drawn by an electrical engineer, and the installation diagrammed and foreseen by the master electrician.  I learned a great deal, and I have attempted to sketch out the procedure here.  The project only went as smoothly as it did because of the foresight and experience of the master electrician.  Nothing is more frustrating than a project that is mismanaged, or is fraught with endless unforeseen set backs and mistakes.  The master electrician even found mistakes in the drawings, and had he followed them blindly, the project would not have been completed.

 While it would have been more interesting to report electrical explosions, or other disasters, there was none to be seen.  Instead we are left with an example of fine tradesman-ship, and the luxury of many years of experience that a skilled tradesman brings.