This week ended with two inspections scheduled for Tuesday, 09/07/10: PG&E will perform the ‘mandrel inspection‘ and the City of Monte Sereno will inspect our mounting system and rough electrical for our solar photovoltaic panels. We scheduled these inspections because we installed our 400 amp combined service entry device (400 amp electric panel) and all of the conduit and electric cables for the solar photovoltaic panels were run through to the appropriate points on the roof.
Bryan was confident that the weekly project review meeting tonight would go reasonably well. Especially since he put two (2) bottles of Rombauer Chardonnay (Carneros 2008) in the fridge to cool …
Completing the Geothermal Ground Loop
The two-person team from 88HVAC, Justin and Michael, completed the test of our ground loop today. Of the 25 concrete piers that go 30 feet into the ground with two U-tubes in each pier, we had one U-tube that failed (low water flow). We could not solve the problem so we abandoned this U-tube and continued to connect all of the other U-tubes.
Bryan spent some time with Justin reviewing his recommendations for the valve configuration for our geothermal ground loops. Justin presented several alternatives and they discussed each one. The conclusion is that we will have copper pipe inside the house going to the underground concrete box in the North West corner of the house. From this box, there will be HDPE pipes going to the four sets of concrete piers on the East and West sides of the house.
Although the copper materials have a higher cost, the labor cost will be the same or less to install the copper fittings. Given the valves to isolate and control the water flow, copper fittings will have a smaller ‘footprint’ inside the flush mount concrete box. The copper fittings will have a cleaner and simple layout and finish.
Background on Our 400 Amp Electric Service
We will have a 400 amp underground electric service. Some people have asked, ‘with such an energy efficient house, why do you need a 400 amp service?’ The short answer is that there are code requirements that are a function of the size of the building footprint that determine the minimum amount of current that a house requires. Since we do not have any natural gas coming into the house, we have electric cooktops and electric clothes dryers. Although the calculated current is just under 300 amps, we will have a 400 amp service. Problems occur with too little electrical current, not more electrical current.
Mungo Hardwicke-Brown, who introduced Jo-Anne and Bryan in June 1991 when Jo-Anne was an Associate with Blake, Cassels & Graydon (now Blakes) in Toronto and Bryan was a Principal with Ernst & Young Canada, spoke with Bryan several times regarding our electric service requirements. Currently, Mungo is completing a major renovation of his family’s home in Calgary, Canada. Although he has a 200 amp electric service, he very much covets our 400 amp service.
The underground electric service enters our house through a 3-inch conduit. This conduit goes through our concrete foundation wall and enters the bottom of our combined service entry device. A ‘combined service entry device’ is the technical term for an electric panel that has an electric meter on one side and circuit breakers on the other side. The side with the electric meter is only accessible to the electric utility and the circuit breakers on the other side are accessible to everyone else. While we would have preferred separate components due to space constraints, the SU3040D400CN model from Square D (a division of Schneider Electric) is only 28-1/4 inches wide and costs less than a separate meter housing and distribution panel.
We will have four distribution panels, two of which will be in the East Mechanical room and two in the West Mechanical room. One of the two panels in each mechanical room will house the circuits that will be connected to the transfer switch for our auxiliary backup natural gas powered generator.
Scott Andersen (from Toronto, Canada) designed the electrical system so we could have two distribution panels in two different physical locations (one in the East Mechanical room and one in the West Mechanical room) that would work as one ‘virtual’ panel. Scott, who has designed and built several unique lofts and homes in Toronto, completed the conceptual design for our house. He is a partner with Burman & Fellows, which is an integrated commercial electrical contractor that focuses on grocery stores in the U.S. and Canada. Scott designed the electrical distribution system to allow the auxiliary backup generator to provide power to circuits on each side of the house, the benefit of which would be reducing the amount of wire that needed to be run to the prioritized electrical circuits throughout the house.
Installing Our 400 Amp Combined Service Entry Device
Doug and Josh, the two-person team from Certified Electric, arrived on schedule to our project site at 9:00 am to install our combined service entry device. They cleared their work area and reviewed the plans with Bryan. Together, they went through PG&E’s electric and natural gas service requirements, which specify the electric meter and natural gas meter location requirements and the layout of the East and West Mechanical rooms.
Also, they discussed where and how the combined service entry device and other distribution panels would be grounded. The Building Official for the City of Monte Sereno, Howard Bell, advised us that we could use the two of the 30 ft long #7 rebar to ground our electric service provided that the two pieces of rebar were more than six feet apart. We had identified the pieces of rebar previously and Izzy had removed the concrete from these two pieces of rebar.
With a solid understanding of the site, PG&E’s ‘Green Book’ requirements, and our requirements, Doug and Josh set to work laying out the conduit and then cutting the wood studs and exterior plywood/sheathing for the electric panel.
The bottom edge of the new electric panel will be at the identical height as the original 125 amp panel, which was installed in 1969. Given the larger size of the 400 amp panel, the top and sides needed to be cut.
Nothing that a new sawzall blade can’t make happen …