I've got a home builder that is building a 3400 sq ft (living space) home and then finishing another 1000 sq ft in the basement. He's running all the basics, (2) electric water heaters, a 240V 20 AMP Well pump, Water softener and a Geothermal furnace (probably another 3 240V Circuits). He is then running a 100 AMP Sub out to a pole barn about 100 feet away from the house. He'll have a ded. 240V 20 AMP circuit, a ded. 120V 15 AMP circuit as well as 2 lighting circuits and 2 general power circuits.
He's wanting a 200 AMP service with a 100 AMP sub (that would be a total of 2 100 AMP subs). I suggested a 400 AMP Service...
Any thoughts or suggestions?
Yes. Do a load calculation to see what size service you need. Don't just guess, don't count panels, and don't add up breaker values...
I don't believe the geothermal heat pumps necessarily have electric backup heat and they don't need to defrost. So it may have one approx 30A circuit for the compressor and a small 15A one for the air handler/controls.
Mark nailed it. Do a load calculation.
Dave
A service calculation is the only way to know for sure.
I wired several small (2,500 sq ft) homes that were all electric, including a heat pump with 18kw supplemental heat.
A calculation revealed 211 amps minimum service size.
I installed a 320-amp(continuous-rated) meter socket and (2) 150-amp service panels.
I installed a 320-amp(continuous-rated) meter socket and (2) 150-amp service panels.
Which table did you use to size the servce conductors to the two panels? Is it one set of conductors or two separate sets?
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Tom Horne
The is a computer program at this site
http://www.electricalknowledge.com/SFDLoadCalc.asp that will give you the answer. Just plug in the numbers.
Thanks, Bob, for the website link.
On the other hand: yet another website to brouse; I'll never get any work done.
Energy 7
Happi_Man
List the load in the house and we will see.
[This message has been edited by Bob (edited 06-24-2006).]
Tom,
Around here it is common to install a 320-amp meter socket and feed either 2 150-amp panels or even 2 200-amp panels using 2 sets of 2/0 SEU, or 4/0 SEU, respectively.
BTW,
In case you were wondering, the combined sizes of the 2/0s or the 4/0s don't equal the sizes for 300 & 400-amp services in Table 310.15(B)(6). But, the table seems to be accepted for the installation described.
The SE conductors feeding the meter will need to be sized according to the table, though.
Tom,
Around here it is common to install a 320-amp meter socket and feed either 2 150-amp panels or even 2 200-amp panels using 2 sets of 2/0 SEU, or 4/0 SEU, respectively.
BTW,
In case you were wondering, the combined sizes of the 2/0s or the 4/0s don't equal the sizes for 300 & 400-amp services in Table 310.15(B)(6). But, the table seems to be accepted for the installation described.
The SE conductors feeding the meter will need to be sized according to the table, though.
According to the NFPA electrical section staff the use of the wire sizes in section 310.15 (6) are for one set of conductors per dwelling. I pointed out the plural in both feeder(s) and panelboard(s) and they told me that the plural was meant to make it clear that it applied to multiple dwelling installations. If anyone is willing to coach me on how to write it I will apply for a formal interpretation to settle the matter once and for all.
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Tom Horne