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 05-11-2012, 05:19 PM #1 Coaster Sparky     Join Date: Aug 2010 Location: Western Massachusetts Posts: 1,871 Two-Family Optional Method Calculation I've got a customer who's looking to have a back up generator installed at his two family home in which he resides. His service is around 40 years old, both panels are FPE Stab-lok. I'm pushing him to consider changing out the service first, for ease of future work. There is no permanent means of A/C installed on either floor but there is 102 linear feet of electric baseboard heat between both floors. For calculation purposes only, I used a figure of 250w/ft for the heat. 102' x 250w = 25,500w or 25.5kw or 25,500va The house is 2,073 sq. ft. according to the research I've done online. I'm just looking for a double-check on my calculation. 2,072 sq. ft x 3va 6,219va (4) Sm. App. @ 1,500va ea. 6,000va (2) Laundry Cir. @ 1,500va ea. 3,000va (2) Ranges per Column C T220.55 11,000va Water Heater 4,500va (2) Refrigerators 2,800va Freezer 600va Dishwasher 1,030va (2) Disposal 1,380va Range Hood 400va (2) Microwaves 3,260va Pool Pump 2,880va (2) Clothes Dryer T220.54 10,000va Hot tub 600va Total 53,669va 1st 10kva @ 100% 10,000va Remaining @ 40% 21,468va Total General Load 31,468va 25.5kva of Heat @ 40% 10,200va Total 41,668va 41,668va / 240v 174A Any feedback would be appreciated. I used the calculator over at MH but found it to be a little complicated. __________________ I saw a girl texting & driving the other day & it really made me mad, so I rolled down my window & threw my beer at her.

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 05-11-2012, 05:50 PM #2 Heavily Armed Member     Join Date: Sep 2010 Location: Fascistchusetts Posts: 30,272 I don't see any mistakes.. Do you have to have the whole house tied into the generator? Remember also they will never be running the house at full load anyway. __________________ ES2 Flat Rate , The best \$99 I've ever spent ..
 05-11-2012, 06:10 PM #3 Coaster Sparky     Join Date: Aug 2010 Location: Western Massachusetts Posts: 1,871 Customers looking only to supply his 1st floor with enough of a generator to supply heat, lights and a refrigerator. His elderly mother lives on the first floor, he lives on the second. I'm working out those calculations right now. I'm going to tie the generator parallel into each panel so it can run either panel if need be. If either panel falls out, they're both covered this way. If the entire service drops out, only enough to keep them getting by on the first floor. There's 65 linear feet of baseboard heat on the first floor. 27 linear feet on the second. I'm using 40% of the heat for the calculation, so I'm using the respective figure for the first floor which would be 6.5kw. The second comes in at 3.7kw. So with the 6.5kw figure, I also need to account for 2 refrigerators and at least 1 circuit for lighting. I used the figure of 2,800va for the calculation so that brings me to 2.8kw for the refrigerators and I'll account for 1,500va for lighting. That brings me to a total of 10.8kw to keep his food fresh and heat on in the first floor. I've never sized a generator, but those numbers look sound to me. __________________ I saw a girl texting & driving the other day & it really made me mad, so I rolled down my window & threw my beer at her.
05-11-2012, 07:39 PM   #4
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Quote:
 Originally Posted by thegoldenboy Customers looking only to supply his 1st floor with enough of a generator to supply heat, lights and a refrigerator. His elderly mother lives on the first floor, he lives on the second. I'm working out those calculations right now. I'm going to tie the generator parallel into each panel so it can run either panel if need be. If either panel falls out, they're both covered this way. If the entire service drops out, only enough to keep them getting by on the first floor. There's 65 linear feet of baseboard heat on the first floor. 27 linear feet on the second. I'm using 40% of the heat for the calculation, so I'm using the respective figure for the first floor which would be 6.5kw. The second comes in at 3.7kw. So with the 6.5kw figure, I also need to account for 2 refrigerators and at least 1 circuit for lighting. I used the figure of 2,800va for the calculation so that brings me to 2.8kw for the refrigerators and I'll account for 1,500va for lighting. That brings me to a total of 10.8kw to keep his food fresh and heat on in the first floor. I've never sized a generator, but those numbers look sound to me.

What code cycle are you under? You size the generator based on the amps of the circuits you are backing up. You can't feed both panels since the code change in 2008 like you plan. The generator has to be big enough to back up everything it supplies.

Last edited by Bulldog1; 05-11-2012 at 07:42 PM.

05-11-2012, 08:23 PM   #5
Coaster Sparky

Join Date: Aug 2010
Location: Western Massachusetts
Posts: 1,871

Quote:
 Originally Posted by Bulldog1 What code cycle are you under? You size the generator based on the amps of the circuits you are backing up. You can't feed both panels since the code change in 2008 like you plan. The generator has to be big enough to back up everything it supplies.
2011. It's one service drop, two meters, two panels. The Inspector of Wires says having the generator in parallel with both panels is fine. What change are you citing?

I have to redo my entire calculation, I just left the guys house and he forgot to mention that the entire 1st floor of the house is baseboard hot water, not electric baseboard heat.
__________________
I saw a girl texting & driving the other day & it really made me mad, so I rolled down my window & threw my beer at her.

 05-11-2012, 08:50 PM #6 Coaster Sparky     Join Date: Aug 2010 Location: Western Massachusetts Posts: 1,871 Total General Load 31,468va 9.25kva of heat @ 100% 9,250va Total 40,718va 40,718va / 240v 170A I lost 4 amps. I'm not controlled at 4 locations so I have to take it at 100%. It doesn't change much on the service, but he only wants the furnace to be operational which is on a 120v 15A circuit. __________________ I saw a girl texting & driving the other day & it really made me mad, so I rolled down my window & threw my beer at her.
05-12-2012, 10:25 AM   #7
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Join Date: Oct 2011
Location: No where, USA
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Quote:
 Originally Posted by thegoldenboy 2011. It's one service drop, two meters, two panels. The Inspector of Wires says having the generator in parallel with both panels is fine. What change are you citing? I have to redo my entire calculation, I just left the guys house and he forgot to mention that the entire 1st floor of the house is baseboard hot water, not electric baseboard heat.

The code changed in 2008. I posted what the change says. If you are under 2005 your inspector is correct. If your under 2008 or 2011 he is wrong if your generator is not large enough to supply all loads connected to it. Before 2008 you could use am undersized genny.

05-12-2012, 01:04 PM   #9
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Quote:
I was assuming you were using an ATS. If you are you can't manually shed the loads. You have to use our load control module or set a panel with the circuits you are backing up and your generator must be big enough to back up all the circuits in the panel.

Last edited by Bulldog1; 05-12-2012 at 01:08 PM.

 05-12-2012, 01:29 PM #10 Coaster Sparky     Join Date: Aug 2010 Location: Western Massachusetts Posts: 1,871 I was planning on putting in two manual interlock kits, one for either panel with the generator in parallel to both panels. Out of the first panel, the only thing he wants to run is one or two circuits for lighting, the furnace, a microwave if need-be and the refrigerator. Out of the second panel, the only thing he wants to run is the upstairs refrigerator and nothing else. The easiest and most straightforward approach I can come up with is marking the handles of the breakers in red paint, so he knows to leave those on and shut everything else off. I can't think of a feasible way to bring circuits into one panel from two separately metered locations. Am I still compliant with 702.5(B)(1) in this approach? __________________ I saw a girl texting & driving the other day & it really made me mad, so I rolled down my window & threw my beer at her.

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