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Joined: Mar 2005
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I'm trying to get a 2nd opinion...
I've got a 200A main panel now in a residence, with a 150A breaker. The addition will double the size of the house (1500 to 3000 sqft) and add a 2nd 3-ton heat-pump with emergency-heat backup, which alone sucks up the spare 50A on the panel. I can just *barely* justify the minimum service load calculations to fit on this 200A panel, but it's close- to the point where if I add the refrigerators into the calcuation on a dedicated circuit vice assuming them included in a 1500VA kitchen circuit, the calculations fail. Do you think we'll be OK with the 200A service, or is a call to VEPCO in order to get the service upgraded? I'd really rather avoid having to upgrade the existing main panel, but it seems to be quite a risk.
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We don't use heat in homes here so I have to ask. Does the heat pump draw 50a or is it just a 50a breaker? We can't check your math with out all the information. Myself I'm not the best person to ask on calc's. Depending on who you ask you can have a different interpitation of how to figure it.
I can say that 3000 sf does not seem out of line for a 200a service. For friges most new ones don't draw that much. A lot of home now have a few friges/freezers around the house. The other thing to figure is do you have enough circuit space or do you need a sub.
If it is close you may tell the HO that and let them make the call.
Tom
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The heater is an electric resistance emergency heater built into the air handler for when the temp drops below where the heat pump can operate efficiently. I'm sure it's not drawing exactly 60A 240, but finding out *anything* technical about heat pumps has been consistantly frustrating as their product information consists only of meaningless marketing gibberish, and SEER is about the only solid number you can get from them without being a HVAC professional. The air handler manual lists the blower as 15A 240, but I don't have any documentation on the resistance heater unit. Long story short, I'm conservatively estimating 14,400 VA for it.
Same goes for the electric range- I assumed the worst at 40A 240V, though I know that's going to be high as nobody will ever broil with all 4 burners on max. All-in-all, my numbers came to 409A for the house. Which I assume is slightly high because of my conservative estimates; but I doubt the heater is only drawing 25 or 40A, else it wouldn't be on a 60A breaker.
Actually, how long does a residential breaker typically run at overload- are there curves availible?
[This message has been edited by SteveFehr (edited 03-19-2005).]
[This message has been edited by SteveFehr (edited 03-19-2005).]
[This message has been edited by SteveFehr (edited 03-19-2005).]
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Calcs:
For minimum service: VA A (120)
3VA/sqf (existing) 4500 38
3VA/sqf (addition) 6000 50
1500A App Ckts (exst) 1 13
1500A App Ckts (new) 2 25
Water Heater 4500W 32
Range 40A 240 80
Dryer 28A 240 56
Subtotal: 35217 293
First 10k: 10000 83
40% of rest: 10087 84
New Subtotal: 20087 167
Furnace 60A 240 120
Furnace 60A 240 120
[b]Total: 48887 407
per phase: 24443 204[/b]
Here's the panel loadouts: Old
150A Main Panel
Dryer 30 A/C 30
Dryer 30 A/C 30
Bedroom 15 Bedroom 20
Bedroom 15 Fridge 20
Lights 15 Kitchen 20
Liv Rm 15 Kitchen 20
Bedroom 15 Washer 20
Furnace 60 Water 30
Furnace 60 Water 30
Range 40
Range 40
PH-A 260 PH-B 295
Reconfigured
200A Main Panel
Dryer 30 A/C 30
Dryer 30 A/C 30
Bedroom 15 Bedroom 20
Bedroom 15
Lights 15
Liv Rm 15 Library 20
Bedroom 15 Washer 20
Furnace 60 Water 30
Furnace 60 Water 30
Feeder 100 Range 40
Feeder 100 Range 40
PH-A 340 PH-B 375
New:
125A
Furnace 60 A/C 30
Furnace 60 A/C 30
Lights 15 Bedroom 20
Lights 15 Sewing 20
Lights 15 Kitchen 20
Bath 20 Kitchen 20
Doors 15 Fridge 20
Shed 20 Garage 20
Shed 20 Dining 20
Micwv 15 Living 20
Outlets 20
PH-A 240 PH-B 255 [This message has been edited by SteveFehr (edited 03-19-2005).] [This message has been edited by SteveFehr (edited 03-19-2005).] [This message has been edited by SteveFehr (edited 03-19-2005).]
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Steve, what is the wattage of the emergency heat? As Tom stated you need to use the actual load not the circuit size. I also think the way you are doing the calcs is over inflating the numbers. Use volt-amps for all of you numbers then divide the final number by 240. Don’t forget to include the microwave, garbage disposal or dishwasher if they are going to be used. Provide some more information and we will help with the calcs.
Curt
Curt Swartz
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I forgot to mention in my last post that 220.31 allows loads to an existing dwelling to be calculated using 100% for the first 8 KVA and 40% for the remainder.
Curt Swartz
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I also think, the way he is doing the calcs, is over inflating the numbers.
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Thanks everyone! I see I had a bunch of misleading values in there (like showing squarefeet in the VA column for the 3VA*sqft, etc.) which might have been confusing. Unfortunately, I don't know the true watts of the emergency heat. The current is between 50-60, I can glean that much off the breaker panel, but I don't know what the existing heater is and was just going to provide for whatever the docs that come with the new heat pump call out. They're both 3-ton units heating the same sqft of finished space, so I assume they will be similar if not identical. Likewise, I don't have hard numbers on the freestanding range, and (40A 240) UL listings don't help, so 20*240=probably overkill. Oddly enough, adding up all the heating elements on the range gives about 60A 240...
Service Calcs: VA:
3VA/1500 4500
3VA/2000 6000
1500VA Ckts 4500
Water Htr 5196
Range 9600
Dryer 6720
Subtotal: 36516
First 10k: 10000
40% of rest: 10606
New Subtotal: 20606
Furnace 1 14400
Furnace 2 14400 Amps:
Total: 49406 206
per phase: 24703 206
Swapping 10k for 8k gives exactly 200A load, coincidentally enough! Since the furnace and range were conservative estimates, that gives a *little* fudge room, but it's still awfully close. As an aside, why would existing homes be allowed 8k vice 10k? [This message has been edited by SteveFehr (edited 03-19-2005).] [This message has been edited by SteveFehr (edited 03-19-2005).]
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I have not seen a res. drier that draws 28 amps. Loads should not be more than 80% of the breaker. So a drier that has a 30a breaker should only draw 24a max continously.
You did not figure in for the water well pump or detached garage.
Tom
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Active 1 Loads should not be more than 80% of the breaker. So a drier that has a 30a breaker should only draw 24a max continously. It is NEC and UL compliant to load a circuit 100% for non-continuous loads. A dryer would be a non-continuous load as defined by the NEC. It does not operate for more than 3 hours at a time.
Bob Badger Construction & Maintenance Electrician Massachusetts
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