 alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | Is this calculator accurate? Amp demand for residence »www.electricalknowledge.com/SFDLoadCalc.asp
I'm getting 108A average load.
Is this for CODE that says I need a 125A service?
I have a 100A service and I've been doing fine with the AC + range + dryer running at the same time.
This is just a curiosity question regarding the calculator being code vs. reality. Like the 5700VA for lights/receptacles + 3000VA small appliances they add, it's unlikely especially during the summer as there would be no space heater, and in winter the AC wouldn't be turned on (Heating is NG). |
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 HallPremium,MVM
join:2000-04-28
Dayton, OH
kudos:2 | Fill out a "summer" version and a "winter" version and take the worst case (higher usage).
I think one downside to something like this is it is based on running ALL of these various items at the same time. In the real world, it doesn't happen. |
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 DraimanLet me see those devil horns in the sky
join:2012-06-01
Kill Devil Hills, NC | reply to alkizmo
Make note that calc is based on the 2002 code so there could be changes made over the last decade. |
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alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | reply to alkizmo
said by Hall:Fill out a "summer" version and a "winter" version and take the worst case (higher usage).
I think one downside to something like this is it is based on running ALL of these various items at the same time. In the real world, it doesn't happen.
The posted scenario is a summer scenario.
Summer is the worst case scenario. I heat with NG, so I basically take off the AC load in winter, which is an improvement. Nothing electrical runs in winter more than summer except for two space heaters (2x 1800W max but I run them at 800W each).
said by Draiman:Make note that calc is based on the 2002 code so there could be changes made over the last decade.
Ya but code revisions don't make my 100A main fuses suddenly pop 
My curiosity is in regards of reality vs. code. Obviously my current 100A service can't supply all my appliances at the same time and the code is there to make sure I COULD.
I made a thread a month or two ago about adding a second dryer but realizing that it would be too much especially with the in-laws moving in for 6 months.
They've been with us for almost 2 weeks now and I see what I was anticipating: Dryer + washing machine + range + AC + TV/PC + central vac + one 15A power tool all being used at the same time!
I think the dish washer is the tipping point, but they're not using it! |
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HallPremium,MVM
join:2000-04-28
Dayton, OH
kudos:2 | A TV and/or PC don't pull enough load to be a factor, do they ?
All of those are being used at the same time ? Damn, gotta be quite noisy, yes ? |
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nonymousPremium
join:2003-09-08
Glendale, AZ Reviews:
 ·Callcentric
| said by Hall:A TV and/or PC don't pull enough load to be a factor, do they ?
All of those are being used at the same time ? Damn, gotta be quite noisy, yes ?
Depends. On startup some laser printers pull quite a bit of power. Then some on this site have really good custom computers.
Now a TV with all the surround sound equipment etc. So yes just a home theater setup or decent computer setup could be a tipping point on an already strained circuit. |
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alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | reply to Hall
said by Hall:A TV and/or PC don't pull enough load to be a factor, do they ?
All of those are being used at the same time ? Damn, gotta be quite noisy, yes ?
They pull maybe 500W combined, but ya not much of a factor. Sorry I even mentionned them 
Ya all those things running is quite noisy. Mostly it's the range hood and vacuum making the noise, the dryer is in a closed room and the AC is central, so it's outside.
The power tools, that's basement work and it's noisy for whoever is near it  |
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 nunyaWho is John Galt?Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:8
 ·Charter
 ·surpasshosting
·voip.ms
| reply to alkizmo
Yes, it's pretty accurate as long as you give it the right information (don't guess). This calculator used the "standard" method. There is another called the "optional" method. If you are borderline, you normally calculate with both methods and use the lower.
It needs the greater of heat vs. A/C. It's quite obvious both won't be on at the same time.
--
...because I care. |
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robbinPremium,MVM
join:2000-09-21
Leander, TX
kudos:1 | reply to alkizmo
said by alkizmo:Summer is the worst case scenario. I heat with NG...
I made a thread a month or two ago about adding a second dryer but realizing that it would be too much especially with the in-laws moving in for 6 months.
They've been with us for almost 2 weeks now and I see what I was anticipating: Dryer + washing machine + range + AC + TV/PC + central vac + one 15A power tool all being used at the same time!
I think the dish washer is the tipping point, but they're not using it!
Off Topic -- did you ever consider changing your dryer to a natural gas dryer? That would seem to eliminate the electrical issue. |
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 SparkChaserPremium
join:2000-06-06
Downingtown, PA
kudos:3
 ·Verizon FiOS
| said by robbin:Off Topic -- did you ever consider changing your dryer to a natural gas dryer? That would seem to eliminate the electrical issue.
He's in Canada where they give the Hydro away for free. |
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BobAccount deleted
join:2012-07-22
New Jersey | reply to alkizmo
A 20 amp dishwasher? Really? Mine uses less than half that. |
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alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | said by nunya:Yes, it's pretty accurate as long as you give it the right information (don't guess). This calculator used the "standard" method. There is another called the "optional" method. If you are borderline, you normally calculate with both methods and use the lower.
It needs the greater of heat vs. A/C. It's quite obvious both won't be on at the same time.
Well, AC is a guess, I just know it's 20A max overcurrent, 2 ton 14 seer. However it would't change the amp demand by more than 10A if I overstated.
Since I heat with NG, the A/C would be the highest demand scenario.
said by robbin:Off Topic -- did you ever consider changing your dryer to a natural gas dryer? That would seem to eliminate the electrical issue.
For the cost of a new NG dryer + NG branch to hook it up + air intake requirements, I'd rather just pay for a 200A upgrade.
said by Bob:A 20 amp dishwasher? Really? Mine uses less than half that.
Now you might be right, I did that calc while at work, now I checked the tag inside the dishwasher (Im home) and found the following specs:
2.7A motor
9.6A max
Though I don't know if the 9.6A max is for the LRA or if it's the total dishwasher amp usage. My dishwasher has a heating element to heat up the water and dry the dishes.
All in all, if none of my main fuses pop while the in-laws live here, then they will never pop as long as I don't add new LARGE appliances |
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Reviews:
·AT&T U-Verse
| reply to alkizmo
Looks *WAY* over the reality. I put part of my stuff, came up with 115A@240V (27600VA) while the highest load that I've seen in months of monitoring was under 15000W (sure power factor can lead to increased VA, but the biggest consumers were resistive (range + drier). |
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BobAccount deleted
join:2012-07-22
New Jersey Reviews:
·Optimum Online
| reply to alkizmo
said by alkizmo:I checked the tag inside the dishwasher (Im home) and found the following specs:
2.7A motor
9.6A max
Though I don't know if the 9.6A max is for the LRA or if it's the total dishwasher amp usage. My dishwasher has a heating element to heat up the water and dry the dishes. Mine says: quote:
MOTOR/MOTEUR
2.7 AMPS
60 Hz 120 VOLTS
9.6 TOTAL AMPS
So I would say 9.6 Amps is the whole shebang. |
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HallPremium,MVM
join:2000-04-28
Dayton, OH
kudos:2 | reply to alkizmo
LRA = locked rotor amp
That's the amount of amperage a motor will pull at startup, typically in the 3x range of normal pull. I'm not sure if you have to size circuit breakers or fuses for LRA or for normal load. I thought breakers or fuses were designed so they wouldn't trip for this scenario. |
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| reply to alkizmo
I would get a clamp on amp probe and check each leg. There is no guarantee the load is split evenly between the two legs. |
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| reply to Hall
said by Hall:I think one downside to something like this is it is based on running ALL of these various items at the same time.
This is not at all true. A demand load calculation is far more complex than that. |
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| reply to Automate
said by Automate:I would get a clamp on amp probe and check each leg. There is no guarantee the load is split evenly between the two legs.
This is actually a pretty worthless measurement. All this will do is give you a quick snapshot of what is going on at one particular time of the day.
You'd have to do this every few minutes all day, and record and analyse the data for this to do any good. |
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alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | said by Hall:LRA = locked rotor amp
That's the amount of amperage a motor will pull at startup, typically in the 3x range of normal pull. I'm not sure if you have to size circuit breakers or fuses for LRA or for normal load. I thought breakers or fuses were designed so they wouldn't trip for this scenario.
Well, a fuse for a motor needs to be time delayed. But the LRA of the motor on my dishwasher probably doesn't apply at the same time that the heating element is active.
Well, I'd size the circuit based on what the manufacturer states.
Currently it's on a 20A circuit.
said by Speedy Petey:said by Hall:I think one downside to something like this is it is based on running ALL of these various items at the same time.
This is not at all true. A demand load calculation is far more complex than that. Correct, that calculation is for code, it's LESS than everything running at once. For example my 11.7kW range is calculated to be 8kW (because code says so).
said by Speedy Petey:said by Automate:I would get a clamp on amp probe and check each leg. There is no guarantee the load is split evenly between the two legs.
This is actually a pretty worthless measurement. All this will do is give you a quick snapshot of what is going on at one particular time of the day. You'd have to do this every few minutes all day, and record and analyse the data for this to do any good. Only 120V loads can put more weight on one leg than the other.
Since I rearranged my fuse panel, I balanced the 120V loads the best I could. For example my fridge, furnace blower, TV and garage door opener are on one leg while the microwave oven, central vacuum, washing machine are on another. |
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| reply to Speedy Petey
said by Speedy Petey:said by Automate:I would get a clamp on amp probe and check each leg. There is no guarantee the load is split evenly between the two legs.
This is actually a pretty worthless measurement. All this will do is give you a quick snapshot of what is going on at one particular time of the day. You'd have to do this every few minutes all day, and record and analyse the data for this to do any good. Obviously he would turn on all his large load items before taking a reading. |
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