8 ms·

At 250 volts, it is only 1000 Amps. Normal houses come with 200 Amp service. Older ones may be 100 Amp, and larger modern ones are 400 Amp. So that is about 5

by burfog 8y ago

At 250 volts, it is only 1000 Amps. Normal houses come with 200 Amp service. Older ones may be 100 Amp, and larger modern ones are 400 Amp. So that is about 5 houses. You could buy that service. I hope Tesla would sell you the supercharger for it.

caf 8y ago
250KVA is a common rating for a moderately sized distribution substation. The utility certainly doesn't put only 5 houses on one - more like 50.
- burfog 8y ago
  Ah, just like internet service: it is oversubscribed. The utility can not deliver what has been promised for all customers at the same time.
  - bonzini 8y ago
    Which would be a problem when everyone gets an electric car and every night the owners will request 20 kW for up to 8 hours (hence sustained, not peak). For a condo that could easily be half a megawatt.
    - jerven 8y ago
      That is an unreasonable number. That is 160 kwh of power which is double the largest model 3 battery. This would require everyone to drive nearly 600 miles a day at highway speed. Roughly nine hours of driving a day at 75miles an hour. The expectation is that people drive 30ish miles a day. This is about 11kwh. Over 8 hours a night, well within reasonable limits.
      - bonzini 8y ago
        I was thinking of 10 kW * 2 cars, but actually even for a single car you need 120 kWh to charge 85 kWh. You're right that it won't happen every night for 8 hours, I was wrong about that. Problem is that you have to size for the worst case, which may happen only once a year, but it will happen. Everyone coming back after Thanksgiving. Everyone reaching a vacation place on a Sunday evening in the summer. Bam, 20 kW sustained for a few hours. It takes only a few big condos before you need to bring 400 kV lines downtown...
    - URSpider94 8y ago
      Although your power requirements are somewhat overblown, this is one reason that companies like EMotorWerks are developing grid-connected EVSE’s (“Chargers”) that can be centrally controlled to manage load. Ultimately, EV’s will be plugged in for the 20+ hours a day that they aren’t being driven, and the grid will use them as a giant variable load to soak up excess solar and wind power and shed load when everyone turns on the A/C on a hot day. Lots of plugged EV’s are also the perfect pairing to rooftop solar — in Hawaii, they’ve had to stop people from installing panels on their homes because the neighborhood feeder circuits can’t handle the power being generated by all of the homes. Just redirect that power to the EV in the driveway (or your neighbor’s driveway), problem solved!
  - snowwindwaves 8y ago
    No. Because if there is too much power demand the overload results in some people getting no power. You dont often hear of rolling blackouts or brownouts in North America. Everyone can use as much power as they have subscribed to whenever they want. Your panel is rated for a certain amount of power and protected by a breaker or fuse if too much is used. Same for the transformer your panel is connected to. Same for the distribution line your transformer is connected to. Same for the transformer it is connected to. And so on. There is enough capacity in the system to meet the demand. If there wasn't the lights go out due to some overload. When demand grows more capacity has to be added before the limit is reached. Capacity takes years to build. Utilities have planning departments that decide where they need to add capacity next and how much.
  - caf 8y ago
    Yes, although it not really "promised". A 200A residential service isn't a promise you can consume 200A 24/7, it's just the "never exceed" rating. If you need significantly more power than normal residential needs, I'm sure the utility will be happy to talk to you about your requirements.
    - deleted 8y ago
      [deleted]
- snowwindwaves 8y ago
  A moderate distribution substation is probably more like 50 MVA. A house with a 200A service at 240 V is about 50 kW. You might see a 250 kVA padmount transformer feeding half a dozen big houses but that is not the same thing as a substation.
  - caf 8y ago
    I have worked at an electricity utility. "Distribution substation" is the term of art for a 250KVA padmount transformer and associated HV and LV switchgear (or even just a 50KVA pole mount transformer). A 50MVA installation is what we would refer to as a Zone substation. 5KVA per residential lot is not an uncommon allocation rule. The network is simply not designed to supply every house 200A simultaneously (the same is true of water services: the maximum flow rate of your connection to the water main cannot be sustained if every house in your neighbourhood tries to consume at that rate).
    - snowwindwaves 8y ago
      We must live in different climates. Electric heat is common around here and a house can easily have over 10 kW of heat. An electric range gets a 50A 240V circuit (12 kVA). An electric clothes dryer has a 30A 240V circuit (7.2 kVA). All it would take to exceed 5 kVA per house is for everyone to be cooking christmas dinner on a cold night. Maybe somebody has a shower (electric water heater turns on) and then uses the hair dryer (1.5 kW). Granted you can probably overload a transformer a fair bit on a cold night. I'll ask next time I'm talking to someone in distribution what their allocation rule is. I feel like I'm used to seeing a 3 x 33 kVA cans feeding only a few houses (that incidentally had natural gas heat and hot water...)
dreamcompiler 8y ago
My house has 200 Amp service. But I never use that much at once. The average US home uses an average of about 1.2KW at any given time [0]. So I was wrong above. It's more like 200 houses. [0] https://www.eia.gov/tools/faqs/faq.php?id=97&t=3 https://www.eia.gov/tools/faqs/faq.php?id=97&t=3
- lazyjones 8y ago
  > The average US home uses an average of about 1.2KW at any given time [0]. So I was wrong above. It's more like 200 houses. You're comparing average with peak usage. Doesn't really make any sense.
- bonzini 8y ago
  Isn't that a waste of copper? My house has about 20 Amps (3.3 kW at 230 V).
  - rypskar 8y ago
    Are you sure your intake fuse is only 20A? Where I live it is normal for each circuit to have 16A, and if you have induction stove at least 20A for it. My intake fuse is only 55A (230V) since I have an old house, but should be upgraded
    - bonzini 8y ago
      I checked now and the fuses are 15 A + 15 A, but the utility company disconnects me if I go over about 4 kW (18 A), or over 3.3 kW for more than a few minutes. My sister-in-law has an induction stove, so she gets 40 A and the stove is connected directly to a separate bigger fuse.
      - burfog 8y ago
        That is really strange. Here, the utility company would be happy to have you buy lots more power. Are you lacking a meter? Is the utility company unable to read your meter remotely and unwilling to send a truck out to read it? This would explain things, in which case you'd want to charge batteries (for free!) whenever you don't need all the power you have purchased. Fuses are weird too. Those went out of style 60 years ago. Maybe you will find this weird: I have a device that lets the utility company cut the power to my water heater. They can remotely activate it if they are having problems. In exchange for having this, I get a discount.
DannyBee 8y ago
No, you can't buy that service. Not even close. 400amp service is usually 2 200 amp panels. Done with 2/0 cable. It's rarely, if ever, 1 400 amp panel. 1. There is no way you would get "1000amp service" at 250v. It would be a minimum of 480v 3 phase (and not 1000amp). You may even want a lot higher, because as you'll see, getting that many amps is ... very very hard. 2. You can't even buy 1000amp cable gauge anywhere commercially, because it would be insane. The NEC ampacity table doesn't go anywhere near that high it tops out at 2000kcmil, 665 amp cable. Due to various factors[1], doubling the cable mils will only get you a hundred or so amps here, so it's probably close to 4500kcmil (i'm too lazy to do the mm^2 math, it's 1.89" conductors) Which doesn't really exist for purchase (if you really needed it, you have the means to make it :P). To try to also put the size in perspective: 2/0 cable has conductors that are about 3/8" in diameter. 2000kcmil cable, which again, tops out at 665 amps, has conductors 1.6" in diameter (they are often also segmented, so while the bare size may be 1.6" in theory, you don't find that). Generally the insulation size on them is ridiculous as well (because they are usually used for like 10kv+ applications) [1] Current is related to surface area of conductors, or combined surface areas of all the strands in a conductor. So you'd need to double diameter, at least, to come close.
- TheSpiceIsLife 8y ago
  A new 1MW power cabinet with a similar design to our utility-scale products supports peak rates of up to 250kW per car. Somebody is buying this service. It's probably delivered more in line with your reasoning here.
  - DannyBee 8y ago
    Sure, but they are probably buying >1 KV service, which is not, as the comment I responded to claims, a thing any of us would/could buy similar to "house service".
    - TheSpiceIsLife 8y ago
      That's a fair point. A residential customer wouldn't be able to buy anything like it.

by burfog 8y ago

caf 8y ago

250KVA is a common rating for a moderately sized distribution substation. The utility certainly doesn't put only 5 houses on one - more like 50.

burfog 8y ago
Ah, just like internet service: it is oversubscribed. The utility can not deliver what has been promised for all customers at the same time.
- bonzini 8y ago
  Which would be a problem when everyone gets an electric car and every night the owners will request 20 kW for up to 8 hours (hence sustained, not peak). For a condo that could easily be half a megawatt.
  - jerven 8y ago
    That is an unreasonable number. That is 160 kwh of power which is double the largest model 3 battery. This would require everyone to drive nearly 600 miles a day at highway speed. Roughly nine hours of driving a day at 75miles an hour. The expectation is that people drive 30ish miles a day. This is about 11kwh. Over 8 hours a night, well within reasonable limits.
    - bonzini 8y ago
      I was thinking of 10 kW * 2 cars, but actually even for a single car you need 120 kWh to charge 85 kWh. You're right that it won't happen every night for 8 hours, I was wrong about that. Problem is that you have to size for the worst case, which may happen only once a year, but it will happen. Everyone coming back after Thanksgiving. Everyone reaching a vacation place on a Sunday evening in the summer. Bam, 20 kW sustained for a few hours. It takes only a few big condos before you need to bring 400 kV lines downtown...
  - URSpider94 8y ago
    Although your power requirements are somewhat overblown, this is one reason that companies like EMotorWerks are developing grid-connected EVSE’s (“Chargers”) that can be centrally controlled to manage load. Ultimately, EV’s will be plugged in for the 20+ hours a day that they aren’t being driven, and the grid will use them as a giant variable load to soak up excess solar and wind power and shed load when everyone turns on the A/C on a hot day. Lots of plugged EV’s are also the perfect pairing to rooftop solar — in Hawaii, they’ve had to stop people from installing panels on their homes because the neighborhood feeder circuits can’t handle the power being generated by all of the homes. Just redirect that power to the EV in the driveway (or your neighbor’s driveway), problem solved!
- snowwindwaves 8y ago
  No. Because if there is too much power demand the overload results in some people getting no power. You dont often hear of rolling blackouts or brownouts in North America. Everyone can use as much power as they have subscribed to whenever they want. Your panel is rated for a certain amount of power and protected by a breaker or fuse if too much is used. Same for the transformer your panel is connected to. Same for the distribution line your transformer is connected to. Same for the transformer it is connected to. And so on. There is enough capacity in the system to meet the demand. If there wasn't the lights go out due to some overload. When demand grows more capacity has to be added before the limit is reached. Capacity takes years to build. Utilities have planning departments that decide where they need to add capacity next and how much.
- caf 8y ago
  Yes, although it not really "promised". A 200A residential service isn't a promise you can consume 200A 24/7, it's just the "never exceed" rating. If you need significantly more power than normal residential needs, I'm sure the utility will be happy to talk to you about your requirements.
  - deleted 8y ago
    [deleted]
snowwindwaves 8y ago
A moderate distribution substation is probably more like 50 MVA. A house with a 200A service at 240 V is about 50 kW. You might see a 250 kVA padmount transformer feeding half a dozen big houses but that is not the same thing as a substation.
- caf 8y ago
  I have worked at an electricity utility. "Distribution substation" is the term of art for a 250KVA padmount transformer and associated HV and LV switchgear (or even just a 50KVA pole mount transformer). A 50MVA installation is what we would refer to as a Zone substation. 5KVA per residential lot is not an uncommon allocation rule. The network is simply not designed to supply every house 200A simultaneously (the same is true of water services: the maximum flow rate of your connection to the water main cannot be sustained if every house in your neighbourhood tries to consume at that rate).
  - snowwindwaves 8y ago
    We must live in different climates. Electric heat is common around here and a house can easily have over 10 kW of heat. An electric range gets a 50A 240V circuit (12 kVA). An electric clothes dryer has a 30A 240V circuit (7.2 kVA). All it would take to exceed 5 kVA per house is for everyone to be cooking christmas dinner on a cold night. Maybe somebody has a shower (electric water heater turns on) and then uses the hair dryer (1.5 kW). Granted you can probably overload a transformer a fair bit on a cold night. I'll ask next time I'm talking to someone in distribution what their allocation rule is. I feel like I'm used to seeing a 3 x 33 kVA cans feeding only a few houses (that incidentally had natural gas heat and hot water...)

dreamcompiler 8y ago

My house has 200 Amp service. But I never use that much at once. The average US home uses an average of about 1.2KW at any given time [0]. So I was wrong above. It's more like 200 houses. [0] https://www.eia.gov/tools/faqs/faq.php?id=97&t=3 https://www.eia.gov/tools/faqs/faq.php?id=97&t=3

lazyjones 8y ago
> The average US home uses an average of about 1.2KW at any given time [0]. So I was wrong above. It's more like 200 houses. You're comparing average with peak usage. Doesn't really make any sense.
bonzini 8y ago
Isn't that a waste of copper? My house has about 20 Amps (3.3 kW at 230 V).
- rypskar 8y ago
  Are you sure your intake fuse is only 20A? Where I live it is normal for each circuit to have 16A, and if you have induction stove at least 20A for it. My intake fuse is only 55A (230V) since I have an old house, but should be upgraded
  - bonzini 8y ago
    I checked now and the fuses are 15 A + 15 A, but the utility company disconnects me if I go over about 4 kW (18 A), or over 3.3 kW for more than a few minutes. My sister-in-law has an induction stove, so she gets 40 A and the stove is connected directly to a separate bigger fuse.
    - burfog 8y ago
      That is really strange. Here, the utility company would be happy to have you buy lots more power. Are you lacking a meter? Is the utility company unable to read your meter remotely and unwilling to send a truck out to read it? This would explain things, in which case you'd want to charge batteries (for free!) whenever you don't need all the power you have purchased. Fuses are weird too. Those went out of style 60 years ago. Maybe you will find this weird: I have a device that lets the utility company cut the power to my water heater. They can remotely activate it if they are having problems. In exchange for having this, I get a discount.

DannyBee 8y ago

No, you can't buy that service. Not even close. 400amp service is usually 2 200 amp panels. Done with 2/0 cable. It's rarely, if ever, 1 400 amp panel. 1. There is no way you would get "1000amp service" at 250v. It would be a minimum of 480v 3 phase (and not 1000amp). You may even want a lot higher, because as you'll see, getting that many amps is ... very very hard. 2. You can't even buy 1000amp cable gauge anywhere commercially, because it would be insane. The NEC ampacity table doesn't go anywhere near that high it tops out at 2000kcmil, 665 amp cable. Due to various factors[1], doubling the cable mils will only get you a hundred or so amps here, so it's probably close to 4500kcmil (i'm too lazy to do the mm^2 math, it's 1.89" conductors) Which doesn't really exist for purchase (if you really needed it, you have the means to make it :P). To try to also put the size in perspective: 2/0 cable has conductors that are about 3/8" in diameter. 2000kcmil cable, which again, tops out at 665 amps, has conductors 1.6" in diameter (they are often also segmented, so while the bare size may be 1.6" in theory, you don't find that). Generally the insulation size on them is ridiculous as well (because they are usually used for like 10kv+ applications) [1] Current is related to surface area of conductors, or combined surface areas of all the strands in a conductor. So you'd need to double diameter, at least, to come close.

TheSpiceIsLife 8y ago
A new 1MW power cabinet with a similar design to our utility-scale products supports peak rates of up to 250kW per car. Somebody is buying this service. It's probably delivered more in line with your reasoning here.
- DannyBee 8y ago
  Sure, but they are probably buying >1 KV service, which is not, as the comment I responded to claims, a thing any of us would/could buy similar to "house service".
  - TheSpiceIsLife 8y ago
    That's a fair point. A residential customer wouldn't be able to buy anything like it.