undefined | Better HN

0 pointsDannyBee7y ago0 comments

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.

0 comments

burfog7y ago

My local utility seems to offer it, though they prefer that you install a transformer. They also offer 3-phase for residential usage. Yes, this is in the USA. From what I can tell, most likely you'd get 480 volts at 500 amps.

There is actually a home not far from me that gets 3-phase. It is hooked up to a commercial-style air conditioning unit (huge house) and has a separate power meter; the home has separate 2-phase service as well.

DannyBeeOP7y ago

(I'm going to abuse the hell out of terminology to make this understandable)

I'm sure there are some utilities somewhere that will offer you that :)

480 volt at 500 amps is actually fairly reasonable in terms of cable requirements (it only requires 800 kcmil cable, which, while, i'd never want to buy a ton of it, is not completely bonkers). I would be a little surprised if they offer 500 amps though, because that's a lot more than you'd ever need.

Remember that a 3 phase amp carries a lot more kilowatts than a single phase amp.

In particular, 20 amp 240 single phase = 4800watts But 20 amp 240 three phase is a factor of sqrt(3) more = 8313 watts

so 500 amp 480v 3 phase would carry 415692.19382 watts, while 500 amp 480v single phase (which nobody uses) would only carry 240000 watts.

So you'd be getting 415kw service out of that, not 240kw service. Which is a lot of power.

Usually i've seen them offer 250kw service (IE not in amps) and let you do the stepdown. This would step down to 300 amp 480v 3 phase.

240v 3 phase in residential areas is also more common (I can get it), but it's only 100-200 amp service at least here, and i pay for power factor, blah blah blah.

Faaak7y ago

And to be more pedantic, it's actually kVA and not kW.

Or kW with a power factor of 1, but that is (almost) never the case

dreamcompiler7y ago

Which implies that Tesla is either using a much higher voltage than 250, or they're using superconductors. And I doubt they're using superconductors.

DannyBeeOP7y ago

Yes. Residential/basic commercial wiring is the limit of my knowledge here, so i don't know what sort of voltage service they are buying here.

Staring at things like http://bpu.org/electric-service-rates-commercial/

(and similar pages on other utilities)

make me believe they'd end up with some medium voltage application here (IE take it in as somewhere between 3.3kv and 45kv and do step down themselves)

HALtheWise7y ago

The Tesla supercharging cables are pretty short, so they can also tolerate the higher losses associated with a thinner cable. They were even experimenting with a liquid cooled cable at one point in order to get thinner conductors and a more flexible cable by allowing to to be less efficient.

Reason0777y ago

The experiment must have been a success, because the v3 supercharger uses liquid-cooled cables.

In fact, it is becoming standard in high-power chargers, with the new 175-350kW CCS units also using liquid cooling.

URSpider947y ago

They are using 480V, and their cables are liquid-cooled.

dreamcompiler7y ago

Ha! I started to suggest "or they're using small copper and cooling the heck out of it," but that would waste energy so I assumed they wouldn't do it. Wrong, apparently.

TheSpiceIsLife7y 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.

DannyBeeOP7y 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".

TheSpiceIsLife7y ago

That's a fair point. A residential customer wouldn't be able to buy anything like it.

j / k navigate · click thread line to collapse