General > General Technical Chat
The US electrical system
Monkeh:
--- Quote from: james_s on June 26, 2020, 08:31:37 pm ---
--- Quote from: Monkeh on June 26, 2020, 06:37:06 pm ---
... a 30kVA transformer won't handle a single 200A service.
And we're the underbuilt ones?!
--- End quote ---
I don't recall anyone saying anywhere is underbuilt? :-// Or do you just like being a dick?
--- End quote ---
https://www.eevblog.com/forum/chat/the-us-electrical-system/msg3104258/#msg3104258
--- Quote ---I may have been mistaken in the rating so I just went and looked, the (pad mount, underground wired) transformer that feeds my house and I believe 3 others is 50kVA. This is as far as I know the continuous rating at max ambient temperature. A 200A service will *never* be pulling 200A continuously and it's typical to have 300A-400A cumulative in branch circuits off a 200A main, nobody is ever going to load them all up 100% at the same time. I've seen as small as 5kVA, I don't know what those are used for and at least as large as 75kVA. The only transformer of this type I've personally messed with is a 25kVA unit we used to step up 240V to 4800V to power a series streetlighting regulator, it was the smallest 4800V transformer we could find at the scrapyard.
--- End quote ---
50kVA makes more sense - at least it's capable of 200A. And yes, I get that in normal conditions you're not going to see full load from a single building, but it's not a 200A service if there isn't 200A behind it.
Stray Electron:
--- Quote from: themadhippy on June 24, 2020, 09:44:47 pm ---
7kw to dry yer clothes, aint you guys heard of washing lines
--- End quote ---
Seriously, not since the 1960s. Besides with the now popular zero lot line subdivisions, there's NO room for one. I literally haven't seen a clothes line since probably 1968.
tom66:
My clothes dryer uses 2.2kW and a total of ~2.7kWh to dry 8kg of clothes straight from the washing machine.
I don't understand how you'd need 7kW to dry clothes. One of the important things is to not overheat the clothes which damages fabrics and risks fire.
ciccio:
About NEW meters, I know (by experience) that the new electrical meters installed in Italy can be remote controlled (using some kind of signal over the power line) allowing the Utility Company to:
-read your meter, and bill you according to the (optional) tariff that changes day/night and workdays/weekends
-reduce the tripping current of the meter (if you forgot to pay a bill, the max power available will be reduced from 3.5 kVA to 0.5 kVA for (I believe) 15 days, then to ZERO ).
Now they changed my GAS meter with a new one than can do the same things. It uses some kind of Wi-Fi (with some problems because most meters are installed in metal enclosures) and will allow for remote reading the meter and remote cutting off the gas supply.
Cutting the gas supply to a defaulting customer required physical access to the meter, that in old buildings is many times inside the house, and this created problems to the field technicians. Now the supplier can do this from their control room...
bdunham7:
--- Quote from: Monkeh on June 26, 2020, 06:37:06 pm ---
... a 30kVA transformer won't handle a single 200A service.
And we're the underbuilt ones?!
--- End quote ---
You'd have to understand what that rating means to make that statement. Where I live, one 25kVA plated xformer is feeding 4 houses that were originally built 50 years ago with 100A service, but with many upgraded to 200A since. If they need service, the utility company is swapping them out for 50kVA versions, but mostly they are still fine. Using too large a transformer increases losses at low power, so they use low-Z oil-cooled transformers that can sustain massive overloads from their rated power. IIRC, a typical xformer of this type can sustain a 175% continuous overload at 68F ambient and a 400% overload for an hour. Or something like that.
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