Batteryless current clamps?

If you make a 'tap' upstream of the revenue meter, even with just transformer action, you're stealing. Revenue meters (kilowatt-hour meters) have always had terminal voltage as one of their inputs. An illegal tap upstream may affect the voltage at the service entrance some small amount, but the metering will reduce the billed kWh accordingly. So regardless of the exact voltage supplied by the utility (it often varies slightly throughout the day), the amount of energy delivered at the service entrance is what is billed for. Power drawn off before the meter isn't measured and is 'stolen'.

Of course if you just 'wrap some turns around the power line' without orienting the coil properly in relation to the line, you're not going to get any power because transformer action won't work when your turns of wire are parallel to the power line's magnetic field (i.e. 'wrapped around' the power line). And I think that was John Field's point.

daestrom

? "John Larkin" ?????? ??? ?????? news: snipped-for-privacy@4ax.com...

Anyway, current transformers must always be operated with the secondary shorted. In the generating facilities in Kozani, West Macedonia, where 400 kV current transformers were involved, the operators of the plant had a special indicator whether the secondary was shorted.

Some old switchboard CT's I worked on in the Navy had very thin insulator between two spring clips. Whenever we wanted to remove a meter for cal, we slip the insulator out so the two clips would short together, shorting the CT. Then we could open circuit the meter and remove it from the panel. I don't remember exactly what the blade was made of, but it's surface wasn't perfectly smooth like polished material, more porous like unglazed ceramic (of course it wasn't any metal).

The reason they built the insulator so thin was that if one accidentally open-circuited the CT without removing the wafer first, the high voltage developed by the CT would just 'punch thru' the wafer and safely short the CT. Then all you had to do to repair things was make sure you closed the circuit and replace the wafer-thin insulator blade.

Was kind of surprised when I moved to commercial power systems that they didn't use something similar. Just has to have a breakdown voltage that is low enough to avoid damaging the CT.

daestrom

Lower-power CT, like residential-metering size, 100 amps or so, will generally tolerate being unloaded. They will saturate and make two not-too-huge voltage spikes per cycle and not get very warm. The nasty part is that, once the burden is reconnected, they are very likely to wind up magnetized, which will mess up low-current accuracy.

John

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Wrapping turns around a high voltage power line probably wouldn't be a good idea.

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There is no CT in residential metering, the energy meter is connected directly. Even commercial / light industrial you do not see CTs in the meter circuit until 600 A, and before that you are typically at

Of course there is. I delivered over 1800 electronic submetering units for the Battery Park City apartment complex, and, trust me, we used CTs. Lots of electronic meters use CTs. You should get out more.

John

My uncle's house (in the US) has a 400A service with current transformers. They're not common but they do exist. IIRC 200A is the largest residential meter.

It's dangerous to make catagorical statements like "There is no CT in residential metering." It only takes one counter-case to make you wrong.

John

Like the claim that no US homes have three phase power that was made on this group (alt.engineering.electrical) a few years ago.