New Brultech Energy Monitoring Model (ECM-1240) due in 2009
- Thread starter sic0048
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WayneW
Senior Member
Technically speaking, it isn't "two phases". It is a center-tapped transformer with the middle being the neutral (zero volts) and the ends being the mains feeds (the so-called two phases). End-to-end is 240V and end-to-neutral is 120V. Since it is coming off the same transformer, then end voltages must be nearly identical (but opposite). There is some possibility of inaccuracy, but not enough to worry about for residential use. I think BrettS took a bunch of readings in his house and only saw a couple volts difference between the legs in a worst-case scenario.
The need for the voltage reading in a power meter is primarily for two things: 1) to read the peak voltage and 2) to know where in the voltage wave cycle you are. For true power metering you have to compare the current reading with the voltage reading at that particular instant. On some device (incandescent lamps) the volt and current curve will match nicely, producing a power factor of 1. On some devices (computer switching-mode power supplies), the voltage and current curves are not lined up and you have a power factor less than 1. It is these types of device (PF<1) that require the voltage reading to get the true power reading. If your house was nothing but incandescent lamps and toasters, you wouldn't really need a constant voltage reading (assuming your voltage was stable and reading the voltage once was good enough)
I see a couple of volts difference between two phases on a permanent basis, right now it is 121V vs 117.5V Besides, the voltage on both phases varies unpredictably during the day, from 114V to 122V. So if the current is taken from the 121V phase and the voltage from the 117.5 phase, for a 75W electrical bulb the reading would be about 73W which is about 3% lower than in reality, or you under-count slightly less than a day worth of your electricity consumption per month. It may or may not matter in someone's case.
I am not sure if the phase error introduced by the distributed power transmission line capacitance/inductance and unbalanced load is substantial. Since the distance from the split-phase transformer to a typical house is pretty short, it should not be.
Anyway, my understanding is that with ECM-1240 only one phase voltage is measured and the other voltage is assumed to be the same. Is that correct ?
Thanks.
This question was asked last year and I do not believe I have seen the answer.
How far can the CT's be extended? I would like to use CAT6 to carry the CT outputs from a JB with terminal strips under my panels to the 1240.
I would rather mount the unit in a panel on my structured wiring wall. About 50' away from both panel boards in my house.
Thanks.
How far can the CT's be extended? I would like to use CAT6 to carry the CT outputs from a JB with terminal strips under my panels to the 1240.
I would rather mount the unit in a panel on my structured wiring wall. About 50' away from both panel boards in my house.
Thanks.
WayneW
Senior Member
That appears to be correct. I believe that all of the residential monitoring devices we have seen or discussed on CT only measure one leg (unless they don't measure at all, which makes them inaccurate).
Perfect. Thanks.
Whether or not the CT connection can be extended depends on how the load resistor is connected to the CT. If the resistor (typically 10-100Ohm) is located inside the transformer enclosure, then the connection wire influence is minuscule. If the resistor is on the device board, then the Cat5 100' would be equal to about 5 Ohm and the error with an on-board resistor would be about 6% and 60% with a 10 Ohm resistor.
I imagine the 1240 CT has a built-in load resistor.
Pretty much what Wayne said on the "phase". For practical purposes most homes have a single Phase feeding the service panel. The transformer out on the pole will step-down from 7200 volts (approx.) to 240volts and the secondary windings are center-tapped so that you get 240v from end to end, and 120 when measured from the center tap to either end. Most of the Electricians I know will also refer to "end" of the secondary Taps as "phases", but from an engineering point of view that isn't correct. If you could monitor the voltages of a true Three-Phase system with multi-channel O-Scopes, you see three separate ac waveforms but the "peak" of each will be separated by 120 electrical degrees relative in time.
And now I've got a question, since the basic unit with just RS-232 comms aren't in stock yet. Is the A+ package with "wireless" (plus the RS-232 serial output) basically an internal zigbee transmitter with an INCLUDED Zigbee to USB dongle? I couldn't be quite sure from the Online store description. I didn't want to order that package and find out that, yes the 1240 did have a built in wireless data transmitter/xcvr, and find out when I received it that the wireless to USB dongle was extra...
And now I've got a question, since the basic unit with just RS-232 comms aren't in stock yet. Is the A+ package with "wireless" (plus the RS-232 serial output) basically an internal zigbee transmitter with an INCLUDED Zigbee to USB dongle? I couldn't be quite sure from the Online store description. I didn't want to order that package and find out that, yes the 1240 did have a built in wireless data transmitter/xcvr, and find out when I received it that the wireless to USB dongle was extra...
And now I've got a question, since the basic unit with just RS-232 comms aren't in stock yet. Is the A+ package with "wireless" (plus the RS-232 serial output) basically an internal zigbee transmitter with an INCLUDED Zigbee to USB dongle? I couldn't be quite sure from the Online store description. I didn't want to order that package and find out that, yes the 1240 did have a built in wireless data transmitter/xcvr, and find out when I received it that the wireless to USB dongle was extra...
It sure looks to me like the Zigbee <-> USB adapter is not included in any of the packages, but is a $60/70 extra.
moridin1138
Member
And now I've got a question, since the basic unit with just RS-232 comms aren't in stock yet. Is the A+ package with "wireless" (plus the RS-232 serial output) basically an internal zigbee transmitter with an INCLUDED Zigbee to USB dongle? I couldn't be quite sure from the Online store description. I didn't want to order that package and find out that, yes the 1240 did have a built in wireless data transmitter/xcvr, and find out when I received it that the wireless to USB dongle was extra...
From what I can tell it does not include the Zigbee to USB dongle. It seems to be $99 extra (AFAIK a decent price). I am not interested in the wireless right away, but may need it someday. PKG A+/100 seems reasonable.
Now I have a question. I will need the micro-CT's that support aluminum wiring (which I have some of), which I imagine are just a little larger. Will these same micro-CT's work on the copper wiring as well that is slightly smaller?
Yes. The only difference is the physical size to allow for large Al wires for a given current rating.
moridin1138
Member
Great, thanks. I was concerned the accuracy or effectiveness would be affected by a larger CT attached to a smaller wire.
And now I've got a question, since the basic unit with just RS-232 comms aren't in stock yet. Is the A+ package with "wireless" (plus the RS-232 serial output) basically an internal zigbee transmitter with an INCLUDED Zigbee to USB dongle? I couldn't be quite sure from the Online store description. I didn't want to order that package and find out that, yes the 1240 did have a built in wireless data transmitter/xcvr, and find out when I received it that the wireless to USB dongle was extra...
From what I can tell it does not include the Zigbee to USB dongle. It seems to be $99 extra (AFAIK a decent price). I am not interested in the wireless right away, but may need it someday. PKG A+/100 seems reasonable.
Now I have a question. I will need the micro-CT's that support aluminum wiring (which I have some of), which I imagine are just a little larger. Will these same micro-CT's work on the copper wiring as well that is slightly smaller?
That's kinda' how I read it too, so I hope they stock the "plain jane" unit with just RS-232 at the store pretty soon...
moridin1138
Member
Well, I made the leap. Got killed on the exchange rate (USD-CDN), and it's a little weird that the entire shopping process is through Paypal (I hate Paypal). Had to put the aluminum wiring special comments in Paypal as well.
Ah well, I hope it comes soon. I can't wait to get started!
Ah well, I hope it comes soon. I can't wait to get started!
