Hi All,
I am making a 3 Phase power meter using a MICROCHIP IC ATM90E36A. They recommend to use neutral wire as a GND reference to measure voltages at 3 hot legs but in my loads (Air Conditioners) there is no neutral wire. We will only have an earth ground.
According to your expertise : is it safe to use GND earth instead of neutral for the reference ? Will I be violating any of the NEC codes?
Thanks,
NO. The neutral cannot be used for equipment grounding. The earth cannot be used for equipment grounding. You need to run/install more conductors in the circuits. This is all required by the electrical codes (NFPA NEC, OSHA, etc.)
Grizzy - Professor Emeritus OSHA National Training Institute
oshaprofessor.com
Do you really need a ground refence to measure power? The voltage that really matters is phase-to-phase if you want to measure the power that the equipment is using. I do recommmend you ground the power measuring equiment, and the green wire works for that.
Are you simply asking if you can use the ground for a reference voltage reading? If so then yes. But the ground moy not carry any load/current!
If the meter is permanently connected, it is running continuously and it is a load (albeit small/light) however the load current level is not the test or deciding factor. As you stated the ground is not permitted to carry any load/current!
This device would also need to be UL listed (or listed by an OSHA NRTL) as well as other applicable standards.
There are too many details missing and the question isn't clear so we cannot really answer it. I do think however, he or she is asking about using the earth as a reference point in order to measure voltage. So I don't see the question being framed as "using the neutral to carry current." I agree with Dewayne, but I would still like more clarification from the OP.
Nick, he's not just making a momentary voltage measurement. He states in his original question that he is building a "power meter". That would measure both current as well as voltage for power.
Have a great weekend ahead.
Grizzy
I would still like more clarification from the OP.
No violation. When it's 480VAC and a Ground, there is no Neutral from the Delta Power source.
I'm not claiming that the Fluke 1735 Power Logger uses the Atmel M90E36A, but typical throughout Energy Meters is the following:
This Chip is DC powered. CT's (Current Transformers) {Rogowski Coil} convert to Analog to the Chips Pins, and Voltage connects thru PT's to Analog.
Thanks for your response. Even I am using ATM90E36A chip for making a power meter. My target load will be the Air Conditioners units which have only 3 wires and no Neutral. Do you think I should use phase B voltage as the reference instead of taking Earth GND as Neutral reference??
Regards
Arshdeep
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This is a very cool Project however, not practical. Even if you obtained this Chip for free (as an Engineering sample), you still need the CT's, PT's and go to some Data Acquisition Terminal for processing. The Output of the Chip is pulses. The Manual says that [In] can be calculated (programming the Data Acquisition System) as opposed to measured [ In = Ia + Ib + Ic ]. Precisely how that is accomplished is not straightforward. Unless your Employer intends to Manufacture a thousand of these for profit, you have all ready burnt your payback in the time it has taken to correspond on this Forum.
This is why I referenced the Fluke Energy Meter. For $5k the system is complete - every aspect of this application has been sorted out AND, if you get stumped with a particular situation … call the help line. Perhaps $5k is a little costly, then look at Extech. Far less expensive and you will get results as soon as the Meter Leads touch the Terminals and the CT's are clamped around the Wires.
I do not fully understand what you are asking. You are manufacturing a type of metering device? You are the manufacturer?