I want to run an experiment which compares the readouts of the newer electronic smart meters against older electromechanical meters.

Is there anything in the NFPA 70 or any other law or code which prohibits feeding the loads from the utility's power meter into a private electromechanical (analog) meter inside my home before passing the lines to the main breaker panel?

This would essentially make the analog meter a private submeter hooked in series with the utility's smart meter.

Some things to consider are whether one meter could interfere with the readout of the other or whether this would violate any terms of the utility company.

For the legal aspects of this question, I am a resident of California. Assume that the county uses the NEC 2013 or 2014 without amendments.

  • 1
    You may have more of a contract dispute with the utility company rather than an electrical code or regulatory issue. – bib Aug 1 '14 at 2:41
  • You'll have to check with the utility to know if this violates their terms and conditions. – Tester101 Aug 1 '14 at 10:22

The meters shouldn't interfere with each other. They're just ammeters, after all; current is current. You will be charged for the parasitic load your new meter introduces, of course, which may vex your test.

Bigger problem is that you'll need the electric company's cooperation to turn off your circuit so you can rewire—and they are almost certainly not going to be happy about having anything upstream of the main cut-off.

You're more likely to get approval if you install a new box with its own main breaker, and make the old box a subpanel of the new one, with the meter between them. That puts the weirdness firmly inside the domain that you are entirely responsible for, and leaves a clear way to isolate it from their lines if necessary. Essentially, that's the normal setup for apartments which are paying for electricity separately; you're just setting up a single apartment.

I suspect you're going to find that the electronic meters really are as accurate as the mechanical ones, or if anything are more accurate.

Wouldn't it be easier to just ask the manufacturers of these meters what their error tolerances are? Or to ask apartment building owners who have a mix of meter technologies whether their numbers add up reasonably?

(Especially since the cost of installing the second meter is going to swamp anything you think you might challenge on the bill, never mind the legal costs of trying to convince folks that your meter is the more trustworthy of the two. If you're concerned about your bill, putting the same money into energy efficiency upgrades would be a far better investment.)

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    +1 For checking manufacturer error tolerances. My understanding is that any meter would have to be tested and shown to conform with ANSI C12.20. – Comintern Aug 2 '14 at 3:42
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    @Comintern Actually I suspect that anyone who is asking this question will assume that the manufacturers, the ANSI standards committee, and the laws of physics are jointly conspiring against them, or at least that the meter on their house MUST be defective... – keshlam Aug 2 '14 at 15:53
  • +1 for putting the same money into energy efficiency upgrades would be a far better investment – user24166 Aug 2 '14 at 18:55

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