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Author Topic: Spyder Totals vs MTU Totals
breaker man
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« on: January 20, 2018, 05:23:11 PM »

Is the information(KW,KWH,MTD) recorded by spyders totally independent of the information recorded by the MTU?  When I add up the recordings by the spyders they always total more than what the MTU has recorded.
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pfletch101
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« Reply #1 on: January 20, 2018, 05:47:22 PM »

They are totally independent, and cannot be expected to 'track' perfectly (even without allowing for the specified accuracy of the hardware), though the direction of your discrepancy is unusual, even if you have Spyders monitoring all your loads, since Spyder channels read zero at low positive currents and will consequently (usually) accumulate lower totals over time than the MTU(s).
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Peter R. Fletcher
TED Pro Home - main MTUs monitoring utility and PV Solar feeds; 2 Spyders monitoring selected individual circuits
breaker man
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« Reply #2 on: January 21, 2018, 03:08:16 PM »

I am monitoring all the circuits in the panel and realized that the spyder totals would not equal the MTU however I was surprised to see that the spyder totals were greater than the MTU. At the last comparison I did the MTU total for today was 42.3 KWH and the spyder totaled 59.9 for the the day.

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pfletch101
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« Reply #3 on: January 21, 2018, 03:59:59 PM »

Something is definitely wrong. Have you got any of your Spyder CTs set up to double the reading when they shouldn't be - e.g. monitoring both 'sides' of a 240V breaker and doubling one or both? Have you got any of your logical Spyder Channels set up to include more than one CT, with the same CT included in more than one logical Channel? Have you got any of your Spyder CTs shown as 20A in Spyder setup, when they aren't?

Correction (1/22/18 09:10) - the last question should be the other way round, i.e. "Have you got any 20A Spyder CTS not shown as 20A in Spyder setup?" The opposite error I originally suggested should actually give lower readings.
« Last Edit: January 22, 2018, 10:15:47 AM by pfletch101 » Logged

Peter R. Fletcher
TED Pro Home - main MTUs monitoring utility and PV Solar feeds; 2 Spyders monitoring selected individual circuits
breaker man
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Posts: 4


« Reply #4 on: January 26, 2018, 10:44:59 AM »

I am only using 60A CTs and measuring all circuits separately.  Do not have any 20A checked.  Mult is set to 1 on all circuits.  Only one block checked for each circuit in the graph description.  Have also switched one of the spyders just to make sure it was not a bad spyder
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pfletch101
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« Reply #5 on: January 27, 2018, 05:11:30 PM »

Up until now, I think that we have been implicitly assuming that the main MTU/CT is reading correctly and the Spyder Channels are reading high. The possibility exists that the Spyder totals are correct and the MTU is reading low. Do your Spyder values match the load that the individual circuits should be drawing, when they are drawing it? When a heavy load (electric heater, oven, microwave, ....) is turned on, do both the relevant Spyder Channel and the MTU indicate the same, approximately correct (i.e. consistent with the load's faceplate wattage), increment in power flux? If not, does the Spyder reading increment seem high or the MTU reading increment seem low?

In my experience the MTU/CT combos are pretty reliable unless the CTs are not properly applied to the power feeds which they are monitoring. Assuming that you are using the standard 'clip-on' main CTs, are the clips completely closed, and are they both 'facing' in the same direction?

Out of interest, are any of your loads very reactive (e.g. high-power motors) - I believe that Spyders may overread on reactive loads (VA value rather than true wattage)?
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Peter R. Fletcher
TED Pro Home - main MTUs monitoring utility and PV Solar feeds; 2 Spyders monitoring selected individual circuits
breaker man
Newbie
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Posts: 4


« Reply #6 on: January 28, 2018, 03:57:31 PM »

In trying to zero in on the problem.  I pick the circuit for the AC Furn.  While watching the spyder load at it's peak the spyder read .304KW or 304watts and at that moment I checked the amp load of the circuit with a multi meter and the amp load was 1.5 amps which equates to .180KW or 180 watts.  I am using a 60A CT for this circuit which the spyder spec say that a reading below 200W will record as zero  Not sure why it is reading anything.  I am using a 60A CT since it is a 60A breaker.
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pfletch101
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« Reply #7 on: January 28, 2018, 09:08:54 PM »

A couple of things:
1) To get meaningful power readings from a Spyder Channel for testing purposes, you need to apply a steady load to it for 3-5 minutes, and ignore (at least) the values from the first and last minute. Spyder channels are supposed to average over a minute, but my experience is that their readings may not totally settle in the first full minute after the load changes.
2) The specified accuracy of the Spyder channels is relative to full scale - you can't draw useful conclusions about potential problems if you are applying a load near the bottom of the channel's measurement range.
3) You also won't get meaningful power readings from a motor circuit (I assume, from the current/power draw, that you were looking at the AC circulating fan load) by separately measuring AC Volts and Amps with a multimeter and multiplying them. It is the 'reactive load' issue I alluded to in my last message. The voltage and current are not in phase with each other. Indeed, in the extreme case of a frictionless motor turning a flywheel at constant speed with no mechanical load applied to it, they will be 180 Degrees out of phase, and no electrical power will be being drawn at all, even though the separate measurements of Voltage and Current will not be hugely different than when power is being used by the motor to drive a moderate mechanical load.

For test purposes, you should, if possible, use a large, steady, resistive load (electric oven, electric hotplate, electric space heater, immersion heater, microwave oven).
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Peter R. Fletcher
TED Pro Home - main MTUs monitoring utility and PV Solar feeds; 2 Spyders monitoring selected individual circuits
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