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3-Phase Power / Induction Motor Theory
« Last post by Dave Loucks on January 15, 2018, 01:00:12 PM »
Not sure how helpful this will be, but I presented a talk on how an induction motor operates.  Covers some basic rules about Faraday's Law, Lorenz Forces and just in general how you convert electrical current into motion. 

Modbus / Re: Modbus MINT - 02 Illegal Address exception
« Last post by Dave Loucks on September 01, 2017, 09:39:41 AM »
Have you attempted to read what should be a valid register and you get the Modbus Exception Code 02 (Illegal Address)?

Two fixes:
  • Write a 0 to 42001
    Writing a zero to this register relaxes the error checking on the mMINT such that if you read a block of registers and one or more of those registers within that block are not supported by the connected device at that address, the mMINT will "zero fill" the response and not send a 02 exception
  • Extend the length of block read to include prior registers
    For example, attempting to read frequency (406197) alone on a DT1150, even if the 42001 register is set to zero can result in an 02 exception.  The fix is to read the prior register 406195 [3-phase apparent power factor] and frequency 406197 as a complete range.  Note that for this trick to work 42001 must be set to 0.
Video Tutorials / Directory
« Last post by Dave Loucks on June 06, 2017, 07:54:02 AM »
These videos are mostly throughout this website.  I've just copied them here to a single page for convenience.

LTSPICE simulation export, resampling and decimation tutorial
Low Voltage Underground Utility Networks
Ethernet Networks
Using Excel to Display Waveforms and Phasor Diagrams
Using Excel to Display Three-Phase Phasor Diagrams From X-Y Data
SFTP Connection to PXMP Meter
Using Excel to Generate and Display 3-Phase Harmonics
Adding the Analysis Tool-Pack to Excel
Calculating, Displaying and Normalizing FFT Collected From Multiple Devices
Measuring Harmonic Attenuation Using Programmable Phase-Shifted Transformers
Performing Arbitrary Math Functions Within COMTRADE Excel Importer Program
Comparison of Performance Using Zone Selective Interlocking (ZSI) Versus Arcflash Reduction Maintenance System (ARMS)
Understanding Differential Relay and CT Matching
Using the COMTRADE Excel Importer to Determine RMS Values
Understanding Security When Connecting to a Java Enabled Power Xpert Meter
Harmonic Summation and Cancellation (Phase and Ground)
LTSPICE Quickstart Tutorials Part 1:
LTSPICE Quickstart Tutorials Part 2:
LTSPICE Quickstart Tutorials Part 3:
Power Systems Rule of Thumb (Recording of Instructor Led Class)
Using Excel to Create Harmonic Trend Viewer for PXM4/6/8K Meters
Comparing Fault Current Calculations using “Z Method” Versus the “R+jX Method”
Designing Higher Efficiency Mission Critical Power Systems
Power System Load Flow and Power Factor Correction Calculations (Recording of Instructor Led Class)
Power System Protection and Coordination (Recording of Instructor Led Class)
Predicting, Measuring and Abating Transients on Medium Voltage Systems with Vacuum Switching
Modbus MINT Programmer Tutorial
Modbus MINT Programmer Cloud Backup and Restore
Modbus MINT Programmer Issuing Control Commands to INCOM Device
Creating PXG900 Offline Configuration File
Differential Ground Fault Sensing
Legacy Motor Control / Westinghouse Advantage MCC
« Last post by Dave Loucks on April 20, 2017, 12:21:49 PM »
The Advantage MCC was introduced in 1991 and was Westinghouse's first networked motor control. 

I wrote a paper on this way back in 1993 entitled "Low-voltage motor control centers utilizing microprocessor technology".  See

Download the Instruction Booklet IB 8922-1 attached below.
Legacy Motor Control / Westinghouse Type W MCC
« Last post by Dave Loucks on April 20, 2017, 11:55:24 AM »
Legacy Westinghouse MCC that was available from roughly 1965 to 1979

Download the instruction book IB12-129 dated July 1978 below.

You can learn more about vintage Westinghouse products (and parts for those products) at
Numa Logic Programmable Controllers / PC700/900/1500/1700 I/O Modules
« Last post by Dave Loucks on February 24, 2017, 03:59:23 PM »
As I get around to it, I'll scan and add more cards.  If you need an instruction booklet for an I/O module that isn't listed here, let me know (dgloucks at gmail dot com)
  • NL-740
    2-channel, 12-bit isolated, differential input analog input module
  • NL-742
    8-channel, 10 bit singled ended input analog input module
  • NL-743
    16-bit TTL register input module
  • NL-744
    8 or 16 multiplexed 16-bit TTL register input module
  • NL-750
    2 channel, unipolar 12 bit analog output
  • NL-751
    4-channel, 11 bit (10 bits + 1 sign bit) analog (voltage) output
  • NL-752
    4-channel, 10 bits, analog (current) output
  • NL-753
    16-bit TTL register output module
  • NL-753
    8 or 16-channel multiplexed TTL register output module
Article 240.87 in the NEC mentions that ZSI and something called "energy reducing maintenance switching with local status indicator" are two ways of meeting the requirements of this article. 

What is ZSI?  How is Eaton's version of the "energy reducing maintenance switching" (called ARMS) different from other vendor's versions?

Click on the image below to view a screencast of me presenting the contents in the attached PPT file below.

3-Phase Power / Differential Relaying and CT Error Calculations
« Last post by Dave Loucks on February 06, 2017, 10:11:34 AM »
Article 240.87 in the National Electrical Code describes using differential protection as one of the options to use if you have a breaker rated 1200 A or higher.  But just what is differential protection and why should or shouldn't be used?

This presentation gives an overview of how differential relaying operates and includes a discussion of CT accuracy and how high resistance loads (e.g. long CT conductors, small wire gauge CT conductors or high impedance loads) affect differential relaying accuracy.

Click on the image below to view a screencast of me presenting the contents in the attached PPT file below.

3-Phase Power / Conductor Temperature Ratings
« Last post by Dave Loucks on January 10, 2017, 01:52:05 PM »
Conductors and bus generate heat when current flows through them.  How much heat?  That depends on the conductor size, the application and many other factors.

For electrical equipment, such as switchgear, switchboards, motor control centers and panel boards, the manufacturer has received certification from UL that at rated current the bus, terminals, connection points and lugs are below the maximum temperature rating permitted by UL.

But what if you want to operate the equipment at an even cooler temperature than this maximum allowable temperature?  How much would you need to reduce the current to reduce the temperature?

That's a tricky question because the temperature of equipment likely isn't proportional to the power dissipated.  Cooling plays a factor and that cooling too is non-linear with temperature.

Can we at least estimate changes in temperature based on changes in current flow?

One place to start as a first pass approximation is IEEE 399-1997 (Brown Book) where in section 13.4.1, equation 13-5, an "adjustment factor" is calculated for when you want to change either the conductor temperature rating or the ambient temperature:

Tc  Conductor rated temperature in oC at which the base ampacity is specified
Tc'  Maximum allowed conductor temperature in oC
Ta  Ambient temperature in oC at which the base ampacity is specified
Ta'  Other ambient temperature oC at which the conductor will be applied

I'm assuming copper conductors here.  You'd use equation 13-6 if you wanted aluminum conductors (just change 234.5 to 228.1 both times).

In our example:
Tc            = 105oC (40 + 65)
Tc'          = 70oC (40 + 30)
Ta           = 40
Ta'          = 40 (no change)

So, this would imply that if you ran the conductor at no higher than 72% of its rated capacity (or better, 71%) the conductor temperature would not rise more than 30oC above a 40oC ambient.

Consider this only back of the envelope calculations since it could be better (there is might be better air circulation) or worse (you might have harmonics which will induce eddy current heating)

Here's a calculator that automates this math:

You can click on the image above to download, or select "conductor_temp_rerating.xlsx" from below.
Power Xpert Gateway / PXG Configuration
« Last post by Dave Loucks on January 03, 2017, 02:02:28 PM »
While you can certainly just plug in a browser and configure a PXG900, there are a couple of things you should know to make things go more smoothly.

If you are using a Windows PC and have admin rights, you might want to consider using the micromini-USB connection on the front of the PXG900 (formerly a type A USB connection on the "E" series gateways).  The default address for that port is always  The disadvantage is you will need to load a USB driver onto your computer (instructions) and you will need Admin rights to allow that.

If instead you use the Ethernet port, you should know that this port supports Zero Config and that means that the default IP address can move around!  While the default IP address on the Ethernet port following a factory reset is (or, that will only be the case if nothing else is "heard" when the PXG boots.  Best bet is to make sure nothing is connected to the network 1 port during a factory reset. 

Once you are able to connect with the gateway and have changed the IP address to a new fixed (static) value, zero config is disabled and you'll have a good known fixed IP address for the PXG.

But why mess around with all this?  Did you know there was an "low touch" loading method for the PXG900? (actually also works on the "E" series, i.e. PXG200E, 400E, 600E, and 800E gateways with latest firmware too).  You'll still need admin rights to both load this program and load the USB driver (which the installer does automatically).

The "Configuration Automator" program (link at end of this topic) removes a lot of the complexity when you are tasked with loading the PXG configuration.  It does this by semi-automatically installing an XML file that contains the settings you wish to install.

This XML file can be created a number of ways, but perhaps the easiest is to use the PXG offline configuration spreadsheet.

You can download a copy of the offline configurator and try it yourself (if this deep link has expired -- which it might when the program is updated -- just navigate to and select "PXG900 Offline Config Tool" under the "Software Downloads" section in the "Documentation" tab.

Here are some screencast videos that explain how these programs work:
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