Do North American electricians test impedance?
- Thread starter John Frum
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If you are referring to neutral to ground impedance, it is easier to just measure AC voltage between the neutral and ground. It should be < 2VAC when pulling a heavy load from an outlet.
Trying to measure ohms on AC wiring is difficult unless you kill power to the entire house. Otherwise power from other energized circuits can coupling into the circuit you are trying to measure resulting in garbage readings.
Trying to measure ohms on AC wiring is difficult unless you kill power to the entire house. Otherwise power from other energized circuits can coupling into the circuit you are trying to measure resulting in garbage readings.
Warpspeed
Solar Wizard
I can understand why an ELECTRICIAN would be vitally interested in measuring resistance.
But impedance ?
But impedance ?
2009Bounder2020
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very open ended question... I build and rebuild solid state and tube amplifiers. For this yes impedence testing is part of the process.
John Frum
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This video shows the test I'm interested in and the tool used.
I guess they start at the panel and then go around the ring.
Warpspeed
Solar Wizard
What I am seeing in that video is an ordinary low ohm measuring resistance meter.
The guy talking is constantly saying the word "resistance". Its a dc measurement.
Impedance is an ac measurement and it must be made at a specific frequency.
Why would that be necessary to simply check out some house wiring ?
The guy talking is constantly saying the word "resistance". Its a dc measurement.
Impedance is an ac measurement and it must be made at a specific frequency.
Why would that be necessary to simply check out some house wiring ?
Hedges
I See Electromagnetic Fields!
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In the electronics world, we use complex impedance which is real resistance in series (or parallel) with imaginary reactance from inductance or capacitance. The math for impedance magnitude of series connection Z = R + jX is calculated as |Z| = sqrt(R^2 + X^2)
Basically Pythagorean theorem; it is adding vectors at right angles to each other.
Loads with such impedance have a phase shift in the current, up to +/- 90 degrees relative to voltage.
Grid impedance is a thing. Also available fault current. Just as batteries have IR which limits the current they can dump into a short, utility transformers have winding resistance and there are cables in the circuit as well, allowing perhaps 20kA fault current in a residential neighborhood and 200kA in commercial areas. So our OCP have ratings appropriate for that.
Grid impedance also matters when determining if a big PV installation will be able to shove the power it produces into the grid. I think that may extend beyond the local transformer.
EICR? Not in the U.S., at least not for small residential property.
eicrtesting.com
www.lettingaproperty.com
We've had a few code requirements upon transfer and some at any time. Maybe GFCI in select locations. CO alarm for homes with gas or attached garage. Even on sale, inspections including electrical are optional. Arc-fault now required in new construction. Maybe your circuit resistance tests hope to catch the bad connections AFCI is supposed to protect against.
Basically Pythagorean theorem; it is adding vectors at right angles to each other.
Loads with such impedance have a phase shift in the current, up to +/- 90 degrees relative to voltage.
Grid impedance is a thing. Also available fault current. Just as batteries have IR which limits the current they can dump into a short, utility transformers have winding resistance and there are cables in the circuit as well, allowing perhaps 20kA fault current in a residential neighborhood and 200kA in commercial areas. So our OCP have ratings appropriate for that.
Grid impedance also matters when determining if a big PV installation will be able to shove the power it produces into the grid. I think that may extend beyond the local transformer.
EICR? Not in the U.S., at least not for small residential property.
How often do I need an EICR? - EICR Testing
Whether you are a homeowner, school, hotel, business or landlord this article discusses how often you need an EICR Test on your electrics
eicrtesting.com
Mandatory Electrical Safety Inspections for 2023 - What You Must Know
Mandatory electrical safety inspections have been introduced for landlords in England. As of April 1st 2021, all rentals must have an EICR.
www.lettingaproperty.com
We've had a few code requirements upon transfer and some at any time. Maybe GFCI in select locations. CO alarm for homes with gas or attached garage. Even on sale, inspections including electrical are optional. Arc-fault now required in new construction. Maybe your circuit resistance tests hope to catch the bad connections AFCI is supposed to protect against.
Pierre
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Impedance is a complex resistance determined by capacitance , inductance and frequency.
e.g. the inductive reactance XL of a coil is given as XL = 2piFL in ohms. Xc = 1/2piFC . Normally impedance is relevant only at higher frequencies. In household electrical installations ( 50 / 60Hz ) the term ‘loop resistance’ is more applicable.
In the above F is frequency , L is the inductance of a coil and C is the capacitance of a capacitor and pi is 22/7 .
To add them together to get Z you use the formulae as mentioned by @Hedges above.
I hope my memory is still good - have not used these for 30 years or so ?
e.g. the inductive reactance XL of a coil is given as XL = 2piFL in ohms. Xc = 1/2piFC . Normally impedance is relevant only at higher frequencies. In household electrical installations ( 50 / 60Hz ) the term ‘loop resistance’ is more applicable.
In the above F is frequency , L is the inductance of a coil and C is the capacitance of a capacitor and pi is 22/7 .
To add them together to get Z you use the formulae as mentioned by @Hedges above.
I hope my memory is still good - have not used these for 30 years or so ?
Last edited:
Warpspeed
Solar Wizard
Oh yes, we have power factor, surge impedance (of very long transmission lines) conductance measurement, insulation resistance measurement , non destructive voltage breakdown testing, all kinds of wonderful things that can be measured and tested in an electrical distribution system.
The only instruments a "normal" working electrician really needs, or would use, are an ordinary multimeter, a clamp on amp meter, perhaps a low resistance ohm meter and definitely a high voltage megger.
The only instruments a "normal" working electrician really needs, or would use, are an ordinary multimeter, a clamp on amp meter, perhaps a low resistance ohm meter and definitely a high voltage megger.
As an electrican trained under British standards, perhaps I can shed some light on the subject. During the inspection all circuits were tested for impedance and insulation dielectric strength, this was to ensure everything was safe, basically it was a verification of sorts before the electrican signed off on their work, there were other tests for grounding and bonding as well. This process, as can be imagined, was time consuming, often taking the good part of a day to complete for a single family home, so electricans would pre test their work.
Later I moved to Canada, which is similar to the U.S., no such testing was performed either by the installing electrican nor during the inspection, in fact most elecricans had no idea what a megger tester was, let alone how to use one.
Perhaps the nominal voltage being 240V has something to do with the higher standard, 120V is far more forgiving. Electrical inspectors, in Canada at least, are spread pretty thin, they now use registered representatives, usually the site forman as the inspector and once trusted, the inspector will likely not even show up.
Note. The past tense is used as my involvement in the British electrical industry is dated, but it would appear the tradition continues.
Later I moved to Canada, which is similar to the U.S., no such testing was performed either by the installing electrican nor during the inspection, in fact most elecricans had no idea what a megger tester was, let alone how to use one.
Perhaps the nominal voltage being 240V has something to do with the higher standard, 120V is far more forgiving. Electrical inspectors, in Canada at least, are spread pretty thin, they now use registered representatives, usually the site forman as the inspector and once trusted, the inspector will likely not even show up.
Note. The past tense is used as my involvement in the British electrical industry is dated, but it would appear the tradition continues.
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