Human Fault Loop Impedance: Understanding IPZ, IEC 60364-4-41, and Effects on 230V Systems

Question

Hello, at the beginning, I note that I do not have an electrical education and I am interested in the issue of the above-mentioned impedance (ipz for short) purely hobbyist. Well, I heard that for an installation in a flat ip 0.4 ohms is good, but 1 ohms is bad. Wanting to explain to myself what...

Anonymous · Accepted Answer

It tells you what will switch off / break the circuit-protection faster, or a shorted wire which, due to too high impedance, took over the 'protection' function. Low impedance is a good chance that the damaged section (loop) will disable the protection. High loop impedance threatens to break (even arc) the loop without triggering the protection and maintaining the lethal potential at these broken ends of the loop. As for the times of protection activation, it is required at various points of the installation that they activate immediately or with a specific delay. And this is an ordinary time mechanics, given to the electrician with the symbols A, B, C, D. Eg INS.16A C / 1P switch -single field

MrMazi · Accepted Answer

Does this coefficient depend on the control and measurement equipment used? Therefore, it cannot be administered with theoretical consideration of the prolem. Well, unless my colleague was about another measurement error?

retrofood · Answer

3.1.13. (10.9, 15) It is forbidden to publish entries that violate the spelling rules of the Polish language, which are careless and incomprehensible.

3.1.17. (10.9, 16) It is forbidden to publish entries lowering the general level of discussion, resulting from laziness or containing the demanding nature of statements.

Łukasz-O · Answer

At the request of the topic, however, it does not release the author from correcting the spelling of the units, reading the content of the section, etc. This is a technical forum, we require a minimum of knowledge and a lot of details.

topikpl · Answer

Thank you for bringing the topic back and for the answers.

I improved Ohm to Om, because that's what the moderator meant - I'm not quite sure. I can see that the electrician community is sensitive and likes to be enigmatic :-)

@ 15kVmaciej: ok, I think I understand, but what causes "too" high impedance in practice? Probably the cross-section and length of the cable (for which the wrong protection was selected), and for a circuit with a correctly selected fuse? Circuit damage?

@HeSz: ok, I will read it again, but this later, in the morning I won't make it.

I remind everyone of the basic electric units:
wat [W] - we write "watts"
kilowatt [kW] - we write "kilowatts"
ampere [A] - we write "amperes"
volts [V] - we write "volts" (not "volts")
kilowatt hour [kWh]
ohm [?] - ohms (not "ohms", not "ohms", not "ohms")
[retrofood]

MrMazi · Answer

Hi
Ia is the trip current Ia = k * In [A]

k is the coefficient which is determined from the fuse characteristics.
It is assumed that for the circuit breakers it is:
characteristic B; k = 5
characteristic C; k = 10
characteristic D; k = 20

So with the S301 B16 protection, the current causing it to trip at the right time is 16 x 5 = 80A.
The permissible fault loop impedance is then 230/80 = 2.87 ?.
As you can see, assuming 0.4 is good and 1 is bad is bad reasoning.

retrofood · Answer

And where is the coefficient taking into account measurement errors?

topikpl · Answer

Thank you for your answers and for drawing attention to the units. I will definitely not write more Ohm or Om in my life :wink:

My understanding is that after accounting for the error of the measuring device, the impedance value will be somewhere in the range of 0.5-2 ohms. So whether it is "good" or "bad", in practice it depends on the device with which the measurements are made.

MrMazi · Answer

Maybe another way. To understand me well.
If the measured impedance is 2 ? and the meter error is 1%, then the actual value of the fault loop impedance can be from 1.98 to 2.02 ?.
We take the worst value, i.e. 2.02 ?.
It does not change the fact that 2.87 ? is allowed.

It doesn't depend on the device!
Installation parameters (including fault loop impedance) do not depend on what they are measured.
This is not the case in any area of life.

topikpl · Answer

I expressed myself wrong. Naturally, reality does not depend on measurement (although there is a theory about this ). My point is that different meters give different ranges, if you measure with a big error you can get a range that goes wrong, even though measuring with an accurate device would show good.

MrMazi · Answer

When measuring standard S301 B16 protected socket circuits, the value of this allowable impedance is 2.87 ?.
Let the meter readings be about 1? (which is already a big result).
You do not have to worry then that the meter is lowering so much that you may be above the maximum allowable impedance.
There are no such measures whose error would be 300%.
It's worse when the result is 2.5 ?. Then the risk of being above the requirements is much greater

Miniax · Answer

Whether the IPZ is satisfactory (ie day or bad) depends on the equipment used in the installation. In general, if the condition of the automatic shutdown of the power supply is met, then the impedance can be considered satisfactory (at least in terms of protection in the right time). In addition, the layout of the grid is essential - whether it is TN or TT. Of course, in average home installations, it can be assumed in advance what a relatively satisfactory value will be. However, it does not change the fact that each installation should be approached individually and it is not possible to clearly define what values of fault loop impedance are satisfactory.

Anonymous · Answer

It is for sure, the selection of protections has nothing to do with IPZ, the way the circuit is arranged and the coexistence of others may affect the final result of the IPZ measurement. @retrofood , tesla [T] we write tesla

Human Fault Loop Impedance: Understanding IPZ, IEC 60364-4-41, and Effects on 230V Systems

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