What stopped them from making an AFCI with actual restraint?

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mbrooke

mbrooke

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I'm curious. Why didn't they just make an MHO (step distance) branch circuit breaker?

You will always get consistent fault reach no matter the fault current at the panel, with a few cycle delay built in to allow for inrush.

At lost less complicated and cheaper than what we're doing now.
 
How would that detect "arcs"? The intent of the AFCI is to clear faults that draw current below the standard breaker's time trip curve.
 
That is all way beyond me. The AFCI has to look at the arc signatures and try to determine if they are part of the normal equipment operation or they are a harmful arc, and clear the circuit where the device determines it is a harmful arc.
 
don_resqcapt19 said:
That is all way beyond me. The AFCI has to look at the arc signatures and try to determine if they are part of the normal equipment operation or they are a harmful arc, and clear the circuit where the device determines it is a harmful arc.
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Its not beyond you. Its ohms law. Ohms law can be understood, purely searching for current ripples, not so much...
 
don_resqcapt19 said:
Like I said this is way beyond my electrical understanding.
If that will work and would be cheaper why don't you design it sell it.
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Oh, I could. And say that equation is a "trade secret" "proprietary knowledge" so now one can say for sure I have nothing more than a simple MHO relay with some time/rate of change restraint built in.
 
When I can afford a house large enough that 'transmission line' issues come into play, I will be happy to fund research into mho distance breakers for my home. Transmission line effects come into play when circuits are a large fraction of the wavelength of the AC line frequency. In other words, this is an issue for circuits perhaps 300km long....

The issue with _all_ circuit protective devices is to reliably differentiate between faults and loads.

Ordinary OCPD looks for excessive current. But even something as simple as a 20A breaker can't simply instantaneously trip at 20.01A, because totally reasonable loads on a 20A circuit might draw transient currents that exceed 20A.

GFCI differentiates from real loads by looking for current flowing via some path other than the desired circuit conductors.

AFCI looks for current 'signatures'.

When AC circuits get large enough, 'transmission line' effects come into play. The key point is that 'power factor' (relationship between current and voltage phase) is not constant on a transmission line. One of the things you will find in a transmission line is that the apparent impedance of the load _changes_ as you change the length of the transmission line between your test point and your load. (At least if the load is not 'matched' to the transmission line impedance.) In particular, this means that a short circuit right next to your breaker looks like an entirely different sort of load 500km away. My very crude understanding of mho distance relays is that they can be set to look at the apparent impedance of the line at the supply end, and to detect impedance changes that are consistent with a fault some distance away, even if the current level is the same as normal load current.

-Jon
 
winnie said:
When I can afford a house large enough that 'transmission line' issues come into play, I will be happy to fund research into mho distance breakers for my home. Transmission line effects come into play when circuits are a large fraction of the wavelength of the AC line frequency. In other words, this is an issue for circuits perhaps 300km long....
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Since you brought up transmission lines (utility circuits), MHO relaying is used even on short lines- ie 1/4 of a mile. #14 isn't immune to being a combination of R+jX.


The issue with _all_ circuit protective devices is to reliably differentiate between faults and loads.

Ordinary OCPD looks for excessive current. But even something as simple as a 20A breaker can't simply instantaneously trip at 20.01A, because totally reasonable loads on a 20A circuit might draw transient currents that exceed 20A.

GFCI differentiates from real loads by looking for current flowing via some path other than the desired circuit conductors.
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Right. Problem is some OCPDs can't tell the difference between the two.

Current 'signatures'.
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The question is, are these signatures "operate" or "restraint"

When AC circuits get large enough, 'transmission line' effects come into play. The key point is that 'power factor' (relationship between current and voltage phase) is not constant on a transmission line. One of the things you will find in a transmission line is that the apparent impedance of the load _changes_ as you change the length of the transmission line between your test point and your load. (At least if the load is not 'matched' to the transmission line impedance.) In particular, this means that a short circuit right next to your breaker looks like an entirely different sort of load 500km away. My very crude understanding of mho distance relays is that they can be set to look at the apparent impedance of the line at the supply end, and to detect impedance changes that are consistent with a fault some distance away, even if the current level is the same as normal load current.

-Jon
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Same applies to a 15 amp, 120 volt branch circuit. If not more so.
 
mbrooke said:
Oh, I could. And say that equation is a "trade secret" "proprietary knowledge" so now one can say for sure I have nothing more than a simple MHO relay with some time/rate of change restraint built in.
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All of the existing internal firmware for the AFCIs is "proprietary knowledge".
The only thing you have to be able to show is that your device passes all of the tests required by the product standard. ANSI/UL 1699, "Arc-Fault Circuit-Interrupters."
 
winnie said:
set to look at the apparent impedance of the line at the supply end, and to detect impedance changes that are consistent with a fault some distance away, even if the current level is the same as normal load current.

-Jon
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I like you (y) 😎 😁 😁
 
mbrooke said:
What is it proprietary? What do they have to hide?
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They all have their own ideas of how the firmware needs to work. There is no need for anyone else to know how they choose to make their devices work. The only criteria is that they pass the tests specified in UL 1699.

When they first came out all of the brands had a GFP function because that was the only way they could pass one or more of the specified tests. Now, at least two manufacturers have found a way to pass those tests without a GFP detection circuit. That is a cost advantage to them and results from how they made their firmware work. Why should they share that with others?
 
don_resqcapt19 said:
They all have their own ideas of how the firmware needs to work. There is no need for anyone else to know how they choose to make their devices work. The only criteria is that they pass the tests specified in UL 1699.

When they first came out all of the brands had a GFP function because that was the only way they could pass one or more of the specified tests. Now, at least two manufacturers have found a way to pass those tests without a GFP detection circuit. That is a cost advantage to them and results from how they made their firmware work. Why should they share that with others?
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Because people have a right to know AFCIs aren't as special as they are made out to be.

I mean the IEC market still hasn't been told what AFCIs were replicating in the first place. You think we'd know the rest of this massive lie?
 
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