Really, shall we carry out a touch voltage exercise, then you will see R2 determines the touch voltage
---------- Post Auto-Merged at 23:48 ---------- Previous post was made at 23:46 ----------
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Rcd's in series..
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---------- Post Auto-Merged at 23:48 ---------- Previous post was made at 23:46 ----------
oh right, so now we assume things,
does this also take into account Ra? or Ze?
that has a massive influence on touch voltage.
does this also take into account Ra? or Ze?
that has a massive influence on touch voltage.
Hi All,
Going to well and trully stick my newbie neck out here, so all feel free to shoot me down!!!!
Touch voltage....Hmmm, well for a start off, bonding and R2 has nothing at all to do with touch voltage as far as i can see, unless of course you are trying i imagine, to calculate the voltage that may arise under fault conditions between exposed conductive parts and extraneous ones....
Here though, I presume that here we are on about the touch voltage referenced to true earth, that which you will feel if you touch an exposed part during a fault, whilst standing on say, a damp concrete floor.
So, as for the other answers, everyone is nearly right!!!!
Touch voltage is indeed heavily influenced by Zs, as during a fault, it is Zs that determines the fault current that flows.
So, firstly; We have a fault current that is purely determined by the Zs of the circuit concerned. All agreed on that one???
Next, so, we have a [usually] large fault current flowing round our "earth loop"
Now, you touch an exposed part during a fault, and what determines the voltage that will be applied to you???
One thing, and one thing only; as Sidewinder says, the impedance of the "earth" side of the "earth loop"
The voltage we would feel, would be the product of the total fault current flowing x the impedance of the "earth side" of the earth loop, measured from the point of the fault, back to the star point.
In other words, if the "earth side" of the loop were to be likened to a giant, [but hopefully low impedance] resistor, what we would have the dubious pleasure of feeling, would in effect, be the voltage appearing across this "resistor" when it is carrying whatever the total fault current may be...
Got my tin hat ready!!!!!!
john....
Going to well and trully stick my newbie neck out here, so all feel free to shoot me down!!!!
Touch voltage....Hmmm, well for a start off, bonding and R2 has nothing at all to do with touch voltage as far as i can see, unless of course you are trying i imagine, to calculate the voltage that may arise under fault conditions between exposed conductive parts and extraneous ones....
Here though, I presume that here we are on about the touch voltage referenced to true earth, that which you will feel if you touch an exposed part during a fault, whilst standing on say, a damp concrete floor.
So, as for the other answers, everyone is nearly right!!!!
Touch voltage is indeed heavily influenced by Zs, as during a fault, it is Zs that determines the fault current that flows.
So, firstly; We have a fault current that is purely determined by the Zs of the circuit concerned. All agreed on that one???
Next, so, we have a [usually] large fault current flowing round our "earth loop"
Now, you touch an exposed part during a fault, and what determines the voltage that will be applied to you???
One thing, and one thing only; as Sidewinder says, the impedance of the "earth" side of the "earth loop"
The voltage we would feel, would be the product of the total fault current flowing x the impedance of the "earth side" of the earth loop, measured from the point of the fault, back to the star point.
In other words, if the "earth side" of the loop were to be likened to a giant, [but hopefully low impedance] resistor, what we would have the dubious pleasure of feeling, would in effect, be the voltage appearing across this "resistor" when it is carrying whatever the total fault current may be...
Got my tin hat ready!!!!!!
john....
Hi Plumber,
Got my tin hat on, eeekkk!!!!
john.....
Got my tin hat on, eeekkk!!!!
john.....
Hi again,
I give up...cannot get the quote thing to work, anmd it will not let me highlight text either.. Just typed the whole lot out three times...
john..
I give up...cannot get the quote thing to work, anmd it will not let me highlight text either.. Just typed the whole lot out three times...
john..
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John, the quote function is to the very far right of the tool bar in the post quick reply box.
AndyGuinness
AndyGuinness
Hello!! Just testing to see if the colour is working now..
obviously not.....
john
obviously not.....
john
philbas
Well-known member
It works if the colour you wanted was black
What about now??
---------- Post Auto-Merged at 20:10 ---------- Previous post was made at 20:01 ----------
Hi Again,
I do not know how to work the quote thing, so i have done the best i can!!
Originally Posted by apprentice87
Hi All,
Going to well and trully stick my newbie neck out here, so all feel free to shoot me down!!!!
Touch voltage....Hmmm, well for a start off, bonding and R2 has nothing at all to do with touch voltage as far as i can see, unless of course you are trying i imagine, to calculate the voltage that may arise under fault conditions between exposed conductive parts and extraneous ones....
I hope your joking lol
No...I cannot see how bonding or R2 for a circuit would affect touch voltage unless you were taking about a voltage that might appear between exposed parts, and extraneous ones that they may be bonded to. The extraneous bit are not going to act as "extra" earthing, as they are already connected to the MET and therefore have already been "allowed for" in the figure for Zs and the "earth side" of the fault loop.
Here though, I presume that here we are on about the touch voltage referenced to true earth, that which you will feel if you touch an exposed part during a fault, whilst standing on say, a damp concrete floor.
No, im referring to effective touch voltage as per IEC 6**5*-826
Ahhh, i have no idea what that is,,,, [newbie see!!]
So, as for the other answers, everyone is nearly right!!!!
You think?
I hope!!
Touch voltage is indeed heavily influenced by Zs, as during a fault, it is Zs that determines the fault current that flows.
You need to be far more specific than that
Why? Zs is Zs. It is Zs for a circuit, [assuming a fault of negligible impedance, as the textbooks like to put it] that determines fault current, that in turn determines touch voltage
So, firstly; We have a fault current that is purely determined by the Zs of the circuit concerned. All agreed on that one???
Agreed
Agreed!
Next, so, we have a [usually] large fault current flowing round our "earth loop"
Agreed
Agreed!
Now, you touch an exposed part during a fault, and what determines the voltage that will be applied to you???
Well are we assuming an equipotential Zone here?
No.....I think we were just talking about touch voltage as if you just stood on a stone floor and touched an exposed part during a fault. [Putting on wellies first does not count!!]
One thing, and one thing only; as Sidewinder says, the impedance of the "earth" side of the "earth loop"
The voltage we would feel, would be the product of the total fault current flowing x the impedance of the "earth side" of the earth loop, measured from the point of the fault, back to the star point.
In other words, if the "earth side" of the loop were to be likened to a giant, [but hopefully low impedance] resistor, what we would have the dubious pleasure of feeling, would in effect, be the voltage appearing across this "resistor" when it is carrying whatever the total fault current may be...
Got my tin hat ready!!!!!!
I hope it's ready lol
So do I !!!!!
john....
---------- Post Auto-Merged at 20:11 ---------- Previous post was made at 20:10 ----------
Yeah!!! It worked!!!
[Tin helmet at the ready again!!!!]
john..
---------- Post Auto-Merged at 20:10 ---------- Previous post was made at 20:01 ----------
Hi Again,
I do not know how to work the quote thing, so i have done the best i can!!
Originally Posted by apprentice87
Hi All,
Going to well and trully stick my newbie neck out here, so all feel free to shoot me down!!!!
Touch voltage....Hmmm, well for a start off, bonding and R2 has nothing at all to do with touch voltage as far as i can see, unless of course you are trying i imagine, to calculate the voltage that may arise under fault conditions between exposed conductive parts and extraneous ones....
I hope your joking lol
No...I cannot see how bonding or R2 for a circuit would affect touch voltage unless you were taking about a voltage that might appear between exposed parts, and extraneous ones that they may be bonded to. The extraneous bit are not going to act as "extra" earthing, as they are already connected to the MET and therefore have already been "allowed for" in the figure for Zs and the "earth side" of the fault loop.
Here though, I presume that here we are on about the touch voltage referenced to true earth, that which you will feel if you touch an exposed part during a fault, whilst standing on say, a damp concrete floor.
No, im referring to effective touch voltage as per IEC 6**5*-826
Ahhh, i have no idea what that is,,,, [newbie see!!]
So, as for the other answers, everyone is nearly right!!!!
You think?
I hope!!
Touch voltage is indeed heavily influenced by Zs, as during a fault, it is Zs that determines the fault current that flows.
You need to be far more specific than that
Why? Zs is Zs. It is Zs for a circuit, [assuming a fault of negligible impedance, as the textbooks like to put it] that determines fault current, that in turn determines touch voltage
So, firstly; We have a fault current that is purely determined by the Zs of the circuit concerned. All agreed on that one???
Agreed
Agreed!
Next, so, we have a [usually] large fault current flowing round our "earth loop"
Agreed
Agreed!
Now, you touch an exposed part during a fault, and what determines the voltage that will be applied to you???
Well are we assuming an equipotential Zone here?
No.....I think we were just talking about touch voltage as if you just stood on a stone floor and touched an exposed part during a fault. [Putting on wellies first does not count!!]
One thing, and one thing only; as Sidewinder says, the impedance of the "earth" side of the "earth loop"
The voltage we would feel, would be the product of the total fault current flowing x the impedance of the "earth side" of the earth loop, measured from the point of the fault, back to the star point.
In other words, if the "earth side" of the loop were to be likened to a giant, [but hopefully low impedance] resistor, what we would have the dubious pleasure of feeling, would in effect, be the voltage appearing across this "resistor" when it is carrying whatever the total fault current may be...
Got my tin hat ready!!!!!!
I hope it's ready lol
So do I !!!!!
john....
---------- Post Auto-Merged at 20:11 ---------- Previous post was made at 20:10 ----------
Yeah!!! It worked!!!
[Tin helmet at the ready again!!!!]
john..
Ha ha!!!!!!
john..
john..
