K
Kev2632
Should the rcd trip everytime if somebody had softly touched the live core of a cable? Or does it depend on wha current is flowing?
As Paul M has said the coil in the RCD moniotors the flow of the Line and Neutral conductors.
If either conductor flows to earth it will put the coil out of balance and trip the unit.
The amount of imbalance differs on each RCD but up to 15mA it should not trip but anything after that its down to each RCD.
That is why a series of tests are performed to make sure that the unit will trip out in the specified time.
That is for a BSEN RCD 300m seconds and a BS RCD 200 m Seconds.
Only a Ramp test will tell you at what stage the unit trips and it will record the mA it trips at!
If you softly (whatever that is ) touch a uninsulated live conductor and you are earthed the RCD is doing its job but the cable should have least insulation on it !
I hope this helps!!
If either conductor flows to earth it will put the coil out of balance and trip the unit.
The amount of imbalance differs on each RCD but up to 15mA it should not trip but anything after that its down to each RCD.
That is why a series of tests are performed to make sure that the unit will trip out in the specified time.
That is for a BSEN RCD 300m seconds and a BS RCD 200 m Seconds.
Only a Ramp test will tell you at what stage the unit trips and it will record the mA it trips at!
If you softly (whatever that is ) touch a uninsulated live conductor and you are earthed the RCD is doing its job but the cable should have least insulation on it !
I hope this helps!!
Hi KEV
The RCD may not have tripped for many reasons and it is impossible to guess writing on the forum.
If you have any concerns you should have the RCD checked out by someone with the necessary test equipment and competance to do so to put your mind at ease.
I would also mention that touching any live conductor is frought with danger even if it is RCD protected as they are mechanical and can fail !
The RCD may not have tripped for many reasons and it is impossible to guess writing on the forum.
If you have any concerns you should have the RCD checked out by someone with the necessary test equipment and competance to do so to put your mind at ease.
I would also mention that touching any live conductor is frought with danger even if it is RCD protected as they are mechanical and can fail !
K
Kev2632
Yea I understand what your saying, but in reality it should have tripped because the person was earthed standing on e concrete floor yea?
P
Paul.M
No Kev, your mate was isolated from a return path to earth because he was standing on a none conductive material (and hopefully wearing shoes).
If he touched something that was earthed i.e. a backbox he would be part of circuit, live to earth. Therefore receiving a shock up to the value of the protective device (30mA in this case) until it tripped.
If no contact to earth is made you are just a part of the line conductor and electricity will flow through you, that's why crows etc can sit/stand on HV overhead lines without being killed but don't try any home experiments, could be fatal.
This is what I believe happened to your friend, he became part of the conductor and did not complete a circuit by touching earth or neutral.
If he touched something that was earthed i.e. a backbox he would be part of circuit, live to earth. Therefore receiving a shock up to the value of the protective device (30mA in this case) until it tripped.
If no contact to earth is made you are just a part of the line conductor and electricity will flow through you, that's why crows etc can sit/stand on HV overhead lines without being killed but don't try any home experiments, could be fatal.
This is what I believe happened to your friend, he became part of the conductor and did not complete a circuit by touching earth or neutral.
K
Kev2632
B
brooky25
Birds are not in contact with terra firma so no path to earth. You can sit there with them if you fancy it
K
Kev2632
haha yea nooo bother
well why was it then that when the person touched the live conductor whilst standing on a concrete floor he received a shock? as the concrete isnt a conductor...is this not the same as the sitting on a live wire then?
B
brooky25
If your feet are not touching terra firma (ground) there is no path to earth.
You still create the shortest path to earth if you are stood on the ground, be it concrete or whatever.
Have you never seen anyone checking overhead lines ? Dropped out of a helicopter ie not touching ground so no earth path
You still create the shortest path to earth if you are stood on the ground, be it concrete or whatever.
Have you never seen anyone checking overhead lines ? Dropped out of a helicopter ie not touching ground so no earth path
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K
Kev2632
So even if the current cant get to earth it will still flow through the person is at correct, even thought your standing on concrete is at correct??? but stop at the concrete because its not a conductor and cant get too earth ?
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G
GaryM
Come out of this thread, into the forum, choose a sub forum then click 'post new thread'
http://www.electriciansforums.net/
B
brooky25
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K
Kev2632
so basically then yea, because he was standing on the concrete floor, the current was trying to get to earth but it cant because concrete doesnt conduct, where as working on HV lines the current wont look to go anywhere because you have contact with the ground is at right????
K
Kev2632
so that i understand, but i mean like when the person was standing on the concrete floor where does it go because the concrete doesnt conduct ? does it just stop?
know the answer?
I can't take it any more. Here goes...
The effect you get from touching a live part depends on the current that passes through your body (and the path it takes through your body), which depends on the voltage present and the total resistance of the "fault" circuit. The resistance varies hugely depending on how dry your skin is, how much of your skin area is in contact with the live part, and how you are connected to earth.
If you stand on dry concrete in your dry boots and touch a 230V line conductor, a small amount of current will pass through your body, boots and concrete, to earth. Not enough to kill you and maybe not enough to trip an RCD, but you'll probably feel a tingle.
If you take your boots off and stand in bare feet on wet concrete, or even better in a muddy puddle, the current through your body will be greater. Certainly enough to make you jump. Maybe enough to trip an RCD. Maybe enough to kill you (if the RCD wasn't there).
The effect you get from touching a live part depends on the current that passes through your body (and the path it takes through your body), which depends on the voltage present and the total resistance of the "fault" circuit. The resistance varies hugely depending on how dry your skin is, how much of your skin area is in contact with the live part, and how you are connected to earth.
If you stand on dry concrete in your dry boots and touch a 230V line conductor, a small amount of current will pass through your body, boots and concrete, to earth. Not enough to kill you and maybe not enough to trip an RCD, but you'll probably feel a tingle.
If you take your boots off and stand in bare feet on wet concrete, or even better in a muddy puddle, the current through your body will be greater. Certainly enough to make you jump. Maybe enough to trip an RCD. Maybe enough to kill you (if the RCD wasn't there).
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