Ungrounded source question
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maghazadeh
Senior Member
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Ungrounded source question
My answer is NO, current can not flow if the source of voltage has no connection to ground. Current will flow in a closed circuit. for example, a 12 volts car battery has a + and a - poles and non of poles has any connection to ground. You can be barefoot on a wet surface and touch any of the poles one at the time without getting zapped, so no current flows.
My answer is NO, current can not flow if the source of voltage has no connection to ground. Current will flow in a closed circuit. for example, a 12 volts car battery has a + and a - poles and non of poles has any connection to ground. You can be barefoot on a wet surface and touch any of the poles one at the time without getting zapped, so no current flows.
This is true however as Augie mentioned there is a capacitive coupling between the phases and ground. This capacitve coupling allows a very small current to flow in the magnitude of mA. Remember it only takes 50mA or so to cause damage to the body to this capactitively coupled current can indeed cause harm to the body.
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I am joining the Augie band wagon.
On paper no shock, in real life, with a large enough ungrounded system you can get your socks knocked off.
This is aimed at electronics but the idea is the same.
http://en.wikipedia.org/wiki/Parasitic_capacitance
On paper no shock, in real life, with a large enough ungrounded system you can get your socks knocked off.
This is aimed at electronics but the idea is the same.
http://en.wikipedia.org/wiki/Parasitic_capacitance
This is commonly used in Operating rooms to make the electrical supply safer.
The capacitive coupling is monitored and has strict limits. To keep the coupling to a minimum, the isolation panels are kept close to the load, and the number of branch circuits is usually kept to a minimum. Even the type of wire is chosen to minimize the capacitve coupling.
I'd be curious to know weather this capacitance coupling effect would be worst upstream or downstream in a system? In other words on these systems would you recieve a larger shock upstream in a system or downstream (effect of impedance)
I know that for grounded systems the amount of current that flows through your body is primarily determined by the resistance of your body (aprox 1Mohm) and therefore has no bearing on the avaliable fault current in a system for a given voltage level. In other words the current flowing through your body will be roughly the same weather you touch a 480V main switchboard, or some 480V downstream branch circuit because the 1Mohm resistance of your body is much greater than either two of the system impedances for the upstream and downstream locations.
I know that for grounded systems the amount of current that flows through your body is primarily determined by the resistance of your body (aprox 1Mohm) and therefore has no bearing on the avaliable fault current in a system for a given voltage level. In other words the current flowing through your body will be roughly the same weather you touch a 480V main switchboard, or some 480V downstream branch circuit because the 1Mohm resistance of your body is much greater than either two of the system impedances for the upstream and downstream locations.
M4gery
Senior Member
Does anyone else agree with this?
rcwilson
Senior Member
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No. Capacitive coupling to ground is same through out the system. Doesn't change with distance from the source. So shock hazard is the same.
If it is ungrounded with good insulation, you can still get a very healthy shock from capacitive discharge. (Actually it is not healthy, it kills you).
ggunn
PE (Electrical), NABCEP certified
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I hate it when that happens!
Yes this is what I was saying.
That shock hazard from a grounded or ungrounded system does not matter where in the system you are since your bodies large impedance will be the predominant impdeance.
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