Residual Current Device

Not sure what your "RCS" is referring to.

However, to prevent extreemely dangerous ground loops, a common ground is required by law in North America. Many operators were killed before this law. If there is not a common ground, a piece of equipment will build up hundreds of volts of potential, and just touching it will discharge through your body like a lightning bolt.....

The joints of the common grounds and any high power systems need a special solder or connector to prevent arcing across the joint. Electricity will take the shortest and easiest path. for high current devices, this can be through air. Arcing, besides the electrical hasard, is a fire and explosive initiater.

OK , I found it. Here we call it griound GFI or ground fault interupters.

Houses here all use the joined common. We use GFI's anywhere in vicinity of water such as bathrooms. It is required by code.

The code in different places is different.

While some GFI's allow say, 4 items to be connected, the building code may only allow two.

The purpose of these devices are to prevent shock by measuring ground current

Faster cct breakers will not work, since the surge of the start up of some electrical devices take longer than it takes to electrocute a person. GFI's react much faster than the CCT breakers. CCT breakers trip on an over current condition. you do not need an overcurrent condition to electrucute a person.

RCD means residual current device (you know it has ratings like 30 mA or 300 mA) so you can understand what i mean? i know the merits of joint grounding recently most in usage. But excuse me i could not understand what the case is when we have a joint grounding, do we need a residual current relay in the system? pls let me know of this. Techno my lad, thank you already..

The RCD does no replace the grounding system.

An RCD measures the loss of current, this can be through a grounding network or something else.

You need to look to these two technical items separately: the RCD will save your life, the grounding wire will make it easier for him to do this.

Joining grounding systems is needed to be sure that there is no equipotential difference between two metal parts in your house. But you may never connect the neutral wire to the general grounding, as there might be a residual voltage due to unbalance.

It is advisable to use a general 300mA RCD on electrical entrance of your house and a 30mA for all your wet area's. Typical North American style of protection is on appliance level (GFI wall socket), European protection is on circuit level (Din rail mounted RCD that protects the complete system). But the two systems are merging to the safest solution.

thank you but there is a point which i couldnt get. What if we use the joint grounding system as neutral how can develop an unbalance? or you meant "in case an unbalance"? pls make a more clear statement my friend. thank you already for your kindness..

The device works by measuring the difference in currents in the neutral conductor and the live conductor, and tripping if the difference exceeds the rated value, inferring a loss of current somewhere to ground/earth.

By definition, the neutral conductor downstream of the device cannot be connected to ground/earth. Were it to be, then the relationship between the current flowing in the conductor and the current flowing in the ground/earth path would be indeterminate, and the device will trip if the difference exceeds its rated value; that is what it is designed to do in order to protect an individual connected to the circuit and forming the ground/earth path from possible electrocution.

In the UK, RCDs are now a requirement for new installations for power socket outlets for kitchens, garages and those mounted outside the building, and for power showers.

It is always good practice to upgrade existing installations as opportunity permits, though not a requirement in the UK as regulations are never retrospective. It is good practice to use either an intervening RCD on appliances used outside or to fit an RCD plug, though not a requirement, as an exterior circuit may already have one if installed or upgraded to today's regulations.

ah i mean you wanna tell the fact that the earthing wire is not included into the toroid when we mount it.i mean this is what you wanna tell ? ok thank you again..

Correct.

If the earth wire is included, then the device will not register a difference when there is a fault between neutral and earth, or when there is a fault between live and earth insufficient to rupture the circuit protection device.

These devices are largely available over-the-counter, with proven reliability and indemnity as part of the purchase. Why is there any need to build one?

who said such a thing? building what? also can u tell me of bank protection of transformers, is there any protection type with which u can protect two transformer with one relay? (perhaps with 3 current transformer but not 6 ) have you any idea of this?

Jin,

Are you telling no that you are working behind a transformer?

This is called an IT system. Please call in specialists, as in an IT system the RCD will never trip.

You also can't protect a transformer with it, the current leaks are internal and undetectable.

An RCD is a nice invention that should be in every installation, but does not replace God or craftmanship and electrical knowledge.

The unbalance: when you have no equal load on the three phases your resulting voltage will not be equal. Normally the sum of all the current vectors in the star-point is 0, but when not equally loaded the sum will not be 0 and you need a forth vector to have a 0. (Kirchoff)

To drag this current through the neutral wire a voltage is needed and this voltage is also applied on the connected grounding pin (not every installation will have this extra pin), Imagine that your resistance is 1Ω and you need 10A to compensate: a 10V signal will be on the neutral wire. If you now have connected the neutral to your grounding and your shower is also grounded, you will find a 10V AC signal in your shower. It tickles the balls but harmless, unless a phase wire gets disconnected and you are confronted with 200V AC. The RCD will not react and you are dead.

everything is okey except the last sentence "unless a phase gets disconnected" so how can develop a 200 volt on the shower? pls explain in more detail. (what about the broken phase: it is earth fault or just broken without touching anywhere?) pls go on doing your favor my brothers..

It can happen that one or more phazes are disconnected due switching on the grid.

The grounding pin on the neutral wire will then catch and protect your installation.

This could also happen with the Neutral, then the full compensation will come from the ground connection.

As ground can't compensate the full fault your grounding circuitry will show a serious voltage.

what does" The grounding pin on the neutral wire will then catch and protect your installation" ?

Jin,

: the neutral ground system will protect your installation by leading the overcurrent to the ground but not yourself.

Normal AC systems can handle peaks of + 20% for a short period. The resulting peak on the ground can be > 50V AC, it depends on your ground resistance and typical load.

What sometimes happens is that the cables are disconnected and reconnected and neutral gets mixed up with a phase: at that moment your grounding system connects the faze to the earth and a circuit breaker will disconnect the lines. But this can take a few seconds, until that moment you will see voltages on your grounding that can reach 200V AC. When you would have a connection between your installation ground and the neutral ground your complete ground network will be at 200V.

This kind of errors can happen outside your will or premises but you can be the victim of it.

Gwen

I have never seen so much rubbish written as here. The RCD residual current device works by sensing any current from either Live or Neutral to earth and if this is over the rated current it will trip. Even if the Live is disconnected from the circuit if you accidental touch Neutral to earth it will still trip out. A multiple earthing system can either connect all metal cases sinks and baths to earth via a 10mm minimum cable in series with no joins or via several individual cables that will protect by offering a low enough leakage path back to the earth combining block at the consumer unit.

The idea being to both protect from shock (death) and to prevent any two metal surfaces being at unequal potential from each other. There should never be enough voltage to produce more than 5 to 10mA to flow between any two metal objects.

Unlike an RCD a fuse or circuit breaker is there to protect against cable failure and fire risk. Cables should be rated for the minimum voltage drop and lowest temperature rise under max load conditions.

hi guest. you say rubbish bla bla but u dont say anything new. do a favor to me and just tell me if we use RCD with a joint- earthed system for example in premises, in case there happens a leakege. in theory we are not harmed with a joint-earthed system without RCD but our system should know that there is a fault on the system am i right?.. also tell me how can it be that when your live wire is disconnected, the fact that you touch the neutral(of course there is a path to earth ) will make the device trip out? if you have no live so you dont have a current on your neutral.so how can be there a difference of current magnitude and afterwards the device acts? you mean the systems in which there are more than one feeder?

Jin,

The RCD does not measure the current through the ground. As stated by the guest: it measures the current in the life wires and calculates the difference.

But it will only detect an error downstream.

Gwen

Gwen i think you have not yot read what i wrote carefully. i say the same thing but guest says if we touch the neutral even if the live is disconnected the device trips out. i think this sentence is false. what do you think?

i also want you to give me a clear answer. You know my real problem? if we have a joint-earthing system we need RCD?

It depends on the neutral residual signal: if your neutral is perfect you will see no sine on this line and your RCD will not react.

It is also not needed as there is no danger.

As soon as the current through your body goes up the RCD will react (this happens when the voltage on the neutral goes up)

As soon as you have currents flowing though your cables you will see a residual sine on your neutral line.

You always need an RCD, either which kind of earthing you use. The Type of RCD can vary depending on the type of electrical system you are using. As long as you are in a normal grid connected system you don't need to worry about this. (But think about is as soon as you have a separation transformer, on a boat, in a plane, ...)

Gwen