Sleepy Wombat

What Rcd Symbol Do You Use ?

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In electrical schematics I use the following RCD symbol...mainly because i have not found a simple generic one. What do u guys use ? Note in the attached pic on leg is the Active and the other the Neutral.

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Ok, I was going to wait till some replies before I asked a stupid question since I probably can't help you, but it doesn't look like you are getting any replies. What is a RCD Edited by TWControls

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Thanks for the response. RCD - Residual Current Device. Typically used on power cicuits for sockets to provide protection for the end user. For example on a house I would have an RCD, it would be typically have a trip sensitivity of 30mA so a short to earth (ie a person touching active and neutral) would be detected and cause a trip, thus saving their lives. Other similar terminology is RCBO - Residual Current Circuit Breaker with Overcuerrent Protection Don't you guys in the states have similar portective devices ?????

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To my knowledge, which is limited on this, No. I know there is a new standard for breakers coming out or it may be out now, but I think it has to to with the response time of the breaker and the 80% maximum current (a 20 A breaker has to trip at 16 A) Let me make sure I understand. You are saying that it will trip on a small load up to around 30 ma. Is that correct? That would not be the same as a Ground Fault Interrupt (GFI). How long have you guys had these? May be will have them and I am not understanding the terminology. Australia is 380 Volt? Could this be more important for having 220 Volts on the outlets? Edited by TWControls

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Yep, thats what we call a GFI. The basic operating principle is two wires (such as line/neutral) are passed through a torroidal current transformer. As long as the current flowing in each conductor is exactly the same and in opposite directions then no voltage is induced in the CT. As soon as there is any imbalance at all (such as from a ground fault) then a voltage is induced on the CT and the breaker opens. SW, the symbol makes sense because it shows how the contacts are operated. GFIs exist primarily in two form factors here. The most common is integrated direcly into the wall outlet. This has the advantage of ground fault protecing only part of the circuit. For example in the kitchen the counter outlets are protected while a lower outlet for floor cleaning equipment - which would be more prone to nuissance trip - is not protected. The other common form factor is as a breaker, where both overcurrent and ground fault current protection is provided by a single device in the breaker panel. On a drawing we usually just show a generic outlet and just label it as GFI, or show a breaker and label it also as GFI. Edited by Alaric

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Thanks for the terminology clarification Alaric, I must admit i have never heard of them referred to as a GFI. Does that mean Ground Fault Current ? BTW i tend to use them is i am supplying an outlet for my laptop internally to the board. Or another example is when Socket are supplied from my panel. Another industrial example is if i was running a heat trace for pipes which is 240VAC a little bit of protection for a user doesn't go astray. BTW in Australia 3 phase is 415VAC with single phase being 240VAC.

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Ok so it is a GFI. Thanks for the info Alaric GFI = Ground Fault Interrupter or sometimes GFCI = Ground Fault Circuit Interrupter Usually required in wet/damp locations. I'll look when I get to work. I have a symbol for that we can compare

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Can't find the electronic file, but looking at a paper copy of what I used, yours is probably better. Mine has the CTs around the wires and takes the CT reference to ground. Ground and neutral have to be separate wires going to the GFI/RCD over here, so I do this to show the ground being hooked up on the wiring diagram. But I do not show the imbalance mechanically tripping the breaker as you do. I will add this to my symbol.

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In Australia it is LAW thus compulsary for all new electical domestic installations for power outlet circuits to be fitted with RCD's.

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In the US it depends on where the outlet it. All kitchen counter, bathroom, laundroom outlets, and anywhere there is water, must have a GFI. Also outlets in an unfinished basement or garage and outdoor outlets must also be GFI and anywhere there is an unfinished concrete floor on earth. All outlets in sleeping areas must have an AFI breaker (arc fault interruptor). These detect if there is an arc in the circuit and shut it down.

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I did a quick search on the net and found out that there are many acronyms refering to the same thing. RCDs (Residual Current Devices), common usage in Australia RCCBs (Residual Current Circuit Breakers), common usage in Australia ELCBs (Earth Leakage Circuit-Breakers), common usage in Singapore, Malaysia CBRs (Core Balance Relays), I don't really know where it is commonly used GFIs (Ground Fault Interrupts), common usage in USA GFCI ( Ground Fault Circuit Interrupter), common usage in USA

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Once again the world of Electronics comes up with multiple names for the same device. And we thought the tower of Bable was a mess.

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I know this is an extremely old post & I only discovered it by accident doing a search. However, I just have to comment on this as stated above: 'a short to earth (ie a person touching active and neutral)' This is incorrect in a couple of ways & I hope it was just down to a perhaps rushed answer. First, an RCD's purpose is not to detect a 'short' to earth, although it certainly will. A circuit breaker or fuse is designed for that purpose. For a start, a person caught in an 'earthed' situation is not considered to be 'shorted', which has the connotation of being a direct short to earth .i.e minimal resistance. A person has much resistance & is just another load on a circuit to a fuse or circuit breaker, hence they will not trip & even if they did, never in time to save a life. Secondly, & most importantly, an RCD will NEVER trip when a person is connected between active & neutral if that person is NOT touching earth. i.e if you are working in a roof space & lying across timber trusses working on a 'live' circuit & manage to get hooked up between active & neutral & cannot disengage from the connection ( i.e. get belted off by the shock like I have on 2 major occasions), on an RCD protected circuit...you are dead. It is all over for you. An RCD will never trip in this instance as it monitors the current out v's current back in between the active & neutral. In this case it will be equal as you are across active & neutral. If you have some leakage to earth then the RCD will trip depending on its rating & the leakage. I will detect that not all current is coming back on the neutral therefore the difference must be going to earth & it will trip. In most cases an RCD will save you because most electrocutions are in earthed situations. They have saved many lives. I just thought that this needed clarifying. Cheers.

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