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how do rcd's work?


Lee321

Question

regarding the flow path of electricity?

the situation is a faulty metal bodied kettle that is not earthed and has developed a live fault to its casing and someone is touching the case with there hand, the person is not touching anything else i.e an earth or neutral

i'm looking for calculations of current draw and how?

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They sense a difference between L&N. Some current will pass through the person to the general mass of earth.

In a true vacuum the RCD wouldn't trip.

Can't do cals sorry.

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whatever goes through live (sorry, line!), must come back through neutral. so it monitor exactly what flows through each, and any imbalance means current is going somewhere is shouldnt. i.e through you. then it switches off.

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whatever goes through live (sorry, line!), must come back through neutral. so it monitor exactly what flows through each, and any imbalance means current is going somewhere is shouldnt. i.e through you. then it switches off.

Only if its been tested now and then though.

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whatever goes through live (sorry, line!), must come back through neutral. so it monitor exactly what flows through each, and any imbalance means current is going somewhere is shouldnt. i.e through you. then it switches off.

yes i know the theory but enough must be lost to begin with!

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regarding the flow path of electricity?

the situation is a faulty metal bodied kettle that is not earthed and has developed a live fault to its casing and someone is touching the case with there hand, the person is not touching anything else i.e an earth or neutral

i'm looking for calculations of current draw and how?

current draw?

that would be the current rating of the RCD surely..

e.g. 30ma imbalance between current in L & N..

so 230v / 30ma = 7666.66ohm approx,

so you would have a path to an earthy surface of around 7.6Kohms, to get 30ma flow..

is that what you were after??:|

or am I treeing up the wrong bark!?:pBlushing

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because were generally in contact with something thats conductive. standing on concrete, and your in contact. same for soil, or you ali ladders on grass. your trainers/boots are probably conductive (unless insulated), so overall resistance will be high, but enough to allow current to flow

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yes i'd call those situations as reduced resistance but its weird how standing in jeans and trainers inside dry circa 1744mega ohms to earth and they still trip

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and how did you measure this?. voltage comes into it too.

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nice 1 SL.

but how does a human draw that much current?

30ma is NOT that much current... More like that Little current IMHO.

anyway... this is a very complex with many many variables to take into account.

Rough guide to typical shock currents can be found in some books by "Brian Scaddan"

e.g.

1ma -2ma barley perceptible, no harmful effects

5ma - 10ma Throw off, painful sensation

10ma - 15ma Muscular contraction, cant let go

20ma - 30ma Impaired breathing

50ma & above Ventricular fibrillation and death

(patch will know what all the big words mean!:D:P)

Also the NICEIC have some interesting information in their Technical manual.. but it is deep reading & has reference to loads of other documents and tables:

heres a taster of the sort of variables and stuff that has to be considered...

The magnitude and duration of current cannot categorically be classified into dangerous or safe values or times. However, the concepts of current thresholds and time/current zones (combined with heart-current factor, where applicable), employed in IEC 60479-1, allow the probable dangerous effects of a current to be predicted.

Current thresholds

Current thresholds are the limiting values of current causing distinct effects on the body. The following current thresholds are defined in IEC 60479-1 :

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i was told muscle contraction was more with dc, ac would grab then through u back

yes you don't want to be messing with upper voltages of dc

that will f you up lol

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not sure tom. i think you have to start a new thread for it to come up in new posts oddly

your posts are working here tho ;)

or maybe the op has a setting that allows it to go in the new posts if there is any ?

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am i doing it wrong?

yes. according to search, you have not made any threads

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you have no new threads, but you have visitor messages in your user profile....

where exactly are you going to make new threads?

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