RCD mAmp or Amp

whitts

am doing an assingment for college and i cant seem to find if RCD's are measured in amps or milli-amps?.
can any one tell me 100%..
cheers \P

whitts

domestic RCD that is...

whitts

http://www.youtube.com/watch?v=Y0ouXt069t8

@ 0.09 he says ''32 milli amp''
yet in this one...

http://www.youtube.com/watch?v=Fvm_3ZkPYnc&feature=related

@1.25 he says ''i know i have a 32 AMP protective device

ft9

Domestic rcd is generally a 32mA, which is the leakage allowed before it trips.

It will be capable of 40A load

whitts

SO rcds are measured (as such) in mA not A... ?? RIGHT?

Davy

Rating is 32Amps, or whatever size you get, 25 etc.

The sensitivity is 30mA, even if the load rating changes

brightspark

In the first video the test is referring to a 30mA RCD (in simple terms the device trips when more than 30mA flows to earth).

RCD's also have a current rating specifying how much current they can safely carry. (as Davy said)

The second video is referring to a 32A MCB (B rated) and the test is whether the earth resistance is low enough to allow sufficient current to flow. He refers to the RCD because it is important that the test device is suitable and does not trip the RCD.

Bruthal

whitts wrote: »

am doing an assingment for college and i cant seem to find if RCD's are measured in amps or milli-amps?.
can any one tell me 100%..
cheers \P

milli amps and amps are really the same thing, it takes 30 milli amps or just over of residual current to trip an rcd, where as a 32 amp mcb can continously carry 32 amps without tripping.
milli amps is amps x 1000, amps is milli amps/1000

30 milli amps is 0.030 amps
32 amps is 32,000 milli amps

Its the exact same as comparing meters to kilometers, A 100 meter sprint is 0.1km, and 30km is 30,000 meters
meters are km`s x 1000 and km`s are meters/1000

So the answer is the tripping current of RCD`s is measured in milli amps, because its a very small current to trip it, less than a 30th of an amp, so they rate that in milli amps.

2011

With a healthy single phase circuit the current flowing down the live = the current flowing back on the neutral.
When an RCD is installed on a circuit this device compares the current on the live to the current on the neutral.
If the difference > a certain threshold (generally 30mA for domestic RCDs) the device should operate (trip).

On RCDs this difference in current is generally shown as "IΔn". This can often be seen written on the RCD.

The more common IΔn values in Ireland include:
10mA
30mA (this is the most common)
50mA
100mA

In theory 50mA at mains voltage can kill, this is why IΔn on many RCDs is a lower value (such as 30mA).

The lower IΔn the greater the risk of "nuisance" tripping i.e. the RCD operating when there is no significant fault present.

A 40A RCD is rated to safely and indefinitely carry a current no greater than 40A. This same RCD may have an IΔn value of 30mA.

A unit called an "RCBO" is a single unit that contains both RCD and MCB.

The test button on an RCD performs an electrical test on the unit by ensuring that there is a difference in currents on the neutral and live that is large enough for the device to operate.

30 milli amps is 0.030 amps
32 amps is 32,000 milli amps

+1

Bruthal

The RCD test button is actually a bit different in that the same current actually does come in on live and neutral on that test. Did you ever trip one through getting a shock? One of best devices brought out in electrical.

M cebee

2011 wrote: »

With a healthy single phase circuit the current flowing down the live = the current flowing back on the neutral.
When an RCD is installed on a circuit this device compares the current on the live to the current on the neutral.
If the difference > a certain threshold (generally 30mA for domestic RCDs) the device should operate (trip).

On RCDs this difference in current is generally shown as "IΔn". This can often be seen written on the RCD.

The more common IΔn values in Ireland include:
10mA
30mA (this is the most common)
50mA
100mA

In theory 50mA at mains voltage can kill, this is why IΔn on many RCDs is a lower value (such as 30mA).

The lower IΔn the greater the risk of "nuisance" tripping i.e. the RCD operating when there is no significant fault present.

A 40A RCD is rated to safely and indefinitely carry a current no greater than 40A. This same RCD may have an IΔn value of 30mA.

A unit called an "RCBO" is a single unit that contains both RCD and MCB.

The test button on an RCD performs an electrical test on the unit by ensuring that there is a difference in currents on the neutral and live that is large enough for the device to operate.


+1

i've never heard of 50ma rcds -are they available

Bruthal

50ma at mains voltage could kill alright, although 50ma could kill if it was 100 volts putting it through a person, but it would indeed take around the mains voltage of 230v to put 50ma(0.05 amps) through a person.
Its one of those tricky ones, its the resistance at the point of contact that is the most variable, dry hands v wet hands and contact surface area, etc while the resistance through the body itself is fairly constant,

The shock is actually the I^2xR one, so the higher the body internal resistance the higher the voltage needed to reach the fatal level of current, so therefore 50ma is a worse shock at 230v than it would be at 110v, but as the internal resistance is fairly constant for most of us, its the contact resistance and voltage which determines the shock. It would not be too easy to receive a fatal shock from 110v but very easy at 220v which is double, but you actually get up to 4 times the shock.

M cebee

robbie7730 wrote: »

50ma at mains voltage could kill alright, although 50ma could kill if it was 100 volts putting it through a person, but it would indeed take around the mains voltage of 230v to put 50ma(0.05 amps) through a person.
Its one of those tricky ones, its the resistance at the point of contact that is the most variable, dry hands v wet hands and contact surface area, etc while the resistance through the body itself is fairly constant,

The shock is actually the I^2xR one, so the higher the body internal resistance the higher the voltage needed to reach the fatal level of current, so therefore 50ma is a worse shock at 230v than it would be at 110v, but as the internal resistance is fairly constant for most of us, its the contact resistance and voltage which determines the shock. It would not be too easy to receive a fatal shock from 110v but very easy at 220v which is double, but you actually get up to 4 times the shock.

ya? -im familiar with the first paragraph

i^2 *r is news to me-must have missed that bit

Bruthal

M cebee wrote: »

ya? -im familiar with the first paragraph

i^2 *r is news to me-must have missed that bit

Well its not something we hear much, we just hear its the 50ma as example current level, but i would imagine it must be the same as any load, a 1kw load at 100v is taking 10 amps, the same load across 200v would now be 20 amps and 4kw, so i would tend to believe we receive 4 times the shock when the current level is doubled, i dont think i heard anyone say it before, must be my own sort of theory on it.

The shock is definitely far more severe at 230 than 110v, i dont mean the 55v Line to earth, the 110v is actually tolerable to touch, where as 230v is severe, dont try it at home though:D

Higher voltages do break down the skin resistance better on dry hands, but its still far more than double the shock each time voltage is doubled.

M cebee

yes you may be right- i wasn't thinking straight

Bruthal

M cebee wrote: »

yes you may be right- i wasn't thinking straight

A no id say you were, its not certain what i am sayin is right, i would just think it probably is, no doubt the shock gets worse at a higher rate than the voltage increase rate, The skin resistance when dry definitely is a big factor, wet hands and direct contact on 230v is extremely dangerous when there is contact with each hand across the 230v, 110v would be a lot less severe.

whitts

many thanks lads!!. i know where to come if i need any more info, much appriciated!!