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Discuss RCD trip time in the Electrical Forum area at ElectriciansForums.net

telectrix

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300mSec @ x1. typically see <40mSec.
40mSec. @ x5. typically see <20mSec.
 
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  • #3
Thank you- these are the values I was looking for.

From what I understand the mechanism does not differentiate between 1x and 5x, both trip around the same time without an inverse curve.
 

telectrix

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on testing RCDs (in this country) we generally find results of around 30-40mS @ x1, and 10-15mS. @ x5.
 
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Why the faster trip? I always thought of it as a magnet which lets go as soon as the current goes over 25ma.
 

telectrix

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the RCD detects imbalance between L and N. the higher the current causing the imbalance, the faster it will trip.
 
An RCD with BSEN 61008 or 61009 is 300ms @ x1
But the old BS 4293 is 200ms @ x1
I think I am right is saying that, I’m sure if not someone will say,
But you don’t really see any of the old BS numbered rcds anymore, there are some Crabtree C50 Rccb about mainly schools,
 
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Andy78

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Here are the results from a BS 4293 I tested today and a picture of the device in question.
2019-11-26 11.46.56.jpg
2019-11-28 13.30.30.jpg
 
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I understand, but what makes it faster? Its kind of like a solenoid, it either pulls in or it does not. Of course could be wrong here.
 

telectrix

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Never knew that. Thanks :) How does the science work for RCDs?
RCDs work by sensing a difference on current flow between L and N ( in your case hot and N). close to the threshold, they trip, as they see an imbalance., i.e when the current i 1 of the conductors leaks to earth (ground) in the event of a fault. the test button simulates earth leakage by putting a resistance across L and E.
 

ruston

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@Andy78: Big thanks, I needed that. How much does a tester like that cost?
This is a link to a site sponsor doing a good deal on these type of testers.
Hope it helps you.
 
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Might just get one. Are the cheap ones good? How will the tester tolerate 120 volts and line-line 230 volts?
 

Andy78

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@Andy78: Big thanks, I needed that. How much does a tester like that cost?
That's a multifunction tester, also known as an installation tester, that performs all the tests required to verify safety.

That particular model is about £500 new. It's quite a basic model compared to some. Across all brands they range from about £400 to over £1000 depending on what features are included.

You can get dedicated RCD testers which are a bit cheaper.
 

davesparks

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.
[/QUOTE]
Might just get one. Are the cheap ones good? How will the tester tolerate 120 volts and line-line 230 volts?
You would have to look at the details in the specs or contact the seller/manufacturer to find out.
I think some of them do work on those kind of voltages but can't say for certain.
 

DPG

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@Cookie you seem to have a good degree of knowledge on this stuff do you not use Multi function testers stateside? 😁
I can only go on what I've seen on here and the Web, but they don't seem to put as much emphasis on testing and then evaluating the test results as we do over here. Happy to be corrected though.
 

Baddegg

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I can only go on what I've seen on here and the Web, but they don't seem to put as much emphasis on testing and then evaluating the test results as we do over here. Happy to be corrected though.
I did suspect that.....just made me more curious as to how they verify installations over there?.....
 
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There is no testing requirements in the states, in fact when I bring it up on US forums it does not go all too well.
 

Baddegg

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There is no testing requirements in the states, in fact when I bring it up on US forums it does not go all too well.
Thanks cookie, what about for fault finding what instruments would you use for that?
 
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Multi meter, clamp on amp meter and a pigtail socket with a bulb in it. Circuit tracer as well.
 
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I know how they work, they use a differential coil to sum zero sequence currents. The thing is I don't exactly get how eletrmechanical RCDs respond faster to high current ground fault vs low current ground faults.
 

DPG

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There is no testing requirements in the states, in fact when I bring it up on US forums it does not go all too well.
This backs up what I thought. Seems a bit worrying really.
 

littlespark

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It might take the US time to catch up with UK on testing as we do.
Reading a US forum would really be interesting

How long ago did the UK actually fill in test certificates on every job?

Even I can remember a lamp holder with 2 single cables for voltage testing and an actual doorbell for continuity testing.
 
I remember and still have an MK plug top with lamp holder and pygmy lamp. One live wire to the plug and lamp holder the other just to the lamp holder. Plug in and touch the floating wire to the socket cover screw, if it lit polarity and earth all good.
 

davesparks

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Cookie RCDs have a transformer built in the RCD which detect voltage leaking. Does that explain it better
They do incorporate a transformer, but that's not how an RCD works.
Voltage doesn't leak, it can't, voltage is a measure of the energy difference between two points.
Current flows, and can 'leak', but an RCD does not detect leakage (not directly).

An RCD (single phase version) has two transformer coils wound around a common core, one is for the live and the other for the neutral. There is a third coil around the same core which operates the tripping mechanism.
If the current flowing through the live coil is equal to the current flowing through the neutral then they are balanced and the cancel out and no current is induced in the tripping coil.
If a more current flows through one coil than the other then they are not balanced and a current is induced in the tripping coil and the RCD trips.
So an RCD detects an imbalance of current between live and neutral.
It doesn't matter why there is an imbalance, it could be leakage, someone receiving and electric shock, a caoacitir charging, incorrect wiring, short circuit etc etc.
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I know how they work, they use a differential coil to sum zero sequence currents. The thing is I don't exactly get how eletrmechanical RCDs respond faster to high current ground fault vs low current ground faults.
I don't know how many RCDs are purely electromechanical these days, I think a lot of them incorporate some electronics.
This probably has something to do with the faster reaction to higher fault currents.
 

DPG

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I remember and still have an MK plug top with lamp holder and pygmy lamp. One live wire to the plug and lamp holder the other just to the lamp holder. Plug in and touch the floating wire to the socket cover screw, if it lit polarity and earth all good.
I'd like to point out that it was Westy that said 'plug top' this time.
 
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  • #35
My understanding is the EM RCDs use a magnet resting against a metal electromagnet, that when current flows it cancels the field from the magnet and it lets go triggering the trip mechanism.
 

Megawatt

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My understanding is the EM RCDs use a magnet resting against a metal electromagnet, that when current flows it cancels the field from the magnet and it lets go triggering the trip mechanism.
Cookie you are putting to much science into RCD or GFCI breakers. My question is what does it matter how fast it trips. In the US if it sees 30ma leaking it trips. No we don’t do all the testing that the UK does because if it don’t trip or trip fast enough all you can do is buy another one. Let’s pick another topic to discuss it
 

DPG

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Cookie you are putting to much science into RCD or GFCI breakers. My question is what does it matter how fast it trips. In the US if it sees 30ma leaking it trips. No we don’t do all the testing that the UK does because if it don’t trip or trip fast enough all you can do is buy another one. Let’s pick another topic to discuss it
How do you know if it is tripping correctly without doing the sequence of tests though?
 

Megawatt

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How do you know if it is tripping correctly without doing the sequence of tests though?
DPG honestly we don’t test them, how do y’all test them ? We are not required to but I’ve got my continuing education class Saturday to renew my license and I’m going to ask the instructor, so I guess I’ll have an answer next week. The only way I would trip them and make sure they reset. I’ve been on this forum since June and y’all have to test everything. We get accused of bang testing but if I wire something I can guarantee you it will work properly and I can’t speak for the dumb asses who think their (electricians) but couldn’t stick their finger up there but without a map
 

Andy78

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DPG honestly we don’t test them, how do y’all test them ? We are not required to but I’ve got my continuing education class Saturday to renew my license and I’m going to ask the instructor, so I guess I’ll have an answer next week. The only way I would trip them and make sure they reset. I’ve been on this forum since June and y’all have to test everything. We get accused of bang testing but if I wire something I can guarantee you it will work properly and I can’t speak for the dumb asses who think their (electricians) but couldn’t stick their finger up there but without a map
We test the by applying a test current to them with a meter that records the time they take to trip in ms. We are essentially testing that they comply with the product standard they have been built to.

An example of this test, or at least the results of it, I have posted in post#8, and the resource I posted in post #28 describes test procedure and requirements quite well.
 

Megawatt

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We test the by applying a test current to them with a meter that records the time they take to trip in ms. We are essentially testing that they comply with the product standard they have been built to.

An example of this test, or at least the results of it, I have posted in post#8, and the resource I posted in post #28 describes test procedure and requirements quite well.
Andy to my knowledge I’ve never seen one and thanks for the info
 

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