Previous in Forum: 11kV Line Insulator Sparking   Next in Forum: Leroy Somer R450M AVR Problems
Close
Close
Close
17 comments
Rate Comments: Nested
Active Contributor

Join Date: Jun 2009
Posts: 23

RCCB Trip and Downstream

03/17/2016 9:56 PM

hi,

i had a 100ma rccb at DB side,and the final circuit to the equipment we also fitted a 100ma rccb.

why when there is short circuit at equipment side the rccb at this equipment never trip,

but it trip the DB side.

thanks

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Guru

Join Date: Oct 2008
Posts: 42355
Good Answers: 1693
#1

Re: rccb trip and downstream

03/17/2016 10:25 PM

Have your electrician look at the wiring and report back to you.

We can't quite see it from here.

Register to Reply
Guru

Join Date: Mar 2012
Location: Out of your mind! Not in sight!
Posts: 4424
Good Answers: 108
#2

Re: rccb trip and downstream

03/17/2016 10:27 PM

Your welcome!

Why did you take the RCCB on the DB side (yeah acronyms are so cool) away?

Seems it was the only one that tripped!

__________________
Common Sense Dictates
Register to Reply Off Topic (Score 6)
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21017
Good Answers: 795
#3

Re: rccb trip and downstream

03/17/2016 11:01 PM

If both are 100ma, it may be random (or just blind luck) which trips first. For better coordination, it usually helps to place the more sensitive components "closer to" the loads.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9684
Good Answers: 468
#4

Re: RCCB Trip and Downstream

03/18/2016 6:00 AM

Don't know where you're from, but in the UK it is "against code" (BS7671, AKA "the regs") to have more than one rccb on the same feed, whether they're the same trip rating or not.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#5

Re: RCCB Trip and Downstream

03/18/2016 8:12 AM

Because there is a connection between earth and neutral somewhere between the two rccbs that should not exist. The fault current is therefore being shared between the neutral conductor and the earth conductor between these two rccds, causing an imbalance between live and neutral at the upstream rccd sufficient for it to trip as described. The same phenomenon can be caused also by the presence of high current normal loads downstream of the second rccd.

Please don't cause deliberate short circuits, as they can be hazardous to health and also give rise to unpopularity with the premises' fire insurance cover provider.

  • Been there, done it, secondhand T-shirt available on eBay (other internet auction sites are available) right now. In this particular case it turned out to be a woodscrew holding the earthed bracket of a wall light to a vertical partition wall timber inadvertently just puncturing the insulation and kissing the neutral conductor of an incoming cable incorrectly located too close to that timber. The symptoms were a whole-house trip when the third ring of an electric cooker was turned on, and the 30mA circuit cooker circuit rccd remaining un-tripped. It took just three days' work to find it and 20 minutes to eliminate it, allowing for swearing time.

<Ahem>

Cannot agree with above statements on rccds in series, because on a domestic TT system, a 100mA rccd is needed on the incoming supply to cater for the prospect of a poor local earth connection; downstream rccds for final circuits need to be 30mA to comply with current UK codes for minimising the risk of electrocution.

</Ahem>

If in doubt, consult a qualified local Electrician.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Good Answer
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#13
In reply to #5

Re: RCCB Trip and Downstream

03/20/2016 2:36 AM

LOL!!

__________________
"What others say about you reveals more about them, than it does you." Anon.
Register to Reply
Guru
United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#6

Re: RCCB Trip and Downstream

03/18/2016 10:27 AM

Normal practice would be to have discrimination between cascaded RCCD's. IE 100mA-S (time delayed) feeding the DB and 30mA for the equipment. You'll find all the information in BS7671

As suggested get a qualified electrician to look at the set up. He will be able to carry out ramp tests and issue test certificates.

__________________
The reports of my death are greatly exaggerated.
Register to Reply
Power-User

Join Date: May 2008
Posts: 136
Good Answers: 2
#7

Re: RCCB Trip and Downstream

03/18/2016 5:54 PM

I do agree with Tornado in this <<For better coordination, it usually helps to place the more sensitive components "closer to" the loads.>>,.. But my question addressed to the questioner: Why do you intend to use the suggested number of RCCBs as depicted in the question? As you know such kinds of CBs are mainly used in wet places of houses (like kitchens, bath rooms)..

__________________
Just live and .. Learn!!
Register to Reply
Guru

Join Date: Aug 2014
Location: Port Macquarie N.S.W. Australia
Posts: 1071
Good Answers: 225
#8

Re: RCCB Trip and Downstream

03/18/2016 6:41 PM

Is it possible that your second RCCB is installed downstream of a VFD or other waveshape modifying device?

Standard RCCBs are not very effective on non-sinusoidal waveforms and may not trip as intended.

I'm guessing that you're referring to a short circuit to earth, as an RCCB will not normally trip on a short between live conductors

Register to Reply
Participant

Join Date: Mar 2009
Location: Kuala Lumpur, Malaysia
Posts: 1
#9

Re: RCCB Trip and Downstream

03/19/2016 1:16 AM

Our protection system is based on the level of device discrimination that is standard in most countries. What we sometimes fail to see is the minor details in the specifications of each device we installed. In your case, u have installed both RCCB of the same rating (100mA) which makes tripping becomes random on either device when a fault occurs. For a start try looking at the sensitivity rating of the mechanism in each device. This is represented by the (kA) rating. Try getting a lesser kA rating for the device installed at the final circuit and a higher kA rating at the mains side. Normally for mains it is recommended at 25kA and for final circuits, recommended rating is at 15kA or lesser depending on the design of your earthing system.

Hope this helps.

__________________
Hattasan@AGE
Register to Reply
Member

Join Date: Aug 2015
Posts: 9
#10

Re: RCCB Trip and Downstream

03/19/2016 6:39 AM

Hi , Your problem is simple but needs more technical knowledge. Whatever you are using TT or TNC we can evaluate a true solution. * Firstly I consider the two RCCB are operating at the same Earth fault loop impedance while the earth fault current is occurring.So ,the same rating of RCCBs ( generally ) receive the same differential current at operating CT built inside the RCCB case. ** This 'Criterion ' is very similar to a professional wiring contol sequence having Transformer ,Line side CT , GCBs Relays and Load side CT ,we consider as an example. Same as above phenomen of RCCB tripping ,two CTs have same CT ratios and operating characteristics ,thus we have to do coordination between two upstream CT and Relay and Down stream CT and Relay .If relaysettings are the same , coordination between two CT is essential and must be coordinated not to trip primary incomer GCB prior to the Fault current at load side . * As a conclusion , the best solution for your RCCB tripping problem is as follows . , -According to IEC -60364-4-41 you are liable to fix time-delayed 'S' Type RCCB in Up Stream ( DB) and instantaneous RCCB in down stream loadside. * Here is a another best solution ,The Discrimination between RCCBs can be achieved by exploiting the several levels of standardized sensitivity of RCCB 30mA,100mA,300mA and 1A. ( If you are still misterious please refer to the page numbers 187 ,188 and 189 of Electrical Installation Guide Book 2015 published by Schneider Electric ) **** Thanking you All. *KZM*

Register to Reply Off Topic (Score 5)
Guru

Join Date: Feb 2013
Posts: 2004
Good Answers: 31
#11

Re: RCCB Trip and Downstream

03/19/2016 6:43 AM

In simple terms, the rcd cannot look backwards to an earth fault. Only forward. So 2 devices on one circuit, one at each end, DB and equipment, the DB side looks towards the equipment and any leakage detected on this circuit, the DB side will trip. If the leakage was in fact at the equipment and ahead of the rcd, then only the equipment rcd would trip.

RCD units are not equal in leakage current detection, so no two rcd will trip on the same leakage current rating. They will trip within a narrow range. They do not calibrate the coils to be the same and the coils vary in sensitivity. If the CB's are functioning correctly they would trip before the rcd trips on a short, on the equipment, preventing sufficient current getting to the coil of the rcd and not causing an imbalance on the circuit to trip the rcd.

Register to Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#12

Re: RCCB Trip and Downstream

03/20/2016 2:29 AM

Someone is not understanding what an RCD is and does!! Same as I don't know what a DB is! Some sort of breaker maybe? The web gave me this:-

Dbsymbol

  1. the chemical element dubnium.

Read here for RCD infos:-

Residual-current device

What you APPEAR to need is a "RCBO, residual-current circuit breaker with overcurrent protection!

Or simply add an over current circuit breaker to what you already have.....

A circuit diagram would also have been a really intelligent idea as well.....(assuming that there is not one "later" in this blog!! There isn't)

Do please never forget "GIGO", it will be easier to find accurately on the web than DB!!!!!!

__________________
"What others say about you reveals more about them, than it does you." Anon.
Register to Reply
Guru

Join Date: Aug 2014
Location: Port Macquarie N.S.W. Australia
Posts: 1071
Good Answers: 225
#14
In reply to #12

Re: RCCB Trip and Downstream

03/20/2016 2:43 AM

Distribution Board

Register to Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#15
In reply to #14

Re: RCCB Trip and Downstream

03/20/2016 3:22 AM

Many thanks.

That is here its a "SK"......

Google was no proper help either!!

Sadly, anyone posting here with just Acronyms faces the "luck of the draw" always.....also, not placing a simple diagram here as well "increases the risk!" so to say....

Happy Solstice Day to everyone!!

__________________
"What others say about you reveals more about them, than it does you." Anon.
Register to Reply
Guru

Join Date: Aug 2014
Location: Port Macquarie N.S.W. Australia
Posts: 1071
Good Answers: 225
#16
In reply to #15

Re: RCCB Trip and Downstream

03/20/2016 5:58 PM

I thought it would be a happy Equinox day..But perhaps it's different where you dwell

Register to Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#17
In reply to #16

Re: RCCB Trip and Downstream

03/21/2016 6:38 AM

Its the same the world over, on those 2 days a year!!

This particular one in German is "Frühlingstagundnachtgleiche".....

What a mouthful!!!

Generally speaking, translating a document from English into German, increases its size, (not necessarily the word count!), by around 20%, but is VERY variable.....

__________________
"What others say about you reveals more about them, than it does you." Anon.
Register to Reply
Register to Reply 17 comments

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

Ali18 (1); Andy Germany (4); Hattasan019 (1); IdeaSmith (1); IQ (1); JohnDG (1); Khinzawmyint (1); lyn (1); PWSlack (1); spades (3); TonyS (1); Tornado (1)

Previous in Forum: 11kV Line Insulator Sparking   Next in Forum: Leroy Somer R450M AVR Problems

Advertisement