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Topic Title: 60898 (10kA) / 60947-2 (15kA)
Topic Summary: A Question Regarding Different kA Values-
Created On: 06 August 2014 08:30 AM
Status: Post and Reply
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 06 August 2014 08:30 AM
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Sanft

Posts: 37
Joined: 22 August 2011

Good Morning All- I hope you're all keeping well,

I just had a query regarding Circuit Breakers (Specifically Hager) and their Breaking Capacity Values (kA). I can't seem to wrap my head around it, even using the mighty internet search engines!

I've been asked to install a New Distribution Board within an Installation which is a Recycling Centre (Effectively, a Dump) so straight off the bat it is going to be a Commercial Installation. The problem I have is that the measured PFC at the distribution board has been measured to be between 11kA and 12kA (measured on more than one occasion).

I've been told by Hager that their standard MCB's (NBN, NCN and NDN Ranges) are suitable for use for 10kA Complying to 60898, and 15kA Complying to 60947-2, it also states this in the Catalogue- I just wanted to know what the theory is behind this exactly?

If I'm perfectly honest, this is the first I've heard of this arrangement, as I've always thought of 60947-2's as being MCCB's that would be put into a Panel board, and 60898's as being your standard B, C and D Type MCB's. I'm sure I can't be alone in thinking this (or at least I hope not!)

My Question, purely because I just want to understand why rather then just nodding my head and installing the gear, is how a single protective device can comply to two different standards, or if there has to be something in place in order to ensure a standard MCB from Hager complies to 60947-2 (I have a suspicion it has something to do with installing a lock to the distribution board so it is not accessible to 'unskilled' or unsupervised personnel?)

I'm also assuming that it must have this information written somewhere on the protective device as I wouldn't want another electrician to come along on the install- look at the MCB which has the '10000' written on the MCB, and then tell me off because it doesn't comply

Any insight to this would be greatly appreciated- you guys have been very helpful and good to me with the few posts I've done in the past and I've always walked away wiser,

Thank you guys- Look forward to hearing from you,

Andrew
 06 August 2014 10:00 AM
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davezawadi

Posts: 2657
Joined: 26 June 2002

The number you are looking at is the fault current breaking capacity. A 10kA breaker may not be able to disconnect a 15kA fault and could weld up solid instead, so would be useless.
Your installation has a PSSC of more than 10kA but less than 15kA so you should install breakers with 15kA breaking capacity, because a fault close to the DB could have a fault current sufficient to prevent disconnection by a 60898 breaker.
In domestic installations we often fit 6kA breakers because the PSSC of faults will be cleared by the DNO BS1361 fuse, and faults remote from the CU will very rapidly fall to less than 6kA because of the small cable sizes and consequent significant resistance. More than 6kA PSSC is also fairly unusual in domestic installations unless they are right next to the substation, because relatively small cables are used to supply each house, which again will limit the current.
In commercial installations cable sizes are often much larger, so the PSSC rises and we use larger DNO fuses, so the consequences of a high current fault are greater and could result in a big explosion in the DB if the breaker fails!
I would code commercial breakers of inadequate rating as a serious danger so you would not look good!

-------------------------
David
CEng etc, don't ask, its a result not a question!
 06 August 2014 10:10 AM
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Sanft

Posts: 37
Joined: 22 August 2011

Hi David- Thanks for the response-

This is what is confusing me with Hager, as they are advising me that their MCB's are compliant to 60898 @ 10kA and ADDITIONALLY compliant to 60947-2 @ 15kA, I just don't quite understand how a single protective device (i.e. an NBN106, 6A Type B Hager MCB) can be Compliant to two separate standards? Hager are basically telling me installing these MCB's will be acceptable- The best I can do is attach the following link and ask you to look at the top-right-hand corner, it states 'Complies With, 60898 10kA and 60947-2, 15kA'

http://www.luckinslive.com/pro...-Distribution/NBN106A

Open up the PDF and have a look for yourself!

Let me know what you think-

Andrew
 06 August 2014 10:21 AM
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AJJewsbury

Posts: 11467
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I think Sanft is asking why the one breaker has two different breaking capacity ratings - 10kA when employed under the standard for 'household and similar' situations (BS EN 60898), but 15kA under the more general BS EN 60947 standard.

I guess it's down to the different standards making different assumptions. That's not unusual - for instance (as David hinted at above) the standard for domestic consumer units (BS EN 60439) allows the use of much lower rated devices (e.g. 3kA) in anything up to a 16kA situation. It could be that BS EN 60947 accepts greater damage to the device or assumes certain backup protection (which BS 7671 allows in general, not just for domestic CUs). Some with knowledge of the standards will have to comment on that one.

- Andy.
 06 August 2014 10:24 AM
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whjohnson

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Might it be a simple as the mcbs being manufactured to the higher rating and thus complying with the lower one by default?

I.E - they are actually 15ka rated?

-------------------------
Political correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
 06 August 2014 10:27 AM
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IanLloyd

Posts: 63
Joined: 17 April 2002

Not sure if this helps...

file:///C:/Users/illoyd/Downloads/guide_to_low_voltage_circuit_breaker_standards%20(1).pdf
 06 August 2014 10:29 AM
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IanLloyd

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 06 August 2014 10:33 AM
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IanLloyd

Posts: 63
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Just a thought - is it to do with the rated voltage level of the MCB? 60898 as a "domestic" type is rated for 230V, say and 60947 "commercial or industrial" types are rated for 400V? See p36:

http://www.schneider-electric....9_Launch_Catalogue.pdf
 06 August 2014 10:37 AM
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IanLloyd

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 06 August 2014 10:48 AM
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Sanft

Posts: 37
Joined: 22 August 2011

Thank you for the responses guys-

To whjohnson, this is practically what I'm thinking, it would be a simple answer, occam's razor and all that- and I would like to see people on here agree with that statement to put my mind at ease so I can install this particular switchgear on the job which is swiftly approaching-

Some good info there IanLloyd- still not clearcut as manufacturers can be just as cloudy as BS7671 Ahah =] Thank you for the forum link there to the other thread, it was a good read also- Going by GN1 and OMS's comments I have come to the conclusion that these MCB's from Hager will have the following ratings-

60898 Standard - 10kA (Ultimate, Icn) - 7.5kA (Service, Ics)
60947-2 Standard - 15kA (Ultimate, Icn) - ??? (Service, Ics)

(The ??? will presumably down to Hager to tell me- GN1 does not include 60947-2)

It sort of says to me that these multi-standard protective devices can be installed in either a domestic environment (although seen as overkill for the situation) and also within a commercial and industrial environment also, not sure why they don't keep it simple really and have a single range for domestic (6-10kA) and another for Commercial (15 - 25kA)

Regardless, I think the question is answered as best as it will be- thank you very much for the input all, I look forward to Installing my TP+N 12-Way Hager Distribution Board with Multi-Standard MCB's ^__^

Grateful as always-

Andrew
 06 August 2014 12:54 PM
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Sanft

Posts: 37
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Just had a thought- if anyone wants to help me out with this one- when it comes to writing up the EIC- what do you think the best way to put the Protective Device Characteristics down would be?

60898 B 32A 10kA 30mA 1.44
60898 B 32A 15kA 30mA 1.44
60947-2 B 32A 15kA 30mA 1.44

I only ask because if I saw a Certificate with a >10kA PFC, and 60898 MCB's rated at 10kA, I would be querying this quite swiftly,

I'm guessing by the Thread link above, that I should be going for 60898 15kA option?

Let me know your thoughts guys-

Andrew
 06 August 2014 12:58 PM
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IanLloyd

Posts: 63
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Since you said in your original post, it's essentially a commercial installation, then would 60947-2 B 32A 15kA 30mA 1.44 be more appropriate?
 06 August 2014 01:12 PM
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Sanft

Posts: 37
Joined: 22 August 2011

Yeah, I totally agree, and I think I'll progress as such- I will have to put a note on the comments of the Certificate stipulating that the MCB's are installed in accordance with BSEN 60947-2 as per Manufacturers Instruction- because again, if I were to visibly see this on site, I would sort of think "Hang on, these looks like 60898 MCB's!"

Point Taken, 60947-2 It is, with an accompanying comment to explain the situation to whomever inspects the installation next time around-

Thank you Ian-

Andrew
 06 August 2014 01:35 PM
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Parsley

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How accurate is the measured PFC likely to be? The designer might have selected the submain's protection to provide back up protection as per 434.5.1 worth checking before coding.

Regards
 06 August 2014 01:54 PM
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sparkingchip

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Generally I don't use Hager, however I have a MTN in my hand and it is not marked in any way to show what standards if conforms to.

I have just Googled Hager MBN and from the image it is not clearly not clearly marked either, the only marking indicates it is 6kVA device.

You would think that the equipment is unfit for use with appropriate information and a CE mark on it.

Andy
 06 August 2014 02:19 PM
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mapj1

Posts: 2805
Joined: 22 July 2004

You don't legally have to have labelling if the device is impractically small and it could be hard to read. It is acceptable for lists of standards and CE marks to be in the instructions or hand books instead. Equally other MCB makers manage on a similar surface area

-------------------------
regards Mike

Edited: 06 August 2014 at 02:43 PM by mapj1
 06 August 2014 02:25 PM
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burn

Posts: 125
Joined: 06 June 2003

Simplistically,

BSEN60898 requires device to safely clear a fault of its rating and still be operable after clearing a fault of 75%

BSEN60947 requires a device to safely clear a fault of its rating and still be operable after clearing a fault of 50%

In a domestic type situation where Joe Public might reset the device it would be prudent to use BSEN60898
For industrial situations where a device will only be reset by an engineer who has given the reason for tripping some thought, BSEN60947 should be acceptable

burn
 06 August 2014 03:28 PM
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Sanft

Posts: 37
Joined: 22 August 2011

Parsley- The protective device is a BS88 Type Fuse, but is quite some distance away- in my heart of hearts I suspected that with the fuse not being directly adjacent to it, it meant that it was not a factor in having a reduced kA for protectives devices thereafter, much like the 3 meter rule for downstream protective devices and limiting the size of the conductor, when tapping off a Bus Bar system for example (434.2.1), It makes sense now that the BS88 would take the brunt of the Fault current through to Earth-Fault Path, your statement is a perfect knot in the loose end that is this topic-

I think to be honest, this thread became more about why there are two sets of standards and two different kA Values on one individual protective device, of which we have come to a conclusion of thankfully =] You would think that they would label the protective devices as such though! Much like Sparking says,

Thanks for the input guys- Never disappointed when it comes to the IET Forums

Kind Regards-

Andrew
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