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Topic Title: MWC certificate
Topic Summary: Just want to check
Created On: 09 June 2006 08:38 pm
Status: Read Only
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 09 June 2006 08:38 pm
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deleted_liveone

Posts: 100
Joined: 28 February 2006

When completing a mwc certificate for say an item of equipment like boiler time clock etc etc when completing the ticket what do you put down as the protective device (the main 60898 mcb say or the 1362 fuse in the FCU supplying the switchgear)

many thanks

just that i have seen both done!

now making me doubt what i have been doing lol
 09 June 2006 08:46 pm
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alancapon

Posts: 7492
Joined: 27 December 2005

The protective device is the one that is supposed to clear the fault. If the boiler you have repaired is supplied from a FCU, then it is the BS1362 fuse in the FCU that should operate first in the event of a fault, so this is the one that goes on the certificate.

Regards,

Alan.
 09 June 2006 09:06 pm
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sparkiedave

Posts: 232
Joined: 23 January 2006

just get complicated when it comes to disconnection times, if it's on a 6 amp mcb, on a short cable run, with say 1.5 (or 2.5 if it's an old immersion feed as is often used), I've known a breaker go without blowing the fuse
 09 June 2006 09:15 pm
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alancapon

Posts: 7492
Joined: 27 December 2005

Yes maybe it would, but the fuse in the FCU is supposed to operate first.

If you had a shower on a 40A mcb, you could probably demonstrate that under some circumstances the DNO cutout fuse would operate first, but you wouldn't put the cutout fuse down as the protective device if you fitted a new shower.

Regards,

Alan.
 09 June 2006 09:21 pm
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gkenyon

Posts: 5354
Joined: 06 May 2002

quote:

Originally posted by: sparkiedave
just get complicated when it comes to disconnection times, if it's on a 6 amp mcb, on a short cable run, with say 1.5 (or 2.5 if it's an old immersion feed as is often used), I've known a breaker go without blowing the fuse
Our kettle developed a short between parts of the element last week (it's one of those with a "spiral" element on a PCB).

The 13 A BS1362 plug fuse did not blow.

The C32 (yes Type C not B) went first !

Before anyone asks - no other appliances running on that circuit, and no other faults.


We'd never have had that problem with discrimination with fuses. The problem is, the BS7671 requirement to minimise inconvenience in the event of a fault.


With mcb's, I see that we are really heading towards each major appliance and each small group of outlets being on its own 16 or 20 A RCBO ? I could convert the space under the stairs into a mini LV switchroom to accommodate the requirement !

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 09 June 2006 09:37 pm
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extrasockets

Posts: 392
Joined: 14 May 2006

just out of interest would a 10A 1362 blown before your 32A C breaker? Dont really see many fitted tho to appliances,

Edited: 09 June 2006 at 09:38 pm by extrasockets
 09 June 2006 09:41 pm
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Karlsjones

Posts: 91
Joined: 10 May 2006

Hi all,

When carrying out minor works, I have always looked at it as an extension to an existing installation and the minor work certificate should compliment the original test schedule, which shows circuit design characteristics. I therefore, document the circuit protective device at the consumers unit.

I take Alans point about the fuse most likely to disconnect in a fault condition but if you were to carry out a PI on the installation, the testing would be carried out at the consumers unit and the minor works certificate could contradict the true findings.

Kind regards,

Karl.
 09 June 2006 10:31 pm
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gkenyon

Posts: 5354
Joined: 06 May 2002

quote:

Originally posted by: extrasockets
just out of interest would a 10A 1362 blown before your 32A C breaker? Dont really see many fitted tho to appliances,
A 10 A may well generally pip the C32, but may well have blown in normal use of the kettle if there were any "spikes" - rated at 3 kW.

Interestingly, though, only 3A, 5A and 13 A should be fitted to plug-tops, with only 3A and 13 A being preferred.


But this is missing the point. A B32 can operate before a 3 A BS1362 fuse - and maybe same for a C32, but I've never actually witnessed that. Reason is, if the available fault current is high, and the mcb operating in its "magnetic" region, it is likely to pop out before the fuse blows properly.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 09 June 2006 11:46 pm
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alancapon

Posts: 7492
Joined: 27 December 2005

Karl,

I guess it depends on how you define the scope of work. If you are replacing the timeclock on the boiler (where this thread started), which is fed from a FCU, do your tests start from the FCU, or do you go back to the CU, where you could conceivably have to correct wiring faults on a ring-main as well.

I can accept that you would want to check the main bonding is in place, but if the electrical characteristics you measure at the FCU show that the BS1362 fuse will operate for a fault & the boiler wiring tests ok, how much more of the installation do you include.

Regards,

Alan.
 10 June 2006 08:19 am
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extrasockets

Posts: 392
Joined: 14 May 2006

Graham, Ive never heard of that one, wheres the information, thanks.
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