Form 4 - Overcurrent Device - What to put down

[chrisgc]

The information is on the fuse itself but of course you can't see it because it's sealed.

Then again, you could just isolate all load, cut the seal, remove the fuse, record the details and put everything back neatly but that would be illegal.

So that would be the fuse with the already broken tag on then lol.

Come to think of it where can you get the metal tags which have accidently on purpose been cut??

 

[IQ Electrical]

Maybe a well-known auction site?

 

[telectrix]

loads on ebay. but some are flimsy and cheap cack. but you got to put something on when you find a broken one!

 

[chrisgc]

Hi again

I have managed to view the MAIN FUSE and it has the following markings on:

100A
ASTA 20
BS 1361

Would I be right in saying that the info I would put down in the box/section I am on about (Overcurrent Device - Short-circuit capacity.........kA) is in regards to the MAIN FUSE and NOT the individual circuit breakers???

I just want it clarified thats all.

Also how do I go about finding out the kA of this as thought the max for domestic would be 16.5kA but unsure where to found this info in relation to the main fuse I have?

 

[pushrod]

This is what I was told by an assessor.

I originally thought it was the Short Circuit Capacity of the MCBs that was recorded in this box - but he said it wasn't, it's the rating of the cutout.....e.g. 16 KA

Well for my 2pennyworth i think you were right and the assessor was having a bad day or talking out of his a***!

Note 4 on P141 of the OSG tells you that it is the mcbs by referring you to table 7.4!

We were taught that you check all the short circuit capacities on the mcbs and if they are different you record the lowest. If that is not greater than the PFC there is a problem because it means that a fault current could cause an mcb to explode!

You then have to sort it out - either upgrade the offending mcbs (maybe 6kA to 10 kAs), or put them in an enclosure that was rated to withstand that size of pfc or investigate lowering the pfc .

Seemed to make sense to me.

 

[WayneL]

I think you're right, Pushrod.

Looking at the sample 'Schedule of Test Results' on Pg 140 of the OSG, they have filled in '6 kA' for this box.

The only devices that rate that low are MCBs, so it can't be the cutout value that's required.

 

[IQ Electrical]

This is correct but BS60439-3 UK annex ZA allows us, in a domestic situation, to rely on the short circuit capacity of the supply fuse if this is to BS1361.

If this is the case then you do not have to upgrade your devices.

Guidance Note 3, page 54

 

[pushrod]

This is correct but BS60439-3 UK annex ZA allows us, in a domestic situation, to rely on the short circuit capacity of the supply fuse if this is to BS1361.

If this is the case then you do not have to upgrade your devices.

Guidance Note 3, page 54

Agree but this is only if you have a modern consumer unit with the BS 60439 enclosure that has a high enough rating to withstand problems with lower rated mcbs. You can then rely on the breaking capacity of the BS 1361 fuse.

 

[Jimmy Boy]

So how do identify a 1361 to be a type 1 or type 2 ? I thought they were all type 2's in domestics a type 1 has a Ka of 16.5 a type 2 is 33.0 Ka although OSG does say the max fault current for 230v up to 100A will not exceed 16Ka

 

[chrisgc]

I am a little confused by it all.

I think I have opened up a can of worms with my original question.

So is it the circuits individual Circuit Breakers OR the main cutout fuse???

Is there anywhere we can get a definitive answer???

Just so that it can be clarified and we all know (especially me lol)

 

[IQ Electrical]

Ok, let's start again:-

If by 'form 4' you mean the schedule of test results then the value you would enter under 'short circuit capacity' would be the lowest value of the mcb's/fuses etc protecting the outgoing circuits.

The Supply fuse details are entered on 'form 1' under 'supply protective device characteristics'

 

[IQ Electrical]

The post I made on domestic consumer units complying with BS60439-3 or BS5486-13 and being protected by a BS1361 fuse of 100A or less is refering to Guidance Note 3, page 54.

In this case, we can rely on the incoming device to interrupt the fault current, thereby negating the need to install mcb's/fuses etc with a higher kA rating.

 

[Jimmy Boy]

As above, the over current device short circuit capacity is the short circuit maximum of the device hence the rating in Ka normally stamped as 6000 (6Ka) type B (Usually for a domestic) In in A (Amps) 6- 32 or whatever your protecting

 

[pushrod]

The post I made on domestic consumer units complying with BS60439-3 or BS5486-13 and being protected by a BS1361 fuse of 100A or less is refering to Guidance Note 3, page 54.

In this case, we can rely on the incoming device to interrupt the fault current, thereby negating the need to install mcb's/fuses etc with a higher kA rating.

I know what you mean but just being a little pedantic in the attempts of clarity as there is obviously confusion about on this, not intended as a criticism of your statement.

It will still be the MCB that interrupts the fault current even though it will be permanently and perhaps dangerously damaged by a pfc in excess of its rating. However, because of the rating of the enclosure no one should be harmed by it. As a consequence you could have safe interruption of supply up to the short circuit capacity value of the incoming device. The design does not rely on the incoming device to operate.

 

[IQ Electrical]

I know what you mean but just being a little pedantic in the attempts of clarity as there is obviously confusion about on this, not intended as a criticism of your statement.

It will still be the MCB that interrupts the fault current

Not necessarily, the MCB could be rated at 3kA and could support an arc but this will not happen as the BS1361 will 'step in' interrupt the fault current.

the link to annex ZA is here: http://www.google.co.uk/url?sa=t&source=web&cd=1&ved=0CBoQFjAA&url=http%3A%2F%2Fwww.evs.ee%2FCheckout%2Ftabid%2F36%2Fscreen%2Ffreedownload%2Fproductid%2F192658%2Fdoclang%2Fen%2FEVS_EN_60439_3%3B2007_AC%3B2009_en.aspx&rct=j&q=bs%2060439-3%20uk%20annex%20za&ei=C-C6TPy2IuCK4gaWxPHVDA&usg=AFQjCNH0TGArTTI6q86dY6AmKpGf6_zrcA

It's great bedtime reading