BS 3871 mcb's
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Try Appx.2 in the RED OSG. Page 103 in particular - table 2D!
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The data is gone from 7671 thus the kit does not comply for new installs to the standard, as the standard does not contain the required info...
If you get what I mean
If you get what I mean
JPA
Junior Member
Although the BS 3871 has been superseded by BS EN60898, IMO there is nothing stopping you from reusing existing BS3871 overcurrent protective devices (if adequate). The Regs are not retrospective and IMO no different from utilising existing pre-harmonised cable. I would make mention of this as a deviation on the EIC though. The Zs figures can be found in the OSG or can be calculated using (1)x4,(2)x7,(3)x10 and (4)x50....
Jon
Jon
If they are in an existing board and you are connecting to them or making changes IMHO no problem.
If you were fitting a new board, then I would say no way, as you don't have the info in the BGB.
You can't buy them new now and the regs only look current and forward as they are based around new installs.
I may not even put a deviation on the EIC depending on what I was doing.
You should not really use figures outside of BS7671 unless from the manufacturer "really".
Honestly though, a 3871 device is now getting old, and you have no idea of it's history, say how many times it has operated, thus how far though its expected life it is, you could find that the next time it trips it will not reset, or that it won't even trip, then you are in big trouble!!!
If you were fitting a new board, then I would say no way, as you don't have the info in the BGB.
You can't buy them new now and the regs only look current and forward as they are based around new installs.
I may not even put a deviation on the EIC depending on what I was doing.
You should not really use figures outside of BS7671 unless from the manufacturer "really".
Honestly though, a 3871 device is now getting old, and you have no idea of it's history, say how many times it has operated, thus how far though its expected life it is, you could find that the next time it trips it will not reset, or that it won't even trip, then you are in big trouble!!!
JPA
Junior Member
Totally agree with you, but in these times of 'im not paying for a board change or theres no money in this job' and the device looks to have no obvious damage, I would be inclined to use it, take the money and run.
"You should not really use figures outside of BS7671 unless from the manufacturer "really"." - I thought the figures I quoted were from the BS3871 and BS7671 16th Ed, same as 3x,5x and 10x for BS 60898s
"You should not really use figures outside of BS7671 unless from the manufacturer "really"." - I thought the figures I quoted were from the BS3871 and BS7671 16th Ed, same as 3x,5x and 10x for BS 60898s
Technician
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From what I have read, there was a change from the
older BS 3871 to the BSEN 60898 which was an
alteration of the characteristic (bullrush chart).
IIRC the "knee" of the curve for the 3871 was lower
than for the same position on the BSEN 60898.
I think this caused issues with loss of discrimination
between the 3871 device and some fuse types but
some guys on here might shed some light on this.
HTH
I have just had a thought; what was the Rated Short
Circuit Capacity of the 3871 device?
older BS 3871 to the BSEN 60898 which was an
alteration of the characteristic (bullrush chart).
IIRC the "knee" of the curve for the 3871 was lower
than for the same position on the BSEN 60898.
I think this caused issues with loss of discrimination
between the 3871 device and some fuse types but
some guys on here might shed some light on this.
HTH
I have just had a thought; what was the Rated Short
Circuit Capacity of the 3871 device?
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JPA,
You know what I "mean", the figures are no longer in the current version of BS7671, thus the devices are no longer recognised, thus, you can't really "use" them!
So, there in lies the issue for re-using kit, I generally agree, however, it seems that in the scenario you are describing then you would need to have a deviation on the cert.
Along with some other contractual docs to back up your re-use of the kit else you could get into bother in some other way perhaps under performance requirements in the event of early failure of the MCB, this may be a risk you are prepared to take, it may not, it would depend on the scenario.
The issue with MCB's is you'll never know what internal damage they have until they trip or not as the case may be or they won't reset etc.
That is unless you have some serious test kit and then the test you do may be the "straw that breaks the camels back" as it were!
The risk thing you may think is irrelevant?
An example, the client I am working for at the moment has an 1kV ring under their property and feeding the on site 11kV transformer.
They were having some civil works undertaken.
The site manager gave the civils guys permission to dig and stake.
They staked 11 times through the 11kV cable, it was the last one blowing up and blowing a hole in the ground that got things moving!
Client got sued by neighbouring factories for loss of production, loss of business etc. & charged by DNO for repairs.
Big time example I know, but, would you be happy putting an old unknown 3871 on the control supply say for a process plant, coz if it failed your efficacy cover could be in for a hammering!!!
You know what I "mean", the figures are no longer in the current version of BS7671, thus the devices are no longer recognised, thus, you can't really "use" them!
So, there in lies the issue for re-using kit, I generally agree, however, it seems that in the scenario you are describing then you would need to have a deviation on the cert.
Along with some other contractual docs to back up your re-use of the kit else you could get into bother in some other way perhaps under performance requirements in the event of early failure of the MCB, this may be a risk you are prepared to take, it may not, it would depend on the scenario.
The issue with MCB's is you'll never know what internal damage they have until they trip or not as the case may be or they won't reset etc.
That is unless you have some serious test kit and then the test you do may be the "straw that breaks the camels back" as it were!
The risk thing you may think is irrelevant?
An example, the client I am working for at the moment has an 1kV ring under their property and feeding the on site 11kV transformer.
They were having some civil works undertaken.
The site manager gave the civils guys permission to dig and stake.
They staked 11 times through the 11kV cable, it was the last one blowing up and blowing a hole in the ground that got things moving!
Client got sued by neighbouring factories for loss of production, loss of business etc. & charged by DNO for repairs.
Big time example I know, but, would you be happy putting an old unknown 3871 on the control supply say for a process plant, coz if it failed your efficacy cover could be in for a hammering!!!
JPA
Junior Member
Sidewinder
I know what you mean and I know that it is a risk that the device maybe nearing the end of its life. But you say, would I be happy reusing an existing device?, possibly at the risk of being sued etc etc? Of course I wouldnt be happy and would prefer to do the right thing, perhaps I may loose some sleep, but if I demanded a board change for the sake of changing from 3871s to 60898, then lost the work as I know I would.......well take the money and run every time.
I know what you mean and I know that it is a risk that the device maybe nearing the end of its life. But you say, would I be happy reusing an existing device?, possibly at the risk of being sued etc etc? Of course I wouldnt be happy and would prefer to do the right thing, perhaps I may loose some sleep, but if I demanded a board change for the sake of changing from 3871s to 60898, then lost the work as I know I would.......well take the money and run every time.
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