Todays PIR
- Thread starter Sidewinder
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This is a bit of a 2400 exercise
thats what i was hoping for.
So we compare the characteristics of the fuses to find out the level of discrimination they give. So i take it we have to have manufactures info for this, which i am unable to find on the manufactures websites at the moment?
thats what i was hoping for.
So we compare the characteristics of the fuses to find out the level of discrimination they give. So i take it we have to have manufactures info for this, which i am unable to find on the manufactures websites at the moment?
wozz,
Yes sort of, however then you are relying on the same manuf' fuses during the lifetime of the install.
Better using BS88 data.
However, you will not get all the info you need from this!
TBH did not take all the manuf' data off the fuses when we were there as the maker did not seem that important at the time!
Yes sort of, however then you are relying on the same manuf' fuses during the lifetime of the install.
Better using BS88 data.
However, you will not get all the info you need from this!
TBH did not take all the manuf' data off the fuses when we were there as the maker did not seem that important at the time!
I fiund the notation on the fluke programmable RCD after querying here mate - BTW - Flukio is home again, with nice shiny calcert.
Right - what I was thinking here is:
I wouldn`t personally get bogged down on all the OCPD discrims -we did work on the proviso that 2 of the DBs would be replaced - and I cannot envisage any of the final ccts needing HRC fusing - OOTOMH.
The main dist. panel - yes, that`ll have to have discrimination the DNO fuses, ideally; but determination is only really going to be possible once the load on the subs in decided, and the fuses for each of those chosen. Then we`ve got diversity to deal with on those - Only then can we consider what "our" main protective device characteristics will be, and if / what the DNO requirements are.
Or I am on a different bus route?
KME
Right - what I was thinking here is:
I wouldn`t personally get bogged down on all the OCPD discrims -we did work on the proviso that 2 of the DBs would be replaced - and I cannot envisage any of the final ccts needing HRC fusing - OOTOMH.
The main dist. panel - yes, that`ll have to have discrimination the DNO fuses, ideally; but determination is only really going to be possible once the load on the subs in decided, and the fuses for each of those chosen. Then we`ve got diversity to deal with on those - Only then can we consider what "our" main protective device characteristics will be, and if / what the DNO requirements are.
Or I am on a different bus route?
KME
Same route mate!
Can't remember the origin PFC OTTOMH but, I don't think we need HRC fusing either however, we could achieve high current fault protection by using the upstream fuses in the panel board IF the PFC>10kA and we fit mcb DB's.
MCB/Fuse discrimination get a bit more complex though!
Can't remember the origin PFC OTTOMH but, I don't think we need HRC fusing either however, we could achieve high current fault protection by using the upstream fuses in the panel board IF the PFC>10kA and we fit mcb DB's.
MCB/Fuse discrimination get a bit more complex though!
just noticed this,
depending on your tester you can ramp your RCD,
quite a lot of testers have 10mA, 30 , 100, 300, 500 on them,
so you by default have you x 1/2 and x5 using the 10 + 100 ranges, then ramp the 20mA.
you could also run it in series with a 30mA , that would give you 50mA
= 1/2 of 100mA
so you now have a X1 and removing the 30 will give you 20X5 = 100
personally I would ramp it.
depending on your tester you can ramp your RCD,
quite a lot of testers have 10mA, 30 , 100, 300, 500 on them,
so you by default have you x 1/2 and x5 using the 10 + 100 ranges, then ramp the 20mA.
you could also run it in series with a 30mA , that would give you 50mA
= 1/2 of 100mA
so you now have a X1 and removing the 30 will give you 20X5 = 100
personally I would ramp it.
Thanks Albert:
The ramp test, however, wouldn`t provide a time to trip; just the current necessary.
I was thinking of using both our MFTs, on the 10mA range, at the same time. That would put 20mA on it, and one of the testers would pick up the trip time; the other would be a lot higher, if "test" was pressed first. However, SW has another way of doing this; using the 1653.
Supply PFC WAS >10KA; as we had more than that at the sub-board, IIRC
The ramp test, however, wouldn`t provide a time to trip; just the current necessary.
I was thinking of using both our MFTs, on the 10mA range, at the same time. That would put 20mA on it, and one of the testers would pick up the trip time; the other would be a lot higher, if "test" was pressed first. However, SW has another way of doing this; using the 1653.
Supply PFC WAS >10KA; as we had more than that at the sub-board, IIRC
SW some of my stabs
the dno A ratings and the MS A Rating is surely not an issue?
this arrangement happens 99% of the time surely?
while you say its not blown the dno's in 12 yrs the design is flawed should the buildings change electrical requirements simply the capacity is not there to supply the demand
FS1 is likely not to discriminate as other sub boards likely supplied by 63a ?
FS2 can't see an issue
FS3 none
FS4 all done to insufficent supply via dno's fuses
FS5 as above
as i know you like your fault current discussions i'm guessing this is more of your concerns and is where i'm in for the lesson.
i should know all this having done mostly industrial with design too :coat
the dno A ratings and the MS A Rating is surely not an issue?
this arrangement happens 99% of the time surely?
while you say its not blown the dno's in 12 yrs the design is flawed should the buildings change electrical requirements simply the capacity is not there to supply the demand
FS1 is likely not to discriminate as other sub boards likely supplied by 63a ?
FS2 can't see an issue
FS3 none
FS4 all done to insufficent supply via dno's fuses
FS5 as above
as i know you like your fault current discussions i'm guessing this is more of your concerns and is where i'm in for the lesson.
i should know all this having done mostly industrial with design too :coat
Don't need to press simultaneously.
The Fluke 165x series will apply the 10mA fault current for 2 sec.
We both have these instruments, KME also has a Kewtech.
However, the idea was to start one fluke with a 2sec pulse then the 2nd, thus the 1st would apply a standing 10mA leakage, the 2nd would apply another, which would in turn measure the trip time at 20mA, from there we could calculate which other values we required, 50% 10mA, 5x=100mA etc.
Point 1 not blown DNO fuses, in 12 years the install is about 34 years old changed use 12 years ago (ish) I believe the incomer was changed about this time, downsized to save the new occupier cost, but the install was not assessed & addressed to accomodate.
FS1 sub mains fom DB01, final circuit & sub main loading not assessed at yet (LIM)
FS2 agreed, but not really used!
FS3 agreed.
FS4 agreed, but other issues such as 16mm sq tails from isolator to DB at the other end of the sub main!
Load clamped in use at R-1A, Y=4A, B=5A!
Full load assessment required, suspect 63A fuses for sub main fine!
FS5 agreed, still to be fully assessed.
Yes, but, KME remember WPD limit the max PFC on such supplies to 25kA by design.
From the horses mouth so to speak!
Hi,
First off, I am not sure i understand the description really, for example you say that "fs 1" is a 63A submain. What do you mean by a 63A one? I thought you might mean it had a 63A isolator/switchfuse supplying it, but you have already said that Fs 1 has got a 100A fuse, so is it a 63A switchfuse that someone has put a 100A fuse in? I am baffled now??
Anyway, from what i can understand of your description i shall have a go??!!!!!!!
1, The DNO cutout has, [as you have deduced from the fact that the installation has "whole current metering"] 100A fuses in it, BUT HAS IT??
Why then, is the rest of the install so massive, especially as it feeds more than several tenants, and all on 100A board fuses!!. You say they have never blown in 12 years?? How have they never blown?? How do you know there are not bits of brass bar in there instead of fuses!!, are the seals still there??
Is there any indication as to what the maximum or usual demand of the entire installation is and would this in you opinion be suitable, or even possible for a mere 100A supply??
What size are the tails from the cutout to the internals of the panel? are there any signs of overheating??
2, Are you saying that FS1 [the 63A jobbie] has a 100A fuse in it?? As the supply is TN/C/S and it feeds buildings remote to the origin, what earthing/bonding arrangements are in place for the remote buildings, and are they suitable??
3,If FS2 is a 30A sub main, then are you saying [i think] it has a 100A fuse in it?
4, FS4 [remote building] Same comments as regarding earthing/bonding arrangements.
5, if FS5 is a "150A submain", why has it got from what i can make out, a 200A fuse??
As the fuses are all so huge, is the cabling equally proportioned, and suitable to be protected by these sizes of fuse?
What about ELI and disconnection times?? As Zs x Ia must be less than Uo, and this seems to be a fairly huge installation, how have they managed to achieve the required disconnection times?? especially if they have TT'ed the remote buildings.
As the fuses are so huge they are going to need very very low ELI values, unless of course they have suitable small rating devices protecting the final circuits. Then again i suppose, if all the sub main cables are of suitable size to match the fuses protecting them [huge] and have therefore very low impedance, and they have got sensibly sized fuses or whatever protecting the final circuits they might just be ok, at least as regards the final circuits anyway. Still leaves the bonding and earthing arangements and if bits are TT'ed the requirement for all poles to be isolatable.
Did not the person that installed this lot make his own enquiries as to the suitability of the incoming supply??, and if he did, why the massively overrated accessories.
Personally, i would be trying to work backwards to ascertain the the max demand required for what ever it feeds, and compare this with the supply capacity, and then go from there, with properly rated protective devices. I cannot for the life of me see that this supply is suitable and there will be NO CHANCE that the remote buildings anr bonded correctly for the type of supply, and disconnection times will be a joke i would think.
Be kind to me!!!! I am only a beginner!!!!!!!!!!!!!!!!!!!!
john
First off, I am not sure i understand the description really, for example you say that "fs 1" is a 63A submain. What do you mean by a 63A one? I thought you might mean it had a 63A isolator/switchfuse supplying it, but you have already said that Fs 1 has got a 100A fuse, so is it a 63A switchfuse that someone has put a 100A fuse in? I am baffled now??
Anyway, from what i can understand of your description i shall have a go??!!!!!!!
1, The DNO cutout has, [as you have deduced from the fact that the installation has "whole current metering"] 100A fuses in it, BUT HAS IT??
Why then, is the rest of the install so massive, especially as it feeds more than several tenants, and all on 100A board fuses!!. You say they have never blown in 12 years?? How have they never blown?? How do you know there are not bits of brass bar in there instead of fuses!!, are the seals still there??
Is there any indication as to what the maximum or usual demand of the entire installation is and would this in you opinion be suitable, or even possible for a mere 100A supply??
What size are the tails from the cutout to the internals of the panel? are there any signs of overheating??
2, Are you saying that FS1 [the 63A jobbie] has a 100A fuse in it?? As the supply is TN/C/S and it feeds buildings remote to the origin, what earthing/bonding arrangements are in place for the remote buildings, and are they suitable??
3,If FS2 is a 30A sub main, then are you saying [i think] it has a 100A fuse in it?
4, FS4 [remote building] Same comments as regarding earthing/bonding arrangements.
5, if FS5 is a "150A submain", why has it got from what i can make out, a 200A fuse??
As the fuses are all so huge, is the cabling equally proportioned, and suitable to be protected by these sizes of fuse?
What about ELI and disconnection times?? As Zs x Ia must be less than Uo, and this seems to be a fairly huge installation, how have they managed to achieve the required disconnection times?? especially if they have TT'ed the remote buildings.
As the fuses are so huge they are going to need very very low ELI values, unless of course they have suitable small rating devices protecting the final circuits. Then again i suppose, if all the sub main cables are of suitable size to match the fuses protecting them [huge] and have therefore very low impedance, and they have got sensibly sized fuses or whatever protecting the final circuits they might just be ok, at least as regards the final circuits anyway. Still leaves the bonding and earthing arangements and if bits are TT'ed the requirement for all poles to be isolatable.
Did not the person that installed this lot make his own enquiries as to the suitability of the incoming supply??, and if he did, why the massively overrated accessories.
Personally, i would be trying to work backwards to ascertain the the max demand required for what ever it feeds, and compare this with the supply capacity, and then go from there, with properly rated protective devices. I cannot for the life of me see that this supply is suitable and there will be NO CHANCE that the remote buildings anr bonded correctly for the type of supply, and disconnection times will be a joke i would think.
Be kind to me!!!! I am only a beginner!!!!!!!!!!!!!!!!!!!!
john
Hi yourself. Flippin` heck; this was a while ago - but I`ll see how much I recall as we go along (Sidewinder has the paperwork for this, not I )
The installations "change of use" means that, as far as we could ascertain, 100A/phase was in excess of their requirements, at the time of inspection
It appeared that, as I referenced above, following the change of circumstances, a mere 100A was more than adequate.
iirc, the metering and HED are within the panelboard; supply was via busbar, I think? No overheating signs apparent
I can`t honestly remember. Sorry. Maybe snakehips can.....
Wow! good post John; even if it IS an old thread, and I can only just recall the layout of the intake room.
I intended to answer each point in turn; but realised I`d be making so many guesses that rely on my memory (it USED to be good.......but recently I`m not so sure.).
So I`m going to simply say that old Snakey`ll be glad to see someone "have a go" at this, and NOBODY`ll be "hard on you" - you`ve offered your opinions, which is the best you can do. I`m going to bow out now, `cos I`se knaffered, and can`t remember as much as I thought I could.
KME
Manator
©Honorary Essex Boy™
It is an old thread, but I like the thinking and the time taken to ponder the post. Learning is fun sometimes, and this forum loves those who will have a go, well done.
I will let Sidewinder instruct you on this one though.
I will let Sidewinder instruct you on this one though.
Hi KME, Thanks for that!! I am only a beginner, and i really do mean a beginner, but i do try!! Hard to judge things from written descriptions, but i thought i would have a bash!! Only way to learn!! [and i really want to]
john..
john..
Hi Manator, Thanks for that!! As i say, i am VERY new to all this but i do like to learn. I do NOT want to be one of those who just does things because, "that is how i always do it" or even; "that it the way it is meant to be done"
I want to have a proper UNDERSTANDING as to why something is done in a certain way, and not merely do things "parrot style" if you see what i mean.
I did not realise the thread was so old, [i found it by accident] but i saw that, as one of the other posters said, not many people were willing to stick their neck out and have a go, but as Sidewinder took the time to compose his post with the deliberate intention of "spreading a bit of knowledge about" so I thought the least i could do is to have a go!!!!
People might laugh at my feeble efforts, but i do not care!!
john..
I want to have a proper UNDERSTANDING as to why something is done in a certain way, and not merely do things "parrot style" if you see what i mean.
I did not realise the thread was so old, [i found it by accident] but i saw that, as one of the other posters said, not many people were willing to stick their neck out and have a go, but as Sidewinder took the time to compose his post with the deliberate intention of "spreading a bit of knowledge about" so I thought the least i could do is to have a go!!!!
People might laugh at my feeble efforts, but i do not care!!
john..
apprentice,
It is a long time ago but i do have the PIR & my site notes still, though I will have to dog them out.
Originally the building had a massive supply, this was downgraded on change of use.
Since then it has been bodged big time.
The PIR ran to around 40 pages IIRC.
The incoming tails are around 50mm IIRC, I'd have to check so fine on the 100A fuses, and yes they are.
Metering I can't remember whether it was direct or CT now.
The main board is a panel board rated at well in excess of the incoming fuses.
The switch fuses for the sub mains are installed in the panel board.
They may have fuses in bigger than their rating.
The panel board has bus bars which as I say are well in excess of the incoming supply.
No signs of overheating, supply is PME with a local rod at the origin.
MEC is flat copper out to the rod and between the panel board and some of the local db's it's the same.
One of the outbuildings was excluded from the PIR.
One was disconnected as it was a code 1.
As far as I know nothing has been done, we did works to eliminate the requirement for EDN's, & Code 1's but no more.
I can lay my hands on the PIR, but not sure where my site notes are now.
I'll have to look through.
Install is industrial and was what would now be classed as "Zoned" under DSEAR, but is no more being used in that application.
That is it has Ex fittings in many places.
It was a fuel tanker repair depot.
The original wiring is all steel conduit & trunking with separate cpc.
This may rear its head again shortly.
It is difficult to comment on such things remotely I appreciate, I just wanted to stimulate debate/discussion, but there was not much so I left it!
I rarely can get my head around faults and stuff described on here or over the phone, but in the flesh I find it much easier.
I'll try to deal with one point at a time later on.
It is a long time ago but i do have the PIR & my site notes still, though I will have to dog them out.
Originally the building had a massive supply, this was downgraded on change of use.
Since then it has been bodged big time.
The PIR ran to around 40 pages IIRC.
The incoming tails are around 50mm IIRC, I'd have to check so fine on the 100A fuses, and yes they are.
Metering I can't remember whether it was direct or CT now.
The main board is a panel board rated at well in excess of the incoming fuses.
The switch fuses for the sub mains are installed in the panel board.
They may have fuses in bigger than their rating.
The panel board has bus bars which as I say are well in excess of the incoming supply.
No signs of overheating, supply is PME with a local rod at the origin.
MEC is flat copper out to the rod and between the panel board and some of the local db's it's the same.
One of the outbuildings was excluded from the PIR.
One was disconnected as it was a code 1.
As far as I know nothing has been done, we did works to eliminate the requirement for EDN's, & Code 1's but no more.
I can lay my hands on the PIR, but not sure where my site notes are now.
I'll have to look through.
Install is industrial and was what would now be classed as "Zoned" under DSEAR, but is no more being used in that application.
That is it has Ex fittings in many places.
It was a fuel tanker repair depot.
The original wiring is all steel conduit & trunking with separate cpc.
This may rear its head again shortly.
It is difficult to comment on such things remotely I appreciate, I just wanted to stimulate debate/discussion, but there was not much so I left it!
I rarely can get my head around faults and stuff described on here or over the phone, but in the flesh I find it much easier.
I'll try to deal with one point at a time later on.
Hi Sidewinder,
First off, i will assume that the installation was all ok when it was installed, with all the correct bonding etc to the remote buildings [if they pme'd them that is, which i presume they would have] and that it was all "fit for purpose" at the time, and that all cable/switchgear ratings were properly co-ordinated and everything was broken down into sensibly sized circuits [to enable proper protection of them] and that all complied with whichever regs were out at the time.
Then, it seems that bodgy additions must have been made to the installation, as otherwise why would they want to fit over rated fuses?
Now though, it seems that they have thrown away all the huge equipment they no doubt had before, [plus the bodgy additions] and have therefore removed the overloading that required the "too big" fuses in the first place, and now they just have very small loads on the end of a humungeous system.
It would seem to me that now then, that if they refitted the original size fuses, and threw away the bodgy additions, [to get back to how the system was intended to be when it was first installed] the system itself might be ok, [or at least the "middle" bit would be] if it were not for a few rather large problems at the start and finish of the thing.
As all the cabling and switch gear is so hugely rated compared to the fuses in the "new" 100A cut out, i suppose that they are in effect relying on the cutout fuses, to effectively as it were, protect near enough their entire installation up to the point where their no doubt "new" final circuits start. Do not think the DNO would be very happy with that.
Another thing that occurs to me is that;
If they have this monster system, with huge cabling [and there might only be short runs of it for all i know] and then they have PRESUMABLY just gone and plonked a new small DB on the end with small MCB's to protect their new small loads, then i would be a bit concerned as to whether the MCB's are capable of breaking, the no doubt rather large [as a result of the low impedance huge cabling] PSCC and PEFC at that point, because they do not seem to have any other suitable devices as "backup" for the MCB's upstream as it were, other than the DNO's cutout.
As it no doubt cost an arm and a leg for you to go and inspect this installation, and it is obviously not being used as was originally intended by its designer, and is obviously not suitable for its new usage either, i would think that the best thing to do, would be to rip the lot out, and have a new, properly "designed and fit for purpose" new system installed from start to finish.
I suppose you could re-use all the old sub-main cabling, just install sensibly sized switchgear etc!!
john..
First off, i will assume that the installation was all ok when it was installed, with all the correct bonding etc to the remote buildings [if they pme'd them that is, which i presume they would have] and that it was all "fit for purpose" at the time, and that all cable/switchgear ratings were properly co-ordinated and everything was broken down into sensibly sized circuits [to enable proper protection of them] and that all complied with whichever regs were out at the time.
Then, it seems that bodgy additions must have been made to the installation, as otherwise why would they want to fit over rated fuses?
Now though, it seems that they have thrown away all the huge equipment they no doubt had before, [plus the bodgy additions] and have therefore removed the overloading that required the "too big" fuses in the first place, and now they just have very small loads on the end of a humungeous system.
It would seem to me that now then, that if they refitted the original size fuses, and threw away the bodgy additions, [to get back to how the system was intended to be when it was first installed] the system itself might be ok, [or at least the "middle" bit would be] if it were not for a few rather large problems at the start and finish of the thing.
As all the cabling and switch gear is so hugely rated compared to the fuses in the "new" 100A cut out, i suppose that they are in effect relying on the cutout fuses, to effectively as it were, protect near enough their entire installation up to the point where their no doubt "new" final circuits start. Do not think the DNO would be very happy with that.
Another thing that occurs to me is that;
If they have this monster system, with huge cabling [and there might only be short runs of it for all i know] and then they have PRESUMABLY just gone and plonked a new small DB on the end with small MCB's to protect their new small loads, then i would be a bit concerned as to whether the MCB's are capable of breaking, the no doubt rather large [as a result of the low impedance huge cabling] PSCC and PEFC at that point, because they do not seem to have any other suitable devices as "backup" for the MCB's upstream as it were, other than the DNO's cutout.
As it no doubt cost an arm and a leg for you to go and inspect this installation, and it is obviously not being used as was originally intended by its designer, and is obviously not suitable for its new usage either, i would think that the best thing to do, would be to rip the lot out, and have a new, properly "designed and fit for purpose" new system installed from start to finish.
I suppose you could re-use all the old sub-main cabling, just install sensibly sized switchgear etc!!
john..
