Todays PIR

[kme]

John:

In an ideal world; that`ll ALWAYS be the "best possible solution". However, knowing customers, estate departments, accounts depts, etc. ; they`re likely to be unwilling to spend huge amounts of cash to downgrade/ replace the whole installation; you have to settle for the "best solution possible" - a subtle but important difference.

If the submain protection is correctly determined and installed; the issues you discuss will be nullified - However there are still the add-ons and bodges; we only resolved the code 1 issues.

You could say that always installing Ex fittings is safer; irrespective of the use of the premises. However the costs involved would generally make that prohibitive unless required for some reason.

If you look back to last year`s posts, I had a thread regarding a hotel -

 

[Sidewinder]

Later guys, got to go downstairs to bed!

Will try to respond later sorry.

 

[apprentice87]

Hope you are not going to laugh at my feeble efforts!!

john..

 

[Manator]

Hope you are not going to laugh at my feeble efforts!!john..

Practical work through from actual situations is a great way to learn, laughing at anyone who is willing to have a go is for those who can not even try to have a go. Right or wrong its always best to at least have a go, its a great way to learn and lessons learned this way are often best remembered.

 

[apprentice87]

Hi Manator, Yes, that is right!! Well done me for having a go i say!!!!

 

[Sidewinder]

I'm gonna try to answer the points from here on and for a minute ignore what has been posted from this point.

Sorry i have been so long and if I ramble or don't make sense it is coz I'm tired again already!

Have a lot to do at the mo, but not all of it profitable paying!

Anyway, hopefully my red replies below!

IF I mess it up sorry, I learned to drive this forum pretty well then some Muppet upgraded the software!!! ROTFWL

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??

OK, BTW the PIR was 71 pages!

I can't find this in the final PIR so we may have coded it 1 & rectified, but IIRC your description above is correct.

I will try to find my site notes as soon as I can.

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??

The DNO cut out did have 100A fuses, the metering is whole current rather than CT, thus whole current is cappeed at 100A/ph.

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??

The install had a change of use 12/13 years ago.

The DNO fuses are 100A BS88's.

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??

We did not undertake a maximum demand calculation formally. The installation use has decreased over the last fewe years after reaching apeak between the change of use and then.

It was reported that the fuses had not blown.

What size are the tails from the cutout to the internals of the panel? are there any signs of overheating??

The tails were 35mm sq. No evidence 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??

This building was not part of our PIR, however it is fed from the origin of the supply, we did not have full access or remit to PIR this building unless we did this as a freebie!

This building may have other links between itself and the building housing the origin as it was originally part of the same undertaking. It is now sub let.

It may well, in fact, probabaly have a 100A fuse in it if that is what my OP says, this is nearly a year ago and my memory is NOT that good, though this may be in my day book.

The remote building was excluded from the PIR thus coded a 2 as was the bonding etc.

The remote building has considerable structutal steel so it may have a very low local earth path.

However I cannot fully comment as it was excluded and under a maintenance contract with a large regional electrical contractor who obviously (well the guys they sent there) were not worried or "up" on the full requirements and status of the supply.

They may have missed the fact that it was a sub main as it had local landlord metering and if I had reasonable pics you may have missed this too.

Remember the DNO cut out can be remote to the metering and the main db for the install.

3,If FS2 is a 30A sub main, then are you saying [i think] it has a 100A fuse in it?

Probably yes, again I'd have to check my site notes as it may have been re-fused or decommissioned.

4, FS4 [remote building] Same comments as regarding earthing/bonding arrangements.

In which case see above, sorry.

5, if FS5 is a "150A submain", why has it got from what i can make out, a 200A fuse??

Same again really as above.

As the fuses are all so huge, is the cabling equally proportioned, and suitable to be protected by these sizes of fuse?

Yes IIRC the sub mains were cable sized in accordance with the capacity of the origin isolators.

However the fuses installed by persons unknown did not relate to the FS sizes or the cable sizes or the requirements etc.

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.

I doubt the remote buildings are TT'd they are probably all within the EEZ for the main install in effect, bar one or two points which may come up later.

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.

The ELI values were quite low IIRC, the PSCC & PEFC are capped at 25kA by the DNO anyway in this area.

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.

He almost certainly did as the install was designed by probably a Chartered Electrical Engineer who could probably knock my knowledge into a cocked hat!

Thing is since the original install was designed and constructed, there has been a change of use.

Also that change of use allowed a supply downgrade, thus this will have been undertaken by the DNO.

IT is very doubtful that they will have questioned the original install at that stage as the building was taken over quickly after the original occupier moved out, due to the design and management of the original install.

The bodged jobs have been done in the intervening 12 (ish) years.

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.

I doubt there is an issue with the max demand else the mains fuses would have blown, which it was reported that they had not.

We proposed to work backwards, however the client did not want any remedials doing.

This will rear its head within the next few months as the insurance is due again!

Unless the client has paid someone to sign off our code 2's then he will not get business insurance with the same insurer, and has been winging it for best part of a year now!

Be kind to me!!!! I am only a beginner!!!!!!!!!!!!!!!!!!!!

I don't do kind I do IMHO fair!

john

Good try, I'll do some more later on the following posts.

At least you were man enough to have a go, many on here who profess to be experts would not, though there are quite a few who are familiar with such things so left the thread to those who were not.

G-H being one who posted early and is sorely missed around here!

 

[Manator]

apprentice87, I see a great future for you in electrical circles, you ask all the right questions. Never be afraid to put up argument, it helps to teach you what you will always remember,it is never how! it is always why? For its only when you understand why, that you know how.

 

[apprentice87]

Hi Manator and Sidewinder,... What can i say but thank you... I am only a beginner, and your comments are a great encouragement to me..... Thank you so much.

john.

 

[Sidewinder]

OK John,

I'll have a go at this one.

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.

The original install may not have been PME as there is a great big earth rod just outside the switchroom still connected, however, there is no issue with that.

I in fact doubt the original install was PME as it was a Hazardous Area!

The circuits were sensibly sized for the work they were doing,

It almost certainly did comply with the regs at the time as it was constructed for a large multinational oil company from scratch as a dedicated building, the structural design was by consultants, the electrical design would have been by an electrical engineer.

However, the only things that got passed on to the new owners were those essential in law.

The electrical installation data is not part of that statutory duty.

Then, it seems that bodgy additions must have been made to the installation, as otherwise why would they want to fit over rated fuses?

The fuses were probably fitted by someone who has no idea, possibly the same person who put 4 bits of 2.5mm sq copper in a 32A rewirable fuse carrier!

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.

There are no large loads anymore you are correct. However, the current owner never had any!

The fuses were probably (doubtfully) never fitted to cope with overloading as the whole site was originally under a permit to work system with controls in place on who could do what, have you ever worked in a PetroChem environment?

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.

The system can never go back as it was designed as the building is no longer used for its original purpose.

It is no longer a hazardous area under DSEAR, as it is no longer a Petro Chem depot.

It does need some rework, but perhaps not to the extent you think.

The fuses are all capable of interrupting the fault current, and all are backed up at the main DB anyway.

The fault current is a max of 25kA anyway.

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.

Well the DNO installed their "new" cable, cut out and meter into the clients panel board without any issues it seems.

I suspect however that this was done very early in the change over to the new buyer, thus the install would have been up to the Ex standards at that time, unless it had been vandalised, but there is no evidence of that still present.

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.

Yes mate some runs are short, some are longer.

They have had boards fitted with 6kA mcb's in, also they have 1361's there as well downstream of the main db, HOWEVER, one of the 1361 boards was original, thus this may be acceptable.

I can't recall fault levels etc.

We had a limitation on some aspects as we would have been there literally weeks otherwise, we were there a week as it was or there abouts!

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.

It was not that cheap, but it could have been more expensive!

It is not being used as originally intended as the building has had a change of use.

As KME responded earlier to rip the old out would be great couple of k's at least in scrap!!!

It is not economically viable though.

What is needed is correct and safe isolation and partial removal as appropriate of the disused equipment.

Followed by full circuit checks down to the last device and then assessing the requirements and replacing the damaged and unsuitable boards with correct circuit protection.

Replacement or repair of the damaged accessories, wiring and containment systems.

Full documentation of the installation and the addition of a few earth rods.

It is not possible to separate the earthing systems to TT the buildings separately, or convert the whole thing to TT, which would necessitate big changes to the origin and addition of RC D's in an environment where they would not really be suitable.

I suppose you could re-use all the old sub-main cabling, just install sensibly sized switchgear etc!!

There is nothing wrong with over sized switch gear, or sub mains, it is just that the circuit protection needs to be correctly sized and co-ordinated.

I would also want to remove the 1361 boards due to the poor maintenance they have been given over the years and the damage that has occurred to them.

john..

My red above, hth.

 

[apprentice87]

Hi Sidewinder, Thanks for that! I learn little by little!! Thank you for the considerable time you take on replying to my posts, it is very much appreciated i can assure you, and i learn a lot too!!

Thanks, john..