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Topic Title: Your advice please
Topic Summary: Old, TPN 400A, seemingly unfused.
Created On: 03 April 2013 07:37 PM
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 03 April 2013 07:37 PM
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Zs

Posts: 3049
Joined: 20 July 2006

Evening chaps,

Before I put pen to paper I would like to run this past you.

A commercial building/public space which I have powered down over the last few days.

2 x 400A incomers, one serving the general electrics and one serving the plant room. TNCS.

Built and installed in 1959.

The control panel was made by Royal and includes switches for each of the destination DBs in the form of levers, which, when switched off and the lid unscrewed offer a drawer. The drawer brings the three fuses forward. I think you'll know the ones I mean. They all have a significant porcelain lining and were not designed for easy Z testing...

I would have expected to find the main switches to be offering fuses forward but in fact they show me significant steel bars and not fuses. It means the supply fuses are being relied upon. I would describe these as unfused links. Big mamas.

For the general electrics each of the downstream switches, about 15 of them, is fused in its own switch, and local to the incomer.

For the plant room, four floors up and a convoluted route not through a standard riser cupboard set-up the steel links are the same. So not fused at the beginning of the journey.

On arrival at the plant room, another unfused link on the incomer and a live TP bus bar, exposed . This area can only be isolated from the main intake room four floors down by operating the lever. There is no way of shutting off the plant room control panel from within the plant room.

Because this is an unusual set-up, and somewhat historic, I'd like your permission to freak-out before I actually do it.

It was code 1 city up in the plant room but the original infrastructure of the installation is so lovely. Must have taken months.


Thank you,

Zs
 03 April 2013 07:43 PM
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dickllewellyn

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Permission granted!!!

Don't suppose you took any snaps while you were there? I'm afraid I can't offer any valuable response other than to wish you luck. I'll be following this one!

-------------------------
Regards
Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 03 April 2013 08:09 PM
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Zs

Posts: 3049
Joined: 20 July 2006

Yes Dick, I have a phone full of photos but I don't know how to post them on here, or don't have the time . I may do an avatar change for a few days later on so that you can see it. Proper horrible sight to see, that plant room panel, and so neglected. Brace yourself.

When I first visted the plant room in Feb last year, there was a huge hole in the roof and a plane tree growing in the muck in the corner. It's gone now in favour of a new air con system with lots to write about that I don't need to check on here. I miss that quirky tree.

They have changed the squirty soap and hand cream. Until this week it was big bottles of something that I rarely buy but love ( L'occitane, Verbena), because it is very costly. Apparently it is a cut-back to help make the electrics safe. Good call, but I don't smell like I have just been there.

Zs
 03 April 2013 09:15 PM
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slittle

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Zs,

If in doubt follow Alan's rules.......... run :-)

It's easier than screaming.


Stu
 03 April 2013 09:30 PM
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Zs

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Joined: 20 July 2006

Stu, on account of no objections so far I am writing it now. Not easy to find alternatives to the word 'critical'. Long day.

But, is Alan's rule along the lines of 'I'm an electrician, if you see me running try to keep up?'

I'll not send this email until early in the morning just in case anyone comes on here to tell me is is quite acceptable but I'm getting it ready to roll. This installation before my time you understand......close but not close enough...

Actually, when I am bored one day I will have a look at the regs from 1959. I have every copy from 1-15. Which ones were 1959? I'm guessing about 11th or 12th??

Zs
 03 April 2013 09:44 PM
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slittle

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Yep, Alan's rule is worded something like "If you see me running, don't ask why"...

In all seriousness it sounds like it needs a serious report before it kills someone.

We've got a farm site where the switch room is known by all of us as "the room of doom" with 1950's switchgear in places and the incoming supply is straight from the transformer (which is the other side of the wall) into our mainswitch, with the metering CT's around the transformer tails. No great problem with that other than there's no way of UKPN isolating the transformer should we have a problem with our switch without them taking out at least four more pole mounted transfomers which supply other bits of the farm :-(

Stu
 03 April 2013 10:38 PM
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paulskyrme

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Zs,
Pics please that would help!
You know how.
 03 April 2013 10:43 PM
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jamieblatant

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I would be tempted to say its ok as the main switch is that a main switch so why not

Some pictures would help it will take you 15 mins to upload to google Picar and set up an account for future use that 5 if you have a google Id

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 04 April 2013 12:45 AM
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Martynduerden

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leading on from Jamie's post..

Main switch OK in itself,

You don't say the cables are too small for 400A OL / SC ?

What is the nature on the load, can it overload said cables?

Are you saying there are no protective devices downstream of the incommer anywhere?

Exposed live bits - crap - to be expected if your where I think you are.

Not really shocking tho, just another ridiculous unacceptable danger for the list.

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Martyn.

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 04 April 2013 09:50 AM
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Zs

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I expect the cable is capable of carrying the load and I would not comment on that to them until I have measured it. That will take place though. Heating is all off this week while the building is closed.

There is a set of BS88-2 fuses protecting the aircon as an outgoing way from the plant room cabinet but this also does not have a switch, just the three fuses in line. I can't tell you what rating they are because they are very faded but each is about 6 cm in diameter. Given the size of known 200A devices in the building I suggest these are higher than 200A.

However, the incoming cable itself relies entirely on the DNO supply fuses for protection. It also cannot be isolated in the case of emergencyin the plant room. This is the bit I am asking about.

The steel links do not look as though they have been added as a botch, they look as though they are part of the original design. They do not look to be under any stress and the metal links are clean and not blackened. It's why I'm checking.

My photos of the whole panel show stickers with the company logo on them so I can't post. May crop one later.


Zs
 04 April 2013 10:23 AM
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AJJewsbury

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I have a phone full of photos but I don't know how to post them on here

Zs, if you like, just e-mail them to me and I can upload them to my photobucket account and link here easily enough. I can edit out stickers etc if you want.

I would have expected to find the main switches to be offering fuses forward but in fact they show me significant steel bars and not fuses.

I think a number of suppliers offered switch fuses + solid links as an alternative to isolators - so it sounds like you have a setup equivalent of a giant "REC 2" after the meter - so if it was a little 100A supply I'd be looking at the supplier's <3m-ish "meter tails" limit.

400A supplies are way outside my comfort zone, but I guess similar principles apply - the supplier will authorise the use of their fuses for a certain length of customer's conductors. For that size of supply there might even be (or have been) some bespoke agreement. My gut feel is that it wouldn't have stretched to four floors up!

In one way, I could see that the debate about who's fuses (DNOs or customers) provide protection is "political" rather than physical safety. So if Zs readings (if that's not a silly idea given the likely low impedance of the supply - maybe calculation would be better) and (DNO) fuse ratings don't suggest that 5s disconnection is going to be achieved, then you can show a serious non-compliance straight away. If disconnection times look plausible, then there's a lot less in the way of immediate danger. I guess the converse view would be if one of the DNO cut-outs was in the plant room, with the supplier's cable wending its way up four floors.

- Andy.
 04 April 2013 12:15 PM
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OMS

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Originally posted by: Zs

I expect the cable is capable of carrying the load and I would not comment on that to them until I have measured it. That will take place though. Heating is all off this week while the building is closed.

There is a set of BS88-2 fuses protecting the aircon as an outgoing way from the plant room cabinet but this also does not have a switch, just the three fuses in line. I can't tell you what rating they are because they are very faded but each is about 6 cm in diameter. Given the size of known 200A devices in the building I suggest these are higher than 200A.

So it's a 200A or greater supply from effectively a DB then - didn't you mention switches with links upstream of this ? - isolation may well be achieved - it doesn't have to be local to the equipment or the protection


However, the incoming cable itself relies entirely on the DNO supply fuses for protection. It also cannot be isolated in the case of emergency in the plant room. This is the bit I am asking about.

Not unusual, ESQCR and before that Electricity supply regs make the responsibility for protecting the installation up to the first point of consumer switchgear the DNO's anyway - by far the vast majority of switchboards fed by DNO (or similar supplies) and reliant on the DNO fuses would have bolted links rather than fuses in the main switc - ditto for MCCB's or ACB's - they would tend to be no auto anyway.

You would only offer protection if the DNO isn't - ie direct connection to your own LV transformer protected on the HV side by the DNO.


The steel links do not look as though they have been added as a botch, they look as though they are part of the original design. They do not look to be under any stress and the metal links are clean and not blackened. It's why I'm checking.

Are they steel - or bright tinned covering copper ?. I would go along with them being original, if no sign of heat stress then they'll be fine.


My photos of the whole panel show stickers with the company logo on them so I can't post. May crop one later.

Zs


I'm not actually sure you have any problem there that would warrant a Code 1 or an escalating commentary to the client Zs - I don't follow the set up the the HVAC MCC, but it seems to me you have overload protection at the plant room - several points of isolation along the supply cable to the plant room (albeit with links rather than fuses) and short circuit and EF protection by the DNO fuses, with again, isolation at the intake position.

Because this is an unusual set-up, and somewhat historic, I'd like your permission to freak-out before I actually do it



Not just yet -


regards

OMS

-------------------------
Failure is always an option
 04 April 2013 04:27 PM
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Zs

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This is all sounding quite good. Thank you.

I have found photobucket so when I get home from guitar later on I will join that and will also try to draw you a diagram of the circuit with the isolation device. Don't expect axiometrics I only do those when I'm trying to impress. A row of contactors I seem to remember?

In the meantime, I have registered a concern with them but not gone into details. They know I am seeking advice before commenting. Sometimes I think it is ok to say I don't know but I'll find out for you.

Zs
 04 April 2013 04:33 PM
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AJJewsbury

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Sometimes I think it is ok to say I don't know but I'll find out for you.

Absolutely!

- Andy.
 04 April 2013 04:56 PM
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OMS

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Don't expect axiometrics I only do those when I'm trying to impress. A row of contactors I seem to remember?


LoL - the old memory cells are still working fine then - it was a set of contactors (with countdown timers) -

Sometimes I think it is ok to say I don't know but I'll find out for you


For sure - I wish more people would do it actually

regards

OMS

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Failure is always an option
 04 April 2013 10:01 PM
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Zs

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http://s1306.photobucket.com/u...984008305539244575721

Tried to condense the link....you'll have to tell me how to do that for next time. I think you have to click on the pictures to expand them.

In advance, the advertising on this photo site is grim, really grim and I apologise wholeheartedly if you get them. I will try to find an alternative solution for next time.

The above link includes examples of the fuse drawers, a rather dark picture of the bolted links, a close up of the incoming terminal in the plant room (with pencil to help me size the cable and any help would be appreciated) and 2 pics of the bus bar in the plant room, both taken without unscrewing anything.

There are no switches in the control panel.

the circuit:

Main DNO incomer 400A fuses
bolted links in isolation drawer
cable to fourth floor
Incomer to plant room control panel ( no switch)
bolted links
bus bar
fuses outgoing, chamber bolted to the bus bar ( no switch)
HVAC

Hope this helps and thank you for your help.

Zs
 04 April 2013 10:13 PM
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slittle

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I'll go for bigger than 95mm, possibly 185 or 240 for your cable size but it's hard to tell even with the pencil there.

Now I've seen the pictures, the words do not seem quite so bad, there's isolation on the cable if I read it right because the bolted links are fitted to a switch fuse (without the fuses).

I can think of loads of older panels with no incoming device, and I'm guessing you can lock off the one at the incomer (with the bolted links).

It probably comes down to your maths (or measurements) as to whether the 400A fuses provide protection to the busbar.

Old, yes, Rough by todays standards, yes but it's old.

Stu
 04 April 2013 10:16 PM
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Zs

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Thanks Stu,

Sadly the bolted links, nor any of the drawers can be locked off.

Zs
 04 April 2013 10:33 PM
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Fm

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Zs,cant the bolted links be removed and fuses installed

When the fuses are racked out can a padlock not be applied?
 04 April 2013 10:34 PM
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AJJewsbury

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Sadly the bolted links, nor any of the drawers can be locked off.

Old school method - remove the links and keep them in your pocket? ... or just lock the room?
- Andy.
IET » Wiring and the regulations » Your advice please

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