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Topic Title: Home made DBs
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Created On: 15 January 2013 06:14 PM
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 16 January 2013 12:01 AM
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AJJewsbury

Posts: 11251
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I don't think its multiple "B" type stacks Andy as the breakers appear to use a single sided busbar comb assembly.

Agreed - I was just attempting (and probably failing) to make the point that mixed L1/L2/L3 in a single row/column isn't of itself unusual. Most MCB manufacturers do make shrouded cut-to-length 3-pole bus-bar assemblies for the purpose (although you might have to look in the continental version of their catalogues to find them).
- Andy.
 16 January 2013 12:29 AM
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Zs

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From 1 year ago before the board was changed ( it used to be two boards of the Dorman Smith D type):

Ze(db) 0.24 ohms
three phase so about 2K.

Those measurements were taken by Pete TLM so I reckon we can trust them.

In this particular case the stack on the left is all three phase breakers and the other two stacks are entirley single phase circuits.

I took that picture on the QT a little while back. I just got to wondering how the bus bars are configured to make three columns too. It is definitely a schneider box though. It is not my remit to look inside them but I hope it will be soon. I'm not sure about the flexible tails inside this particular one but have seen it in the others, which are smaller than this one and just a single row. I've a snap of one of those too.

Electrical installation et al is becoming complicated isn't it? Why do these wealthy companies use a mosaic of trades? One to dig the hole, one to put the pond liner in, one to fill it with water and one to come in and see if it is leaking?

Zs

Edited: 16 January 2013 at 12:40 AM by Zs
 16 January 2013 12:31 AM
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OMS

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That was going through my mind Andy - if it was three stacks of single phase MCBs the creepage and clearance wouldn't be quite as important.

If it's a commercial insulated busbar then fine - but I thought Zs also mentioned a lot of made on site internal wiring going on - so the ends of those busbars (possibly both ends) also have terminations on them - all adding to the risk of flashover under a fault condition.

Regards

OMS

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Failure is always an option
 16 January 2013 03:03 AM
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rogersmith7671

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Quote;
all adding to the risk of flashover under a fault condition.
Nothing, that might not be cured with a bit of reinforced insulation or dare i say it... double insulation.

regards

Edited: 16 January 2013 at 03:09 AM by rogersmith7671
 16 January 2013 06:41 AM
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normcall

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"Electrical installation et al is becoming complicated isn't it?"

Nope. That's exactly why a few of us spent long apprenticeships being involved in all sorts of electrical works. Looking back, I was 'lucky' to be involved in every 'sh*tty' job that our local electricity board was involved with (in the days when private contractors were rare beasts).

-------------------------
Norman
 16 January 2013 06:47 AM
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Fm

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Siemens do nice insulated 3 phase combs for making your own dbs a bit of try rated and hey presto a db.

Get the torque driver out test the connections and make the recomendations.

Dont get too involved
 16 January 2013 09:10 AM
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OMS

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Originally posted by: Zs

From 1 year ago before the board was changed ( it used to be two boards of the Dorman Smith D type):

Ze(db) 0.24 ohms

three phase so about 2K.

OK - so not particularly high and should be well within the capability of the breakers - which just leaves the busbars and interconnecting tails as the question. That said, it'll be the connections and the physival configuration that may fail rather than the component parts themselves


Those measurements were taken by Pete TLM so I reckon we can trust them.

Fair enough


In this particular case the stack on the left is all three phase breakers and the other two stacks are entirley single phase circuits.

OK - when you say single phase breakers I'm assuming not all of the same phase though - ie the stack is threee phase suppling single phase loads - otherwise there could be extreme imbalance in the board loading (and back into the submain as well) - the issue there is has the designer assumed roughly equal loading as part of the determination of Ib


I took that picture on the QT a little while back. I just got to wondering how the bus bars are configured to make three columns too. It is definitely a schneider box though. It is not my remit to look inside them but I hope it will be soon. I'm not sure about the flexible tails inside this particular one but have seen it in the others, which are smaller than this one and just a single row. I've a snap of one of those too.

OK - a good look inside will reveal more - and may raise more concerns - what you can't see you can't worry about


Electrical installation et al is becoming complicated isn't it? Why do these wealthy companies use a mosaic of trades? One to dig the hole, one to put the pond liner in, one to fill it with water and one to come in and see if it is leaking?

Cost basically - if you give the job of creating a pond to one company they'll price for management, risk, co-ordination, partial working days etc. Give it to 4 individuals and they'll cost thier bit, but more importantly, the group dynamic will result in (usually) the same co-ordination and management being provided by them without them realising they haven't priced it in.

You'll have seen it in your desk job - give the work to one engineer and let them pull in the team needed - you effectively get them doing a lot of the PM role for free as part of the actual design role. Leaves the real PM free to idle about making a nuisance of themselves -


Zs


regards

OMS

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Failure is always an option
 16 January 2013 09:12 AM
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OMS

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Originally posted by: rogersmith7671

Quote;

all adding to the risk of flashover under a fault condition.

Nothing, that might not be cured with a bit of reinforced insulation or dare i say it... double insulation.

regards


LoL - of course Roger - but at the cost of increasing the busbar CSA to compensate for the much lower operating temperature of the insulation and it's inability to lose heat effectively due to that insulation. DB busbars can often run to about 105C at full load - you'd probably be limited to about 70C with a DI or RI busbar assembly.

Regards

OMS

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Failure is always an option
 16 January 2013 09:15 AM
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OMS

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Originally posted by: normcall

"Electrical installation et al is becoming complicated isn't it?"

Nope. That's exactly why a few of us spent long apprenticeships being involved in all sorts of electrical works. Looking back, I was 'lucky' to be involved in every 'sh*tty' job that our local electricity board was involved with (in the days when private contractors were rare beasts).


I think Zs was talking about the often convoluted management approach to the installations couped with divided responsibilities rather than the "red to red, black to black" aspects of it, Norm.

regards

OMS

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Failure is always an option
 16 January 2013 09:20 AM
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OMS

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Originally posted by: Fm

Siemens do nice insulated 3 phase combs for making your own dbs a bit of try rated and hey presto a db.

Get the torque driver out test the connections and make the recomendations.

Dont get too involved


For sure, building bespoke DB's isn't difficult - the problem essentially is being able to determine if your creation meets any acceptable standards and how to demonstrate that - which is where the money is of course.

Would you want a home brew panel in say an escape corridor only to find out after the fact that most of the insulation and shrouds inside it were PVC and produced choking black smokewhen the board faulted and set fire to the local area that delayed escape and resulted in fatalaties - that's what you are buying - not a collection of bits in a box.

Regards

OMS

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Failure is always an option
 16 January 2013 10:22 AM
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AJJewsbury

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Would you want a home brew panel in say an escape corridor only to find out after the fact that most of the insulation and shrouds inside it were PVC and produced choking black smokewhen the board faulted and set fire to the local area that delayed escape and resulted in fatalaties - that's what you are buying - not a collection of bits in a box.

I recall someone on here did a 'cigarette lighter test' on an offcut from an official complies-with-all-standards CU box. The results didn't exactly inspire confidence. Maybe it has value as a transfer-of-risk rather than actual risk reduction.
- Andy.
 16 January 2013 11:05 AM
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OMS

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Maybe so Andy - although I was thinking metalcald with an internal fire rather than a plastic enclosure exposed to an external source.

I guess when we, as a sector, spend vastly more on litigation than we do on education, then risk transfer is an inevitable consequence. As a designer it's a pretty big part of my role to be honest - what is it they say about contractors on the receiving end of consultant spec and drawings - "they sit at the late night poker table but never get the chance to cut,shuffle or deal" -

regards

OMS

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 16 January 2013 11:06 AM
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AJJewsbury

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I just got to wondering how the bus bars are configured to make three columns too.

I would guess using a few of something like these: http://www.meteorelectrical.co...r-57-modular-10mm.html (available in a number of different ratings) and a few wires.

If you want to see what our continental cousins do routinely in terms of self assembly of DBs, try googling for "tableau electrique" and switch to the images tab. Bear in mind that they probably work within the same basic set of EN standards that we do these days, and certainly the same laws of physics.

- Andy.
 16 January 2013 11:18 AM
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OMS

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It might be me Andy, but i get the feeling that the actual DB's in question aren't simply a self assembly dist board kit (or "tableau electrique") where the installer is simply collecting the specific kit of parts from predesigned equipment lists with know configurations available - ie type tested as a "worst case" so generally partially type tested when assembled to a particular configuration.

That photo suggests to me something else is going on behind those covers.

regards

OMS

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 16 January 2013 02:01 PM
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rogersmith7671

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Now that this thread has attracted over thirty posts it might be hoped that the concept of "some installer type person" having the temerity to assemble a distribution board/fuse box all by their little selves, so it cant possibly be any good be accepted. And ask If any "fundamental principles" have been observed. such as the requirements of 133.1 to 133.1.3 say? It might be worth asking just who the "installer" actually is?
Normally, after completion such confirmation of "provision of degree of safety" should be in the hands of the person who ordered the work. In cases of dispute that may not be the case and the designer may not want to be helpfull.
If any dispute between the original parties are not resolved then an expert witness will be appointed by the court and their decision will almost certainly be final.
So really, if it all goes Pete Tong in the small claims dept, it will be the opinion of the expert witness that you might have to second guess.

Regards
 16 January 2013 04:41 PM
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Zs

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Originally posted by: OMS

That photo suggests to me something else is going on behind those covers.

OMS


From what I remember when I suggested the board be covered, alongside each column of breakers sits a long cover which conceals the terminals and connections to each breaker. I'm pretty sure I have a snap of that which was texted to me and will change avatar later if I can find it, but it might be on the old phone.

The neutral bar along the top was completely exposed, as were the terminals into the contactors. But the rest was tucked up nicely behind covers. I remember that brief conversation vividly. Me 'exposed neutral bar?' He ' It is not a live part'.

Going back a bit to my original question; Given that home made DBs, or kit-style DBs are becoming more prevalent in commercial environments, and given that I'd prefer not to march around London telling installers to 'Rip it Out' without it being absolutely necessary. Where do we draw a line between fit for purpose and not, and so on.

However, all these undesigned installations are keeping my busy. I think I'm about to start a directory of standard paragraphs to cut and paste into letters and reports.

Are any more of you coming across these?

Be careful of today's google header by the way, the one where you drive a little truck around the ice rink to clean up the ice. it is addictive. I'm on 630 points a about 20 banana spins. Supposed to be working.

Zs
 16 January 2013 04:45 PM
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AJJewsbury

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The neutral bar along the top was completely exposed

Is that after removing the front cover (using a tool or key)? - if so, sounds about the same as a typical CU.
- Andy.
 16 January 2013 04:54 PM
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kj scott

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Zs,
It is not down to you to prove the DB construction one way or the other, section 511 requires all equipment to conform with relevant standards; it rests with the installer to demonstrate that they do.
That of course assumes that the contract specified compliance with BS 7671.

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 16 January 2013 05:07 PM
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OMS

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Originally posted by: Zs

Originally posted by: OMS

That photo suggests to me something else is going on behind those covers.

OMS


From what I remember when I suggested the board be covered, alongside each column of breakers sits a long cover which conceals the terminals and connections to each breaker. I'm pretty sure I have a snap of that which was texted to me and will change avatar later if I can find it, but it might be on the old phone.

OK

The neutral bar along the top was completely exposed, as were the terminals into the contactors. But the rest was tucked up nicely behind covers. I remember that brief conversation vividly. Me 'exposed neutral bar?' He ' It is not a live part'.

Nice

Going back a bit to my original question; Given that home made DBs, or kit-style DBs are becoming more prevalent in commercial environments, and given that I'd prefer not to march around London telling installers to 'Rip it Out' without it being absolutely necessary. Where do we draw a line between fit for purpose and not, and so on.

Fit for purpose is a subjective (and dangerous) approach.

Not a case of saying "Rip it Out" - All you can say is that the installed DB's do not appear to comply with BS EN 60439-3, do not appear to have any form of 3rd party testing/approval and are probably not type tested or partially type tested assemblies. As such, the performance under predictable fault scenarios (my initial post) is unknown. The designer/installer should satisfy themselves that the installation complies with BS 7671, however without knowledge of the distribution boards capability and oerformance, this will be difficult to demonstrate.


However, all these undesigned installations are keeping my busy. I think I'm about to start a directory of standard paragraphs to cut and paste into letters and reports.

LoL - spoken like a true consultant - sell the reports by weight -


Are any more of you coming across these?

Not personally - I wouldn't accept one if offered by a contractor, without relevant approvals on it at least. That said, I've designed similar arrangements where a bespoke DB is the appropriate design solution with the caveat the manufacturer/assembler demonstrate relevant approval - ie I've had them made up in a system house somewhere.

as an example, a client of mine has power distribution units in IT rooms that start life as a merlin gerin 8 way TPN pan assembly, but into a bespoke box with metering, MCCB main switch, EPO and alarm monitoring and has a pre wired section to terminal blocks to the outgoing cables including isolatable neutral links - it's a glorified DB, made from a collection of parts but the key issue is it's certified as in compliance with a BS EN and is a partially type tested assembly



Be careful of today's google header by the way, the one where you drive a little truck around the ice rink to clean up the ice. it is addictive. I'm on 630 points a about 20 banana spins. Supposed to be working.

LoL - I could do with a real one - it's a bit brisk standing ouside the office puffing my way through a dunhill -

Zs


regards

OMS

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 16 January 2013 05:09 PM
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Zs

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Andy, as soon as you opened the door of the box, using a removable handle which lives on top of the box. In effect, getting to the breakers to reset an RCBO would also get you to the exposed neutral bar. I do not consider that to be safe for the users.

I'll do the two sets of EICR certificates I'm supposed to be doing because I have promised them by seven and then go searching for that photograph.

Thanks for that KJ. I care about my clients and I'm not nit-picking for faults and non-compliances especially. That'd make me very unpopular with clients and give me some time off after a while. I am looking to make sure they are as safe as they can be. At the moment it is the smoke risk which bothers me most from the comments made. I think this one is a pretty good board, given that I've not seen the connections.

Zs
IET » Wiring and the regulations » Home made DBs

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