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Topic Title: electromagnetic effects
Topic Summary: is the regulation required
Created On: 18 December 2012 01:17 PM
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 18 December 2012 01:17 PM
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MrP

Posts: 848
Joined: 24 March 2006

On my little site it is common practice to install tails through steel gland plates; tails vary in size from 16mm to 300mm.
The tails are installed via bushed single entry holes
When I mentioned electromagnetic effects others insist that this is normal practice and nothing gets the slightest bit warm.
So while in the UK if we came across an installation installed in this manner it would be a pointing finger and a sharp intake of breath.
So is ferrous enclosures electromagnet effects really the end of the plant as we know and therefore is this regulation required.

MrP tomorrow is one day to going home
 18 December 2012 01:37 PM
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AJJewsbury

Posts: 11696
Joined: 13 August 2003

I tend to agree - I know of a metal-clad DB where the tails have been taken through individual 20mm holes - L2 usually carries close to 70A and while the tail itself is slightly warm to the touch, the steel is quite cool.

Certainly the instance that c.p.c.s are taken through the same hole seems unjustifiable - any intended effect is surely lost by the inevitable interconnection of exposed- and extraneous- parts downstream - and the exception only for g/y run alongside SWA just makes it all seem inconsistent. (521.5.1).

- Andy.
 18 December 2012 01:58 PM
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normcall

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I can only express concern.
Many years ago I was a member of the emergency call out team (before the days when you had to go on a course to blow your nose!!).
I was called out to a no supply in a small office block in a nearby town centre. It was winter and chilly.
On arrival I found a neat set of 3 phase tails from the meter, passing through 5 holes in a a 4x4 metal trunking and feeding a selection of single phase and 3 phase boards. The paint on the trunking was charred around 2 phases and the neutral holes. The cable insulation had melted and obviously blown 2 of the three main fuses as everything 'touched'.
I managed to 'repair' (OK, slight rewire/bodge) to get everything operational again. The contracting dept. (those days, the electricity boards did everything) attended a couple of days later to sort out the damage properly.

Until you have seen it, like me, you would not believe the damage caused.

Of course, nowadays, I wouldn't b allowed within a mile of this situation as I haven't been on a course!

-------------------------
Norman
 18 December 2012 02:16 PM
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OMS

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So is ferrous enclosures electromagnet effects really the end of the plant as we know and therefore is this regulation required.


It can be the end of the planet for sure - if in the wrong place.

A combination of sheath circulating currents and light, mild steel glandplates on a set of tails between a 1250kVA taransformer and LV switchboard (groups of 500mm2 AWA Singles) genetated enough heat to strip the paint from the glandplates and actually melt the cable gland shrouds - the heat in the main switch terminal chamber was over 105C and the insulation was virtually dripping off the conductors.

You may have been lucky through a combination of cable disposition and thickness of steel plates but if you chuck enough amps through the system the plates will get hot - very hot in fact.

Based on the science and my direct observation, the regulation is very much required.

My experiences designing for jobs in your corner of the globe, getting the message across to contractors is difficult - everyone has a story of how they did just that previously with no problems - until it all goes horribly wrong of course - - the phrase " I hate to say I told you so, but ................." is oft heard

Regards

OMS

-------------------------
Failure is always an option
 18 December 2012 04:28 PM
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normcall

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Quite right OMS.
And it still goes on, and when I mention it, everyone thinks I'm too old, unqualified and ought to know better (mind you, they are right, but we've had this debate before!)

-------------------------
Norman
 18 December 2012 07:30 PM
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OMS

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Old and unqualified eh - it's what we used to call "Old Skool" - area board trained apprentice with a good chunk of common sense - there's a place for you still, Norm - the new breed don't know everything just yet - even if they think they do

Regards

OMS

-------------------------
Failure is always an option
 18 December 2012 07:34 PM
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MrOther

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Originally posted by: OMS

Old and unqualified eh - it's what we used to call "Old Skool" - area board trained apprentice with a good chunk of common sense - there's a place for you still, Norm - the new breed don't know everything just yet - even if they think they do



Regards



OMS


OMS what is this common sense you speak oft of? Can I get it on a course? Does it have an expiry date and stupid expensive refresher courses?

Otherwise I'll think I'll pass.
 18 December 2012 07:44 PM
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OMS

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Originally posted by: MrOther

Originally posted by: OMS

Old and unqualified eh - it's what we used to call "Old Skool" - area board trained apprentice with a good chunk of common sense - there's a place for you still, Norm - the new breed don't know everything just yet - even if they think they do

Regards

OMS


OMS what is this common sense you speak oft of?

I may speak oft of it but it's still a rare thing

Can I get it on a course? Does it have an expiry date and stupid expensive refresher courses?

Well, not really - you can gain information from a course - it's your personal evaluation that turns it into knowldge and gives you an insight into where you can and can't apply that knowledge - that's the common sense bit

Otherwise I'll think I'll pass.

Pity - not everything needs a brand to be valuable, don't pass up the opportunity to pick up things by osmosis - it's worth a lot



Regards

OMS

-------------------------
Failure is always an option
 18 December 2012 07:48 PM
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MrOther

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Originally posted by: OMS

Originally posted by: MrOther



Originally posted by: OMS



Old and unqualified eh - it's what we used to call "Old Skool" - area board trained apprentice with a good chunk of common sense - there's a place for you still, Norm - the new breed don't know everything just yet - even if they think they do



Regards



OMS




OMS what is this common sense you speak oft of?



I may speak oft of it but it's still a rare thing



Can I get it on a course? Does it have an expiry date and stupid expensive refresher courses?



Well, not really - you can gain information from a course - it's your personal evaluation that turns it into knowldge and gives you an insight into where you can and can't apply that knowledge - that's the common sense bit



Otherwise I'll think I'll pass.



Pity - not everything needs a brand to be valuable, don't pass up the opportunity to pick up things by osmosis - it's worth a lot







Regards

But I won't get a shinney new card to put with my otehrs in my wallet.

OMS
 18 December 2012 08:30 PM
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OMS

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Well, I guess it depends on the value you place on shiny new cards in the wallet I suppose - qualifications are fine, but not the whole picture

Regards

OMS

-------------------------
Failure is always an option
 18 December 2012 08:38 PM
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MrOther

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Originally posted by: OMS

Well, I guess it depends on the value you place on shiny new cards in the wallet I suppose - qualifications are fine, but not the whole picture



Regards



OMS


OMS -- I'm being saccy, (I should of used smilies.)
 18 December 2012 08:45 PM
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OMS

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You don't say -

Regards

OMS

-------------------------
Failure is always an option
 18 December 2012 09:11 PM
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MrOther

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Barclays sent me a nicly newly schiny card today for my wallet. No value what so ever.
 18 December 2012 09:14 PM
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OMS

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No worries - I've got one just like it - I keep it next to my donor card in my wallet - that way whoever gets any bits of me gets my overdraft as well

Regards

OMS

-------------------------
Failure is always an option
 18 December 2012 09:21 PM
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rocknroll

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Originally posted by: OMS

No worries - I've got one just like it - I keep it next to my donor card in my wallet - that way whoever gets any bits of me gets my overdraft as well

Regards

OMS


LOL

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 18 December 2012 11:54 PM
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OMS

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Did you know 6 out of 7 dwarfs are not happy- statistically speaking

OMS

-------------------------
Failure is always an option
 19 December 2012 12:59 AM
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rocknroll

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Originally posted by: OMS



Did you know 6 out of 7 dwarfs are not happy- statistically speaking

OMS


LOL Neither would you be if people were speaking down to you all the time!!

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 19 December 2012 at 10:27 AM by rocknroll
 19 December 2012 05:14 PM
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maltrefor

Posts: 121
Joined: 01 November 2009

Originally posted by: MrP

On my little site it is common practice to install tails through steel gland plates; tails vary in size from 16mm to 300mm.

The tails are installed via bushed single entry holes

When I mentioned electromagnetic effects others insist that this is normal practice and nothing gets the slightest bit warm.

So while in the UK if we came across an installation installed in this manner it would be a pointing finger and a sharp intake of breath.

So is ferrous enclosures electromagnet effects really the end of the plant as we know and therefore is this regulation required.


I was always taught to use brass bushes and locknuts and to run a cut with a jigsaw blade between the holes in the steel glandplate to stop electromagnetic effects.

Is not this the correct procedure ?
 19 December 2012 05:24 PM
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AJJewsbury

Posts: 11696
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I was always taught to use brass bushes and locknuts and to run a cut with a jigsaw blade between the holes in the steel glandplate to stop electromagnetic effects.

Is not this the correct procedure ?

It's certainly one correct procedure - other options include substituting the gland plate (or part of it) with a non-ferrous alternative.

(I guess slotting might fall foul of 416.2.2 these days if the cables enter at the top)

- Andy.
 19 December 2012 05:36 PM
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OMS

Posts: 19851
Joined: 23 March 2004

a further alternative is to use a steel gland plate welded in with high resistance (magnetically) welds - brazing with brass rods for example

the non ferous weld stops the propogation of the magetic flux - careful spacing of the entries and thickness of material just accomodates the heating effect - it gets warm but doesn't cause a problem.

regards

OMS

-------------------------
Failure is always an option
IET » Wiring and the regulations » electromagnetic effects

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