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Topic Title: Earth din rail terminals
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Created On: 07 January 2016 05:49 PM
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 07 January 2016 05:49 PM
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celtic1967

Posts: 78
Joined: 15 August 2014

Hi all

Question regarding earth din rail terminals. I was looking over a job that was needing done on a motor control panel and there is several isolaters for each motor and inside each section is there controls for that motor with external connection l1,l2,l3 and earth din rail connectors. But as I have seen before the earth din rail terminal does not have a cable going to terminal block fia main earth bar as such. All it has is the centre screw of the earth din rail terminal clamped to the metal din rail which in turn is connected to the metal of the whole motor control panel which is earthed fia main supply to motor control panel Is this regarded as good continuity and what about fault current on the return of the external earth cable is the din rail suitable to carry the fault current? Comments will be much appreciated?

Thanks
 07 January 2016 06:27 PM
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paulskyrme

Posts: 1311
Joined: 12 February 2003

It's fine.
As long as the panel is correctly constructed.
Nothing to do with BS7671 really though BTW.
 07 January 2016 09:54 PM
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sparkingchip

Posts: 10543
Joined: 18 January 2003

 07 January 2016 10:15 PM
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celtic1967

Posts: 78
Joined: 15 August 2014

Thanks lads for getting back. but for instance if you wanted to build a panel yourself for example- garden lights enclosure and you wanted to use din rail connectors. Would you be able to or to put it safe to have the din rail connectors just screwed to the din rail and all earth cables going to individual terminals but you would still be able to guarantee continuity and protection for fault current? Yeah they look good din rail terminals but what if the din rail terminal does not have a jumper option will you link them with cable or just leave as is on din rail?

Cheer lads
 07 January 2016 10:22 PM
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paulskyrme

Posts: 1311
Joined: 12 February 2003

If you have all "outgoing" cpc connections to DIN rail terminals and, the supply circuit cpc to one DIN rail terminal on the same DIN rail terminal then fine.
There are however as many answers as there are potential connection configurations as to what would or would not be acceptable.
Design it & build it correctly in accordance with the relevant standards and acceptable engineering practice, then no worries.
 07 January 2016 10:31 PM
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mapj1

Posts: 10430
Joined: 22 July 2004

two wagos of the type figured, side by side on a metal DIN rail, don't really need a link wire, any more than you would link two earth studs side by side on the same box.. In a box with a plastic din rail profile then obviously they would.

-------------------------
regards Mike
 07 January 2016 10:43 PM
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celtic1967

Posts: 78
Joined: 15 August 2014

Yeah so you can't allow for the din rail to carry your continuity and fault current then?

Thanks
 07 January 2016 10:43 PM
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celtic1967

Posts: 78
Joined: 15 August 2014

Metal din rail obviously?
 07 January 2016 11:23 PM
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mapj1

Posts: 10430
Joined: 22 July 2004

well, yes. Continuity through the rail needs to be good. But certainly with the wagos it is.

-------------------------
regards Mike
 08 January 2016 09:14 AM
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craigmckee

Posts: 80
Joined: 16 September 2009

The assembly should have been tested to ensure under fault conditions specific to that circuit, the terminal could carry the current without failing and maintain its integrity afterwards. I would ask for proof of testing.

Also remember that there is a specific csa for copper protective conductors, based on current, you would need to confirm that this is met too.

The problem you can get is while the terminal may be reasonable bonded to the din rail. if the din rail is fixed to a painted gear plate. The only earth bonding is a couple of screw threads

-------------------------
Regards
Craig

http://www.3phasedesign.com
 16 May 2018 04:32 PM
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Wheelermch

Posts: 40
Joined: 04 June 2007

I note that at least some manufacturers (e.g. Weidmuller) state in their user information for such terminals 'only terminal rails made of copper or aluminium should be used as PEN busbars'.
 17 May 2018 09:40 AM
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AJJewsbury

Posts: 16623
Joined: 13 August 2003

I note that at least some manufacturers (e.g. Weidmuller) state in their user information for such terminals 'only terminal rails made of copper or aluminium should be used as PEN busbars'.

Probably not surprising. A PEN conductor - as it has to carry N current continuously - is somewhat more demanding role than a plain c.p.c. that only has to carry current for a very short duration (if a much higher current). Same reasoning why T&E can have a reduced c.s.a. c.p.c. but not a reduced N.

Steel has a resistance about 9 times higher than copper for the same c.s.a. - so to run continuously at the same operating temperature as copper (70 degrees say) you'd need something in the region of 9x the c.s.a. (to have the same I²R losses).

But to be just as satisfactory as a plain c.p.c. steel's higher thermal capacity compensates somewhat and to meet the same k²S² requirement a steel c.p.c. needs only to be k1/k2 times as large - e.g. 2.75x (where k for copper is 143 and steel 52).

For a steel DIN rail, the smallest effective c.s.a. is probably the point of contact with the earth terminal - it feels reasonable that such a point of contact might meet a 2.75x the c.s.a. of the largest conductor the terminal can accept, but might not meet a 9x.

- Andy.
 17 May 2018 01:04 PM
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tattyinengland

Posts: 1021
Joined: 23 November 2006

I know you can get copper "combs" that common up the din rail terminals - commonly used in controlls for lives, neutrals and earths. May settle your mind...............
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