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Topic Title: Maximum Earth Loop Impedance Values For Common Devices
Topic Summary: What About the Uncommon Devices
Created On: 02 February 2017 11:19 PM
Status: Read Only
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 02 February 2017 11:19 PM
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keithredpath

Posts: 543
Joined: 30 March 2002

I have tables which list the Maximum Earth Loop Values for Common Devices and when I come across "Uncommon" devices usually just enter "A Limitation" on my Report.

However a client has insisted all these values appear on his report.

Is there an easy way to obtain these values? They are mainly all MCCBs, have variable settings and have different manufacturers.

Am I right in assuming this might be a complicated process?

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keithredpath
 02 February 2017 11:36 PM
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Legh

Posts: 4028
Joined: 17 December 2004

Manufacturers of mccbs provide charts of time-current characteristics.
although not always as easy to find as the energy let-through for the larger OCPDs.

they specify leading to trailing edge currents for instantaneous disconnection where standard devices in the regs only give trailing edge disconnection currents.

3-5 Ia for type B
5-10 Ia for type C
10-20 Ia for type D

Legh

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http://www.leghrichardson.co.uk

de-avatared
 03 February 2017 12:14 AM
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alancapon

Posts: 6880
Joined: 27 December 2005

. . . when I come across "Uncommon" devices usually just enter "A Limitation" on my Report.

However a client has insisted all these values appear on his report. . .

I think I would want these completed too. Most manufacturers have the data sheets for the devices available on their websites. I have always understood that "limitations" should be agreed with the client.

Regards,

Alan.
 03 February 2017 07:17 AM
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leckie

Posts: 4320
Joined: 21 November 2008

It depends what model forms you use. The model forms in BS7671 don't have a column for the maximum permitted Zs. Nor do ECA model forms. The NICEIC ones do.
 03 February 2017 11:32 AM
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John Peckham

Posts: 8783
Joined: 23 April 2005

Keith

If you do not know the maximum value of Zs for a particular device how do you know if your measured result is satisfactory and will provide ADS is the the required disconnection time?

As I have already posted on this forum I am the custodian of the "Great Book of Circuit Protection" which contains information on many ancient and modern protective devices. I am happy to provide data if I have it to forum members. If anyone has any data sheets on legacy devices I would be most grateful if they could send me them for inclusion in the book.

If you want data on a particular adjustable MCCB I need the make, model number, In rating,model number of trip and any settings.

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John Peckham

http://www.astutetechnicalservices.co.uk/
 09 February 2017 06:11 PM
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keithredpath

Posts: 543
Joined: 30 March 2002

Many Thanks John, I may take you up on that kind offer shortly.

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keithredpath
 19 February 2017 07:45 PM
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weirdbeard

Posts: 3116
Joined: 26 September 2011

-4 The lowest number of posts ever, congratulations Keith

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:beer)
 19 February 2017 11:16 PM
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mapj1

Posts: 9356
Joined: 22 July 2004

negative scores, perhaps the people who wrote the forum software have been watching QI ? Certainly posting and deleting in rapid succession can both bump a message to the top and muck up the scores... Mind you elsewhere WB, you seem to have problems with multiple postings. If this was another, perhaps the use of the delete button to remove multiples, may be what has done this.

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regards Mike
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