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Topic Title: quick question
Topic Summary: when did discrimination change to selectivity?
Created On: 17 March 2015 05:46 PM
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 17 March 2015 05:46 PM
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Zs

Posts: 3814
Joined: 20 July 2006

L O.

Do you remember when the term discrimination got ditched in favour of the term selectivity? Was it When Big Green came out? Or was it Red?

Not desperately important but I'm going through some comments on a design and the reviewer has asked if I have considered discrimination. No, I considered selectivity. I'd love to know how far back it goes

Shhh, don't tell ...

Zs
 17 March 2015 06:07 PM
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Zoomup

Posts: 3286
Joined: 20 February 2014

Originally posted by: Zs

L O.



Do you remember when the term discrimination got ditched in favour of the term selectivity? Was it When Big Green came out? Or was it Red?



Not desperately important but I'm going through some comments on a design and the reviewer has asked if I have considered discrimination. No, I considered selectivity. I'd love to know how far back it goes



Shhh, don't tell ...



Zs


Hello Zs,
Big Red 2008 uses the term "Discrimination" in the index. Also mentions Co-ordination.

Bye,

Z.
 17 March 2015 06:09 PM
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Zoomup

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Then when I go to the Big Red Book reg. 536.2 after looking up "Discrimination" in the index, it uses the word "Selectivity".

EDIT. In Big Red Book at 531.2.9 "Discrimination" is only used, dealing with R.C.D.s in series.

EDIT 2. Big Red 536.2 uses the word "Selectivity" between over current protective Devices. No "discrimination" used at all.

Bye,

Z.

Edited: 17 March 2015 at 06:31 PM by Zoomup
 17 March 2015 06:12 PM
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Zoomup

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Big Blue 2001 seems to use "Discrimination" only. I looked at 533-01-06.

Bye,

Z.
 17 March 2015 06:32 PM
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Zs

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Joined: 20 July 2006

Mwah,

Thank you Zoomster.

Zs
 17 March 2015 07:29 PM
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mapj1

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co-ordination is something a bit different from discrimination.

Discrimination allows a fault downstream to pop the fuse nearest it, without blowing the bigger one further back.

Co-ordination is ensuring that in a high current fault the overload device will also be protected by some fault protection device.

With an MCB both overload and fault protection are done in the same box, so the distinction is blurred. However, as an example, you don't want a motor starter, which may include a thermal overload trip to catch fire before the fuse protecting it if the motor stalls.
Its more normally a problem designing the inside of equipment, where final installation conditions are a bit of a guess, and the current may be limited by something other than that which the designers intended.

-------------------------
regards Mike
 17 March 2015 09:01 PM
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RB1981

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I believe the term Selectivity emerged when the 17th Edition came out. The 16th Edition solely used the term Discrimination.

-------------------------
Walsh Electrical Services
http://www.walshelectrical.ie/
RECI REC & NICEIC Approved Contractor
 17 March 2015 09:32 PM
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Zs

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Thank you,

I'm at home now and about to look in the books just to see it for myself.

A small thing and it will probably be one of those things that I rise above.

But when we send a project off to the client at the desk job, a proper whack round the head with a frying pan comes back which is a form where they all write their comments and concerns on it. Even to the level of grammar and speeling wot I can do well good when I try. Sad but they don't seem to tell you if you've done anything good and I make a note to self about that for when I am Prime Minister.

Well, I'd done something a bit out of the norm on this one and had directed them to three derogations with reasons why I thought they'd be OK to go through. One of them is a selectivity issue. Not major, but it is there and in truth has probably been there for years. So I pointed it out and gave reasons (we're forced to use the old upstream devices on this one). I think the man who read it - highly respected and no doubt a fine man- I have no axe to grind- hasn't read the opening pages to that bit and has just looked at the 192 pages of actual amtech analysis. His comment is about discrimination. In fairness, the amtech analysis does not flag it (you can't half hide stuff with Amtech as PDF) and he will have worked it out with a calculator which I admire. They probably see hundreds of these things and I expect every cover sheet for the last 20 years has been the same. So I forgive a stranger.

But I have to write a response in the box next to every comment. I want to stick to the term selectivity so I need to put 'formerly discrimination...but changed in 1902..'.

My boss will delete it with a wry smile no doubt.

But thank you, It's in. I suppose it is no more than stamping a tiny dot of personality on something otherwise banal.

Zs
 17 March 2015 10:55 PM
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stateit

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Originally posted by: Zs

...Even to the level of grammar and speeling wot I can do well good when I try.


OT, but I was miffed getting a quote back from the Village Hall Committee with all my instances of 'w.r.t.' changed to 'with respect to'.

A quote for an EICR and lamp-changing... Good Grief. The gent did use to manage power stations, and old habits die hard I suppose.

-------------------------
S George
http://www.sg-electrical.com
 18 March 2015 08:19 AM
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mapj1

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Good to see the hyphenated compound verb in lamp-changing rather than the Americanish "relamping" ;-) nothing like a bit of linguistic controversy.
Imagine an era of brighter shirts and longer hair, and a room with a polished wood floor, and hardwood laboratory benches.
In the distance a lab tech's transistor radio reveals that 'Dexy's Midnight Runners' are in the charts again.
A whiskery old fella is delivering an introductory Electrical Lab Safety instruction session.
Topic what to do if your mate gets electrocuted.

And what's this big Shepard's crook thingy for lad ?

"To pull the live wire off of him with, sir"

" Good god, lad, no! This is the thing with which we pull off the live wire. Tssk . Off of him with. Tut. Youth of today"

Of course I have the doubtful advantage of the two of us, of still actually being alive, though to be fair I'm sure it was old age not escaping electrons or poor grammar that got him.

edited for grammer ironically

-------------------------
regards Mike


Edited: 18 March 2015 at 08:28 AM by mapj1
 18 March 2015 11:04 AM
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Parsley

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I have an ABB technical application paper titled Low Voltage Selectivity with ABB Circuit Breakers dated 2008 no mention of discrimination in it. And also a Schneider one titled Co-ordination of low voltage protective devices dated Feb 2008 that only refers to discrimination.

I'm probably wrong but was the term selectivity in relation to overcurrent coordination of protective devices was introduced when section 536 was added to BS7671, in think in 2008. My old 16 edition brown AMD 2 2004 book states section 536 reserved for future use and I can't see any reference to selectivity in relation to overcurrent or rcd co-ordination in it.

Regards
 18 March 2015 01:24 PM
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leckie

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In the definitions under selectivity, it refers you to discrimination for the definition. So it's still ok to use the term.
 18 March 2015 10:36 PM
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Zs

Posts: 3814
Joined: 20 July 2006

D'you know what?

The reviewers have a God-like status and I've always believed them to be untouchable. The clever ogres who live in a cave and are there at the edge of it poised to jump out and eat designers.

Well, I made a proper blunder on this design without knowledge of something that I'll not bore you with and today it came home to roost. I needed to put hands up and confess. Then get advice.

I managed to track him down on the phone in order to confess and to tell him that I was all over it. Scared witless when he picked up the phone.

What a lovely man. 'That's why we review. These things happen'. I'm invited for tea and have the relevant advice. I deleted my comments about my OP on my documented response because the man is a Gentleman and not an Ogre.

Zs

Edited: 18 March 2015 at 10:43 PM by Zs
 19 March 2015 01:36 AM
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RB1981

Posts: 485
Joined: 16 September 2007

Glad it worked out for you Zs.

-------------------------
Walsh Electrical Services
http://www.walshelectrical.ie/
RECI REC & NICEIC Approved Contractor
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