IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Zs folly
Topic Summary:
Created On: 03 February 2016 07:48 AM
Status: Read Only
Linear : Threading : Single : Branch
<< 1 2 Previous Last unread
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 04 February 2016 10:41 PM
User is offline View Users Profile Print this message



Zs

Posts: 3814
Joined: 20 July 2006

Spin, I get that completely but they're not always earthing the gear tray are they but they are a place to put the end of the CPC away. However, quite a few of them are a bit of connector block and the empty side of it could be construed as a place to connect another CPC and you are right, some of them have the little nub thing in them. (JCC and Aurora to name two) There was a bloke in the wholesaler the other day, returning a whole load of 'faulty' double insulated LED fittings because they didn't have an earth terminal on the outside of them like the ones he used to buy. The bloke standing next to me winked at me and we left the 18 year old behind the counter to it and had a natter in the car park about how his kids are doing with their Karate instead.

Over the years I've watched the regs change and change again. It's always earthing in the amendments isn't it? I said this years ago when I was a rookie-rookie and now that I might have made it to rookie status I still say that even the great and the good are still working on the science of earthing.

Must go connect myself to a pillow. Ridiculously early guitar lesson tomorrow and I don't really do mornings. Eight line poem, yo, you'd be proud of me on this one.

Zs
 04 February 2016 11:17 PM
User is offline View Users Profile Print this message



sparkingchip

Posts: 9953
Joined: 18 January 2003

I own five test meters that can do a loop test, I also have a well used wander lead and I don't hold back on using them.

So intital testing of a new circuit or a modification to a circuit supplying a high level light fitting includes a loop test, you be hard pushed to explain why you didn't do one seeing as access to do the work is already in place.

Erecting a tower scaffold to test at the light fitting when the other end of the conductor is connected at the light switch and the light fitting does not need an earth, also it has not been touched except to relamp since the last test is not productive.

Andy
 05 February 2016 08:55 AM
User is offline View Users Profile Print this message



mapj1

Posts: 9349
Joined: 22 July 2004

Over the years I've watched the regs change and change again. It's always earthing in the amendments isn't it? I said this years ago when I was a rookie-rookie and now that I might have made it to rookie status I still say that even the great and the good are still working on the science of earthing


Ah very true - and the ground is always shifting, so to speak, with new problems every decade or so, and so we must adapt, first high CPC currents at none-mains frequencies on power and lighting circuits designed for heaters and filaments, no sooner have we got all garden power tools double insulated, so PME is OK for domestic, then some so-and-so wants to plug in his metal bodied car to the mains to charge, and there will be more of them every night than there are caravans. It will be a brave, but not impossible step, methinks, to make a double insulated electric car...

The problem of course is that the earthing is many things to many people, and how much current you need it to carry, for how long and under what conditions is not always immediately clear. The other thing that varies is how dangerous it all becomes if that connection is broken - this may vary from
1) 'no effect, its just the first of my two faults' to
2) ' the exposed metalwork is capable of delivering a lethal shock'
and of course a whole spectrum of tingle-iness in between
One size does not fit all situations.

-------------------------
regards Mike
 05 February 2016 08:18 PM
User is offline View Users Profile Print this message



Zs

Posts: 3814
Joined: 20 July 2006

Fantastic post again Mike.

We abide by the regs I suppose. Because they are what we have and they are what we must. I hope science is moving a little more slowly.

Zs
 07 February 2016 01:18 PM
User is offline View Users Profile Print this message



kaichung

Posts: 459
Joined: 02 December 2003

The Electricity at Work Act, 1989 was one of Thatcher's best bits of legislation her government brought in.
It has helped reduce the number killed or injured in electrical accidents over the last twenty five years or so.
I remember that the London Underground had to change a LOT of their distribution boards shortly after 1989, as their old ones did not comply with the then newly introduced 1989 Act.
It may have been the reason that the DNO's started insisting on "Put A Switchfuse In The Tails", even though their main BS88 service cut-out fuse was normally of a sufficient breaking capacity for the intended usage!.
 13 February 2016 06:34 PM
User is offline View Users Profile Print this message



jravenscroft

Posts: 73
Joined: 07 November 2015

Originally posted by: Zs
However, I do use a Z test. Two lead, L-E usually. H&S would be after me for too much wander lead behaviour and I prefer not to dismantle a DB. It gets discussed prior to the event though.


Sorry this is a bit of a late reply and you might miss it. I'm not very regular!

I wouldn't use a wander lead in this kind of circumstance either. Since I'm not taking a Zs reading with a meter, but calculating it by adding an r1+r2 result to the Ze(or s) at the board, I need a complete dead loop reading. An r2 reading obtained using the wander lead method would not be suitable for this, as it only measures part of the fault loop.

This, as far as I understand, is considered the safest practise, as you are able to obtain all the information necessary, without exposing yourself to live elements of a circuit. It's the first method described in guidance note three in the chapter detailing how to obtain a Zs result.


Do you photograph them all?


Not enough! I'm planning to increase the amount of photographs I attach to certificates. It's something I discussed recently during my NIC assessment, and the assessor made some good arguments for increasing the recorded detail in my certificates over and above what is required and provided for in the certificate templates. In theory, it's quite easy to do these days, so it was hard to put forward any reason why I don't already do it. The "Number of points" coloumn (which isn't in the more basic templates, and isn't required by 7671), isn't enough to defend you from damage done by an alteration to your work, he argued, if for example one of the existing points has been moved or extended.


Every socket gets a Z taken because it is so easy to do it but I will put a limitation on the number of light fittings opened.


It's just as easy to get an r1+r2, which, of course, you should have obtained before making the circuit live for the first time (assuming an installation certificate, not so much a condition report)

Regarding taking a CU or DB apart, how else to you read ring circuit end to ends? the r1+rn and r1+r2 reading are the next readings to obtain after these, so I tend to use crocodile clipped leads that came with my test kit to link the legs together in the figure of eight pattern described in guidance note 3. I used to use connector blocks back in the day, and that was a bit of a faff. those modern connectors with the spring release terminals might be a good alternative though.


I'm sure quite a bit gets missed but getting to the end of a circuit is probably going to indicate an issue with further investigation required. Well, that's what I think.


Absolutely. Can't argue with that. Most times that will be the case. Although if there's any chance of a spur or switch that extends out from the direct line from origin to furthest point, then the end of line measurement is not going to give you enough information to verify the health of the circuit. A level of assumption is always present, but some of us are willing to assume far more than others. Personally, I'm not comfortable signing a box to say I've verified what I know I haven't verified. If there's a genuine reason why something cannot be verified, then it should be stated in the agreed limitations.
 13 February 2016 07:11 PM
User is offline View Users Profile Print this message



sparkingchip

Posts: 9953
Joined: 18 January 2003

 13 February 2016 07:23 PM
User is offline View Users Profile Print this message



sparkingchip

Posts: 9953
Joined: 18 January 2003




TLC

Andy
 14 February 2016 10:24 AM
User is offline View Users Profile Print this message



jravenscroft

Posts: 73
Joined: 07 November 2015

Can't see the problem with the pictured engineer using the standard ACME flexi-reach(tm) extension ladder? Presumably his jet-pack is in for maintenance.
IET » Wiring and the regulations » Zs folly

<< 1 2 Previous Last unread
Topic Tools Topic Tools
Statistics

New here?


See Also:



FuseTalk Standard Edition v3.2 - © 1999-2017 FuseTalk Inc. All rights reserved.

..