IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Installation & Testing
Topic Summary: Occupied Offices
Created On: 10 April 2013 09:16 AM
Status: Post and Reply
Linear : Threading : Single : Branch
<< 1 2 3 Previous Next 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.
 11 April 2013 06:38 AM
User is offline View Users Profile Print this message


Avatar for Jobbo.
Jobbo

Posts: 915
Joined: 08 July 2010

SKE

Take a look at table B7 of the OSG and all will be revealed. Obtain I2t values from the manufacturer and check the thermal withstand of the conductors.

Out of interest, what type of distribution board are you working on?

How happy would your client be if you accidentally knocked a few circuit breakers removing the cover? Would there be any financial loss. Ask yourself, who is the responsible person and who is the competent person?

I totally understand the 'real world', as we all know someone will come along and do it, no questions asked.

Regards

Jobbo
 11 April 2013 08:10 AM
User is offline View Users Profile Print this message


Avatar for dickllewellyn.
dickllewellyn

Posts: 1150
Joined: 19 March 2010

If it were me, I would simply walk up to the man in charge, and ask bluntly, "when is going to be the best time to shut everything down". It may be that they hadn't even considered power will need to go off. Have they actually said to you that you can't isolate? O are you assuming they don't want you to?

If you end up connecting into the existing socket circuit, don't forget about earth leakage on computers and make sure you meet the requirements with CPCs etc if relevant.

-------------------------
Regards
Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 11 April 2013 08:59 AM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 1040
Joined: 04 November 2004

Originally posted by: Parsley

Originally posted by: SKElectrical



Sadly the price is almost £700 for just 2 double sockets, tie wrapped t+e above ceiling grid and not more than 30m from board.



£10million insurance. jesus its no wonder our country is spiralling further into debt.







You really wouldn't believe just how many people have got involve din this simple installation, you really wouldn't.... or maybe you would if I told you it was for the Home Office.



It's not funny




Twin and earth & offices possible high fault currents and touch voltages hope you checked that I2t < K2S2.



Regards


SKE, As Martyn and Jobbo have also mentioned you need to be aware of high fault currents as the reduced CPC may not be able to withstand the energy let through by the PD. Have a look at the note on the bottom of the appendix 3 mcb time current graphs. Table B7 of OSG gives you a rough guide but your reduced CPC may be OK depending on the manufacturers data and the fault current on site.

You need to be aware that If the Ze is low and the R2 portion of the circuit is high the touch voltage will be higher than a non reduced cpc circuit possible going the wrong side of 120V.

Why does my governing bodies area engineer always ask me to remove the cover of the DB without isolating it first?

Regards
 11 April 2013 09:32 AM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11587
Joined: 13 August 2003

But how low should the Ze be to worried?

For a 32A B or C-type with a 1.5mm2 c.p.c. a PEFC of over 3kA (Zdb < 0.076) warrants further investigation (i.e. you're outside the limits of BS EN 60898 so need to check manufacturer's data to (hopefully) show compliance).

Or are we more concerned about a very high PFC (being 3ph)?

Not a worry for the c.p.c. of course, the 2.5mm2 live conductors should be good to at least 6kA (probably higher, by manufacturer 's data).

(Bear in mind that MCBs now use European standards and our continental cousins (no rings and no reduced c.p.c.s for small circuits) probably won't even think of using any conductor (live or c.p.c) of less than 4mm2 for a 32A device.)

- Andy.
 11 April 2013 09:40 AM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11587
Joined: 13 August 2003

Sorry, just noticed that the proposed is radial (not sure if 20A or 32A) rather than a ring, but numbers are the same for 20A devices - 4mm live conductors should be good to 10kA whatever.
- Andy.
 11 April 2013 10:15 AM
User is offline View Users Profile Print this message



Ricicle

Posts: 844
Joined: 23 October 2006

A little incident that I witnessed. An electrical contractor on our site was going round checking CTs on the new part of our site which his company had done the installation on. He took the cover off a large mccb panel while it was live and then the inner cover where the busbars were with the CTs.
He then tried to put it back together and realised how close the metal inner cover actually was to the busbars. I then had to go round the site and explain that half the site was going to shut down while he put the covers back on.
So it is the unknown of what is lurking behind those covers when you take them off, it might be ok to take them off but putting them back on ???

Stay safe people.

-------------------------
Empty barrels make the most noise.
 11 April 2013 11:13 AM
User is offline View Users Profile Print this message


Avatar for zeeper.
zeeper

Posts: 1411
Joined: 11 July 2008

Could you not just use a extension reel.

Obviously the Ze will be on prevous PIR's EIC, under EAWR 1989 they are suppose to keep records and information relating to maintence of the site. Or you can get it from the DNO .

The other thing is the distribution board may still offer IP2x, IPxxB even with the front cover removed. The merlin gerins on my site do, this would reduce your exposure to danger.
 11 April 2013 06:15 PM
User is offline View Users Profile Print this message



perspicacious

Posts: 7246
Joined: 18 April 2006

"Subbying on day rate"

So you haven't even got what little protection an employee would have?

Regards

BOD
 11 April 2013 06:47 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19765
Joined: 23 March 2004

A couple of points:

1 - Even as a subbie, there is a vicarious liability to the employing contractor - if working live results in injury, or loss - then the client is going after that contractor - if you are the subbie make sure you've expressely told the contractor you intend working live - they might well stop you

2 - If there is an incident then HSE are going to go straight for the client for allowing the live working - they will effectively see the client as the "employer". Be very sure the client has prohibited live working and it's not just you thinking that he has.

3 - A design has been undetaken here - who by is not known, but the designer had an abligation to advise the employer of his duties under the CDM regs, before commencing design. The work may not be notifiable, so perhaps there is no CDM-C in place but non the less the client has obligations here regarding safety, health and the environment. If an investoigation shows, however indvertantly that a contractor cosnpired with a client to effect a breach of statutory legislation (and keep in mind Reg q14 of EAWR is absolute) then you'll all be calling on your defence regulation for protection - and that defence will be shakey to say the least.

In addition, why do you lot want to play fast and loose with the one pair of eyes, face, life that you have - traded against not upsetting, ever so slightly, the employer.

Regards

OMS

-------------------------
Failure is always an option
 11 April 2013 07:16 PM
User is offline View Users Profile Print this message



aligarjon

Posts: 2878
Joined: 09 September 2005

Lets get real here, you could take the lid off of a decent 3 phase board. with all the blanks in place you could fall against it place a flat hand almost anywhere and not touch a live part. All the live screw heads are countersunk and buzz bars covered.

Obviously the circuit breaker being connected to is off.


I wouldn't do this job mind you because the biggest risk is accidently knocking off breakers.

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 11 April 2013 07:25 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19765
Joined: 23 March 2004

I think the assumption that the board is "decent" and has everything inside it that should be there is potentially problematic Gary - I've had the lids off modern MCB boards (as I'm sure many of you have) to find a complete lashup inside them. Even inserting new cables via existing service openings is fraught with risk - god knows how anyone plans to safely put a 20mm hole and gland in for the T&E's is anyones business - hot metal fragments, swarf etc etc in what is normally a Form 1 pan assembly

Lets not forget who the client is on this one - HSE would be just itching to take them on - as an example to others if nothing else. The sheer embarrasment of picking up a prohibition notice and an improvement order would most certainly result in the most unpleasant backlash for the "guilty" contractor.

regards

OMS

-------------------------
Failure is always an option
 11 April 2013 08:17 PM
User is offline View Users Profile Print this message



aligarjon

Posts: 2878
Joined: 09 September 2005

We are not allowed to judge each job on its merit any more, its just blanket legislation. we are losing all our industry in this country because its too expensive. The only people benefitting are the jobs being created for health and safety officials and lawyers. no wonder we are nearly bankrupt.

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 11 April 2013 09:19 PM
User is offline View Users Profile Print this message



perspicacious

Posts: 7246
Joined: 18 April 2006

Would the lawyers be busy if people didn't go running to them for a bruised finger (or more likely, damaged ego)?

Regards

BOD
 12 April 2013 09:06 AM
User is offline View Users Profile Print this message



dlane

Posts: 690
Joined: 28 September 2007

Originally posted by: aligarjon

We are not allowed to judge each job on its merit any more, its just blanket legislation. we are losing all our industry in this country because its too expensive. The only people benefitting are the jobs being created for health and safety officials and lawyers. no wonder we are nearly bankrupt.

Gary


I disagree with some of this. The legislation is not blanket, it merely requires you to consider all the risks and opt for working dead where at all possible. It does not prohibit live working.

The HSE law also requires you to risk assess each job on its own merits and this is down to all parties concerned. In my opinion it is down to the client to specify the reasons why the board cannot be turned off, and in a lot of cases the justification for this is purely financial, but if more thought is but into the work with alternatives looked at it is quite often that the increase in cost of doing the work dead is relatively low.

You are right that modern boards offer a lot of protection against electric shock and if you are on a site where you are familiar with the installation, have worked on it previously and know its condition, you may be in a position to justify a live working procedure. if you are happy with the training and comfortable with working live and know the precautions to be taken, then you may be able to show that it was appropriate to work live on this occasion.

However, if you are totally unfamiliar with the system you are working on and cannot verify its condition, you would need to make an assumption that all the appropriate covers are in place, that the wiring is sound and cannot be snagged by screws or covers etc. And we all know what is said about assumption don't we? Sadly there are a lot of people out there who have made assumptions and thought they had the knowledge, confidence and experience to carry out live working, some have lived to regret it, some haven't.

It has already been pointed out that there is a potential for an increased fault level, which in turn may increase the severity of arc energy involved, is there an assessment in place of the potential arc energy and the implications of this?

So in my opinion all work requires an assessment, whether you are working dead or working live. In some cases the best option can be to work live but in the majority of cases de-energising the circuit can be achieved. There may be those that don't like the safety culture but at the end of the day its there to give the workforce the best chance of going home at the end of their shift in the same condition that they arrived.

Kind regards

Donald Lane
 12 April 2013 12:58 PM
User is offline View Users Profile Print this message


Avatar for zeeper.
zeeper

Posts: 1411
Joined: 11 July 2008

I think it comes back to the risk/reward. In this case 700 or 800 notes. It would be not be worth taking any risks, throw it back to the person ordering the work.
If you do this live and dont inform the person ording the work you intend to work live. Your problem will not be if you go up in smoke, it will be if you accidently trip another circuit suppling essential equipment, then your wish you had gone up in smoke.
 12 April 2013 02:29 PM
User is offline View Users Profile Print this message



jcm256

Posts: 1900
Joined: 01 April 2006

Some supplies are direct to a main switchboard.
How many Engineers/ Electrician Engineers, take off that panel below the main breaker or main switch, to determine what type the supply and the earthing system is, how many carry out a live Ze and PSCC test. How would you have found the rusted bolts connecting the mains lugs on to the main bus bars without the panel off?
Accidents can happen, but if your annual safety audit is current, and being supplied with the necessary safety equipment, rubber mat, HV gloves etc then the employer has played his part, the rest is up to you.


http://www.hse.gov.uk/electric...maintenance/panel.htm

24 The people doing the work must be adequately trained and experienced in the type of live work being undertaken (regulation 16). They should understand the task and be able to recognise any deterioration in the state of equipment or departures from agreed procedures. They should have the self-discipline to recognise their own limitations and should be encouraged to seek assistance with work that may be outside their area of competence.
25 There must be adequate working space and adequate lighting (regulation 15). There should be adequate headroom, no tripping hazards and no obstructions that could restrict a person's movements. Where there are exposed parts live at 400 V ac the recommended minimum clear working space should not be less than 3 ft or 915 mm measured from the live part. If there are live parts exposed on each side of the working space the minimum recommended clearance should not be less than 4 ft 6 ins or 1375 mm, although this situation should be avoided whenever possible, eg by screening.
26 Only properly insulated tools should be used (see BS EN 609009). They should have insulation that is robust enough to be proof against mechanical damage (regulation 14(c)). These tools should be inspected frequently by a suitably competent person. They should be destroyed if the insulation is damaged. Test instruments should have insulated probes and fused leads (see HSE Guidance Note GS38 Electrical test equipment for use by electricians10

http://www.hse.gov.uk/pubns/priced/hsg85.pdf
 12 April 2013 08:24 PM
User is offline View Users Profile Print this message



cookers

Posts: 205
Joined: 10 February 2012

You never know the TP&N distribution board might be designed for connection of additional circuits without complete isolation.
 13 April 2013 07:08 AM
User is offline View Users Profile Print this message



aligarjon

Posts: 2878
Joined: 09 September 2005

Originally posted by: cookers

You never know the TP&N distribution board might be designed for connection of additional circuits without complete isolation.



Lots of older equipment is designed so that the main switch has to be turned off before the cover is removed where as manufactureres now design them so that they can be removed without doing it. They obviously believe that their design is safe to do this.


Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 13 April 2013 07:44 PM
User is offline View Users Profile Print this message



perspicacious

Posts: 7246
Joined: 18 April 2006

"Lots of older equipment is designed so that the main switch has to be turned off before the cover is removed where as manufactureres now design them so that they can be removed without doing it. They obviously believe that their design is safe to do this."

I'd prefer to see what their instructions require rather than make that deduction to suit my "needs".........

Regards

BOD
 14 April 2013 05:56 PM
User is offline View Users Profile Print this message



rogersmith7671

Posts: 886
Joined: 04 November 2004

Schnider electric provide 3ph distribution boards with an "isobar" disconnection solution at the MCB/bussbar connection which "Features a complete fingerproof key lock-off system that spans across a number of outgoing ways and fixes the Isobar disconnectors in the OFF position".

Regards

Source;
http://www.schneider-electric.co.uk
IET » Wiring and the regulations » Installation & Testing

<< 1 2 3 Previous Next Last unread
Topic Tools Topic Tools
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.