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Posted By Kev S
Hi All,
Can any body throw some light on a problem that I have encountered on one of our customers construction sites.
When carrying out a safety audit I noticed that 240 volt electric tools and extension leads were being used extensively on the site, domestic plug sockets were covered in mud with leads trailing all over the place; However an RCB was in place. When I informed the site manager he smiled and asked me to show him the regs that say "110v tools and equipment should be used on construction sites". After searching it appears that this is just guidance unless someone out there knows different?
If it is just guidance then why do thousands of construction sites up and down the country all use 110 volt tools and leads.
His argument is, with an RCB in place you would not get an electric sock at all; However 110 volt does not have RCB protection and therefore would result in an electric shock albeit a minor one to most healthy people.
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Posted By Pete48
Kev,
I have no idea whether it is contained in any regs, what I do know is that any guidance /codes of practice that you might wish to read is clear about these points.
A reduced low voltage system, which delivers 110V to the equipment is safer than using 230V.It effectively eliminates the risk of death and greatly reduces the degree of injury in the event of an electrical fault.
The following extract from an IEE article seems to sum up the position for you.
"The use of 230 V to supply portable equipment supplied via a 30 mA RCD, although not stated in BS 7671 is permitted (HSE Guidance Note HSG 141 refers). However, the use of automatic disconnection and reduced low voltage supply as prescribed in BS 7671 is the preferred system for use on construction sites in the United Kingdom. There is a possibility of damage occurring to the sensitive operating mechanism of the RCD as a result of the harshness of the environment inherent on a construction site. Any such damage may render the RCD inoperative, removing any protection that it was intended to provide. As such, attention must be given to correct positioning of RCDs and to the choice of enclosures employed. Where an RCD is provided on a construction site, for reasons of safety, its correct operation should be confirmed prior to each use."
The NICEIC also follow this line in recommending 110 volt supply for portable and handheld tools and transportable equipment up to about 3.7kW (5hp) 110V reduced low voltage, single or 3 phase.
Will an RCD prevent electric shock, the answer is mostly-not YES. Is it a must to use 110V? No.
Does it make good risk reduction sense in most cases on construction-clearly.
For example, you may want to ask him to explain to you why it is important to check the correct operation of the RCD before EACH use and how he ensures that happens.
Hopefully some of the guys on here with current(sorry!) construction knowledge will give you a closer hands on reply. My knowledge is really just engineering based in this area of application.
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Posted By Barry Cooper
Kev
110v supplies are usually from a centre tapped transformer. This will limit any electric shock between the tool and earth to 55v (which is the most likely scenario), so limiting the current.
As far as I know no one has been killed when using 110v.
Unless someone knows differently
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Posted By Catman
Hi Kev
Not legislative but certainly enforceable,
google for HELA guidance on Electricity at work regs (LAC 19/3 - section 13(5)).
Does not ban 240v with RCD but certainly suggests enforcers should look for 110v as the standard.
I find things with HSE printed at the top of them tend to focus the mind of the wavering manager.
Cheers
TW
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Posted By GeoffB4
Will an RCD prevent electric shock, the answer is mostly-not YES.
Why mostly Pete? What are the exceptions?
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Posted By steven bentham
The earlier responder was correct - as far as I know there has been no fatal accident with 110v.
240v outside or in wet = PN
Inside with RCB, harder to prove risk = IN (possibly)
Most contractors seem to have moved to battery operated- (with free manufacturers radio!)
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Posted By lewes
Mostly down to a 'safe system of work' and 'duty of care'.
Like others have said nothing in writing and 110v gives greater protection to the user. Most sites are going cordless which is always a good thing but not everything is available in this format
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Posted By Mike Draper
There is no prohibition on the use of 240V, however you should refer to HSG141.
Para 28 - Long experience in the UK has shown that the use of reduced low voltage portable electrical tools and equipment (eg 110V CTE) on building sites will effectively eliminate the risk of death and greatly reduce the degree of injury ...
Para 72 - An RCD does not guarantee safety. If an RCD fails to operate, or is faulty, this will not be indicated ... They only protect against earth faults, and will not operate when there is no connection to earth, ie if current is passing from live to neutral. So it is possible to suffer an electric shock and injury even though the RCD is operating correctly.
Para 73 - It is therefore not possible to place total or near total reliance for personal safety on RCDs. In contrast, the use of passive systems, such as reduced low voltage, can give reliable protection against fatal electric shock.
Mike
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Posted By Robert K Lewis
Kev
The next time you are there ask for the risk assessment that he has prepared to use 240 volt equipment for each work point, I will bet they are not there. The argument is then one around significant risk - the fact that guidance recommends something else clearly indicates the need for a DETAILED assessment.
Obviously control measures such as checks on RCDs will need to be recorded to show they are done, so ask him then to identify the date the first 240 volt tool was used and then ask for the records back to that date. I think the smile will begin to drain away. I do find some site managers rather smug in their attitude of "can I put one over somebody"? They are increasingly rare but still there I am afraid.
bob
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Posted By Ron Hunter
Did risk assessment not enter into your discussion?!
I have personally experienced a hazard condition where an RCD (RCBO for the purists) failed to operate - cable cut by blades of hedge trimmer by instantaneous action, but circuit not interrupted for long enough for RCD to trip!
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Posted By GeoffB4
They only protect against earth faults, and will not operate when there is no connection to earth, ie if current is passing from live to neutral. So it is possible to suffer an electric shock and injury even though the RCD is operating correctly.
I'm trying to think where this could happen, where someone could be hooked between live and neutral and not have some element of earthing.
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Posted By peter gotch
Hi Kev
Are you saying that all this kit was protected by a single RCB - if so the way you describe the site, I would have thought that it would be tripping out rather often [unless the tripping current is too big to enable adequate protection - should be 30mA tripping in 30ms]
Of course, if each user of portable equipment tests the RCB before working, they will be switching off the current and annoying their workmates when their tools suddenly switch off. "I was drilling a hole into the concrete when some idiot operated the RCD. Drill bit broke as I tried to get it back out".
Bet the manager's assessment doesn't run to business continuity considerations.
Regards, Peter
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Posted By GeoffB4
Ron, but surely it would have done if the exposed cable had been touched by someone - I don't see your point?
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Posted By Mike Draper
Geoff
Try standing on scaffold boards or wearing non-conductive footwear. There are lots of situations on a construction sites where you would not be earthed under fault conditions.
Mike
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Posted By Ron Hunter
My point being Geoff that I was left holding in my hands a piece of kit with live exposed metal parts of lethal voltage potential, and that I'd rather see in workplaces systems of control which are slightly more robust than a £10 brittle plastic poorly maintained and untested current-balanced solenoid?
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Posted By Mike Blease
A solution to this type of problem may be to develop a code of practice that contractors have to sign up to. Prescriptive statements such as 'only 110v permitted on site' can then be included as required. The contractor should then be requested to sign to agree to to abide by the COP.
This makes life a lot easier by not having to trawl through regs and guidance to prove a point to an unwilling contractor. you can just produce the COP and remind the contractor that this is what they have signed up to.
Not a lot of help in your situation but something for the future maybe.
Preparing for contractors and setting ground rules is easier than trying to put the genie back in the bottle later.
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Posted By Pete48
An interesting discussion has developed during the morning on this one. I think the question raised for me has already been answered by others.
The real safety point for me is that good safety is about risk reduction or minimisation wherever possible. The use of 110 volt achieves that key objective without a reliance on the specific nature of the risk controls that are required where you intend using 240 volt AC supplies in particular.
To rely upon an RCD as your only type and source of protection in the adverse and complex world of construction and even in manufacturing environments is to ignore safer methods of working that are both known and recommended by the electrical engineering and installation bodies.
Make sure then, as others have said, that you have a quantitative risk assessment and on-going records to support that judgement.
I am sure that construction specific guidance will give you more detailed advice on where using 240 volt ac may be considered, but I am not a hands on construction bod so do not know that detail.
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Posted By Kev S
Thanks for all the good responses folks!
It looks as though not legislative but if he is daft enough to go against guidance then more fool him in the event of an accident! (I do intend to put a halt to this stupidity prior to an accident).
Forgive my ignorance between an RCD and RCB?
Pete48 and Mike thanks for the reference to Guidance Note HSG 141.
Also it seems that RCD's can be temperamental in harsh environments... Got the fuel I need thanks guy's.
Kev
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Posted By Exdeeps
Good Afternoon,
No H&S post nominals but I am an electrical engineer type. Can I refer you to BS7671:2001, other wise known as the 16th edition wiring regs. Section 604 deals specifically with the requirements for building sites. I have it open in front of me and to paraphrase, the only supplies allowed of 230v and above are for fixed flood lighting and for fixed or movable equipment above 3.75KW. There are also some office based items that can be 240V but, in essence, 110v is the supply stipulated by the IEE for use on a building/construction site.
Now, I know, the 16th edition regs are non statutory, however, as with many institute issued regs, they may be used in a court of law in evidence to claim compliance with a statutory requirement. In other words, the site manager must demonstrate that he is compliant with the regs as published by the IEE (an expert body) or that his system at least matches the safety standards as published.
Now going deep
Jim
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Posted By Kev S
Thanks Jim, I may earn myself a few brownie points with that one!
Kev
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Posted By GeoffB4
Ron
'...I'd rather see in workplaces systems of control which are slightly more robust than a £10 brittle plastic poorly maintained and untested current-balanced solenoid?'
I agree completely but if the RCD is being maintained and tested would that resolve the issue?
A couple of contributors have said that 'to their knowledge no one has been killed by 110V'. Not even by falling after receiving a 110V shock?
And one more question, do you get RCDs for 110V?
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Posted By John Murgatroyd
Must be a funny old site.
Most sites won't even allow dual voltage generators on now. IE: 110 and 230 volt. Most sites won't allow any gear on without a valid PAT.....don't see many add-on 230 volt RCDs' with a PAT check......
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Posted By Frank Hopkins
What about the argument 'so far as is reasonably practicable'?
Frank
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Posted By GeoffB4
How do you electrically test an RCD?
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Posted By Pete48
Geoff,
methinks you know the questions to choose??
RCD and 110V
110 V single phase, fed from a transformer, often with an earthed centre-tapped secondary winding, to feed transportable tools and equipment, such as floodlighting, with a load of up to 2 kW. This supply ensures that the voltage to earth should never exceed 55 V (no please don't Geoff!). The primary winding of the transformer MUST BE RCD PROTECTED unless the equipment fed is to be used indoors. (capitals used by me to highlight the phrase)
As to your other question. I took the comment to mean "check correct operation", not "electrically test", didn't you?
What are your views about the use of 240V systems on construction sites? Where would you allow them and where not?
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Posted By GeoffB4
No. I meant how do you electrically check an RCD? Mechanically checking is obvious, but that isn't checking it electrical integrity, ie trip current and trip speed.
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Posted By GeoffB4
So RCDs are required on sites, in the 230V side of the 110V transformer. Are you sure about that Pete?
To answer your other question, I believe all equipment, where 'practical' (not reasonably practicable) should be low voltage.
In some cases there is no option but to use 230V and without protection because of nuisance tripping.
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Posted By Frank Tomei
I must say that I am somewhat surprised at the number of responses stating that ground fault protection for 110 volts is not required and their have been no accidents. Here in Canada (Ontario) where our common voltage is 110 volts the ground fault circuit interruptions are used extensively in our homes and constructions. We are led to believe that this action has been taken on the part of the authorities because of the relatively high risk involved using 110 volts without ground fault protection. I may stand corrected but I believe that this is true for much of North America.
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Posted By Pugwash
Frank
Here the secondary winding of 110V is "centre tapped earth". Any fault on the secondary side cannot bring the operator into contact with a voltage higher than 55V relative to earth. I think that makes it a different beast compared with the Canadian general electricity supply which you mention where there would be 110V to earth. Happy to be corrected if this is wrong.
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Posted By Frank Tomei
Thanks Pugwash for the clarifcation.
Much appreciated.
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Posted By Ken Taylor
We used to use the term 'RCCBs', Kev but now talk about 'RCDs'.
I'm not aware of direct fatalities from 110v but seem to recall a couple of consequent deaths - one being a ladder-fall upon receiving a shock - but this was some years ago.
I note that responses have not referred to the mud-covered domestic socket outlets. If they are using these as trailing sockets on site, they are unsuitable for the environment and likely to be unprotected against physical damage, straining of cables/flexes, and the ingress of water. Additionally wet mud could provide a conductive path within the sockets. All electrical connections on site need to be safe and weather-tight - so this could be further departure from both guidance and legislation.
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Posted By Chris G
Looking at the protection given by RCD. I had a situation a couple of years back where all the rcd protected sockets in the labs area were tested with a nifty piece of kit which checked for operation current and response time. Out of 29 units all new within the previous 3 years 18 failed on trip time. - the calibration of the checking kit was rechecked and found to by OK.
This was a high percentage of rcds from a reputable supplier failing in a clean, moderate usage environment. How doe ones on construction sites survive?
Chris
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Posted By John Hadley
Nobody seems to have answered the issue of RCBOs......don't they give a higher level of protection that an RCD?
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Posted By FJ
Just to add a spanner"- do you recall a previous thread that showed that the failure rate of RCDs is up to 7%- too high for me to risk my life- or can someone reassure me:-http://www.iosh.co.uk/index.cfm?go=discussion.view&forum=1&thread=23733
Also don't most Contracts require a 110V regime?
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Posted By Alan Nicholls
Just to muddy the puddle a bit.
This situation will continue until some unfortunate subcontractor disappears with a flash and sickening bang. Followed by a Fall from some elevated working position.
As long as certain equipment manufacturers continue to push 240volt Breakers, Plainers Mixers etc, joe public will use it then go to work on site and see no reason to do it differently.
110 volt with isolation transformer gets my vote any day.
My opinion
Regards Alan N
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