Why is 110v used on building sites

Given the same resistance the current flowing from v will be over twice that flowing from v so volts is safer init!

Tail-Dragger Nothing is safer than a VP1. I thought that I had learnt " Keef - where are you when I need you? By Mike Cross - Sat Jun 09, It's volts that jolts, it's mills that kills. And annuver fing Normal mains current has the neutral phase tied to around around earth potential so touch the live and you get v relative to earth wot you're standing on.

However the transformers used on building sites are isolating transformers so you only get v between the output terminals. If you're only touching one conductor there's no route back to the other side of the supply. Disclaimer - this is theory, I haven't tried it. Mike Popham and Lee on Solent. By Keef - Sat Jun 09, Just got in, boss. Been in Norfolk, now back in Ethics. Your body's inherent resistance doesn't know what the voltage is.

So if you stick your hand across v, X milliamps will flow. It's very risky, unless you're like me, with unusually dry skin and hence very high skin resistance. Then you swear very loudly. The downside of low voltage systems is that they pull a higher current than V systems. In order to accommodate this higher current without overheating the cable V circuits usually have thicker conductors than the equivalent V circuit.

It's important to match a V transformer with the amount of power required by the tools that will be used on the circuit, and their length of use.

If you are using a W angle grinder on the circuit, you will need at least a 2KVA transformer. If you go over the duty cycle a lot a thermal cutout switch will disconnect the transformer until it cools down a bit.

If it isn't broken, that doesn't mean you can't improve it. Do three negatives make a positive? 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!

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. 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.

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.

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.

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? There are lots of situations on a construction sites where you would not be earthed under fault conditions. 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 v 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. 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.

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 volt achieves that key objective without a reliance on the specific nature of the risk controls that are required where you intend using 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 volt ac may be considered, but I am not a hands on construction bod so do not know that detail.

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. Also it seems that RCD's can be temperamental in harsh environments Got the fuel I need thanks guy's.

Can I refer you to BS, other wise known as the 16th edition wiring regs. Section deals specifically with the requirements for building sites. I have it open in front of me and to paraphrase, the only supplies allowed of v and above are for fixed flood lighting and for fixed or movable equipment above 3.

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. Do you Need V? Like this story? Please Share! Like our site?