So what. A DIY safety improvement is only worth doing if its not way down t he list of what one can usefully do. RCDs have their upside, but at 20 some thing deaths versus over 100,000 a year they're just not the priority. Eat healthily, learn advanced driving, treat infections promptly & vigilantly, take proper precautions with power tools and so on. If all those plus dozen s of others are done, then an RCD becomes worthwhile.
Funny how so many think electricity & gas a big risk, when really the most dangerous things we do are food shopping & smoking.
Harry Bloomfield wrote in news:mmcb0m$s66$ snipped-for-privacy@dont-email.me:
Sounds like a classic case of the 'Peter Pricipal' at play!
Can someone tell me if I can get away with a 45A MCB for a 8.5kW shower without endagering life and limb? The manual tells me to use a 40A one, but I just happen to have a 45A one. I ask, because those things aren't cheap.
So what. A DIY safety improvement is only worth doing if its not way down the list of what one can usefully do. RCDs have their upside, but at 20 something deaths versus over 100,000 a year they're just not the priority. Eat healthily, learn advanced driving, treat infections promptly & vigilantly, take proper precautions with power tools and so on. If all those plus dozens of others are done, then an RCD becomes worthwhile.
Funny how so many think electricity & gas a big risk, when really the most dangerous things we do are food shopping & smoking.
What is not so funny is how many people do not realise how dangerous electrcity is.
It takes 20 to 30 years of smoking or shoveling chips down a big fat gob to cause the damage. If they cannot see what is coming then it is their problem - the NHS spend a fortune on preventative medicine and yet people still live unhealthy lifestyles.
Electricity is unseen and kills in less than a second and may not be the fault of the person that is killed. The IET have decided that RCD protection is the future. It's not expensive and it saves lives - so much so that there are thousands of people who did not receive the smallest of shocks when the RCD operated saving them from becoming a minor statistic.
Just sold my house and survey recommended an electrical report, changing the old fused CU was the result... (There was a hairline crack on the unit as well, which didn't help)
Probably, as you're not relying on the MCB for overload protection (as the load is fixed and unlikely to draw a higher than rated current), merely for short circuit in the event of fault.
snipped-for-privacy@gowanhill.com wrote in news: snipped-for-privacy@googlegroups.com:
It's a 6mm^ T&E cable that is surface mounted all the way to the 8.5kW shower. (about 4ft goes through surface-mounted conduit.
So, I could use the spare 45A MCB. I also have a spare 20A MCB which I could swap with the upstairs ring-main's 32A MCB and use the 32A MCB for the shower instead of the 45A one. Which would be the better option? (I guess the upstairs ring main would be fine on a 20A MCB, since I don't run any heating applicances upstairs and its only a 3-bed house.
The only risk is that someone at a later date might see the 45A MCB and think it's okay to put a higher-rated shower on it without calculating for the 6mm cable size.
Smoke alarms and RCDs are different - however the risks associated with not having either are comparable (although injury from fires per years are far fewer than from electric shock). I seem to recall someone round here was very fond of plastering domestic fire safety stats into every wiki article given the chance. Why the double standards?
Yes... the purpose of the MCB is really to give adequate fault protection to the cable. You can use the adiabatic check to make sure you meet that objective.
Most of that is Method C, but the section of trunking means you need to treat it all as Method B. That gives the cable a continuous rating of 38A.
Your design current is 8500 / 230 = 37A, so you are ok there (just).
Let's assume you are TN-C-S, and we will take the default 0.35 ohms as the supply & EL impedance.
The cable round trip resistance will be 6.16 mOhms / metre.
Did you say the total run was 12m? If so that gives a total round trip (by calculation - may be lower by measurement) 0.35 + 12 x 0.00616 =
0.42 ohms.
That gives a prospective fault current of 230 / 0.42 = 542A. The 0.1ms trip threshold for a B type MCB is 5x In, or 5 x 45 = 225A in this case. So we are safely into the magnetic or "instant" response part of the curve for the MCB.
For piece of mind, treat the design as a non RCD one (even though a RCD is required for other reasons), and ensure the fault withstand capability of the cable is ok with that (nice to know the able won't fail if the RCD does):
s = sqrt( 542^2 x 0.1 ) / 115 = 1.5mm^2 of CPC required (you have
2.5mm^2 of CPC in a 6mm^ T&E, so that is ok as well).
(where 115 is the k factor for PVC clad cable)
So based on a few assumptions - you are good to go. You will have no overload protection for the cable, but that is not required in this case due to the nature of the load.
200 something deaths a year in fires now, 20 something from shock
why the claim of double standards? how would stating the known facts possib ly be that? Its not even worth answering.
I already have. I've shown how I assessed whether RCDs were worth fitting. You simply did not address the necessary points in order to reach a reason based case on the question of whether its a good things to install your RCD s.
I've offered a clear risk & cost asessment, plus placed it in the list of a vailable risk reductions, thereby determining if its a priority or whether there are far bigger priorities. Yours has so far been an assessment of the risk followed by an illogical conclusion.
Unfortunately the approach you've shown is common today. It results in peop le spending on tiny risks and consequently neglecting the big ones. No-one has the resources to address all risks, so the sensible approach is to prio ritise the ones we can reduce the most. That is evidently not RCDs, unless you've effectively tackled a fairly long list of others already.
John Rumm wrote in news: snipped-for-privacy@brightview.co.uk:
Many thanks for the detailed reply. So what would be the ideal rating of MCB to use? I just ordered a 40A one, because that's what the shower manual recommends. The 45A one I had wasn't ideal because it wasn't a Wylex one, and didn't fit without removing the base plate.
In a nut shell, humanity's short sightedness when it comes to deciding how we should spend effort and resources on tackling 'problems'. The Green Party's obsession with wind turbine, solar voltaic and tidal sources of energy is a classic case in point.
They regard these sources of Mother Nature's 'energy bounty' as being 'Low Tech' eco-friendly ways to solve the world population's energy demands when they're anything but 'eco-friendly'.
They choose to ignore that other 'energy bounty' on offer from 'Mother Nature', Nuclear Fission, on the basis that it requires ingenious high tech methods of extraction involving, at the point of energy extraction, highly dangerous radio active materials that have to be properly handled and processed to reduce the risk to the environment at large by two or three orders of magnitude compared to a conventional coal fired power station of equivalent energy output.
Their thinking has been coloured by their experience of the earlier nuclear powered station technologies driven by the needs of the cold war demands to build up stocks of weapons' grade plutonium using power stations sited in remote locations, seemingly to reduce the impact of a Chernobyl like event on the population at large.
The plain fact is, it is now possible to upgrade existing coal fired power stations to nuclear power, based on a Liquid Fueled Thorium Reactor (LFTR) design that was first experimented with half a century ago as a potential method of powering a USAF 'Always Aloft' Bomber Fleet.
Only the American Military had a big enough priority and the budget to bankroll such 'Blue Sky' research projects. ICBMs sidelined the concept of an always aloft bomber fleet so the technology, so promising a solution as it was for civil nuclear power station design, was simply left to languish.
If the 'Green Party' membership were to truly compare the *actual* cost/ benefit ratios of *all* the 'Green Options' Mother Nature Provides, LFTR would win hands down on energy generation, environmental impact *and* pollution costs. They wouldn't be able to tear down all those pointless Wind Turbines fast enough!
Sadly, as you pointed out, it's humanity's propensity to short sighted obsession with seemingly 'nice warm cozy 'cheap' 'feel good factor' solutions that leads to wasted time and resources on sub-optimal solutions. A shortsightedness that's invariably taken advantage of by the "PT Barnum" "Get Rich Quick" type of individual or major corporate business.
At the heart of all this, of course, is a nation's educational system which, in the UK and America at least, is seriously lacking in teaching the fundamental skills required to question gift horse offers and other dubious claims such as that rather outrageous idea that the damaging effects of nuclear radiation levels follow a totally contrary curve of damage versus level which apply to all other forms of radiation exposure such as UV light from solar radiation and the effects of microwave radiation which have lead us into believing that almost impossibly expensive anti-radiation precautions are required in Nuclear Power Station design, making the Nuclear Power option infeasibly expensive.
Actually, the most expensive part of a Cold War type of Nuclear Power Station is its Containment Vessel. A modern LFTR based design totally does away with the need of such containment measures (along with an expensive re-fueling process industry) whilst offering a 200 fold improvement in energy yield from the nuclear fuel itself. As always, "Ignorance"(tm) strikes again at the heart of the matter.
BTW, many a conspiracy theory nut would lay claim that the Oil and Petrochemical industry are doing their best to scupper the idea of a "Nuclear Powered World"(tm) when in fact it would be in their best interests to branch out (diversify) into Nuclear Power Station design and proliferation so they can corner the market in *synthesised* petrochemicals and save the costs in dangerous exploration and drilling for a dwindling natural resource.
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