Electrician installed a whole installation RCD

Willing to bet in the OP's case it is one of his water heaters.

Reply to
Dave Plowman (News)
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Where do you get 100uA from? A class1 piece of equipment to IEC 950 (Information Technology Equipment), a PC for example, can have up to

3.5mA of earth leakage current. Moreover an RCD will eventually trip if continuously subjected to a current imbalance of half its rated value, so 15mA will eventually trip an RCD. Given a worse case but compliant leakage it would require only 5 pieces of Class 1 (earthed) IT equipment to eventually trip a 30mA RCD.
Reply to
Peter Parry

We design this stuff. Maybe 1 milliamp is acceptable in some undeveloped nations. But other standards demand well under 100 microamps. Furthermore, leakage that low is easy. Some venues must have numerous equipment on the same circuit that would trip at 5 milliamps. 3.5 mA leakage from any appliance is a serious design or manufacturing flaw. Especially when microamps are so easily achieved.

I have never seen a standard that permits a leakage that large. A PC leaking

3.5 ma would cause circuit tripouts in many nations - completely unacceptable when a computer must be designed for all world power systems. Those milliamps approach currents that can kill. In many venues, a 5 milliamp leakage would trip RCDs.

If a 100 milliamp RCD is tripping, then the building contains a serious human safety defect. Fix the defect. Many, instead, want to blame the RCD.

Reply to
westom

Just wondered as I this year I have electrically tested a few village halls for insurance purposes. The LA had no specific requirements other than a NICIEC EICR saying the electrics were safe. BTW I would put a lack of RCD on stage sockets as a code 1.

I failed all of them for various reasons - the main failure at two of them was an incredibly high Ze to the properties. As they were both tested within two days of each other I questioned the calibration of test case I was using. Both were, when double checked, DNO faults.

Reply to
ARW

In the case of Guildford, the requirement was a consequence of a musician/singer peforming at th University being electrocuted when he took hold of a microphone stand.

Reply to
charles

3.5mA was (is?) the EU legal limit for fixed IT equipment... About the only thing that came close in the past were large CRT monitors (which could do up to 2mA by themselves - possibly more on inrush when switched on from cold).

These days modern kit should not come anywhere near that limit. If you work on a budget of say 1mA per desk that might not be too unreasonable given PC, screen and a few other IT gadgets powered.

Reply to
John Rumm

I don't think anyone was suggesting otherwise. We were however attempting to guide the OP to finding what was causing the problem rather than just telling him to get it fixed!

Reply to
John Rumm

That is the most worrying statement someone who claims to be versed in this subject can ever make.

If you would kind enough to state who you design for, so I can make a special case of avoiding their equipment?

Reply to
Fredxxx

I presume that means requiring immediate action, why not Code 2 for requiring improvement?

Was the Ze issue a supply issue or an earth spike issue?

Reply to
Fredxxx

Oh dear.

You mean like the EU, the USA, Switzerland, Singapore etc?

Which ones?

Nope.

Try the one quoted - IEC 60950-1 (Information Technology Equipment) (IEC 60950-1, 2nd Ed, 2005-12 to give the current version its full title).

Reply to
Peter Parry

I agree a milliamp is probably closer to reality - the one modern exception seems to be these common plug in "Surge suppression" plugs/sockets which seem to manage quite high leakage.

Reply to
Peter Parry

A quick look at

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and Home > Passive Components > EMC / RFI Suppression > Suppression Filters - Power Line IEC

Suggests that leakage on an IEC filtered chassis mounted plug/socket is a few 100uA, typically 300uA plus. That's without any additional "real" filtering you might have in a piece of equipment.

Reply to
Fredxxx

And that is for some of the better quality items on the market, not the average PC PSU.

Reply to
Peter Parry

+1

I doubt you'll get an answer to that question any time soon.

I suspect westom doesn't know the difference between insulation breakdown leakage and the reactive leakage you see from the 47nF caps typically used in the EMI filtering circuit of ATX PSUs.

If the leakage is due to failing insulation, that *is* a serious issue which does need to be investigated and put right. Reactive leakage due to EMI filtering otoh, is an altogether different kettle of fish notwithstanding that enough PCs hooked up to a circuit where the CPC wire has gone open circuit can present a human safety hazard (but one would hope that someone would start to question the tingling sensation they get every time they make contact with the case of the PC(s) in question).

One thing to consider with a single *un-earthed* PC is that the leakage source is effectively a 120v supply with a leading reactive impedance of

33.863K ohms (voltage divider effect of a pair of 47nF caps in series across a 240v supply with, effectively, a parallel connection to a very low impedance 240v 50Hz ac supply).

Even the combined effect of ten such unearthed PCs is unlikely to pose an electrocution hazard. It's the peripheral connections that are likely to draw attention to a missing CPC on a UK ring main and a call to an electrician to solve the mystery of why so many devices are getting fried whenever they're plugged in or disconnected from the PC (both the peripherals and the interfaces concerned).

Westom may well specialise in the design of equipment that calls for such low leakage requirements (medical or specialist research equipment springs to mind) but if this is the case, then he's specialised his knowledge to just this subset, an extremely narrow field indeed. Consequently, he's no longer qualified to comment on the wider field of leakage currents from general every day kit without the benefit of a refresher course in "Leakage 101".

Such specialisation to that extreme is very worrying. One such example that comes to my mind is the case of all those early PCI based sound cards (and the PCI based on-board sound chips) that started to appear around the turn of the century which all, to a chip, clipped the line (and CD analogue audio) inputs at -2dB FSD due to the sound card and MoBo manufacturers blindly following the reference design offered by the sound chips makers where the -6dB sensitivity option had been hardwired to reduce the noise floor.

Basically, this was achieved by doubling the reference voltage for the ADC but forgetting the need to double the line input buffer amp supply rail voltage to raise the already marginal clipping level that was otherwise sufficient when the more sensitive setting had been chosen.

I think it took a good (well, bad really) 5 or more years before the penny finally dropped and the problem was properly addressed. You had to be overly focussed (specialised) in the digital aspect and totally ignorant of the fundamentals of audio circuitry design to miss that particular "Schoolboy Howler" of design incompetence to make that mistake (and worse still, perpetrate it for so damned long!).

Reply to
Johnny B Good

replying to Peter Parry , westom wrote: For protection of human life, an RCD must trip at 5 milliamps. Higher currents (ie 20 milliamps) are permitted if human protection only requires 'let-go' or ventricular fibrillation protection. One standard (that now applies to North America and will eventually appear in the UK) is UL943.

More facts from design standards. Currents less than 0.5 milliamps are considered safe. Current between 0.5 and 10 milliamps cause involuntary muscle contraction resulting in injuries. Currents between 10 milliamps and 100 milliamps can cause breathing difficulties or even fibrillation. A 100 milliamp RCD is an inferior safety device. Any fault that trips a 100 milliamp RCD is well above human safety requirements.

How does one design equipment to operate without tripping RCDs that do human safety (ie 5 milliamps)? That equipment leaks less than 100 microamps. One ANSI standard permits leakages up to 500 microamps. BS standards will eventually adapt what has long been standard by UL, CSA, IEEE, and others. Many BS upgrades eventually use phrases directly taken from those other, older, and safer standards. Apparently you need not meet international standard.

Properly designed equipment need not leak more than 100 microamps. Designs typically target 60 microamps. JCAHO and NFPA 99 defines less than 50 and 10 microamps. Another standard permits up to 300 microamps from an asssembly of many electronic devices. Another standard for small electric motors with only one layer of insulation permits up to 100 microamp leakage. All well below an obsolete 3.5 milliamp number that would cause problems with current technology 5 milliamp RCDs. Even in the days of vacuum valves (tubes) did not leak that much.

Now back to the OP's problem. If a 100 milliamp RCD trips, then a serious and troubling human safety issue exists. Above numbers say why that is dangerous. Fault can be in appliances or in household wiring. Or even a combination of both.

An informed engineer would not hype on the irrelevant - badly designed hardware that leaks 3.5 milliamps. As if obsolete standard are good enough. Microamp leakages numbers were standard and routinely achieved even 40 years ago. If a fault does not exist, then even 5 milliamps combined from many appliances would not exist.

A design engineer would target the topic rather than promote obsolete safety standards. The OP's tripping RCD indicates a serious human safety issue.

In one case, that fault (that was in building wiring) did not exist until an appliance was powered by that circuit. It was a more interesting problem.

Reply to
westom

Or just a leaky heating element in a cooker.

Reply to
Tim Watts

Or one of the water heaters he has.

Reply to
Dave Plowman (News)

Firstly you need to understand that shock hazards are related not just to current flow, but also duration.

The shock hazard curves are shown here:

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Secondly keep in mind that RCDs to not limit the current flow in a shock situation anyway.

The UK requirement for direct contact shock protection specifies 30mA devices for general use. 10mA threshold devices are available for specialist applications, but are not in general use.

Generally they will operate within two mains cycles (40ms). Its this quick operating time that is the actual protection mechanism, not the trip current.

No one was suggesting otherwise, so you can stop repeating yourself.

Reply to
John Rumm

I suspect that Johnny B may have hit the nail on the head, that westom[1] is talking about actual insulation leakage from a product and not reactive coupling from the RFI filter.

[1[ any relation to w_tom one wonders?
Reply to
John Rumm

Pity that all domestic ones trip at 30mA then.

BS 7671:2008+A3:2015 IET Wiring Regulations Seventeenth Edition came into effect in July 2015. Residual Current Devices must meet the standards in BS EN 61008-1:2012.

You are suggesting that these will in some way be replaced by UL943 (Class A, single- and three-phase, ground-fault circuit-interrupters intended for protection of personnel, for use only in grounded neutral systems in accordance with the National Electrical Code (NEC)), dated

2006?

You do realise a GFCI and an RCD are functionally identical?. However a GFCI incorporates an over current trip so is closer to a Residual Current Breaker with Overload (RCBO) than a RCD. There will normally be 1 GFCI per socket outlet (Often incorporated into the socket itself) or small group of radial wired sockets rather than the RCD covering a ring main which will have many sockets.

Under present UK rules all sockets must have residual current protection, under the somewhat more lax American NEC rules only those for use in wet areas need residual current detection.

What on earth makes you think the older UL943 will replace more modern standards?

Which design standards?

No it isn't, it has a perfectly valid role to play in TT earthed circuits.

That's probably why those installed for protection of the users are rated at 30mA.

If you are referring to the US wiring system of having one GFCI per socket - this will allow for the maximum 3.5mA leakage current from your computer.

Do you actually understand the standard naming conventions and the hierarchy of standards? National standards specify the requirements for application in the particular country. British Standard ? BS denotes Britain's National Standards which are controlled by the British Standards Institute (BSI). EN denotes a Standard which is adopted by the European community and is controlled by the European Committee for Standardisation (CEN). European standards are aimed at facilitating commerce between the countries of the European community. Once a European Standard has been agreed it supersedes any existing national standard and becomes the new national standard. In Britain these Standards are then prefixed with BS EN. ISO denotes a worldwide standard issued by the International Organisation for Standardisation. Once an International Standard has been adopted as a European Standard it supersedes the existing European standard. In Britain these Standards are then prefixed with BS EN ISO.

Why on earth would you make all domestic equipment conform to medical equipment standards when there is no advantage in doing so and a considerable cost increase?

You have obviously never worked on an old USA design TV.

However, here is a clue. Old valve equipment didn't use switched mode power supplies and didn't have to meet any RF emission standards. Indeed many TV['s were quite effective jammers of short wave radio bands).

It is a 30mA RCD which is tripping.

The "obsolete" standard is several years younger than the American one you quote.

40 years ago switched mode power supplies (SMPSU) were uncommon and radio frequency interference wasn't an issue. With SMPSU you need noise filtering to meet the EMC requirements and that introduces leakage paths.

. The standard you are referring to was only published 3 years ago.

I am rather concerned that someone claiming to be involved in the design of electronic devices seems to never have heard of the appropriate International standards.

Next thing you will be telling us to switch to 110V because it is "safer".

Reply to
Peter Parry

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