How common is total RCD protection?

[Iggifer]

I think I have counted two trips in the past 2 years since going all RCBO - I suspect these were both overcurrect as they were both lighting circuits and cleared immediately both times (blown lamps)

I suspect this is down to having 30mA per circuit though, rather than for all/half of the installation.

Prior to going RCD I would get the odd RCD pop, nothing major but every now and again - I suspect that was due to the fact that all socket and lighting circuits were on one RCD - boooo

 

[EFLImpudence]

As to 100 mA read the Wylex data sheet page 5 which shows 100 mA in the main will protect. Hence included...

...I have had shocks but with RCD and without. The worst of recent years was with a RCD at 30 mA and tested to trip within the 40 mS required...

...The belt even with RCD protection put me on the floor. Hard to say if it knocked me out no one else was there...

...So that calls to question how good RCD protection is for direct contact?...

...I am dam sure I got more than 100 mA so the only difference between a 30 mA and 100 mA RCD would have been time.

An RCD does not limit the current, just the time you are exposed to it.

That is why a 100mA will do if the current is more than 100mA (or the current at which it actually trips, >(IΔn)/2).
However, with a current of 49mA, the 100mA RCD would not trip which is why 30mA RCDs are required.

 

[Iggifer]

I would not fancy a sustained 49mA shock thank you very much

Love this diagram

 

[RF Lighting]

I've had my split load setup for maybe 10 years now and have only suffered one problem of nusiance tripping.

It turned out to be a small leak on the header tank for the heating in the loft which was running down the inside of a plasterboard stud work wall and getting into a dry lined socket on the floor below!

I'd say these days that maybe 60% of the properties we visit have some RCD protection, and maybe 10% have the required level of protection.

It's certainly a massive improvement on when I started out in this industry where any RCD protection at all was a rarity, even on TT installs!

 

[ericmark]

Great diagram but a rough value for the internal resistance of the human body is 300-1,000 ohms so to get 30 mA to flow means between 9 and 30 volt it needs to be of a resistance of 1666 ohms to reach 50 volt.

For 100 mA then we drop to 500 ohms to trip at 50 volt so at the upper end you could have 100 volts before the RCD trips so it's all down to the internal resistance of the human body as to if a 100 mA trip will operate as quickly as a 50 mA trip and since we live in the UK where the voltage to earth is 230 not USA where the voltage to earth is 120 volts then a 100 mA non delayed trip will disconnect with direct contact just as quick as a 30 mA trip.

Where it changes is when the fault would have tripped a 30 mA but not a 100 mA before direct contact.

Where the RCD is delayed then clearly it will not protect in the same way but with the shock I got I was holding the saw blades hard so would have had a really good contact into the body. As to where it came out of the body I don't know likely I was touching some earthed item. But I can get a 100 mA to flow through my body from a 24 volt wagon battery with no adverse effect so I assume far more than 100 mA flowed through my body, sorry I have no wish to do it again to test this, but it seems very likely amps rather than milliamps were flowing through my body for less than 40 mS it took for the RCD to trip so it would have not made a scrap of difference had it been a 100 mA trip it would have operated in the same time.

If 1/2 an amps is flowing it makes no difference 10 mA, 30 mA or 100 mA tripping time is the same.

 

[JohnW2]

I've had my split load setup for maybe 10 years now and have only suffered one problem of nusiance tripping. ... It turned out to be a small leak on the header tank for the heating in the loft which was running down the inside of a plasterboard stud work wall and getting into a dry lined socket on the floor below!

That's surely not a 'nuisance trip' in the normal sense - the RCD correctly operated when it should.

As I've said many times before, I've lived with an installation which has a lot of RCDs and a few RCBOs for a couple of decades, and I don't think I've ever suffered what I was call a 'nuisance' trip (unexplained, seemingly not in response to any fault) - other than, until a few years ago, lighting anywhere near seemed to sometimes cause RCD trips (but that hasn't happened for the past few years). Others seem to have much less happy experiences of RCDs.

Kind Regards, John

 

[Iggifer]

Perhaps if they could get them to trip at closer to 30mA everyone would have less problems with them!!

 

[JohnW2]

As to 100 mA read the Wylex data sheet page 5 which shows 100 mA in the main will protect. Hence included.

IMO, some rather worrying things are being said/suggested in this thread.

I'm not sure that I fully understand the Wylex graph, nor where the data on physiological effects came from (for obvious reasons, such data derived from humans are very few and far between - a lot of the available data derive from experiments on pigs).

However, what is clear is that, in the 'worst case' a 100mA RCD may (compliantly, per spec) allow 99 mA to flow through a person indefinitely and, even in the 'typical case', would allow currents of, say, 50-60mA to flow indefinitely. Even with (my attempted interpretation of) the Wylex curves, those situations are well into the 'potentially fatal' range.

Whilst it is undoubtedly the case that some, maybe many, 'direct contact' incidents will result in currents through the body >100mA (hence would result in operation of a 100mA RCD), with dry skin and/or 'poor contact' currents though the body in the 30-100mA range are very possible.

It simply is not appropriate to suggest that a 100 mA RCD can or should be used to provide protection to human beings who may come in 'direct contact' with live parts (and a path to earth).

Kind Regards, John

 

[JohnW2]

Perhaps if they could get them to trip at closer to 30mA everyone would have less problems with them!!

That's obviously true. However, whilst I'm sure it could be done, I suspect that, in practical terms, substantially increasing the maximum current which would not cause a trip, whilst still ensuring that a 30mA current would always result in a trip (given both manufacturing and operational tolerances), would probably be difficult and, perhaps more to the point, probably expensive.

Kind Regards, John

 

[ericmark]

Perhaps if they could get them to trip at closer to 30mA everyone would have less problems with them!!

That's obviously true. However, whilst I'm sure it could be done, I suspect that, in practical terms, substantially increasing the maximum current which would not cause a trip, whilst still ensuring that a 30mA current would always result in a trip (given both manufacturing and operational tolerances), would probably be difficult and, perhaps more to the point, probably expensive.

Kind Regards, John

It has been done. The X-Pole RCD has a monitor built in and does not trip until 90 ~ 100% of the rated value but cost more. An accunt can be read here there was a document on the net Eaton enters the digital age but normally a hunt gets pole dancers instead. But when you try to find one of these RCD's for sale not so easy. It would seem there are so many different RCD's so designed for use with inverters and even so auto resetting.

In industry paying £250 for a RCD to reduce down time may make sense but with domestic then it's a different story. This PDF lists some of the specials and it really is a mine field trying to work out what is required.

 

[JohnW2]

In industry paying £250 for a RCD to reduce down time may make sense but with domestic then it's a different story.

Exactly my point.

Kind Regards, John

 

[plugwash]

Rented flat where I live: RCD only on shower (fitted when shower was replaced)
Parents house: single 30ma RCD covering everything except lights.
Grandmothers house: single RCD (dunno what the trip point is) covering everything.
Sister's house: dual RCD split.

Dunno about other members of my family.

 

[AdrianUK]

30mA overall RCD for me. No plans to change it

 

[ericmark]

So to date 19 all RCD, 6 part RCD, and 1 no RCD so for the 26 homes it would seem only my father-in-law has no RCD protection.

I did not expect to find RCD use so common, but most replies are from electricians so maybe that's why?

 

[JohnW2]

So to date 19 all RCD, 6 part RCD, and 1 no RCD so for the 26 homes it would seem only my father-in-law has no RCD protection. I did not expect to find RCD use so common, but most replies are from electricians so maybe that's why?

Yes, it's a pretty biased population you've asked - but, at least in my case, I had no influence over the electrical installations of any of my family members or neighbours, only my own - so it doesn't really matter who/what I am.

The electricians here should, of course, be able give you much wider figures relating to all the (many) installations they see in their work. RF has already indicated that about 60% of the installations he sees have some RCD protection, and about 10% have "the required level of RCD protection".

Kind Regards, John