Within BS7671 there is a lot of information in the use of RCBOs and was wondering if in certain applications like industrial sockets BS90437 and lighting Circuits whether these would pose a nuisance tripping action.Just wondering what the general consensus

BS 90437 does not exist. Do you mean BS EN 60309 socket-outlets?

Was ment to say BS60947-3

Not my day today was supposed to have said BS60439-3

BS60439-3

That's the old standard for DBs isn't it? (replaced by BS EN 61439-3 about 10 years ago?)

As for RCBOs BS 7671 has no blanket requirement - 30mA RCDs are only demanded for additional protection on lighting circuits in domestic/household situations. Normally no requirement for hard-wired equipment, just sockets (<=32A) used by ordinary persons and for portable equipment outdoors. Soft sheathed cables concealed in walls normally aren't a feature of industrial situations.

Most single appliances suitable for being powered by a plug have relatively low earth leakage (protective conductor) currents - otherwise you'd have other constraints, such as having to provide high integrity c.p.c.s. It can be an issue in some situations though - e.g. server racks containing dozens of mains powered items but the whole thing still on a plug & socket for maintenance purposes. In such cases there is an option to use a risk assessment to avoid the need for 30mA RCD additional protection.

Sometimes high starting currents have been know to false trip RCDs - usually the answer to that is to use an RCCB with a higher carrying current rating (e.g. a 40A/30mA RCCB plus say a 16A MCB, rather than a 16A/30mA RCBO).

   - Andy.

Hi Andy,

Yeah, I've got my standards wrong it should of been BS60947-3 its the Industrial standards and not 90437 which I gave first time round. 

AJJewsbury said:

That's the old standard for DBs isn't it? (replaced by BS EN 61439-3 about 10 years ago?)

Beat me to it. It was in 2012.

Ian Stokes said:

Yeah, I've got my standards wrong it should of been BS60947-3

That is for Switches, disconnectors, switch-disconnectors and fuse-combination units, so I am struggling to understand the question.

I have used C type RCBOs (OCPD characteristics) on lighting circuits, especially with lots of LED lights on the circuit. Obviously you need a lower max Zs than when using B type.

I'll try and get this right but what we have been looking at is the use of RCBOs on sockets for Industrial Applications such as Machinery (ie Milling Machinery and Lathes)and the problems with falsely tripping and finding an alternative requirements.Also whether using RCBO's in lighting requirements has we are using the old standards BS3871 and so boards have been updated to 60898 but in certain applications (ie High current requirements and probably lighting circuits) are these viable cause you wouldn't want them falsely tripping and then your in the dark.So was trying to find an overall concensus approach. 

BS 3871 was replaced by BS 60898 in 1991.

I see no intrinsic reason why lights should lead to nuisance tripping. If you are concerned about high in-rush currents, then either have them wired in banks so that they do not all come on at once, or take OlympusMons's approach. Once they are on, they should stay on.

Motors also have a high starting current, so are typically on C-curve MCBs/RCBOs. That would have been type 3 BS 3871 MCBs. Again, once they are on, they should stay on.

If modernization has gone so far as to fit variable speed drives, there may be some earth leakage, which could lead to nuisance tripping with RCBOs, but as Andy points out, if machines are hard-wired, MCBs should be fine. Clearly, the number of machines per circuit will make a difference. How big are the lathes?

Yeah I get the impression we are going down the replacement of 3871 MCBs with 60898 MCBs but there was a technical area that stated we need to follow BS7671 which states the use of RCBOs through out but we thought as to whether this would cause a problem for high current applications we falsely tripping problems occurring.