When using high current needs equipment like machinery (ie Milling Machinery and Lathes) would the use of RCBOs pose an inderence with constant tripping as with lighting applications could even leave you without lighting. Just wondering the general consensus?
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.
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.
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.
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.
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'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.
we need to follow BS7671 which states the use of RCBOs through out
Not quite.
Lighting final circuits need additional protection by RCDs in domestic premises (411.3.4).
Socket outlets not exceeding 32 A also need it, although there are certain exceptions. > 32 A seems unlikely - for 3-phase that would be a 30 bhp motor, so a rather large lathe.
That's for using RCDs socket not exceeding 32A and lighting Circuits and not RCBOs.Is that correct?.
If the sockets do not exceed 32 A (per phase), they need RCD protection. That could be an RCBO in the board, but it could alternatively be a socket-outlet with a built-in RCD.
MCBs are fine for lighting circuits in commercial premises.
Clear?
Yeah that's my impression as to some of the sockets coming off these distribution board's are stating 30mA RCD so was thinking that the sockets had the RCD built in them.There are some pictures showing the old board and a RCD at the side of the board so assumed this was related to the board itself and not the sockets.
There are some pictures showing the old board and a RCD at the side of the board
Let's have a look then. (Just drag and drop into the text box.)
BS7671 which states the use of RCBOs through out
Oh no it doesn't! (a common urban myth amongst some domestic electricians perhaps, but not at all what BS 7671 says). Other than for some special locations (bathrooms, saunas, swimming pools and so on) there are only a few situations where BS 7671 demands 30mA RCD protection, roughly:
RCBOs themselves barely get a mention - they're just a convenience where an RCD and MCB functions are wanted together. Using an RCCB (plus a device for overcurrent protection) meets the same requirements - and is quite common even in domestics (think split boards) but obviously with a little more inconvenience if the RCCB is shared across several circuits.
Also for TT installations you may well need RCDs to provide ADS - and RCBOs might again be convenient for that (but not necessarily 30mA ones unless specifically required for reasons such as those above).
- Andy.
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