I've recently joined the local wood working club. Wood turning instruction is my reason, plus access to somewhat bigger and better bits of kit than I can afford or have space for.
They just had a new dust extraction system fitted - about half the size of my workshop! It's not been wired in. It's likely to be a local authority electrican to do it but the club chairman wanted to know what was likely to be involved.
It set me thinking afterwards about the earth bonding of all the equipment. The lathes, for instance, are on 13A plugs, which I don't think is a good idea, and if they are to be then surely bonding would be necessary. If the other equipement is hard wired I take the bonding is through the power wiring ?
Grrrr, usual comments about the meaninglessness of the phrase "earth bonding" - no such thing. There is earthing, and there is equipotential bonding. Different things for different purposes.
Firstly lathes on plugs - not a problem unless they are too large to run from a 13A supply. There is some argument that the socket circuit ought to be on a kill switch arrangement in the workshop, but that is a separate issue.
Secondly, equipotential bonding. A workshop is not a special location or one of enhanced risk of shock injury, so supplementary bonding is not required.
(if the lathe were installed in a bathroom or sauna, then EQ bonding probably would be required[1], as would connection via a FCU rather than plug and socket, however the CPC in the flex feeding the device would also double as a bonding conductor and hence a separate one would not be required)
[1] 17th edition installs with RCD protected everything can skip bonding.
Hang on, if you have metal duct work that you are sending a flammable dust along you do need to make sure that all metal parts of the duct are bonded together. Standard 4mm2 should be fine.
With regard to the lathes there should be means of quickly shutting off the power should a person become entangled in one. One suggested way is to have a contactor with stop and start buttons feeding all the circuits in the distribution board and have several E stop buttons round the room.
Dependant on load you could use something like
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and
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the key is usefully it stops others who are not competent to use a lathe turning the power on. The prices should be cheaper at an electrical wholesalers
It was the lathes that concerned me most as the end of each session (twice a day often) the plugs are removed. I don't know what regime is in place to inspect the plugs, but such frequent movement could lead to disconnection of the any of the leads inside the plug, with the corresponding hazard. I also do like the concept of central isolation.
As far as I know everything is covered by and RCD - do you get 3 ph RCD's ?
Yes, unfortunately, cutting the power to a workshop is not the answer any more. I've been trying to get to the bottom of this "should there be a workshop-wide e-stop system" question and I haven't been able to find any guidance from the HSE, IEE or anybody else to clarify current best practice. I would welcome any pointers.
The arguments against are that (1) PUWER[1] doesn't require it and (2) PUWER does require that, even under emergency conditions, work equipment must be brought to a stop in a controlled manner (particularly where "[the emergency stop signal would] trigger or permit the triggering of certain safeguard movements"[2]).
Further, PUWER requires that all guarding and auxiliary circuits (e.g. task lighting, fume extraction) that enhance safety should remain functional in the event of an e-stop.
It is usual therefore to consider e-stop on a per-machine basis.
IMO if it were deemed (on the basis of a full risk assessment) that a workshop-wide e-stop be required, then this e-stop should send an e-stop signal to each machine rather than cut the power. Depending on detailed risk-assessment, this could mean modifying the wiring of a machine to accept an external e-stop signal or fitting a local contactor to cut the power to an individual machine.
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[1] Provision and Use of work Equipment Regulations 1998.
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See clauses 1.2.4 and 1.6.3
[2] AIUI (although I can't cite a reference, it may be the EEC machinery directive) regulations have changed for things like grinding wheels and table saws. They now must come to a complete standstill within a few seconds of being turned off (either normal or emergency stop) and with this being achieved by the provision of d.c. injection braking, simply cutting power to a machine is not an option under PUWER as the machine would not then come to a controlled stop, but would run-on for anything up to several minutes.
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As an aside, clause 1.5.7 of the above document speaks to the avoidance of explosion risk being the responsibility of the designer/manufacturer of the equipment. Therefore, any additional equipotential bonding of a dust extraction system should only be implemented in accordance with the manufacturer's requirements.
I suppose it should keep the contract surfaces clean... might risk breaking a flex in time, but twice a day is not a huge amount (compared to the life of a commercial vacuum cleaner for example).
As others have mentioned, that is not always the ideal solution. Much depends on the type of equipment that is in use. Traditionally there would be a circuit for which power was supplied via a contactor, and stop switches were dotted about to allow the circuit to be de-energised in an emergency. With more modern machines that use active breaking etc or require power for safe operation of emergency stop procedures, that approach is now deprecated, although one might argue that for a small collection of simple wood lathes it is still a reasonable approach.
Also looking back at the question, I did skip one possible aspect of the extraction system; that it might have extensive ducting. If this is metal and snakes from room to room, then it may come under the definition of extraneous conductive elements that could introduce a potential into a zone. Hence should to be included in the *main* EQ bonding.
(there is a separate issue with ducting system regarding providing an earthing path to drain static buildup - where non conductive ducts are used, a bare earth wire is sometimes routed through the duct to facilitate this.
You can yes. Assuming all the equipment is properly earthed, then the electrocution risks from it will be fairly low anyway.
We had this at work - the sockets (MK metal-clad) occasionally failed by falling apart internally sometimes with bang and smoke. Checking sockets mechanically every few years might be necessary. Another consideration is the plug: the sort that has a medial split can fail in a dangerous way, as the operator's fingers can contact the conductive parts if the sccrew fails, so the fully capped type is better (the ones that need a bit cutting out to get on after wiring :-) ).
Clearest I've seen has been school's workshop advice, at the LEA level. Which varies between LEAs. Where a single e-stop system is required, it's necessary to integrate it with the e-stop on each machine (braking etc.), where that's relevant for that machine (which then gets awkward for some).
It does seem however that schools no longer have anything interestingly large, so the e-stop braking issue becomes moot.
There may be a case for having a "teacher's" keyswitch to disable power to the machinery *separate from emergency stop*.
In a factory anyone using the room should be safety-trained; even if they don't operate the machinery there should be a safety induction. In a school or similar facility the workshop may be used for a variety of purposes or levels of instruction, and although people shouldn't be in the workshop unsupervised it is probably going to happen at some point. So the machinery should be locked off when the papercrafting group are using the room.
I'll get my grrr! back now - people who say 'breaking' when they mean 'braking' !! No smileys available so I'll just do [BG].
Anyway it's been an interesting response from you all - thanks. I'll raise the points with the club chairman and possibly point him to this thread. Rob
You need to replace the '13 Amp' BS1363 plugs & sockets with industrial connectors, such as the 'Commando' type, made by many manufacturers to BS EN 60309-2 (formerly BS 4343). These do vary a bit in quality, but these two manufacturers seem to offer a quality product, available in metalclad versions as well as the more common plastic:
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for real class there's the 'Reyrolle' BS196 connectors:
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used by the former nationalised industries, BR, CEGB, LT etc.
BS1363 connectors were only really intended for domestic purposes, to provide sockets which could be mass-produced cheaply for the post-WW2 rebuilding programme, they do not stand up to industrial use. Even BS546 round-pin connectors are better.
Lewden do make a superior weatherproof version of the above types though, both the plugs and the sockets, look up the 'Weathertight' range on their website.
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