ZS for an motor run off an inverter

That Andy, is a definition of the problem. Because there are so many standards, all of which overlap in many ways, it is impossible to define the scope of any particular one, because another one may jump in at any time and "grab" a "competence", using EU talk. This means that an EICR for example is generally impossible. Either you do the inspection to BS7671 alone, (and finding the edges of even that is difficult) which is what BS7671 says, or most people cannot do the job. To do this means that a connected inverter must be considered "out of scope" as must a complex machine, a storage heater, cooker etc. BS7671 has attempted to "grab" all wiring, even network and communications cables for example, or ELV DC wiring, and has found that this doesn't work. I will mention that RCDs were at one point thought necessary for communication cables. We have questions here on the inside of control panels because the exact scope is not clear to Electricians (actually, or very few others). If you read 110.1.1 you will not see the edges at all, BS7671 apparently covers everything electrical in all those locations, if it is "an installation". The definition of "Electrical Installation" is equally vague "An assembly of associated (What does that mean, very vague) having co-ordinated characteristics to fulfil specific purposes". I suggest that this includes the internals of every piece of electronics in the country. I do understand that we normally have a definition of the limits of this which I loosely defined as "fixed wiring" above, but this is completely inadequate when BS7671 does not understand the limits itself unless it is in the list 110.2. BS7671 then makes requirements on inverters (the OP) but has no idea how to achieve what it says. What about cookers? They fall foul of 131.1, in that they have hot parts which could cause burns. I am expecting a new section on optical communication cables soon, as some of them could present danger when high power lasers are in use. There is NO advice in BS7671 on inspection limits or scope to help! It just gives simple tests on normal fixed wiring, which is fine. Does it mean ignore anything else, or is a massive section missing? Even the "Scope" is completely inconsistent, so much for "Standard". Before anyone thinks I am just whinging, I am not. I want to get this fixed, and am willing to put considerable effort into doing so. It will help everyone considerably.

Have to agree David - we should really be returning to the definition of what a 'Fixed Wiring Test' is really about. When I did my 2391 back in 2002 we were instructed to link out the motor starter and to disconnect the motor leads and just test the continuous length of fixed wiring and associated isolators. A visual inspection of connections inside the starter and motor were all that was required. Even now when we go to site to inspect and test trailer-mounted high speed centrifuges, we just teat the outgoing motor leads from the output side of the inverter in the panel  The client is happy with these 'limitations' and everyone is happy.

There is too much 'mission creep' or over-reach in BS7671 these days, which also becoming ever more indistinct in it's actual requirements.

David,


Let's forget BS 7671 for a moment.


How does a duty holder know the VSD, operating in the way you say, meets the requirements of the Electricity at Work Regulations?

Do we simply trust that the manufacturer should have built this protection into the device, and it works?


Are you absolutely sure that the current limit in the drive actually provides adequate protection? I'm sure that additional devices in the Assembly are necessary - and it's really the switchgear/controlgear assembly that we are looking at the performance of here, and not the drive itself. Certainly, VSD instructions to contain recommendations of additional protection equipment, such as an input contactor dropped out by the overload signal, to achieve fast disconnection time ... but the design is left to the assembly manufacturer.


The assembly would of course comply with BS EN 61439, and should be provided with suitable instructions (according to that standard) for safe installation, operation and maintenance.


Don't forget, you mentioned that the VSD itself provided the protection ... but I believe it's the assembly as a whole.

I suspect that many out there 'at the coal face' are aware of what is happening and are just ignoring those parts of the regulations which they cannot understand, and are reverting to what they know actually matters by engaging 1st principles - remember them? Back in the day when critical thinking wasn't a crime, and was indeed encouraged within our educational institutions? I rather suspect that the tome formerly published by that well respected Body formerly known as the Institute of Electrical Engineers is fast become irrelevant to those who have fast become frustrated by it's rebranding and constant over-reach and it's ever increasing vagueness.

I predict a slump in sales with every future amendment as people wake up and realise that they can no longer depend upon it's contents and will go their own way to redefine what actually constitutes a safe electrical installation in future.

Do we simply trust that the manufacturer should have built this protection into the device, and it works?


Surely we have to? After all, if the requirement is covered by a standard, then surely we should be safe in making an assumption that the protection requirement ahs been met - otherwise, why bother with a standard which requires it?

Graham

One might get an overload signal, but this is not by any means common. Following your line, how could I test this disconnection time because I think it is very complex on the output side of an inverter.? I have never seen a set of Manufacturers Instructins which told me how to verify compliance with BS7671 disconnection times, and I have used many drives for all kinds of purposes. I repeat my comment, there is not a believable fault which requires this disconnection time anyway. It is not a case of shock protection is it? So why are you worried? The output current, power, and voltage are all outside the users control. Treating a VSD as some kind of transformer is ridiculous, it is not. The electronic disconnection on fault is many times quicker than a contactor. Contactors are many times less reliable than drives. Is this design sensible? Are there any accident statistics which suggest that it is? You will notice that many machines have drives directly connected to emergency stop systems. They are much the quickest way to stop motors and are capable of doing so in a single revolution or so (which may well wreck the motor) but that is a price of "safety". This action would always signal a fault condition because an instant change in direction at full power is not expected, so would unpower the emergency stop. Not a good idea. I agree rather strongly with whjohnson, we need to have a rethink with the 19th edition, from first principles

But there cannot be a hole where no-one knows who is responsible.

I suspect that's exactly why BS 7671's scope is what it is - it's the 'catch all' standard for anything electrical in the UK - if no other standard says otherwise then it's BS 7671's general (and fairly safe) principles that apply. If you want a cooker with exposed hot parts then you'll need another standard that overrides BS 7671 principles to specifically permit it.


  - Andy..

The "VSD" isn't just the whizzy electronics - it needs to be put into a switchgear & controlgear assembly with all its attendant components and protection.


The assembly is outside the scope of BS 7671.


So, the question is, what did the designer of the assembly do about protection against electric shock?

Mr Kenyon - how far do you wish to take this? Would you have us inspect and test the inner workings of a GU10 LED lamp under the same premise?