When Mrs Secure Sliced Through The Hedgetrimmer Flex...

[JohnW2]

With a three core cable with earth not connected at appliance we have a number of issues. ... 1) How can you test the earth? I have when testing in service electrical equipment already come across the problem of testing. Often the only part which can be accessed is the spindle and 25 amp through a bearing is not a good idea. To test the earth I will use the IT setting so as not to damage the bearings but with a welders extractor fan it still needed some stripping to be able to test.

I don't understand what you are talking about. If the CPC were not connected to the appliance (which it wouldn't/couldn't be with a Class II one), then spindles & bearings etc. are surely irrelevant.

To have to disassemble the handle on the appliance to test earth as well as the plug to check on fuse size would increase the cost of testing.

If the CPC were only there in case the cable was severed, I'm not sure that it would really need to be tested. Don't you have to check that an appropriate sized fuse (and not a nail) is present in the plug, whether there is a CPC or not?

2) Would it actually trip if cut? Consider even a slow hedge cutter maybe an inch movement and the cable core is around 1/16 inch at 375 strokes per minute that means maximum contact time of 1/100 second or 10 ms and the RCD needs 40 ms to operate. So even with an earth wire included it is unlikely to operate a RCD.

You are merely repeating the uncertainties/questions I posted earlier. I agree that an RCD might well not operate in response to a very transient fault, particularly if it occurred around the time of zero crossing of the waveform. However, having a CPC certainly increases the chances that some protective device would operate - I have certainly had an RCD (but not any OPD) operate when I've cut a cable.

3) The cable would be heavier and thicker and more prone to damage when coiled.

I think that you are 'scraping the barrel' a bit there!

So I see little point in using three core cable.

Fair enough - we'll have to disagree about that. I am personally in favour of anything which reduces, even if only a bit, the chances of injury/death resulting from what seems to be a pretty common 'incident' with electrical garden tools.

If you want to make it safer then have a 55-0-55 transformer and a 110 volt lawn mower. But unless made law can't see anyone using one.

That's just not going to happen any time soon with domestic garden tools - and would only happen at all if it became mandatory.

There were battery lawn mowers mainly cylinder type but not seen them for years.

I think that's because they were essentially useless - although they might be more viable now that there have been developments in battery technology.

Kind Regards, John

 

[JohnW2]

A friend had a small metal cased hedge trimmed that had an earth terminal next to the Live and Neutral terminals but the MI stated the appliance must not be earthed. ( refered only to the UK ... Possibly it was built for sale in many countries and in some countries earthing of the applliance was permitted or required by law.

Maybe, but I've never seen that. Indeed, the biggest problem with replacing 2-core flex with 3-core (which I don't do 'routinely'', but do do if I have some reason to replace the flex) is often in working out what to do with the end of the CPC.

Kind Regards, John

 

[EFLImpudence]

Wow.

You may have realised that Mrs.Secure is still alive.

Are the blades electrically connected to the handle of the cutter?

An RCD does not need 40ms. to operate; it must operate within 40ms.
Some do so in considerably less.
Does anyone know the minimum fault duration necessary to cause the operation - or, indeed, to avoid injury?

There is no CPC in class 2 appliance cables because it is not required.
The manufacturers must use thousands of miles of cable so are not going to use more expensive cables when not required.
Not, pedantically, cost cutting but common sense.

 

[AndyPRK]

You want petrol equipment lol !

2 stroke hedge trimmers are very pleasant to use though.

 

[ericmark]

I did a quick look. Sovereign Cordless Lawnmower £99 from Argos so it seems the answer is already there for those who want it.

Looked at Bosch and far more expensive nearly £300 but although in the past Bosch was good today their lawn mowers seem to be cheap rubbish. Qualcast coming in at £190.

However it seems hard to get replacement batteries. On a quick hunt I found one battery at £66 which means cheaper to buy a new corded lawn mower than a new battery.

I have found the same with drills you can often buy a new cordless drill for less than price of new battery. OK when using at work and one buys a good quality drill DeWalt for example but at home likely drill used once a year and first job is re-charge the battery.

 

[JohnW2]

Are the blades electrically connected to the handle of the cutter?

I'm not really sure what you mean - as I've said, apart from the blades and a few recessed screws, every other external part (including handles) of every domestic hedge trimmer I've ever seen has been plastic!

An RCD does not need 40ms. to operate; it must operate within 40ms. ... Some do so in considerably less.

Quite so. However ...

Does anyone know the minimum fault duration necessary to cause the operation ....

That's what I asked. There clearly will be a minimum and, to confuse the issue, that minimum will presumably depend upon what part of the cycle one is at when the transient fault arises. I've never come across, or heard of, an RCD tester which tests with very short duration faults - although many/most give options as to what part of the cycle the fault starts.

... - or, indeed, to avoid injury?

That's much more complicated, and will depend in part on the magnitude of the current though the individual. Contrary to what many people seem to think, limiting the duration of an electric shock to less than 40ms does not guarantee that it will not be fatal, regardless of how high a current flows through a person for that period. Also, as bernard is always pointing out, shocks which (by virtue of current and/or duration) are not large enough to be directly fatal (i.e. because of effects on the heart) can result in secondary injuries (falling off ladders etc.) which can result in serious injuries or even death.

There is no CPC in class 2 appliance cables because it is not required. The manufacturers must use thousands of miles of cable so are not going to use more expensive cables when not required. Not, pedantically, cost cutting but common sense.

Of course they won't - my point is that I'm rather surprised that it's not 'required' that they do.

Kind Regards, John

 

[EFLImpudence]

Are the blades electrically connected to the handle of the cutter?

I'm not really sure what you mean - as I've said, apart from the blades and a few recessed screws, every other external part of every domestic hedge trimmer I've ever seen has been plastic!

Well, there have been some fantastic (literally literally) suggestions to protect someone who was not hurt.

My point was that the blades are NOT connected to the handle so, other than touch the severed end of the cable, the Class 2 protection would seem to have worked.

 

[JohnW2]

I'm not really sure what you mean - as I've said, apart from the blades and a few recessed screws, every other external part of every domestic hedge trimmer I've ever seen has been plastic!

Well, there have been some fantastic (literally literally) suggestions to protect someone who was not hurt. ... My point was that the blades are NOT connected to the handle so, other than touch the severed end of the cable, the Class 2 protection would seem to have worked.

That's the point. Whilst others may have produced some 'fantastic' suggestions as regards hypothetical risks to someone holding the (nearly always plastic) handle, I certainly haven't, and I do not regard that as a significant risk at all.

My concern is about the (upstream) cut end of the cable. Human nature being what it is, a surprising number of people seem to pick it up (as I think I reported here, my neighbour did just that last year - and got a shock) - and if a protective device has not operated, they are then clearly at risk. Having an RCD and a CPC in the cable (not connected to the tool in anyway) increases the chances (but does not guarantee) that some protective device will clear the fault before anyone has a chance to get hold of the live cut end.

Kind Regards, John

 

[JohnW2]

That's what I asked. There clearly will be a minimum and, to confuse the issue, that minimum will presumably depend upon what part of the cycle one is at when the transient fault arises. I've never come across, or heard of, an RCD tester which tests with very short duration faults ...

I've just looked at my Fluke, which I imagine is fairly typical of MFTs. It clearly uses 'continupus' faults - when doing a ramp test, it starts at 30% of IΔn and increases by steps of 10% of IΔn every 300ms.

... - although many/most give options as to what part of the cycle the fault starts.

It's very limited with my meter. The fault always commences at zero-crossing (probably the 'worst case') and one has the choice between positive-to-negative and negative-to-positive zero crossing.

Kind Regards, John

 

[securespark]

Whos the poor sod in the picture with a wooden leg

It'll be me if things don't improve... I shall use the hedgetrimmer to remove the duff one and screw that one on!

 

[mfarrow]

There is no CPC in class 2 appliance cables because it is not required.

Agreed.

The manufacturers must use thousands of miles of cable so are not going to use more expensive cables when not required.
Not, pedantically, cost cutting but common sense.

Yet it would seem extraordinary to clip a length of T&E up a wall in a workshop, lest someone starts clobbering the wall with a hammer.

It does seem odd that in the interest of portability and ease of use, the protection of the live cores (through containment or whatever) seems to have been taken a lower priority. I can see mind that it would be pretty awkward to operate a hedge trimmer up a ladder with a run of quarry cable hanging on the back, and goddam dangerous too!

 

[JohnW2]

Yet it would seem extraordinary to clip a length of T&E up a wall in a workshop, lest someone starts clobbering the wall with a hammer.

You've lost me a bit there. Are you talking about a cable which served no purpose (i.e. was never connected to any load), or what?

Kind Regards, John

 

[EFLImpudence]

I didn't understand either.

Just to say both quotes were mine.