When Mrs Secure Sliced Through The Hedgetrimmer Flex...

[JohnW2]

I should look more closely next time.. I thought that flex did have an earth core!

AFAIAA, virtually all Class II garden tools (and virtually all are Class II) come with only 2 core flex. I'm personally surprised that it is even 'allowed'.

Kind Regards, John

 

[winston1]

(In the circuit were a 1362 13A fuse...

Did I miss something or was the wrong fuse fitted? Surely a hedge trimmer is less than 1000w?

So what? The fuse is to protect the cable not the device on the end of it.

 

[333rocky333]

Whos the poor sod in the picture with a wooden leg

 

[JohnW2]

(In the circuit were a 1362 13A fuse...

Did I miss something or was the wrong fuse fitted? Surely a hedge trimmer is less than 1000w?

So what? The fuse is to protect the cable not the device on the end of it.

True, but if the device is less than 1000W, it is far from beyond the realms of possibility that the cable has an insufficient CSA to be adequately protected by a 13A fuse. Manufacturers of consumer products are not particularly known for being unnecessarily generous with cable size!

Kind Regards, John

 

[ericmark]

What happens if the ground is a different voltage to your house earth? Be it lawn mower or hedge cutter long leads are the norm so the ground at the bottom of the garden could be a different voltage to the ground at your earth rod.

So only way is Class II.

 

[mfarrow]

So only way is Class II.

I think John's suggesting a three core flex for a class II appliance. Whilst this may increase the chance of an RCD trip, it is a bit Russian Roulette unless we fit a braided concentric earth or alicore style arrangement.

 

[bernardgreen]

long leads are the norm so the ground at the bottom of the garden could be a different voltage to the ground at your earth rod..

Same applies when the "earth" at the house is the incoming Neutral ( PME ) when the voltage difference could be much higher. This is probably the reason for not earthing garden tools when the possibility of a lost Neutral is taken into account. There is no problem if the "earth" inside the house goes up to 230 volts above ground but taking that "earth" to anything outside the house could be lethal to anyone in contact with the ground.

I personally feel putting the "earth" into the extension cable is safe and sensbile provided the appliance casing is not connected to it. Maybeto increase safety the appliance case could be earthed to a ground rod close to the work site, effectively the appliance becomes a TT supplied item.

 

[JohnW2]

So only way is Class II.

I think John's suggesting a three core flex for a class II appliance. Whilst this may increase the chance of an RCD trip, it is a bit Russian Roulette unless we fit a braided concentric earth or alicore style arrangement.

That is indeed what I was suggesting. As I said, all, or virtually all, garden tools etc. sold in recent decades are Class II - which (as eric says) makes total sense. However, IMO, having a CPC in the cable which is connected to the house 'earth' (but not the Class II tool) also makes total sense if (as is the case with many of these tools) severing of the cable is a real possibility. Assuming RCD protection, this considerably increases the chance of an RCD operating when the cable is cut (as secure, myself and many others have experienced, it is quite common for no OPD to operate) - if no protective device operates, that leaves a live cut end of cable lying on the ground, just waiting for someone standing on ground to touch. Even a CPC (with an an RCD) is not guaranteed to prevent that, but it would considerably reduce the chance. As I've said, given that regs have, for a long time, required RCD protection for circuits likely to be used for outdoor tools, I am more than a little surprised that 2-core cables for such tools are still 'allowed'.

Kind Regards, John

 

[JohnW2]

long leads are the norm so the ground at the bottom of the garden could be a different voltage to the ground at your earth rod..

Same applies when the "earth" at the house is the incoming Neutral ( PME ) when the voltage difference could be much higher. This is probably the reason for not earthing garden tools when the possibility of a lost Neutral is taken into account. There is no problem if the "earth" inside the house goes up to 230 volts above ground but taking that "earth" to anything outside the house could be lethal to anyone in contact with the ground.

I have not been talking about connecting garden tools to the house earth (or any other earth) - all such tools are, or should be, Class II, and therefore are not (or should not be) earthed at all. As I've just written, I'm talking about having a CPC in the cable, connected to the house earth but not the tool, to increase the chances that a protective device (probably an RCD) will operate if the cable is severed. As you say ...

I personally feel putting the "earth" into the extension cable is safe and sensbile provided the appliance casing is not connected to it.

Exactly. As I keep saying, I'm surprised that is is not actually required.

Maybeto increase safety the appliance case could be earthed to a ground rod close to the work site, effectively the appliance becomes a TT supplied item.

That would obviously be totally impractical with the sort of garden tools we are talking about. It would also be unnecessary unless you do not trust Class II equipment to do what it says on the tin.

Kind Regards, John

 

[AndyPRK]

Maybe they feel it is more likely a OPD will go when a cable is shorted/cut than an RCD.

and therefore the extra cost has little benefit.

 

[bernardgreen]

It would also be unnecessary unless you do not trust Class II equipment to do what it says on the tin.

I do NOT trust them. A bit of damp inside the casing can defeat the best of double insulation. Yes the RCD will ( should ) trip but a 20 mA "tingle" can be enough to cause a reaction that results in injury.

 

[JohnW2]

Maybe they feel it is more likely a OPD will go when a cable is shorted/cut than an RCD. and therefore the extra cost has little benefit.

Maybe they do, but we are always hearing of experiences in which what protective device (if any) operates when a cable is cut seems to be largeley a matter of pot luck. I have certainly personally experienced, or been aware of, situations in which nothing has operated, just one OPD has operated, or just an RCD has operated.

Without a CPC, there is no chance of a CPC operating at the time the cable is cut - it could only operate if a live cut end fell onto the ground (or if current flowed to ground through a person who picked up the live bare end.

Having a CPC therefore increases the chances (but does not guarantee) that at least one protective device will operate if the cable is cut. Without getting totally silly, I can think of no[/u] downsides of having a CPC - so, as you suggest, it's absence is just cost-cutting. Given how common it is for people to chop cables of garden tools, I personally do not think that cost saving is really justified.

Kind Regards, John

 

[JohnW2]

It would also be unnecessary unless you do not trust Class II equipment to do what it says on the tin.

I do NOT trust them. A bit of damp inside the casing can defeat the best of double insulation. Yes the RCD will ( should ) trip but a 20 mA "tingle" can be enough to cause a reaction that results in injury.

I'm not sure what you would propose to do about it. Trying to earth all the exposed metal parts (probably just the blade and some (recessed) screws in the case of something like a hedge trimmer) of a Class II tool would require an awful lot of 'tampering' with the tool. The warranty would almost certainly be invalidated, and one might end up actually making it less safe then it was!

Whatever, as I said, even if you found a way of connecting to all the screws etc., connecting them to a local earth rod would obviously be ridiculously inappropriate for a garden tool with a long lead!

Kind Regards, John

 

[ericmark]

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. 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.

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.

3) The cable would be heavier and thicker and more prone to damage when coiled. I have seen the kinks and cracks with caravan cables due to way wrapped up and they are got out far less than the lawn mower.

So I see little point in using three core cable. 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.

Or battery operated I use a battery operated hedge cutter but problem is batteries only last a couple of years. What is needed is a standard battery and connector so one can use same battery for multi-items. Battery is not that small it comes as a belt I would guess around 12Ah rating.

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

 

[bernardgreen]

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.