RCD consumer unit and lawnmowers

[JohnW2]

Yes, I realise that - but it's a fairly unlikely scenario (for a start, only relevant if the OPD does not operate when the cable is severed)

Actually very possible, quite a few I have repaired in the past have still had the fuses in the plugtops still intact.

Perhaps I wasn't clear, but I wasn't meaning to necesarily imply that failure of operation of an OPD was unlikely (it's obviously largely down to chance) - although I have to say that in the few cases I've encountered (of my own doing or others!), some OPD (plug fuse and/or fuse/MCB in CU) has operated. The main reason I think that the scenario you described (getting a shock from severed cable end) is pretty unlikely is that, despite all that gets said about him, the average Joe Public has more sense than to touch the exposed end of a cable (s)he's just cut!

Measures which stop people from running over the lead in the first instance are the primary measure such as it contrasting from the grass (bright orange cable), working methods etc. The RCD is there purely as a backup should something happen as I described above.

I don't disagree with that, but regulations could have made it much less likely that someone would suffer a shock (which might be fatal, even with an RCD) in the scenario you describe - simply by 'banning' 2-core cable on the sort of outdoor tools we're talking about (I see no advantage in 2-core other than cost). FWIW, I think that safety-orientated regulations ought, wherever possible (and in this case it is possible) to reduce the risk of people suffering shocks, rather than reduce (but not to zero) the risk of their dying if they do suffer a shock. Is that silly?

Kind Regards, John

 

[JohnW2]

Double insulating would mean no risk of shock if touching a the tool itself?

That's correct - unless, of course, the double insulation were to 'fail' in some way (e..g. if the whole tool somehow got 'smashed open').

Or it got very wet and the double insulation was by passed by moisture. In most cases the wet grass and ground would be likely to sink enough current to ground to trip the RCD, but not if the soaking wet mower was moved onto dry concrete, decking or the shed floor.

True, but I guess that's one mode of 'failure of the double insulation'.

Kind Regards, John

 

[bernardgreen]

Severing a lawn mower cable is not as dangerous as severing a hedge cutter cable where the shredded cable can remain jammed in the teeth of the cutter. This can leave the whole tool casing live when it is a non earthed double insulated tool.

Electrics and garden tools in the absence of common sense are a hazard.

 

[JohnW2]

Severing a lawn mower cable is not as dangerous as severing a hedge cutter cable where the shredded cable can remain jammed in the teeth of the cutter.

Not when I did it - but I'm sure you're correct in saying that can happen.

This can leave the whole tool casing live when it is a non earthed double insulated tool.

I presume you mean the 'cutter' - the casing will surely virtually always be plastic?

Electrics and garden tools in the absence of common sense are a hazard.

Indeed, and even with common sense they need to be treated with respect and caution! I still think it's pretty bananas that they are allowed to have 2-core cables - whilst a 3-core cable (+RCD) is not a panacea, I wouldn't mind betting that it would, for example, result in the RCD operating in the vast majority of cases of your 'shredded cable jammed in teeth of hedge cutter' scenario.

Kind Regards, John

 

[Speedy471]

OP - although all the above is good advice please, before you make any further decisions, confirm that the RCD at the consumer unit, covering that circuit, is of a 30mA or 0.03A rating.

There are plenty of installations out there still protected by a 100mA or higher RCD, regardless of incoming earthing system.

Just checked both RCDs on the consumer unit are 30mA

 

[Speedy471]

From reading all these replies, and how strict electric regulations are, I can't believe only 2 cores are used in double insulated garden tools. Surely most accidents involve severed flex rather than a faulty tool?

 

[JohnW2]

From reading all these replies, and how strict electric regulations are, I can't believe only 2 cores are used in double insulated garden tools. Surely most accidents involve severed flex rather than a faulty tool?

As you will realise, in terms of 'electrical' accidents, that would certainly be my view. You say that electric regulations are strict, which in some cases is true - but not this one!

Of course, in terms of accidents with electric garden tools in general, most are due to to mechanical trauma, not electricity (just as are those accidents due to petrol-powered tools and hand tools).

Kind Regards, John.

 

[Scoby_Beasley]

I just find it mildly amusing that some folks can plug in a bright orange cable, then proceed to attack it with the appliance attached at the other end!!

Having said that, I also find it mildly amusing that I can blow holes in my VDE pliers/cutters when chopping through "apparently" dead cables!!

 

[JohnW2]

I just find it mildly amusing that some folks can plug in a bright orange cable, then proceed to attack it with the appliance attached at the other end!!

Agreed, but I can tell you from personal experience that it's surprisingly easily done

Kind Regards, John

 

[Monkeh]

From reading all these replies, and how strict electric regulations are, I can't believe only 2 cores are used in double insulated garden tools. Surely most accidents involve severed flex rather than a faulty tool?

As you will realise, in terms of 'electrical' accidents, that would certainly be my view. You say that electric regulations are strict, which in some cases is true - but not this one!

Regulations are strict where they make money. Adding an entire copper conductor to a cable costs money, it does not make it.

 

[JohnW2]

Regulations are strict where they make money. Adding an entire copper conductor to a cable costs money, it does not make it.

Hmmm. I'm not sure that I completely follow that first sentence - but, in any event, and particularly where matters of safety are involved, regulators are meant to be divorced from any interests in money-making. I know that they sometimes aren't (we've seen that, sometimes with tragic consequences, with aviation regulators), but that's how it should be.

It just seems to me that requiring RCD protection for outdoor electical equipment (which the regs have tried to require for quite some time) without also requiring a CPC to be present in the cable is a half-solution, verging on the irresponsible.

Kind Regards, John

 

[ban-all-sheds]

Of course, in terms of accidents with electric garden tools in general, most are due to to mechanical trauma, not electricity (just as are those accidents due to petrol-powered tools and hand tools).

Someone I know once won a helicopter ride as a result of trauma involving a petrol driven chainsaw.

 

[dhutch]

Or it got very wet and the double insulation was by passed by moisture. In most cases the wet grass and ground would be likely to sink enough current to ground to trip the RCD, but not if the soaking wet mower was moved onto dry concrete, decking or the shed floor.

Doubt it.

Ive dropped a RDC protection drill into the canal from the boat, boats earthed, drill and extension lead earthed, drill carried on running, with the power remaining on. 30mA trip.


Daniel

 

[bernardgreen]

Possibly the length of the current path through water to ground was long enough that the impedance to earth leakage through water was too high for the leakage to reach 30 mA.

To get a 30 mA leakage ( at 230 volt potential difference ) would require an impedance less than 7000 ohms.

The effective voltage difference between the water in the drill and ground would be half the mains supply so the impedance from drill to ground would need to be less than 3500 ohms for the RCD to trip.

 

[dhutch]

Possibly the length of the current path through water to ground was long enough that the impedance to earth leakage through water was too high for the leakage to reach 30 mA.

Presumably so, although as said, there was earth in the extension lead. So effectively, ignoring the fact this was in a canal hanging alongside at steel boat, we're talking about dunking a 13amp plug/socket into the water.

I made up a 'test plug' linking earth and neutral, plug it into the same, still damp, lead and plugged this back into the power, and it tripped. Repeated with the link going earth to live, and trip again. Not a full RCD test, but it proves it will trip with a dead short.

Daniel