Extension lead for mower

[GB]

I got a new electric mower today - Bosch Rotak 430. I am puzzled, very puzzled, by the manual that comes with it, concerning extension leads. It says "your machine is double insulated and requires no earth connection". Protection class is II.

Yet, when it describes extension leads, it says "Note: If an extension lead is used it must be earthed and connected through the plug to the earth cable of your electricity supply..."

That makes no sense to me. Is it just a f*ck-up? They've copied a bit out of another manual for a machine that is earthed?

This matters a bit, because I'll need probably 40m of extension cable and the extra cost and weight of an earth wire is significant. I should be okay with 1mm2 2 core cable.

Also, they recommend that for up to 40m of cable it is okay to use 1mm2, whilst for 40-60m they recommend 1.5mm2. Is the voltage drop down an extension cable so large that it significantly affects the mower? Or is this just more elfin safety nonsense? The mower is rated at 1800w.

[ARW]

What type of plugs and sockets are you intending to use on this lead?

[The Medway Handyman]

Voltage drop over a long/to small cable is a big problem with a pressure washer that has an induction motor - it causes overheating.

Lawn mower is going to have a universal motor, not sure if the same thing applies.

[Andy Burns]

for 1800W a cable sizing calculator shows 1.5mm^2 for a run of 27m and

2.5mm^2 for a run of 41m, any longer than 66m and it'd need 4mm^2

To be fair the calculator is aimed at fixed wiring rather than an extension lead, but it's reasonable to assume you want under a 10% drop.

26m of 1mm^2 drop 9V 27m of 1.5mm^2 drops 6V 40m of 1.5mm^2 drop 9V 60m of 2.5mm^2 drops 8.5V

[GB]

Hi Adam, I take it that the wrong answer is a 3 pin trailing socket, with the join wrapped in a Tesco carrier bag, however traditional an approach that is?

The lead that came with it has a standard 3 pin plug at one end and a 2 pin female plug at the other. My preferred solution will be to find a replacement 2 pin plug and make up a cable that is long enough without a join in it. I'm struggling to find the right sort of plug sold separately.

[polygonum]

Almost all electrical appliances should be fitted with a plug, and that would almost invariably be a standard 13 amp one. So that has to plug into a 13 amp socket. Any extension lead with a 13 amp trailing socket would have to be earthed because there no way of preventing its use with equipment that requires an earth.

As I see it, if you change the supplied plug for a two-pin design, and plug that into a two-core extension lead, you should be fine.

[GB]

The lead it came with looks identical to this:

[John Rumm]

Some "quiet" mowers have induction motors these days (which have the ideal torque curve for mowing grass when you think about it)

[Roger Mills]

I think this is the correct plug:

If you Google for orange 2-core cable, you'll get lots of hits, but you may struggle to find any that's more than 1.0mm^2. The RS site has a

2.5mm^2 version, but it's shown as discontinued.

You'll get 2.5mm^2 in 3-core easily enough - but that's not really what you want. It does need to be suitable for outdoor use, which usually means that it will be orange.

As an alternative, if you don't mind an intermediate connector and don't mind the first part being 3-core, you could consider buying a long hook-up cable as used by caravanners, like this:

Then simply swap the blue male plug with the 13A plug on your existing cable, and connect the cables end to end.

[John Rumm]

Lets say its 1800W, and a universal motor. So current = 1800/230 = 7.8A

1mm^2 flex has approx 18.1 mOhms/metre resistance. Voltage drop therefore = 7.8^2 x 40 x 0.018 = ~44V

So pretty excessive even at 40m...

[Capitol]

Try again time!! Hint IR!

[Tim Streater]

I make it about 5.6V. About 44W is dissipated in the cable.

[ARW]

Well it looks like Roger has found part you need. I was going to suggest

as it could be used for more than one use!

As far as I can tell the manufacturer is probably worried about people making up their own 3 pin extension leads using two core flex -something that could be unsafe if it was used with another appliance.

Of course it goes without saying that the mower lead needs RCD protection.

If you are wanting waterproof connections as an option to no connections then 2 pin plugs and sockets are available - they are similar to the flymo connectors but do not have the cover on the socket.

Cheers

[Sam Plusnet]

Especially when someone has a very long cable & uses it whilst keeping most of it coiled up.

[John Rumm]

Doh, yup make that 44W dissipated ;-)

I thought that sounded like an awful lot of volts!

[F Murtz]

Maybe it is so when you cut it in half with the mower it will trip the safety switch?

[Andy Burns]

When you hack through the lead with the mower, if the current from the live wire goes /anywhere/ other than back via the neutral wire, the RCD will trip. That is to say, that though you or through wet grass to the actual earth is as "good" as returning via an earth wire, unless you don't have an RCD/RCBO, but there's not much excuse not to ...

[Brian Gaff]

Well, some time ago I had to take apart an old eclectic mowere, it had three core cable attached, though the earth appeared not to be used at all. In a strimmer it had 2 core. I guess from the extension lead point of view it depends on how the protection works at the plug end what you use.

The weird thing is that I've also seen 2 and three core versions of those connection extenders that have a quick release as well.

As for drop, yes you get one heck of a drop when you start the motor up I found. If you don't believe it, wire a light bulb across the mower end. Brian Brian

[Brian Gaff]

When I was losing my sight I used white cable, which seemed to survive OK outside. I understand it can be a problem in sun, but then I was never out in the sun long enough. It was very hardy to mechanical damage, an much less a problem with tangling than the orange stuff which seemed to be far more stiff. Brian

[Nick]

I would use an extension cable. In the past I've had problems with very long leads getting twisted and consequently tangled. Probably due to the way I coil them up when I pack them.

I have wondered if I alternately use left or right hands when coiling I might avoid the twist but have never managed it in practice.