Is running over your extension cable with an electric lawn mower dangerous?

Question

I'm currently about to buy a lawn mower, but don't know if I should take a fuel, electric with cable or battery one.

I'm leaning more towards electric with cable, because it's cheaper than battery and the price and the raising price of fuel won't screw me over in a few years.

But the only thing I'm wondering is what would be to happen if I run over my extension cord?

Will I just ruin an extention cord, or are there some serious health dangers to do so?

CactusCake · Accepted Answer · 2018-06-18T17:49:04.420

27

Minimal protection when using a corded electric lawnmower is to power it from a GFCI protected outlet/circuit. If your outdoor outlets do not have GFCI built in, or if you are running your extension from a regular indoor outlet, you can purchase standalone GFCI devices to go between the extension cord and the power source.

To answer your question directly - the lawnmower itself should be double-insulated, meaning the handle bar should be electrically insulated from the mower blade and the motor components. But if you run over the cord you still have the problem of severed cable ends supplying full mains voltage to whatever they touch, which is why using a GFCI is so important.

edited Jun 18 '18 at 17:49

answered Jun 18 '18 at 17:43

CactusCake

1,072
1
7
17

5

'Double-insulated' means that the entire user-accessible metal chassis is electrically double-insulated from the power supply and the live circuitry. Unless there is a special meaning for electric lawn mowers, I don't believe it inclues the blade. – user207421 Jun 18 '18 at 23:56
2

@EJP IME all electric mowers have plastic handles. The definition doesn’t change for them, but they normally are isolated as described here. – Tim Jun 19 '18 at 00:46
The severed cable would be touching ground. haha – Aequitas Jun 19 '18 at 06:02
1

Quite a few hover type mowers have plastic blades, which find it difficult to cut through mains cables in the first place. – Tim Jun 19 '18 at 06:57
@Aequitas - the severed cable may well not touch ground well enough to ground the current and trip the RCD. No laughing matter! – Tim Jun 19 '18 at 06:58
I've seen a number of similar electric devices which have a GFCI built into their own cord, although obviously that would only protect from that point onward and so could still present a hazard if additional extensions are required to cover the entire lawn. – Perkins Jun 19 '18 at 23:11
@tim - I've not seen plastic blades before, but ones with metal blades often have them attached to the motor via a plastic spindle, presumably so that even if the blade becomes live the current can't transfer beyond that. – Jules Jun 20 '18 at 07:25
I suspect also the other way round, so the blade doesn't become live if there is a fault in the motor. – Peter Green Dec 15 '23 at 19:52

R.. GitHub STOP HELPING ICE · Answer 2 · 2018-06-18T20:16:18.620

23

Yes, but the better question is "how dangerous?", and the answer is "not very".

Assuming your outdoor outlets are up to modern code, they're protected by GFCI and will trip even without a high-current short to neutral or ground. If you don't have GFCI outlets, you could upgrade them or just use an extension cord with GFCI protection. But even without GFCI, at the moment the blade cuts the extension cord, you can expect a high-current short that would trip the breaker, and any modern electric mower is going to have the blades electrically isolated from the handle and any part of the chassis you could touch externally.

Sparks at the moment of the short do pose some nonzero risk of fire if you're cutting in dry conditions. Depending on where you live this may be a concern. A GFCI outlet should partly (but not fully) reduce the risk.

Of course after the cord is cut and the mower stops, there is a slim possibility that the cut happened without producing a short that could trip the breaker (or GFCI) in which case the wire lying on the ground could be live and dangerous. This can be managed by unplugging the cable from the outlet before attempting to retrieve it.

Gas and battery operated mowers also have their own risks which should be weighed against those of corded mowers:

Puncture of fuel tank or battery may cause fire.
Corded mowers have a 100% fail-safe mode where they cannot start: unplugged. A unit with a battery-operated motor or gas and battery starter always potentially has malfunctions where it could start unexpectedly (unless you go to excessive lengths to remove parts in the field).

FWIW I highly recommend a cabled electric mower if the area you need to mow is amenable to one (not too far from outlets, few obstacles to work the cord around). The weight difference from an internal combustion engine and fuel, or from a battery, is extreme, and you will notice the difference in effort expended to use it.

edited Jun 18 '18 at 20:16

answered Jun 18 '18 at 19:32

R.. GitHub STOP HELPING ICE

1,081
2
11
23

2

I would consider "uplugged" and "without batteries" equivalent in terms of safety - neither of those is resolve without explicit action. That said, removing the spark plug from gas motors is also common, so I feel that's a bit of a wash overall. – GManNickG Jun 18 '18 at 19:50
"there is a slim possibility that the cut happened without producing a short that could trip the breaker (or GFCI) in which case the wire lying on the ground could be live and dangerous." Definitely happens, see my answer. +1 for unplugging immediately. – tilde Jun 18 '18 at 20:05
1

@GManNickG: OK, of course there's battery (or spark plug) removal but it's generally not something you do in the yard when you stop because the blades have something stuck in them. OTOH unplugging the short mower cord from the extension cord just takes a second and is easy to do. – R.. GitHub STOP HELPING ICE Jun 18 '18 at 20:05
6

(Just wait til the next generation of electric mowers with batteries is "IoT enabled" and has start/stop via UI on phone... ;-) – R.. GitHub STOP HELPING ICE Jun 18 '18 at 20:08
2

@R.. it's coming... – CactusCake Jun 18 '18 at 20:18
3
Self-driving mower runs over something and blades get jammed. 2. You stop it, flip it over, and start to clear out the jam. 3. Skript kiddie who rooted your mower already sends the "start motor" command...

R.. GitHub STOP HELPING ICE

Jun 18 '18 at 20:23

1

@R.. When I flip my electric mower (something I do regularly) I always take the battery out. It's not just safer, it's also easier to turn over that way. There's also a key. I'm not seeing any reason why we should think that unplugging the cable is more likely to happen. – JimmyJames Jun 19 '18 at 15:00

1

@JimmyJames: It's much easier/quicker than removing a battery, and unlike a key the mechanism is visually verifiable. – R.. GitHub STOP HELPING ICE Jun 19 '18 at 15:54

3

Counter point: I've used a gas powered mower for 30+ years and never had one "just start". Usually, it's a fair bit of an argument with the pull cord to get the thing to fire up. I'm not saying that it couldn't happen, but I would consider it extremely unlikely. The amount of effort needed to start a gas-powered mower makes it nearly fail-safe - your 4 year old won't be able to get it started, but he could probably plug in a corded electric and fire it up. – FreeMan Jun 19 '18 at 16:01

@R.. I don't know what you are talking about. The key on mine comes out. You put in in your pocket. It's blaze orange, quite visually verifiable. It takes literally a second to pull the batter. – JimmyJames Jun 19 '18 at 16:01

2

@FreeMan I recall my parent's mower restarting itself regularly when I was a kid. Also gasoline is toxic, carcinogenic, explosive, and there are no pollution controls on mowers so you are flooding the area with toxic fumes. – JimmyJames Jun 19 '18 at 16:04

@JimmyJames: What's not visually verifiable is that there is no way it could start without the key being present. That requires trust or significant work auditing the design. On the other hand with a corded electric, you know, absolutely that unless the manufacturer hid an expensive secret battery or giant capacitor inside the unit, there is physically no way it can start spinning with sufficient force to cause serious injury as long as the cord is unplugged. That's what I mean by "visually verifiable". – R.. GitHub STOP HELPING ICE Jun 19 '18 at 16:23

@R.. The key on the model I have is simply two connectors wired together in a plastic shell. Remove it and you have an open circuit. You can charge the battery through the key slot. Being paranoid I remove the battery which is actually easier than removing a cord from the extension, in my experience. No battery, no spinning blades. You also get the benefit of a DC motor but that's a side issue. – JimmyJames Jun 19 '18 at 16:40

"there is a slim possibility that the cut happened without producing a short that could trip the breaker" Hardly slim. If the cord is lying on the ground, then the blades are travelling parallel to the cord, and the insulation is probably stronger than the actual wire. Result: rather than cutting the cord, the blades just strip off the insulation. – Acccumulation Jun 19 '18 at 18:24

"The weight difference from an internal combustion engine and fuel, or from a battery, is extreme, and you will notice the difference in effort expended to use it." -- the other difference between corded and battery mowers is that the motor in battery mowers is severely underpowered. A typical corded mower has a motor power somewhere between 1 and 2 KW. Battery mowers don't usually list power in their specs, but typically have 36V 3Ah batteries -- if the motor power was 1KW the battery would be drained in about 10 minutes, so they're usually lower power (~250W for 40 mins use, I think). – Jules Jun 20 '18 at 07:40

@JimmyJames - flooding with fumes is a little over the top. Compare time spent mowing with time spent even in a traffic jam! And on my mains electric mowers, I have a plug/socket on or near the machine, so unplugging is two seconds, without having to go back to the socket. – Tim Jun 20 '18 at 07:54

1

@Tim In industrialized nations, cars have pollution controls. Mowers do not. I've read some estimates that the amount of pollution produced by mowing an average sized lawn is like driving 300 miles. – JimmyJames Jun 20 '18 at 13:32

Not very, but perhaps with very sever consequences. I'd rather run over my piled up garden hose than mess with 120 AC. What if a wheel hits a rut. Do you want cause of death on your tombstone? People will laugh. It's like leaning over a table saw blade, or running a corn grinder while wearing a tie. Consequences vs probability. Always make the calculation! – Wayfaring Stranger Jun 27 '18 at 22:42

@WayfaringStranger: "Not very" does not mean just "very unlikely". Did you even read the answer? – R.. GitHub STOP HELPING ICE Jun 27 '18 at 23:42

tilde · Answer 3 · 2018-06-19T21:30:49.483

9

Electric with cable, hands down. They are cheaper than battery powered, and all electric mowers will be much quieter than gas powered mowers. The only consideration is if your yard is too large for a cord to reach the far corners.

The best advice I can give you with regards to the cord is to not run over it. Yes, you might not cut the cord, yes, you might be fine, yes, GFCI might help, yes, the breaker might trip. But pay attention and be mindful of the cord at all times. It is a hassle at first, but I quickly got the hang of "throwing" the cord, swinging it from side to side to move it out of the way.

I have personal experience with running over the cord. The outlet was not GFCI, which was not ideal. Some answers and comments are saying the breaker will provide protection. I don't think this is the case. Someone else was mowing, and ran over the cord, not cutting through, but stripping a good amount of insulation and exposing copper. When I saw it, I assumed it had been unplugged, and (stupidly) touched the bare copper. I got a strong tingle, and fortunately I released the cord before any permanent damage was done. It felt a bit like brief contact with an electric cattle fence (story for another time). The breaker did not trip. I didn't do a full post-mortem, but my guess is only the hot wire was cut, so there was no short. Then, when I touched it, a circuit was completed between my body and the ground (via moisture on my shoes, maybe? not sure).

EDIT: In response to comments, I remembered, I was also using one of those converters to plug a grounded cord in to a non-grounded outlet. Which means that I had even less protection than I should have. I think the moral of my story is "Follow the electrical code, it might save your life."

edited Jun 19 '18 at 21:30

answered Jun 18 '18 at 20:01

tilde

230
1
6

Ideally, the mower should use a grounded plug and the blades should be tied to ground so that cutting/stripping just the hot wire forces the breaker to trip, but maybe there's some reason this isn't done. My model has a polarized, but not grounded plug; in that case maybe the risk that the outlet was wired backwards is too great? – R.. GitHub STOP HELPING ICE Jun 18 '18 at 20:13
1

Yes, electric is much quieter than gas, but they still have "propeller noise". Mine is just on the threshold of annoyance, so still I use earmuffs anyway. – AaronD Jun 18 '18 at 21:31
1

The reason they're called hot is because once it's live, you'll feel it if you touch it, (that's VERY dangerous, please avoid doing so). It's worse when you're holding a neutral or ground wire while touching the hot. It is HOT, avoid touching HOT wires, (or any of them really). Is this exposed wire dangerous? That link shows that they're inside a building, so limited ground, answers are still talking about the danger of being shocked. – Blerg Jun 19 '18 at 04:59
Don't test wires with hands people... Thats like checking if a surface is hard by banging your face against it. A wire with exposed copper should be scrapped, no matter whether it still works or not, and you should not invite mayhem by testing it with your hand, standing in wet grass. I am sorry to be blunt, but mains voltage through the hand to the ground can kill you. What a stupid way to die that would have been. – Stian Jun 19 '18 at 06:56
3

the circuit does not really need to be completed -- your body is slightly capacitive, so you will still get a bit of current flowing from any voltage... especially AC – Florian Castellane Jun 19 '18 at 09:10

score 4 · Answer 4 · answered Jun 19 '18 at 04:51

I use an electric mower with a power cable and have three yards that need mowing. I don't have a problem but have become skilled at cable management. Its important to know where your cable is and flick it away to the mowed area when you need to get past it.

In order to mow as hassle free as possible I always begin from as close to the socket as possible and then mow in straight lines to gradually radiate further away. This way I naturally drag the cable out. I use a 50 metre power cable.

I've never "mowed" the cable but I do have an electric hedge trimmer and I've cut through one with that. My house safety switch immediately turned all the power off. It'd be just like if you blew a fuse. So it was safe but cutting through long power cables is expensive.

score 3 · Answer 5 · answered Jun 19 '18 at 19:50

I have an electric hover mower, and a couple of years ago, I mowed over the electric cable.

It went bang. The blades stopped turning (very quickly 1 or 2 seconds). No sparks or anything untoward.

Within 30 minutes I was back mowing again, after using a screwdriver and some scissors (to cut off the shorter end of the cable).

My daughter did the same thing the previous summer (which I reckon she did deliberately, to get out of mowing duty).

Neither of us were electrocuted, or in any way in danger.

I live in the UK, and have a modern (<20 year old) house. We have circuit breakers on all circuits.

<20 years old in the UK should mean you have RCD on all circuits as well. (For readers in North America an RCD is a bit like GFCI, but it's attached at the fuse box to the whole circuit, rather than at an outlet to part of the circuit). — AndyT, Jun 20 '18 at 11:24

score 1 · Answer 6 · answered Jun 18 '18 at 17:36

1

Yes, it's dangerous. If the extension cord were to be cut and the grass is wet, it could complete a circuit and blow a fuse, or worse, start a fire.

The solution is to make sure not to run over the cord with the lawnmower. The cords are light enough that you should be able to "throw" it out of the way while you're mowing.

answered Jun 18 '18 at 17:36

MattB

111
3

2

Of course you can try starting closest to your outlet, and move out from there to avoid it – Jeff Jun 18 '18 at 17:38
3

Tripping a breaker or blowing a fuse is not generally dangerous, and fire is extremely unlikely, especially in the case of wet grass. – isherwood Jun 18 '18 at 18:03
2

The un-probable is still possible ! Running over the cord and severing it COULD result in electrocution. Electrocution CAN result in DEATH. – Alaska Man Jun 18 '18 at 18:09
4

"electrocution" is the very definition of death by electric shock. – Norm Jun 18 '18 at 19:18
The fuse won't always blow. See my answer. – tilde Jun 18 '18 at 20:03
@isherwood: that's assuming fuses and breakers always work 100% reliably and never, ever fail. They sometimes do. – whatsisname Jun 18 '18 at 20:03
Electrocution means death (Electric-Execution). Shocked is electrocution without death, if I can remember right. – Fredy31 Jun 18 '18 at 20:29
Thread on English.SE https://english.stackexchange.com/questions/73880/if-someone-is-electrocuted-do-they-have-to-die-or-can-they-just-be-injured – Fredy31 Jun 18 '18 at 20:31
1

Wet grass won't burn -- there isn't enough energy involved. The risk is dry grass, where even a brief spark can ignite things. – Mark Jun 18 '18 at 21:12
2

The seems alarmist since a GFCI solves the problem nicely. – Harper - Reinstate Monica Jun 18 '18 at 21:13
@Mark - unless you're basically cutting hay, your grass won't be dry enough for that to happen. Grass only gets that dry when it's dead. – Jules Jun 20 '18 at 07:48

score 1 · Answer 7 · edited Jun 27 '18 at 22:38

First Of All: DO NOT run over any extension cord with any mower. Period.

The suction effect that grabs the grass and throws it in the basket is not strong enough to lift an cable, but if there is a loop on the cord it can reach to the blade.

There are several options how the cable is cut.

It is cut in two pieces. usually the blade cross-cuts the circuit and brakers should open the circuit. Limitted hazzard.
Several wires are cut. If the blade cross-cut the circuit, breakers should open and story ends. If the hot wire is damaged, the current misballance shall trigger the protection to open. If it is neutral wire, the mower just stops. Limitted hazzard.
Insulation is cut off without a blade touching the wire(s). No electrical protection is capable of catching this sort of damage. When the hot wire is exposed this way it is still hot with no insulation. You will feel "your" mains on accidentally touching the wire. Serious hazard!

Summarising the answer. Do not think how hazardous it is to cut the wire. Avoid it at the first place.

Its not like my plan for a nice saturday morning was to go and purposefully run over my cable lol :p — Fredy31, Jun 20 '18 at 13:07

Is running over your extension cable with an electric lawn mower dangerous?

7 Answers7