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?
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.
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:
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.
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."
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.
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.
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.
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.
