Ground on circular saw

[new299]

So I was using a circular saw today and cut through the cable (stupid me I know). I was rather happy that I didn't get a shock and assumed that the (metal) chassis grounding had saved me. However when I went to replace the plug I noticed the cable had no ground wire.

This is a Makita saw (a good brand), so I assume this is not just a bad design. But I'm confused as to why this would be the case. Do such tool incorporate other protection mechanisms? Is there a reason that grounding the chassis in this case would be more dangerous?

[Len]

Perhaps you didn't get a shock because you were holding onto the plastic handles like you're supposed to?

[Rerouter]

from the mid 80's there was a sudden shift from using mains grounded enclosures on power tools, to using double insulated practices, as if you have ever worked in a residential trade, you will soon find you only have about a 1 in 3 chance that ground on the socket is ground, (active and ground flipped, or more commonly nuetral and ground flipped, or simply not connected at the back of the plug in an old house)

It also removes the risk from the issue you came across today, if the first wire you cut through was ground, then the case your are holding would become live after the next fraction of a mm when you hit the active,

Look at just about any portable power tool built from then on, and it should not have a ground pin, if it does, you may want to question its use, and confirm the grips are insulated from that ground,

[T3sl4co1l]

Such appliances count as "double insulated".

I suppose part of the device being used in contact with an electrical circuit is an unusual failure mode.  Have no idea if there are special rules that apply to power tools or what.  This would seem to be a good reason for why "double insulated" is called what it is -- i.e., insulated on the inside for operation, insulated on the outside for safety.  Plastic circular saw blades can't really apply, though...

Tim

[IanB]

Generally speaking, if you come into contact with a live wire you won't automatically get an electric shock. This is not to underestimate the danger of electricity, but it is something to be aware of. To receive a shock your body has to be part of a return path for electric current from the live wire. If, for example, you are wearing shoes, or standing on a dry surface, and not touching grounded metal objects, then there is no path for current to flow.

This means you could sometimes find yourself in danger of electric shock without being aware of it. Don't expect dangerous wires to immediately zap you if you touch them.

[Monkeh]

There's nothing metal on a modern circular saw you should be touching^* while it's running, so there's not exactly a risk.

* My bad habit of holding open the guard notwithstanding

[Paul Moir]

That's not a bad habit, but a typical use of the tool.  Also your knuckle on the other hand is about 1/4" away from the guard at the best of times.
 

[Monkeh]

That's not a bad habit, but a typical use of the tool.  Also your knuckle on the other hand is about 1/4" away from the guard at the best of times.
 

It's a bad habit to keep holding it instead of taking a proper grip of something with that much energy behind it.

[Paul Moir]

I don't know what your talking about.  If you look at the design, they give you a handle for just such an event and it can be comfortably held while also holding the front handle. 
They ought to be grounded due to the frequency of cord cutting but they're not.

[Monkeh]

I don't know what your talking about.  If you look at the design, they give you a handle for just such an event and it can be comfortably held while also holding the front handle.

Err, not on any saw I've used, the front handle is on the other side, the main guard does not have any openings to the left at all.

[Paul Moir]

We must be talking about different things.  This is the sort I'm talking about.  In this example it's for a plunge cut:


Sort of impossible not to be contacting the guard.

[Monkeh]

Most saws I've used are very inconvenient to hold that way. Especially real size ones, not little battery toys. Many don't have a handle that long to begin with, mine included.

You don't have to hold it to plunge cut anyway..

Imagine, if you will, holding this open, and you'll see why I call it a bad habit:


As is watching the blade instead of having a fence, really, and my face will attest to that after abusing it for some plexiglass. It's like supersonic hail..

Anyway, in normal operation I'd not be in contact with any metal on this saw, and mine (same as pictured, otherwise) has the guard painted to boot.

[Paul Moir]

Yuck, what a terrible saw.  Thank God the Makitas I used were nothing like that.I guess you might be able to get a thumb on the guard lever?

My personal favorite is a Skil professional saw from back when Skil actually made professional saws.  The DeWalt one is surprisingly not bad either.  But that thing looks like it's built to cut your fingers off with.

(Never used a battery saw in my life:  left the trades before they were around.)

[Monkeh]

The saw works fine, actually. The placement of the dust port is a minor issue, and actually having it (unlike many) is a great benefit, especially with MDF and chipboard (ultra fine dust and chunks are equally annoying).

[Paul Moir]

The deck looks like a nightmare in the picture, and reaching the guard lever looks pretty awkward, but maybe it's one of those things that is better in real life.  You have to get it in your own hands and see how it fits and how the actions work for you.
The low upper guard blocks visibility but like you said chunks of mdf in your face is a pain and makes you squint anyway. 

I always wanted a saw that had a solenoid or something holding the guard open all the way when it was manually opened all the way, which would release when you released the trigger.  On good saws you can get a grip on the front handle and the lower guard lever without much trouble, but no trouble at all would be safer.  Never found one though.

[Monkeh]

Deck's fine. Nice quick depth adjustment (easy way to avoid cutting your bloody cable off, too). Bevel setting is not a quick job, though, but that's not my main use for it. The guard is indeed awkward, hence tending to just hold it once started. It's doubly awkward with extraction, but I usually rig a fence if I'm extracting, so no need to touch it anyway.

This thing has seen many sheets of ply, 2x4s, worktops, scaffold boards, and the occasional bit of lunacy like cutting plexiglass, with no injuries or cut cables. We won't talk of the flying 2x4 or the missing end of my sawhorse.

[Paul Moir]

Lol! 
My personal keeper is a HD5575, which I thought so much of I took the time to write an epinion entry for back when that was a thing.  IIRC when I got it the deWalts were new and somewhat unprofessional, with unnecessarily gigantic motors so they could proclaim !!15Amps!!!! on the box.  Makita had some quirky dovetail mechanism for adjusting depth which seemed a little delicate, but otherwise were excellent and well thought out saws.

Nowadays I'm likely to be using a circular saw to cut aluminium (and if you think MDF or plexiglass chunks are bad, you really gotta try some aluminium).  Sawdust is purely weekend fun. 

[Monkeh]

Oh, I already know what the aluminium is like.. placing your face into a wind tunnel full of pissed off wasps. One more point towards the easily attached 'dust' port!

Skil made some nice stuff before Bosch decided the brand was better off selling last-gen Dremels and cheap screwdrivers.

[Paul Moir]

Yeah, obviously you've cut aluminium by your description.  "Angry Bees" is what I thought but "pissed off wasps" might be apt as well. 
Poor Skil.  Dead name now.

[Monkeh]

Bees die. The aluminium comes back to bite you again when you go to clean it up!

Many good brands are essentially no more. AEG used to make some very nice tools, now they're just Ryobi in a different jacket.

E: And wow, we've gone off topic.. Starting to think this forum could use a spot for non-electronics tools.

[Fred27]

I was using a mitre saw to cut box section stainless steel yesterday using a multi-purpose blade. The bits bouncing back off the saw and hitting me in the neck were no fun. And the noise as the tube started resonating was incredible.

[Stonent]

You never really know how the outlets are.  The basic $5-$10 testers can't validate certain circumstances.