RCD - How safe?

[Moneybox]

Today I was playing safe, well sort of. I had my safety boots, gloves, goggles and of course a hat. I had to cut the thin end off the concrete slab so I was using a segmented diamond blade on the trusty XU1 240v grinder. Then I ran a trickle of water to look after my blade

About half way across the cut I got a good enough electric shock to have me throw the grinder as far as the lead would reach. I had the trigger locked so it continued to spin until I retrieved it. If I'd been standing on my boots perhaps I wouldn't have felt too much but I was kneeling on my bare knee on the wet concrete and I was holding the grinder through gloves but most likely touching the aluminium gear housing on the front of the grinder.

Anyway I finished the cut by making sure I was not grounded and only holding the plastic housing. I've checked the power box and we have RCDs on everything, four of them so I would have expected the switch to throw. As it happened there was no interruption to the power supply at all. It doesn't make me feel confident that these things would prevent electrocution :argh:

 

[Nightjar]

Moneybox,
First of all I'm not an electrician.
You have a serious wiring problem, and it is most likely your home earthing system. ie: House wiring usually has a copper rod driven into the ground and your earth wires are connected to this.
If your house is old, the earthing was some times connected to the water pipes that were either copper or steel. If the piping has been upgraded, PVC piping is used and the earthing will no longer exist. A RCD will NOT work in these circumstances.
**** Don't waste a minute tomorrow, get licensed electrician to check it out***

 

[Ridge Runner]

Yep RCD's only work if the wiring is correct,

I have them here too they have been in use here for well over 3 years,

I have them in the fuse box Plus my Leads have them on the plug that goes in to the wall outlet and they have another in the centre of of the Extension Lead Reel.

 

[19.3]

Yep - and get the electrician to check out grinder at the same time - and leave it unplugged until it has been checked- just cause the grinder works does not mean it is safe!

 

[Ridge Runner]

This is a problem with Aussie Plugs, Over here all plugs a fuse in them to help protect against this sort of thing ranging from 1A 3A 5A 7A 10A and 13A depending what the wattage if the tool/Item Is.

 

[mbasko]

They should have a test button to manually check they at least trip.
An electrician will also be able to time test them to make sure they are within spec.
Workplace RCD's are supposed to be checked periodically but I'd reckon most of us never check any household ones even by the trip check button.
Faults are usually wiring related but they can also fail.
Should trip in a fraction of a second so something is definately amiss.

RR fuses are only meant to protect equipment not people. 30mA can cause cardiac arrest so safety circuits like RCD's are the only real way of protecting people.

MB hopefully you've sought medical attention? Any electric shock like that should be taken seriously as :heart: fibrillation can still occur hours afterwards.

 

[Simmo]

Hey Phil,
I found this..
Might help explain things for ya!

https://www.explainthatstuff.com/howrcdswork.html

 

[Ridge Runner]

RR fuses are only meant to protect equipment not people. 30mA can cause cardiac arrest so safety circuits like RCD's are the only real way of protecting people.

Yeah the UK system has a ring main, It's also impossible to insert anything in to the plug socket because the holes that carry the power have Gates on them and the long socket at the top has a lever in it where the Earth Pin goes in and pushes the lever down which then opens the Two Gates in the other holes/sockets

Quote

The reason plugs in the UK are so big is that each one must be individually fused. And the reason for that is something called a "ring circuit".

In a ring circuit you have, say, a 40 amp fuse at the mains/box. From this you send out two wires, each rated only for 20 amps, going in a circle around the house. You can now supply 40 amps worth of power using only cheaper 20 amp wires. (Since the current can flow over both wires at once.)

But this means that the wires going to an individual appliance are far too small for the main breaker, so each appliance gets a fuse in the plug. Ring circuits have serious drawbacks, but they helped during a time when there was a copper shortage. And ever since then the UK has been stuck with huge plugs.

There's also a second reason British plugs are robust and fused: they're built to carry up to 3 kilowatts at 230 volts. (None of your wimpish American 110 volt mains juice here! Nothing quite makes your hair stand on end like accidentally touching a live pin carrying 230 volts and 13 amps ...)
To that end, the live and neutral contacts in a British socket are shuttered. The long earth pin on the plug makes contact before the live or neutral pins are in the socket, and once in contact, raises a shutter to permit live and neutral to make contact. And the nether regions of those pins are insulated so that if a plug is halfway into a socket and something bridges the pins, it can't make contact.

This is a great design -- for space heaters and ovens and server racks. It's a bit less useful for the low power consumption devices that have come to dominate the market (where maximum draw is well under 1Kw -- often under 0.1Kw).

 

[Rockhunter62]

Step 1, thank your god that you didn't get killed from the shock,
Step 2, smack yourself in the head for doing something like that, :N:
Step 3, as the others said, get the electrician in to look at the electrical system in the house. :Y:
Step 4, just use your hammer and cold chisel. ower:

Cheers

Doug

 

[mudgee hunter]

True, if an RCD is working correctly, you shouldn't even feel a ZAP.
And yes they can crap themselves, so yes press the test button and it should shut off.
Houses over the last 20 years have had them wired in different ways.
Original way was too fit only one.
But this would shut down everything if tripped.
So today most common practice is to fit one to every circuit.
There was an exemption of the fridge power point not to be protected as the defrosting often tripped them.
But they are meant to labelled saying such.
If your grinder has only 2 pins (active and a neutral), typical set up. And you had no decent contact with earth ... that might actually slip past the RCD!?
I do recall a big debate with workcover years ago about petrol generators needing an earth stake for the RCD to work 100% correctly.
As I think it was the minimum depth Australian safety standard of 900m (?) Depth needed. Good luck pulling that stake back out.
Most of the diamond blades are wet or dry cut these days.
Perhaps be safer to do dry cuts and use a drum vac to suck the dust up!
Check the grinder instructions, I'm sure they say don't take it in the shower with you!!! :lol:

 

[Ridge Runner]

Over here it is illegal to use 240v power tools on any building site or public Area without having RCDs on the extension leads at one end or the other,

All Power tools used in any Trade have to be either Cordless or 110v using a step down Transformer from 240 down to 110v, and they weigh a ton, This one weighs about 40+ Kgs,

 

[Tathradj]

My trade leads have RCD's fitted on the GPO end.

And I have them checked once yearly.

Just not worth it.

 

[Moneybox]

Ok I check it out. Obviously I shouldn't have been using water with the 240v grinder. The electric shock was a bit a surprise but I've had worse from automotive circuits so I'm not worried about permanent damage to my circuitry :8

The RCD definitely should have tripped and I don't think pressing it's test button is going to prove anything but I'll give it a go when I'm sure Mrs M isn't halfway through a cricket match or something more important

Firstly I'll take a look at the earth rod to see that it's still in place and connected although the ground here is so dry that it might have trouble getting a good earth anyway. All should be in order because we had the place electrically checked out before we bought it just a year ago. Not that I trust these tradesmen but sometimes you stumble across a good one :|

Getting an electrician is in a reasonable time frame is not an option out here.

 

[Moneybox]

True, if an RCD is working correctly, you shouldn't even feel a ZAP.
And yes they can crap themselves, so yes press the test button and it should shut off.
Houses over the last 20 years have had them wired in different ways.
Original way was too fit only one.
But this would shut down everything if tripped.
So today most common practice is to fit one to every circuit.
There was an exemption of the fridge power point not to be protected as the defrosting often tripped them.
But they are meant to labelled saying such.
If your grinder has only 2 pins (active and a neutral), typical set up. And you had no decent contact with earth ... that might actually slip past the RCD!?
I do recall a big debate with workcover years ago about petrol generators needing an earth stake for the RCD to work 100% correctly.
As I think it was the minimum depth Australian safety standard of 900m (?) Depth needed. Good luck pulling that stake back out.
Most of the diamond blades are wet or dry cut these days.
Perhaps be safer to do dry cuts and use a drum vac to suck the dust up!
Check the grinder instructions, I'm sure they say don't take it in the shower with you!!! :lol:

That's interesting. Surely no earth wire on the appliance can't bypass the RCD? Most modern electrical things come without and earth pin on the plug.

But I had good contact with the earth. I had my bare knee resting on wet concrete

 

[Tathradj]

I hate double insulated for a good reason.

If there is an issue with the neutral circuits,
there is no reference to earth.

 

[Moneybox]

I hate double insulated for a good reason.

If there is an issue with the neutral circuits,
there is no reference to earth.

Tathradj, are you saying that is the case. You can actually bypass the RCD?

 

[Tathradj]

Yes and no MB.
I am not an electrician but know how
it all works and have a healthy respect
for 240v ac.
Yep, It freaking hurts as I have had a
few hard whacks from it.

The earth reference is in double insulated
stuff these days. I got a boot of TV once. Metering
it out I had 50 milliamps of 240 on the antenna plug
outer.

I was working on a repeater site and had a test set running
to take a few measurements.

Grabbed a co ax plug, Came too sitting up against the wall after
being thrown across the hut.

I still have a few scares on my fingers from that one. Some prick had stolen the brophey

connectors that tied every thing to earth from the Antenna mast that was wood. From that
time on I always gave things a quick brush with the back of my hand just in case.

If in real doubt, Out came the test meter.

 

[Swinging & digging]

An RCD will only trip if a current is detected in the earthing system, like an active to earth fault.
If your grinder only has two pins its a double insulated tool.
Get an Electrician to do an Insulation resistance test on your grinder.
This will determine if its faulty. Sometimes a shock from a device can be a warning of a fault, be careful.

If you you using an extension lead, that could have been damaged, check the entire length of the lead looking for damage to the insulation, if you see
exposed copper in the active wire this would allow current flow, if the lead was laying on the ground in water you have a current path and dangerous
situation. An electrician can perform an insulation resistance test and inspection to your lead. This is a legal requirement on construction sites and work
places, its called testing and tagging. Extension leads are prone to damage and have resulted in electric shocks to persons using them.

 

[19.3]

You don't need the earth pin on an appliance for an rcdto work - Money box's knee is fine. If an appliance is not double insulated the earth pin provides a line of defence and should cause breaker to trip in the event a metal component becomes live due to internal insulation failing for any reason.
But a word of warning. RCDs - as illustrated here do not protect against all failure situations and people die even when there are RCDs in circuit.

 

[Jaros]

Moneybox,
First of all I'm not an electrician.
You have a serious wiring problem, and it is most likely your home earthing system. ie: House wiring usually has a copper rod driven into the ground and your earth wires are connected to this.
If your house is old, the earthing was some times connected to the water pipes that were either copper or steel. If the piping has been upgraded, PVC piping is used and the earthing will no longer exist. A RCD will NOT work in these circumstances.
**** Don't waste a minute tomorrow, get licensed electrician to check it out***

Our earth system is a copper rod belted into the ground at the front tap so that catches the drips- or whenever we use the hose.