I got zapped

[Bob Willson]

I am in the process of converting a 40Watt laser that used a Moshi motherboard to DSP using a Ruida 6442XS.

I have many switches on the top panel and I was testing the setup yesterday. The first switch is daisy chained to the second and the third and the fourth. these switches control the power, laser, water and air individually. I also have a master power off switch that breaks the input 240 volts to the whole system. The switch is on one input line only as one side of the switch is push to make and the other side is push to break.

So, there I was looking at the laser's PSU and I turned off all the switches and the master switch, grabbed the connector to pull out the PSU's plug and I got zapped by 240V.

When I stopped swearing, I thought to myself, "hang on, I shouldn't have got zapped, even if I didn't have everything turned off the house circuit should have kicked in immediately and saved me from any pain".

I whipped out my trusty ammeter and tested the 240V plug. I got nothing across the live and neutral plug pins, but 240 across the live and earth. I immediately unplugged everything under the house and measured things again with the same results. Later, I measured again and I then got 240 across the live and neutral and 240 across live and earth. I checked many power points throughout the house and got similar readings.

I phoned an electrician to come and look at it but he at first told me to phone the power company and later said (after I tested the safety switches) that the system seemed to be OK and put it down to 'electrickery'. He is obviously a friend of Rodney's.

Can anyone explain the problem and what might be the solution?



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[ian]

How old is your house?
I believe there was a period where one or more of the power companies deliberately connected neutral and earth

how long have you lived there?
and have you done any wiring work that could have resulted in a live to earth connection. One place to look would be a light fitting.

do you have solar power?
could there be a dodgy connection at th meter board?

[snowyskiesau]

Neutral and earth are, or should be, connected at the switchbox. Lookup MEN - Multiple Earthed Neutral.

[A Duke]

Hi,
Sounds like the switch is in the neutral instead of the active leg.
That is why it pays to pull the plug and not just switch off when working on circuits.
Regards

[benhoskin]

Also what meter are you using to measure the voltage? A lot of digital meters don't add any load and you can read an induced voltage in those lines.

[Cliff Rogers]

Hi,
Sounds like the switch is in the neutral instead of the active leg.
That is why it pays to pull the plug and not just switch off when working on circuits.
Regards


That is what I reckon too.

[RustyArc]

I shouldn't have got zapped, even if I didn't have everything turned off the house circuit should have kicked in immediately and saved me from any pain

You need to be careful with your terminology, particularly when talking about the lethal voltages you're playing with. The phrase "the house circuit should have kicked in" makes no sense. What you might have meant is that the RCD on the circuit should have tripped, and you would have confirmed that the circuit in question was actually protected by an RCD, and you would have tested the RCD to confirm it was working. If all that was the case, there's a serious problem with your wiring that needs urgent attention.


I whipped out my trusty ammeter and tested the 240V plug. I got nothing across the live and neutral plug pins, but 240 across the live and earth.

Again, you need to be careful with your words. You put an ammeter across a mains connection and an explosion will ensue. Secondly, was it the 240V plug you tested, which is typically a male connector with male pins? There should be no voltage anywhere on this as it's the load side. What you might have meant is the mains socket (or power point), unless there's a proprietary connector in the machine.

Again, you are messing with lethal voltages and have been zapped once so far, so being careful and precise in describing the fault is extremely important.

In answer to your question, as others have said, neutral and earth should be at the same potential as they are bonded at the switchboard (and at other points upstream) so seeing 240V between active and earth is normal. Again, as others have said, the most likely cause of getting zapped is incorrect polarity - the neutral was being switched, not the active. However, again, if the circuit does indeed have a safety switch (RCD) on it, and it didn't trip, you have a problem.

One tool that you might want to try, and is much safer than a meter, is a socket tester from Jaycar. It'll confirm the polarity of a power point is correct, and you can use it to test the trip threshold of the RCD on the circuit.

[Bob Willson]

How old is your house?
I believe there was a period where one or more of the power companies deliberately connected neutral and earth

how long have you lived there?
and have you done any wiring work that could have resulted in a live to earth connection. One place to look would be a light fitting.

do you have solar power?
could there be a dodgy connection at th meter board?


Hello Ian
The house is about 45 - 50 years old now.
The whole house was rewired after the floods and it is all in pretty good condition.
I do have solar power as well, but I see no reason why that should suddenly start acting up; but I will check it out.
Thanks

[Bob Willson]

Hi Geoff
I looked at the MEN system and it shows what others have stated in their replies. That the earth should indeed be connected to the neutral wire at all times, but not to the active wire.
It appears that at some point, the active and neutral wires have been switched and that a careful point by point inspection needs to be made to determine where the problem lies.
The tester mentioned by RustyArc (http://www.jaycar.com.au/Test-%26-Measurement/Electrical-Testers/Contact/Power-Point-and-Leakage-Tester/p/QP2000) will help me to find this very quickly.

[Bob Willson]

Thanks Hugh
I am certain that this is a major part of the problem.
I would also have preferred a switch that cut both wires.
Thanks

[Bob Willson]

Also what meter are you using to measure the voltage? A lot of digital meters don't add any load and you can read an induced voltage in those lines.


Hi Ben
I am using an APPA 93T meter. Not the best available, but price constrains most things in our lives. :)

[Bob Willson]

That is what I reckon too.


It certainly looks like it Cliff.
Thanks

[Bob Willson]

What you might have meant is that the RCD on the circuit should have tripped, and you would have confirmed that the circuit in question was actually protected by an RCD, and you would have tested the RCD to confirm it was working. If all that was the case, there's a serious problem with your wiring that needs urgent attention.

I couldn't think of the correct words at the time Rusty. Age often prevents me being as mentally agile as I once was. RCD it is



Again, you need to be careful with your words. You put an ammeter across a mains connection and an explosion will ensue. Secondly, was it the 240V plug you tested, which is typically a male connector with male pins? There should be no voltage anywhere on this as it's the load side. What you might have meant is the mains socket (or power point), unless there's a proprietary connector in the machine.

I t was the female end of the extension lead that I was testing. This was after I had pulled it from the machine but while it was still connected to the house wiring[/QUOTE]


In answer to your question, as others have said, neutral and earth should be at the same potential as they are bonded at the switchboard (and at other points upstream) so seeing 240V between active and earth is normal. Again, as others have said, the most likely cause of getting zapped is incorrect polarity - the neutral was being switched, not the active. However, again, if the circuit does indeed have a safety switch (RCD) on it, and it didn't trip, you have a problem.

One tool that you might want to try, and is much safer than a meter, is a socket tester from Jaycar. It'll confirm the polarity of a power point is correct, and you can use it to test the trip threshold of the RCD on the circuit.

Thanks for that Rusty. I will get one ASAP

[Bob Willson]

I will also try to find a big red switch that cuts both legs of the input power.
I would have thought that this was the standard way to do it; not have one cut and one not cut.
Meantime, I will switch the wires that I am cutting. If I had used my voltage detector (http://www.jaycar.com.au/PRODUCTS/Test-%26-Measurement/Electrical-Testers/Non-Contact/Non-contact-AC-Voltage-Detector/p/QP2268), this would not have happened.

[alexm1]

I will also try to find a big red switch that cuts both legs of the input power.
I would have thought that this was the standard way to do it; not have one cut and one not cut.
Meantime, I will switch the wires that I am cutting. If I had used my voltage detector (http://www.jaycar.com.au/PRODUCTS/Test-%26-Measurement/Electrical-Testers/Non-Contact/Non-contact-AC-Voltage-Detector/p/QP2268), this would not have happened.

Bob, by switching the wires that are "switched" you are fixing the wrong problem. There should be a consistent connection method throughout your house and shed. Do not change the switching, get the inconsistency fixed.
Re you getting zapped, the issue there is that you did not unplug the appliance/machine that you were working on, working on a machine that is still plugged in is asking for trouble.

[Tritonitis]

It's worth mentioning that an RCD will not provide any protection if you get zapped between active and neutral. Good luck with it and stay safe.

.

[BobL]

I will also try to find a big red switch that cuts both legs of the input power.
I would have thought that this was the standard way to do it; not have one cut and one not cut. . . . . .

After repairing / updating the switch gear on about a dozen (older) machines at the mens shed I can assure you that while it is standard, unfortunately it's not what actually takes place, especially if DIY folks are involved Two machines that had newer plugs installed BUT the neutral and live connections had been swapped so it was the neutral only that was was being switched! This is why it is absolutely essential to remove the plug from the wall socket.

If you are still getting zapped, I'd be looking to make sure charged caps are not the source and take appropriate action to discharge them (i.e. not by direct shorting)

[Yanis]

It's worth mentioning that an RCD will not provide any protection if you get zapped between active and neutral. Good luck with it and stay safe.

.

In theory true but there is inevitably some leakage to earth so it will likely trip.

John

[Cliff Rogers]

.... working on a machine that is still plugged in is asking for trouble.Yup, unless you are taking measurements on it for faultfinding.

[alexm1]

Yup, unless you are taking measurements on it for faultfinding.

I would assume if that were the case you would have enough knowledge to stay out of trouble.

[NCArcher]

I would assume if that were the case you would have enough knowledge to stay out of trouble.

Cliff stay out of trouble......:no:

I'm curious as to how you managed to make contact with a live terminal. What exactly did you touch?

And just as a cautionary note, I'm an electrician and have worked in the industry for over 30 years. Every place I have worked, whether government or private has a policy of monitoring in hospital following an electric shock, no matter how minor. Delayed fatal arrhythmia can be a consequence of electric shock and can only be ruled out by monitoring with an ECG. It's not common and may only be of concern to people who have a pre existing heart condition of some kind but nobody (employers) wants to take that chance. Not saying you should head off to hospital Bob but anybody who has a heart condition (of any kind) who receives an electric shock should seek medical advice.

[Bob Willson]

I'm curious as to how you managed to make contact with a live terminal. What exactly did you touch?

The power supply had a plug in the front of it where the power enters the PSU. I pulled on the plug and my fingers must have managed to complete a circuit. this was despite the emergency power switch having been activated. This would not have happened if the switch broke both active and neutral wires.

I have been looking at switches that break both and they seem to start at about $50/$60 each. The single break ones start at about $2.40 from China.
(http://ww.aliexpress.com/item/IMC-Hot-Red-Mushroom-Cap-1NO-1NC-DPST-Emergency-Stop-Push-Button-Switch-AC-660V-10A/32337356426.html?spm=2114.30010308.3.19.MB7f9I&ws_ab_test=searchweb201556_2,searchweb201644_5_10001_10002_10005_301_10006_10003_10004_62,searchweb201560_3,searchweb1451318400_6150,searchweb1451318411_6449&btsid=7efc7011-6bc7-4f19-924d-d53e7d8b5587)

[BobL]

I have been looking at switches that break both and they seem to start at about $50/$60 each. The single break ones start at about $2.40 from China.
(http://ww.aliexpress.com/item/IMC-Hot-Red-Mushroom-Cap-1NO-1NC-DPST-Emergency-Stop-Push-Button-Switch-AC-660V-10A/32337356426.html?spm=2114.30010308.3.19.MB7f9I&ws_ab_test=searchweb201556_2,searchweb201644_5_10001_10002_10005_301_10006_10003_10004_62,searchweb201560_3,searchweb1451318400_6150,searchweb1451318411_6449&btsid=7efc7011-6bc7-4f19-924d-d53e7d8b5587)

Bob that link doesn't work for me. Can you please repost or state your current requirements.
I found that some chinese switches are OK but some are dodgy as.
Also you may want to consider using a "No Volt" or latching type switch.

[NCArcher]

The item you're looking for is a double pole switch. A switch, however, is not an effective isolation. You shouldn't rely on something you can't see. The internal mechanism could stick in the on position even though you have operated the switch and you wouldn't know until you got a shock. Only count on a physical break in the circuit that you can see like removing the plug from the wall socket. And always test before you touch.
Electrical preaching over. Carry on. :doh:

[Cliff Rogers]

Cliff stay out of trouble......:no:.....
It follows me around like a lost puppy. :D

[BobL]

And just as a cautionary note, I'm an electrician and have worked in the industry for over 30 years. Every place I have worked, whether government or private has a policy of monitoring in hospital following an electric shock, no matter how minor. Delayed fatal arrhythmia can be a consequence of electric shock and can only be ruled out by monitoring with an ECG. It's not common and may only be of concern to people who have a pre existing heart condition of some kind but nobody (employers) wants to take that chance. Not saying you should head off to hospital Bob but anybody who has a heart condition (of any kind) who receives an electric shock should seek medical advice.

I was at a public event at the Perth Town Hall when a large 3 Phase coffee machine had a problem and an unqualified, over confident member of the public decided to have a go at fixing it and zapped himself. Luckily he was not fried, and he even appeared OK immediately afterwards and sat down over at the side of the hall for half an hour or so when I noticed he was not acting normal. I suggested to the event organisers that they organise to take him to hospital but the zapped bloke refused and before we knew it he had disappeared.

[Bob Willson]

I suggested to the event organisers that they organise to take him to hospital but the zapped bloke refused and before we knew it he had disappeared.

What do you mean? He turned invisible or something?

The link was to aliexpress.com and then do a search for 'emergency stop switch' One of the first items that comes up is a switch for $2.35

ooooh I think I have found a switch that is 2 x NC. It is: Mushroom head button switch ANE-22with light LED emergency stop button(Mounting hole 22 25mm)(DC 6/12/24/36/48 V AC110/220/380V) (http://www.aliexpress.com/item/Mushroom-head-button-switch-ANE-22-with-light-LED-emergency-stop-button-Mounting-hole-22mm-DC/1899708871.html?spm=2114.10010108.100010.18.IDR9xA) Bugga, just noticed that it isn't. Still 1 x NC & 1 x NO

There is another very pretty switch, but again, it 1 x NO and 1 X NC: ONPOW 19mm 1NO+1NC emergency stop Push button switch (LAS1-BGQ-11TS) CE, ROHS (http://www.aliexpress.com/item/ONPOW-emergency-stop-Push-button-switch-LAS1-BGQ-11TS-CE-ROHS/1332902738.html?spm=2114.10010108.100010.44.IDR9xA)




The item you're looking for is a double pole switch. A switch, however, is not an effective isolation. You shouldn't rely on something you can't see. The internal mechanism could stick in the on position even though you have operated the switch and you wouldn't know until you got a shock. Only count on a physical break in the circuit that you can see like removing the plug from the wall socket. And always test before you touch.
Electrical preaching over. Carry on. http://d1r5wj36adg1sk.cloudfront.net/images/smilies/actions/doh.gif

That is good advice, but I still need an emergency stop that breaks both wires

[DavidG]

Had a mate who got zapped with 3 phase.
He appeared to be ok but then dropped dead.

I have a multimeter that flashed a red led if it is placed near a live cct.
You don't even need to make contact.
Very useful.
Agree with the comment that the safest switch is the end of the cord unplugged and in sight.

[BobL]

What do you mean? He turned invisible or something?
The place was packed with hundreds of people and he just melted (ha-ha) into the crowd.


The link was to aliexpress.com and then do a search for 'emergency stop switch' One of the first items that comes up is a switch for $2.35
ooooh I think I have found a switch that is 2 x NC. It is: Mushroom head button switch ANE-22with light LED emergency stop button(Mounting hole 22 25mm)(DC 6/12/24/36/48 V AC110/220/380V) (http://www.aliexpress.com/item/Mushroom-head-button-switch-ANE-22-with-light-LED-emergency-stop-button-Mounting-hole-22mm-DC/1899708871.html?spm=2114.10010108.100010.18.IDR9xA) Bugga, just noticed that it isn't. Still 1 x NC & 1 x NO
There is another very pretty switch, but again, it 1 x NO and 1 X NC: ONPOW 19mm 1NO+1NC emergency stop Push button switch (LAS1-BGQ-11TS) CE, ROHS (http://www.aliexpress.com/item/ONPOW-emergency-stop-Push-button-switch-LAS1-BGQ-11TS-CE-ROHS/1332902738.html?spm=2114.10010108.100010.44.IDR9xA)
That is good advice, but I still need an emergency stop that breaks both wires

I bought some of those $2 eBay and A/Exp switches and they look and feel like POS and I would not trust them for a second

This is the sort of thing I use on most gear I rewire.
If the power fails they don't automatically reconnect the power without manually activating the switch again,
3251-20-01 | Push Button Switch, DPST, Flange, On-Off | EICHOFF (http://au.rs-online.com/web/p/push-button-switches/3985263/)
They cost more double the similar quality ones on ebay/Ax ones but hopefully the RS ones are more reliable.
But nothing beats physically removing the plug from the mains.

[BobL]

Had a mate who got zapped with 3 phase.
He appeared to be ok but then dropped dead.

At work we had gear up to 100kV (also a small linear accelerator that got up to 2 MV but no one was allowed in the room when that was turned on) that a restricted set of blokes would occasionally need to work on and a few more that worked on 240V. There were a few guys zapped in the 1970's and the problem was they did not usually report because they didn't want to get into trouble. In 1978 as a post grad student the gear in our lab was up too 10kV and I got a 6kV DC boot across the tip of my ring finger to the palm of my hand that threw me across the lab. I was lucky most of the current probably dissipated through the palm. Neither the techo or the Prof I was working reported this.

When I became a staff member I remember it took some f effort to convince staff they would not get into trouble for reporting these events so a few reports started coming in. By 1990 mains and higher V electrical work was restricted to a handful of experienced individuals, and we also installed and purchased more gear with better interlocks, lower current limiters, RCDs etc that the number of reports fell away quickly after that. In fact I don't recall one during my 9 years as head of department.