Do I need an earth wire??

Submitted: Sunday, Jul 25, 2010 at 16:14
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Hi all

I have just hard wired a 25 amp battery charger into my car, attaching it to the cargo barrier. It is connected to one of 3 batteries wired in parallel. I used the wire that came with a 380 Watt Inverter I bought as it already had the necessary lugs and is reasonably thick. Seems to be working ok at the moment and the wire is barely warm to the touch. Do I need to have the charger earthed to the car via a dedicated earth wire? Don’t know too much about electrics as you can guess from the questions. Anything else I should be aware of?

Thanks for your help.

Lyndon
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For the clock may then be still

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Reply By: kend88 - Sunday, Jul 25, 2010 at 17:19

Sunday, Jul 25, 2010 at 17:19
I see a lot of people have read your post but no replies. I don't know much about electricity either, but am I right in assuming you are going to charge the batteries via a 12v to 240v inverter?
There appear to be differing opinions but one is that in the event of an accident, and someone comes to your aid, they could be at serious risk with 240v. flowing through the car. Suggest you talk to a auto electrician.

KenD
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Follow Up By: Allan B, Sunshine Coast, - Sunday, Jul 25, 2010 at 18:03

Sunday, Jul 25, 2010 at 18:03
Ken, There should be no differing opinions. There are established Standards for electrical matters that leave no options for "opinions". If these standards are followed, as they are by qualified electrical practitioners, then there will be no accident or risk or "240v flowing through the car".

An auto electrician is not necessarily qualified to deal with 240 volt matters.

No offense intended mate and I know you mean well, but you are right about "not knowing much about electricity either" so best leave it to those that are qualified, eh?

Cheers
Allan

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Follow Up By: oldtrack123 - Sunday, Jul 25, 2010 at 20:14

Sunday, Jul 25, 2010 at 20:14
Hi
I may be a bit confused but:
I believe the question is" would the cables that came with a 380w inverter be adequate for use with a 25amp charger?"[12v from charger to battery]
If that is the question then answer is yes should be near enough if the run length is short
If the question is relative to running the inverter to run the charger then i would have to ask WHY?

However one important point is it is illegal for anyone other than a qualified person to run fixed wiring for 240v even if that is to only supply one item

Specific rules under the Aus standards cover this in mobile situations
Peter
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Follow Up By: oldtrack123 - Sunday, Jul 25, 2010 at 20:23

Sunday, Jul 25, 2010 at 20:23
Hi
Re :" Do I need to have the charger earthed to the car via a dedicated earth wire? Don’t know too much about electrics as you can guess from the questions. Anything else I should be aware of?
Thanks for your help. "

Again this will depend on if you have done fixed 240v wiring[which should only be carried out by a qualified person]
There are very specific rules covering earthing in such situations in vehicles.
As others have pointed out an auto electrician is unlikely to be aware of the applicable rules

Peter
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Follow Up By: Allan B, Sunshine Coast, - Sunday, Jul 25, 2010 at 22:39

Sunday, Jul 25, 2010 at 22:39
Peter, you seem to be muddying the water here. Lyndon's question was very clear....... "Do I need to have the charger earthed to the car via a dedicated earth wire?"
His reference to an inverter was only that the 12v cable from that was used for the charger output.

There is no suggestion that Lyndon has done fixed 240v wiring. Seems reasonable to assume that he is supplying the 240v to the charger via an extension cable to the charger's supplied mains cord and plug.

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Allan

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Follow Up By: oldtrack123 - Sunday, Jul 25, 2010 at 22:53

Sunday, Jul 25, 2010 at 22:53
Hi Allan
No not attempting to muddy the waters
As his post is a little unclear as to exactly what he has .or is doing
My first post show that ,like you, I assume he is only referring to the 12v side But I am not certain he has not gone further, which is why i have made the 2nd post
240v is not for amateurs to play with ,I am sure you will agree .
Peter
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Follow Up By: Member - Shane L - QLD - Monday, Jul 26, 2010 at 07:54

Monday, Jul 26, 2010 at 07:54
Guys,
The post isn't unclear at all, nowhere does Lyndon mention running 240volts anywhere, question was does he need to "earth" the charger to the vehicle as well as the negative to the battery/s. In my opinion, no it is not necessary as any 240 volt source should have the appropriate protection so as the risk of shock is extremely minimal, after all he won't be driving it when charging off 240 volts


Shane
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Follow Up By: Charles Jenkinson - Wednesday, Jul 28, 2010 at 18:06

Wednesday, Jul 28, 2010 at 18:06
Lyndon, I realise that you were not talking about running 240 V in your vehicle, rather you were talking about the need to earth a charger. I understand that the confusion amongst other posters related to the fact that you SOURCED the wire from a 240 V inverter. My post below is more to deal with the misconceptions that some have placed on this thread. My apologies for being a part of the thread hijack!

Kind regards,
Charles
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Reply By: Allan B, Sunshine Coast, - Sunday, Jul 25, 2010 at 17:25

Sunday, Jul 25, 2010 at 17:25
Hi Lyndon,
The charger will be properly earthed via its 240 volt cable from the mains, just be sure that you use an extension cord which includes an earth conductor. A standard 3-pin extension will have this.
The charger could also be double-insulated and thus require no earth.
The 12 volt side of the charger does not require earthing.

Cheers
Allan

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Reply By: cbucko - Sunday, Jul 25, 2010 at 19:18

Sunday, Jul 25, 2010 at 19:18
Reading your post I assume that you will be charging on board batteries from the mains supply, in which case I would not run a dedicated earth to the vehicle as the charger output will be grounded by the negative connection to the battery.

Chris
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Follow Up By: Allan B, Sunshine Coast, - Sunday, Jul 25, 2010 at 19:50

Sunday, Jul 25, 2010 at 19:50
Chris, the charger negative output will be connected to the battery negative which in turn is connected to the vehicle chassis and body. That is not grounding in the electrical sense.

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Allan

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Reply By: Member - lyndon NT - Sunday, Jul 25, 2010 at 20:56

Sunday, Jul 25, 2010 at 20:56
Thanks for all the replys. Looks like it with be ok, no flames yet anyway :-)
I noticed that the inverter in the car has been earthed to the car, hence the question. The wire I'm using has not got hot which seems to tell me it is handling the current flow ok. Now a new post for the battery and charging Guru's

Lyndon
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For the clock may then be still

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Follow Up By: oldtrack123 - Sunday, Jul 25, 2010 at 22:15

Sunday, Jul 25, 2010 at 22:15
Hi Lyndon
your reply above leaves me a little concerned
How old is your inverter ?
Is it a fully isolated type?
Remember the 240v from an inverter is potentially just as deadly as your mains supply [its the voltage that matter not the amps]
Playing with /using 240v in confined spaces such as a vehicle can be dangerous
Thats why there are very specific requirements if any 240v fixed wiring is involved.
Peter
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Follow Up By: Alloy c/t - Monday, Jul 26, 2010 at 08:35

Monday, Jul 26, 2010 at 08:35
" its the voltage that matter not the amps " ?? What a load of misinformation !! 400amp@12v is just as dangerous if not more so than 1-5 amp@240v.
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Follow Up By: landseka - Monday, Jul 26, 2010 at 09:54

Monday, Jul 26, 2010 at 09:54
"oldtrack123 posted:

Remember the 240v from an inverter is potentially just as deadly as your mains supply [its the voltage that matter not the amps] "

Crikey, I reckon if that is the case then every mechanic that ever got a 20,000v 'tickle' from a car's spark plug should be dead now! :-)

Cheers Neil
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Follow Up By: nigilor6 - Monday, Jul 26, 2010 at 10:11

Monday, Jul 26, 2010 at 10:11
When its come to electricity, dont stuff around with it, the only time the higher voltage does damege is when its high voltage ie powerlines, this stuff burns you to a crisp and WILL blow holes out of you, Allotc/t is correct, the higher the amps the more damage it can/will do, if you like look at as this old diesel motor (12v) has more torque than old petrol motor (240v), but in saying this, the invertor should be double insulated and have its own inbuilt protection to stop the 12v to 249 volt occuring, i havent had a look at these units and probably never will, so no you shouldnt need to earth the invertor as you dont want to be putting 240v onto your car sub frame, hopefully this info helps, but when dealing with 240v or higher use a sparky or if you have a mate that is one give him some blocks of bleep to do the job for you
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Follow Up By: oldtrack123 - Monday, Jul 26, 2010 at 12:58

Monday, Jul 26, 2010 at 12:58
Hi
Well, it does seem we have a lot of "experts" here
An ac voltage over about 40v can kill & the current only needs to be [depending on health] something over 40 milliamps
In very SIMPLE words 40v ac @ 40 milliamps can kill
Those in poor health can be killed by even lower current [milliamps]
THESE ARE FACTS NOT JUST OPINIONS

I have seen a person close to death from 32v ac when caught on it for some time .
I have seen a welder killed on 72 volts ac
Not a pretty sight

My point is /was that even a small 60w inverter can kill..
Many of those still in use & purchased up to about 3<4years ago ARE NOT FULLY ISOLATED!!!!
Their sale is now banned due to deaths that have occurred with them
Again FACTS not opinions or hearsay.



Re :"Crikey, I reckon if that is the case then every mechanic that ever got a 20,000v 'tickle' from a car's spark plug should be dead now! :-) "

Perhaps I should have made it clearer as above it only needs a small current
[depending on health factors 30< 40 milliamps] with the voltage to be deadly
The current from that ignition is not anywhere near the level to kill instantly ,but how would you be if caught up on it for a few minutes or so???


Re :" but in saying this, the invertor should be double insulated and have its own inbuilt protection to stop the 12v to 249 volt occuring

Again many are not aware that many inverters sold up untill 3< 4years ago [ when their sale was banned] are NOT FULLY [doubleinsulated] ISOLATED
THe 240 v is earthed neutral to the frame onTHE !2V SIDE
They are now banned from sale as a result of deaths when using them
FACTS ,NOT OPINIONS


Alloy posted" its the voltage that matter not the amps " ?? What a load of misinformation !! 400amp@12v is just as dangerous if not more so than 1-5 amp@240v.
FollowUp 2 of 4 "

VERYy VERY wrong, I think you need to do a little research before making such a RIDICULOUS statement. !!!!!!!
Again FACTS not just OPINIONS
It is impossible for 12v to force that sort of current through the human body.
It's a little thing called resistance that limits the current flow,
Strange I have never heard of any one being killed by 12v
I can hang on to 12vac all day & it will have no effect
I'll even hang on to 32v ac for maybe a minute or two but higher volts , NO

So again I suggest FACTS not opinions when dealing with electricity.

Peter
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Follow Up By: Alloy c/t - Monday, Jul 26, 2010 at 13:44

Monday, Jul 26, 2010 at 13:44
Oldtrack your the one that states volts are the danger , not I , amps are the danger , you recon you can hang onto 12vac all day lol , love to see you try at 400amp 12v for more than 60sec or so , the smell of fried pork will be in abundance. , Explain static electricity , oh , thats right you get the tingle from very LOW volts but High Amps which are quickly dispersed , ,How Can it be that people SURVIVE a direct lightning strike , oh ,thats right , couple of hundred thousand volts but LOW amps.
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Follow Up By: oldtrack123 - Monday, Jul 26, 2010 at 13:45

Monday, Jul 26, 2010 at 13:45
Hi
Re :
FollowupID: 695792 Submitted: Monday, Jul 26, 2010 at 10:11
nigilor6 posted:
When its come to electricity, dont stuff around with it, the only time the higher voltage does damege is when its high voltage ie powerlines, this stuff burns you to a crisp and WILL blow holes out of you, Allotc/t is correct, the higher the amps the more damage it can/will do

I am sorry to say ,
Alloyc/t has not got a clue
His statement would be some of the most uninformed RIDICULOUS rot I have seen for some time'
Yes HT power line voltages can fry you,BUT you do not need to be fried to be dead!
All it needs is sufficient current [30<50 milliamps] to break your heart rthyme
Due to body resistance this requires a voltage above approx 40v [again depending on conditions]

Peter
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Follow Up By: oldtrack123 - Monday, Jul 26, 2010 at 14:33

Monday, Jul 26, 2010 at 14:33
Hi Alloyc/t

alloy c/t posted:
Oldtrack your the one that states volts are the danger , not I , amps are the danger , you recon you can hang onto 12vac all day lol , love to see you try at 400amp 12v for more than 60sec or so , the smell of fried pork will be in abundance. , Explain static electricity , oh , thats right you get the tingle from very LOW volts but High Amps which are quickly dispersed , ,How Can it be that people SURVIVE a direct lightning strike , oh ,thats right , couple of hundred thousand volts but LOW amps."

Perhaps YOU can explain how 12v can force 400amps through the human body?
It simply cannot, the body resistance[including contact resistance ] is too high!!!
Do you understand Ohms law??
To force 400amps through the human body would need voltages in excess of 100kv
So your statement is TOTALLY WRONG
Simple Electrical FACTS!


Re lightening strikes , yes a FEW survive, But most are fried just as with EHT power lines
However with static / very high frequency there is another effect at work Called skin effect where the current tend to run along the surfaces,
not deep in the conductor, & therefor can have less effect on the heart , but severe skin burns can result

Now how about you putting up some facts to justify your ridiculous statement.?

Peter

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Follow Up By: Allan B, Sunshine Coast, - Monday, Jul 26, 2010 at 16:04

Monday, Jul 26, 2010 at 16:04
Oh no. Here we go again!!!!!!

As soon as there is any expression about electrical matters, particularly 240v stuff, people come out of the woodwork with all sorts of uninformed, weird, and totally incorrect expressions that must totally confuse the poor soul who raised the original query. (No, not you Oldtrack!)

What on earth makes them believe that they have any real knowledge about electrical matters?

For heaven's sake, unless you have full and proper training in electrical theory and practice I sincerely suggest that you keep your weird and uninformed concepts to yourselves and stop confusing those who are asking earnestly for accurate advice. Leave responses to those who are trained and qualified to give proper and accurate advice. And before you ask...... yes, I am totally qualified in electrical matters.

Cheers
Allan

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Follow Up By: oldtrack123 - Tuesday, Jul 27, 2010 at 10:50

Tuesday, Jul 27, 2010 at 10:50
Hi Allan

The sad thing is that some will never admit their weird ideas are wrong no matter what FACTS are put to them .
They will continue to push such unsubstantiated OPINIONS[not FACTS] no matter what
A forum is / should be open for all to put forward their ideas but if they are only opinions, they should be prepared to accept attempts @ correction . OR as a minimum put forward sensible debatable reasons for their their beliefs, not just parrot repetition

I think none of us can say we have never been wrong in something we have said /posted or even believed ,but some can not bear to admit it

I certainly have learnt a lot in the few years I have been on these forums
simply because I have a simple philosophy


YOU ARE NEVER TOO OLD TO LEARN

Peter
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Follow Up By: oldtrack123 - Tuesday, Jul 27, 2010 at 12:31

Tuesday, Jul 27, 2010 at 12:31
Hi Lyndon

Re :"Member - lyndon NT replied:
Thanks for all the replys. Looks like it with be ok, no flames yet anyway :-)
I noticed that the inverter in the car has been earthed to the car, hence the question. The wire I'm using has not got hot which seems to tell me it is handling the current flow ok. Now a new post for the battery and charging Guru's "

Do not be put OFF by some of the crap that has developed on this thread
You just need to read any /all forums VERY carefully ,,ask further questions if needed, then most important ,
"SORT THE WHEAT FROM THE CHAFF"

We ALL try to help[I hope] even if sometimes we are not correct .

Peter

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Follow Up By: Robin Miller - Tuesday, Jul 27, 2010 at 20:24

Tuesday, Jul 27, 2010 at 20:24
I've marked a few papers and I'd give you a pretty good score Peter !
Robin Miller

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Follow Up By: oldtrack123 - Tuesday, Jul 27, 2010 at 20:49

Tuesday, Jul 27, 2010 at 20:49
Hi Robin
Thanks
Although @ times I have to edit /rewrite due to that problem we oldtimers have.[coming up 82]

Since I cannot edit on this forum I have to try & be a bit extra carefull

Peter
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Reply By: Member - Graham H (QLD) - Monday, Jul 26, 2010 at 14:05

Monday, Jul 26, 2010 at 14:05
If in fact you are running it off an inverter doesnt that run off the batteries????????

Are we all missing something here or is it just being explained really badly.

If it is in fact running off the batteries via the inverter I would think the looses in the circuit would negate the charging effect.

No such thing as a free lunch or perpetual motion or making more electricity than you are using ?????????????

Im sure an expert will correct me but this has been hashed over previously and the answer was as I have replied.

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Follow Up By: Allan B, Sunshine Coast, - Monday, Jul 26, 2010 at 15:51

Monday, Jul 26, 2010 at 15:51
Yes Graham, you are missing something here, or rather reading something into Lyndon's original post that was not there.

Lyndon said "I used the wire that came with a 380 Watt Inverter I bought as it already had the necessary lugs and is reasonably thick." He simply used some wire that was supplied with his inverter to connect his battery charger. Other than that, his inverter plays no part in his query or this thread!

Sorry mate. Yes, perhaps it could have been expressed a bit clearer.

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Reply By: Member - Graham H (QLD) - Monday, Jul 26, 2010 at 16:09

Monday, Jul 26, 2010 at 16:09
Thats what I thought but he goes on to say later that his inverter is earthed to the car body so if he isnt charging the batteries with it the same cautions would still apply.

I had one and got rid of it for safety reasons.

Only takes one drink and bye bye.

Cheers

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Follow Up By: Allan B, Sunshine Coast, - Monday, Jul 26, 2010 at 16:24

Monday, Jul 26, 2010 at 16:24
Graham, I am sure that when Lyndon says..."the inverter in the car has been earthed to the car" he is referring to the inverter casing being connected by a wire to the car body or chassis. This is a common recommendation by inverter manufacturers for minimisation of RF interference and is not a connection from either the 240v or 12v wiring to the car body. It is not essential for effective or safe operation but can assist with RF interference suppression. I have applied this connection to my own inverter.

Cheers
Allan

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Reply By: Charles Jenkinson - Wednesday, Jul 28, 2010 at 18:01

Wednesday, Jul 28, 2010 at 18:01
Hmmmm... I realise that this thread last had activity 20 or so hours ago, however I feel the need to provide some "expert" input here. No, I'm not an electrician, or an engineer. Rather, I'm a doctor, who feels quite confident talking about mechanisms of electrical injury. I have seen and treated victims of electric shock, and have a decent understanding of the physics and pathology behind electrocution/electrical injury.

I will not offer an opinion on the matter at hand, which is beyond my area of expertise. However, I will correct some misconceptions about electrical injury, and summarise the topic in a piece I hope will be read by anyone who surfs onto this thread as a result of a future search, or link from another thread.

I mean no disrespect to any contributor on this Forum. You have my admiration for writing, and we all add our input in good faith. Please understand that I am merely combining mostly what others have written into a summary of correct information.

There are three main mechanisms behind electrical injury:

1) thermal effect causing burns, damage to skin/muscle/organs etc caused by the resistance of body tissues, which depends on the length of time a subject is exposed, the voltage, and the location where the current is applied

2) secondary injury caused by muscular contraction/involvement of the nervous system in which involuntary movement places a person in harms way, ie: if a hand were to be propelled into a moving radiator fan, or if tetany caused the palm to grip a live wire

3) cardiac arrest caused by the induction of lethal arrhythmias (ventricular fibrillation) where the only definitive treatment is DC defibrillation - another form of electric shock (delivered by a defibrillator, usually involving 200J of energy)

There are other more subtle mechanisms: increased permeability of cells, diaphragm paralysis, central nervous system dysfunction. These are probably beyond the scope of this discussion for the time being.

There are five main factors that determine the extent of electrical injury:

-Type of current (direct [DC] or alternating [AC])
-Voltage and amperage (measures of current strength)
-Duration of exposure (longer exposure increases injury severity)
-Body resistance
-Pathway of current (which determines the specific tissue damaged)

Alternating current (especially at low frequency, such as the 50-60 Hz supply common in household circuits and power inverters) is 3-4 times more dangerous than DC current, for several reasons, which I will elaborate on later. In fact, 240V at 50-60 Hz, is one of the most dangerous combinations you could select for a power system! (The pathophysiology was not as well understood when Thomas Eddison and George Westinghouse were fighting their "War of Currents").

Voltage and amperage are debated in this thread. The old saying that "current kills", or as one member put it, "It's the voltage that matters, not the current" circle around a larger issue: Ohm's Law.

V=IR states that current is proportional to voltage. You can rearrange that to state that I=V/R. Hence, the larger the resistance at a given voltage, the smaller the current.

The variable is the resistance of the body. It varies depending on the location that the potential is placed across, the amount of callous on one's hands, the presence of metallic jewelry, sweat, water, their fat/water content, and most importantly, the presence of shortcuts to the heart, such as a pacemaker lead.)

The effect of electricity on the body depends on the current flowing, which as we have just discussed (by Ohm's law, and the resistance of the body) is a direct function of voltage and resistance. You cannot "force" 400 A at 12 volts, unless you can control the resistance (ie: make the resistance of the body 0.03 ohms - the resistance of a foot submerged in water is about 100 to 300 ohms, which would cause a current of 100 mA - this is enough to cause severe pain, or difficulty breathing! But it's a long way off 400A.) You could kill with a 1.5 V battery if the resistance to the heart were sufficiently small, but this would require nothing short of direct electrodes (the native potential of a cardiac muscle cell in its polarised state is -70 mV, and it depolarises to +110 mV, so you can see how small the voltages are that we're playing with here).

At a usual resistance of dry skin, approximately 40k ohms, you can see that the current drawn from a 12V source would be 0.0003 A - or 0.3 mA - not enough to be felt by the average male in good health. The current CANNOT be larger than this, unless the resistance is lowered by moisture (which might reduce the resistance to 4K ohms, where you would receive a slight sensation at the hand), or by another means of lowering resistance as described above.

Alternating current is different again - at 0.3 mA (ie: 12V 60Hz AC through dry skin) you will have a slight perception in the finger in contact with the wire. (This is only an example - I'm sure most of us don't routinely deal with AC this low). Generally, the effect seen is three to four times greater with AC - ie: it takes three times less current at 50-60 hz to bring about a particular effect than with DC current. Strangely enough, the effect of higher frequency AC current (ie: 10 kHz) is diminished. It's actually between 5 and 10 times SAFER than DC current.

Pathway of current refers to which parts of the body are in the circuit. The most dangerous pathways cross the heart: left to right hand being the number one. Right hand to right foot is the safest of the limb paths, however this does not account for diaphragmatic paralysis or thermal effect.

Alternating current is more likely to induce ventricular fibrillation (VF) than DC current, although DC can certainly do so (you just have to be less lucky, and you need more current). It takes 500 mA at 3 seconds of exposure to induce VF in a healthy adult with DC, but only 100 mA at AC. (In fact, in some conditions, ie: across the chest, VF can be induced with 17 mA of DC current). To draw 500 mA with 12 V DC requires a resistance less than 288 ohms, which could occur if your hands were immersed in solutions of salt water (a contrived situation, I know). The point is, 12 V can kill. With 240 V 60 Hz AC, the minimum resistance to induce VF after 3 seconds of exposure is 2.4k Ohms - this can occur in a finger/thumb grip of a wire with dry hands.

If a person is unlucky enough to be wearing a ring, or gripping a pipe their resistance may fall to 1000 ohms. In these situations, the DC voltage required to generate 17 mA (the lowest current that can cause VF in ideal conditions) is 17 V. Under less than ideal conditions, 17 V can still induce tetany, which can cause secondary injuries.

Keep in mind, this is for a lethal cardiac arrhythmia - at EVEN LOWER currents, thermal injury, muscular contraction, and diaphragmatic paralysis CAN occur, and these can be lethal.

AC is much more likely to induce fibrillation because it disrupts the electrical pathways of the heart, and continues to do so, creating "circuses" of turbulent current patterns. This is due to the cyclical nature of the current - it "pushes and pulls", so to speak. DC generally depolarises the heart completely, which will cause arrest whilst the current is applied, but the heart may begin beating normally once the current is removed (unless specific conditions are met, which is why 3 seconds can induce VF at 500 mA). In fact, this is how defibrillators work - a DC current is applied across the heart, which causes total depolarisation of the heart muscle, and its intrinsic "pacemaker" (usually) takes over. The term "jump start" isn't correct - it is more akin to a "reboot". Defibrillators can apply a biphasic current of between 15 and 40 A across a chest with a resistance of 50-200 ohms (reduced through the use of the gel conducting pads). The machines are clever - they measure the resistance across the chest (actually the impedance, but enough on that), and adjust the peak current and duration of the shock accordingly.

Thermal injury has been "touched" on, but suffice to say that it is a function of current as well. One contributor talked about static electricity - this is actually due to many thousands of volts, but is with relatively few electrons, and therefore brief, also altered by the large resistance of air (the physics behind it is even more complicated - Q=it comes into play). The currents in a lightning strike are extremely large, as is the voltage. The exposure is very brief. Their injury and lethality often comes from thermal injury - looking at lightning strike victims is not for the weak-stomached! Surviving a direct hit from a lightning bolt is EXTREMELY rare. I also reiterate - you CANNOT alter the current - it is a function of voltage and resistance.

I hope this has cleared up some misconceptions about the role of electricity in injury. To summarise, ANY voltage, AC or DC, can kill under the right conditions. AC (certainly in household voltages) is EXTREMELY dangerous, and much moreso than DC. Current is a function of voltage and resistance. You cannot independently control how much current is drawn, if you have a known voltage and resistance (which is a function of the pathway that the current is flowing, based on multiple factors). Some pathways are more dangerous than others.

Overall, ELECTRICITY IS DANGEROUS and poorly understood. This includes the output of a 240V AC power inverter, which is JUST as dangerous as domestic supply.

With the deepest of respect and noble intentions,

Charles

_______________________________
Charles Jenkinson
Perth, Western Australia

Gracie "The Grey Ghost"
1991 Toyota Landcruiser GXL (HDJ80R)
4.2L 1HD-T Turbo Diesel
358,864 km and counting!

AnswerID: 425552

Follow Up By: Allan B, Sunshine Coast, - Wednesday, Jul 28, 2010 at 19:58

Wednesday, Jul 28, 2010 at 19:58
Hello Charles,

I am an electrical engineer and I must say that your dissertation on electric shock is the most concise yet comprehensive that I have ever read and hopefully will be of much benefit to readers of this forum. With your permission, I will be copying and filing it for possible later reference.

I take particular interest in this subject naturally as an electrical engineer but also for more personal reasons. I started working life as an apprenticed electrician and on only my third day of employment suffered severe hand-to-hand electric shock with tetany causing an inability to let go of the conductors. I was fortunate enough that another worker was able to release me but only after 10 seconds of terror where I was paralysed and even unable to scream. It seemed that I could count each cycle of electric current passing through my body. Subsequently I have experienced other electric shocks but none as severe or frightening as that first one.

Unfortunately there are some who have a conviction of self-expertise in electrical matters but are simplistic in their logic with erroneous conclusions. Those would be hard put to appreciate such components as area of contact and moistness of skin. There was an instance long ago in Adelaide where a woman was electrocuted by a faulty washing machine. The investigation deduced that the voltage presented to her hands was only 14 volts but the wetness of her hands permitted sufficient current to cause death. An example of some of the points you were explaining.

I would agree that 240V at 50-60 Hz, is one of the most dangerous combinations for a power system, but the American choice of 110V is not far behind. These values were chosen as convenient in respect of electrical engineering and economy but soon became a standard which cannot be practically revised. I'm afraid we are stuck with it.

Cheers
Allan

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Follow Up By: oldtrack123 - Wednesday, Jul 28, 2010 at 21:15

Wednesday, Jul 28, 2010 at 21:15
Hi Charles

I ,too , thank you for your time in the above very detailed post
Whilst ,it may appear to be a hijack of the original post, it is very relevant to some of the following posts including the complacency & mistaken beliefs of many
I totally agree with all you have said.

Whilst I am /was well aware of the relationships with Ohms law ,body resistance , voltage ,current, ac , dc , higher frequencies . environmental conditions , time factor etc ,I found your detailed results of electric currents through the human body , very interesting
In one of my posts I referred to 32v ac accident
That man was in a bad area [very confined space ,steel drive shaft tunnel of a ship] faulty light lead draped around neck , hot sweaty.
He tripped & fell between the shaft & floor,it would be a little difficult to get up & the best of time but not easy when your body is humming @ 50cycles
It was estimated he was in that situation for about 5 mins , he did not die but was a very sick man
Not sure if he ever did return to work.
The instance of the welder [hot & sweaty] was again inside a steel vessel & again as was is common with many welders had lead draped around shoulder
to make it easier to drag around .
He actually was with another worker,who had not been trained in how to respond to such a situation.
It was estimated he was only connected to the 72 volts for a couple of minutes but was unconscious by time power was disconnected.
He did not recover.

In both caes I was in the area ,& had the job of finding out just how the shock had been recieved

Thank you for your contribution to what I believe is a very important subject


Peter

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Follow Up By: Charles Jenkinson - Thursday, Jul 29, 2010 at 01:07

Thursday, Jul 29, 2010 at 01:07
Hi Allen and Peter,

Thank you for your kind words. I can certainly see that you have both had a lot of experience dealing with the consequences of electricity when things do not go to plan. These experiences can be incredibly distressing, for sure.

It most certainly is an important subject, and one that is generally poorly understood by many in the public - but I guess such is the irks of topics well-known by professionals and qualified tradespeople in a particular field.

By all means, Allen, file away my spiel! :-) I hope it comes in handy one day :-) My hope is that any further threads on this forum that head down the same path as this one can either have the link to this thread pasted, or the original text copied across by a fellow member. If it saves someone's life, or even prevents an injury by making a reader (past or future) less complacent/more respectful of the dangers of electricity, then it's served its purpose.

Kind wishes,
Charles
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Follow Up By: Member - John and Val - Saturday, Aug 07, 2010 at 11:27

Saturday, Aug 07, 2010 at 11:27
Charles,

Thank you for your authoritative yet highly readable post. It would be good to have your words filed more permanently and accessibly. It is too likely to be lost to sight in the forum. A member blog is ideal for this sort of storage, but I note that you do not appear to be a member.

Allen - Have you stored Charles' essay somewhere we can point to? I'd like to link to it in our Electricity for Camping blog.

Cheers

John
J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein

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Follow Up By: Allan B, Sunshine Coast, - Saturday, Aug 07, 2010 at 14:05

Saturday, Aug 07, 2010 at 14:05
Hi John,

I have simply filed Charle's essay on my computer which is not accessible to others....... at least I hope not!

But I agree that it should be readily available to forum users. Could it not be an addendum to your Electricity for Camping blog? With appropriate acknowledgement to Charles of course.

Cheers
Allan

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Follow Up By: Member - Charles Jenkinson (WA - Saturday, Aug 07, 2010 at 14:55

Saturday, Aug 07, 2010 at 14:55
By all means! Appreciate the link!

I'm actually a member now, so I should be able to put it in a blog.

I'll let follow up when this is done.

Charles
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Follow Up By: Member - John and Val - Saturday, Aug 07, 2010 at 15:39

Saturday, Aug 07, 2010 at 15:39
Hi Allan,

Problem Solved! And Charles, welcome aboard!

Cheers

John
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Follow Up By: Allan B, Sunshine Coast, - Saturday, Aug 07, 2010 at 17:34

Saturday, Aug 07, 2010 at 17:34
Yes, welcome as a member Charles.

I look forward to your participation in what is a diverse and informative forum and hope I get to meet up with you along the track sometime.

Cheers
Allan

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Follow Up By: Member - Charles Jenkinson (WA - Saturday, Aug 07, 2010 at 19:15

Saturday, Aug 07, 2010 at 19:15
Thank you! I have been a visitor for a few months now, so it's good to be taking the next step.

I'm sure it's only a matter of time. Look forward to sharing a fire at some stage!

Charles
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Reply By: Mike DiD - Friday, Jul 30, 2010 at 07:33

Friday, Jul 30, 2010 at 07:33
Appliances are earthed for one reason - to reduce the chance of an electric shock. If there is a fault and 240volts is connected to the case, a fuse will blow.

If the Charger has an Earth Terminal, you connect this to the bodywork of the car and if the Extension Lead has good earth conductor, then you will have similar protection in case of a fault e.g. the Extension Lead gets pinched in the door and only the Active conductor contacts the bodywork. The fuse will blow, even if there is no Safety Switch (RCD).

I don't see any reason to assume that either the Positive or the Negative output of the Charger will be connected to Mains Earth.

Safety Switches and Double Insulation are other approaches which provide protection.
AnswerID: 425719

Follow Up By: oldtrack123 - Friday, Aug 06, 2010 at 21:22

Friday, Aug 06, 2010 at 21:22
Hi Mike
RE :'
#1
Appliances are earthed for one reason - to reduce the chance of an electric shock. If there is a fault and 240volts is connected to the case, a fuse will blow.

#2
If the Charger has an Earth Terminal, you connect this to the bodywork of the car and if the Extension Lead has good earth conductor, then you will have similar protection in case of a fault e.g. the Extension Lead gets pinched in the door and only the Active conductor contacts the bodywork. The fuse will blow, even if there is no Safety Switch (RCD).

#3
I don't see any reason to assume that either the Positive or the Negative output of the Charger will be connected to Mains Earth""

My comments:
#1 Yes The fuse may blow but not with ALL types of faults & you will most likely be dead long before ANY FUSE blows,THAT'S WHY RCDs ARE NOW MANDATORY
#2 As for #1above

#3

The negative of the charger is connected to the battery whose negative is usually connected to the chassis.
The chassis & metal cladding, frame, etc SHALL be connected to the 240v earthing system BY the rules

Peter
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