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Assume that a person is touching a bare wire when the person is connected directly to the ground system of a home electrical system.

If a hot wire from, say, a washing machine, suddenly shorts to its chassis, doesn't that route to ground, and isn't our human suddenly now part of a deadly circuit involving the hot wire?

This question came about from hearing about people who do this on purpose. Many people now practice "earthing", physically linking themselves to the earth ground plug of their home's electrical system. They go as far as sleeping on mesh wire sheets plugged into ground to protect from stray EMF.

This question is not to be a commentary on the earthing theories.

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    $\begingroup$ Those particular "many people" are completely nuts. I bet they wear magnet bracelets and sleep with power crystals. $\endgroup$ Jan 29 '16 at 13:32
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    $\begingroup$ Aside from "earthing", there are other, reasonable, situations where a person may be more grounded than usual. I work with explosive materials, where static shocks can be quite catastrophic. I wear electrically-conductive shoes when working with said material to keep myself grounded and prevent static build-up. The extra grounding of course increases my risk of electric shock due to the mechanism you're asking about. $\endgroup$
    – Carlton
    Jan 29 '16 at 15:06
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No, the whole point of the earth in an electrical system is to provide a safe direct route away from the rest of the system.

If there were any risk to someone connected to earth, there would also be a risk to every other device connected to the same earth. That would defeat the purpose of the earth. When a device develops a fault resulting in power going to earth, then as long as the circuit is designed properly, almost all the current will go through no other device.

People who practice earthing their own bodies out of some peculiar ideas about health benefits may well have problems, but these are the remit of the Cognitive Sciences Stack Exchange and/or problems of science education, not problems from faulty electrical devices.

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  • $\begingroup$ If you earth yourself and com into contact with a live wire, the path of least resistance between live wire and earth is through you. Put another way: the resistance of the path wire - you - earth is lower than otherwise, so more current. What you want to do is earth the electrical system (without yourself in the path). $\endgroup$
    – mart
    Jan 29 '16 at 12:10
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    $\begingroup$ @mart that's not what the OP asked though: the OP has asked about a short in the washing machine that results in current going to the washing machine's earth; not to earth via the earther $\endgroup$
    – 410 gone
    Jan 29 '16 at 12:16
  • $\begingroup$ The first two versions of the question are about a person earthing themselves, then touching a wire. $\endgroup$
    – mart
    Jan 30 '16 at 20:29
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It should be safe. The safety standards already assume a user is connected to ground, since that's the worst case in terms of probability of electrocution. You are supposed to be two independent failures away from getting zapped, already assuming you are connected to ground.

For equipment with a conductive shell, that shell is tied to ground. To get zapped, line has to get shorted to the shell, and the shell connection to ground has to be broken. If the first doesn't happen, then there is nothing "hot" to connect yourself to. If the second doesn't happen, then the breaker will trip.

For insulated equipment, the device often has no ground connection at all. However, things inside are "double insulated". Wires are insulated on their own, but then shell then provides another layer of insulation between hot and user. Any conductive parts then also have minimum clearance and creepage requirements from anything hot, and units are generally "hi-pot" tested and tested for leakage.

Even though you are supposed to be safe when grounded, it does remove one extra layer of protection. Supposed the unlikely failures do happen so that the case of a unit gets connected to line power. If you're grounded, then there is a path thru you, and you get zapped when you touch the case. If you weren't connected to anything else, you might not even notice you were touching something with live power on it.

This is why there are special rules in areas where people are particularly likely to be connected to ground via low resistance, such as in a bathtub or around any sink. In some jurisdictions, outlets in such areas must have ground fault interrupters. That's a special kind of circuit breaker that not only trips due to excessive current, but also when there is a imbalance of current going out one of the AC leads but not coming back on the other. The missing current must be going from the line side to ground via some separate and unintended path, which causes a ground fault interruptor to shut off the power.

So in summary, while you are supposed to be safe, you are one level closer to a the right failures causing you harm, although the probability of such a set of failures is low. If you plan to deliberately ground yourself regularly, it might be a good idea to replace all your circuit breakers with ground fault interruptor types.

Of course grounding yourself to somehow protect yourself against EM waves is silly, and can have the opposite affect in many circumstances, but that's another discussion.

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  • $\begingroup$ In areas where GFCI outlets are not commonly used, such as a bedroom, what is the current safety precaution for a hot wire faulting to ground? I assume it's a breaker at the box, tripping at a much higher current than would've been needed to pop the GFCI? Or does a breaker even get involved in a fault like this? $\endgroup$ Feb 3 '16 at 1:26
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I'm no electrical engineer and my last training in safety around voltages is ages back. I will answer the question according to the wording it had in the first versions:

Many people now practice "earthing", physically linking themselves to the earth ground plug of their home's electrical system. They go as far as sleeping on mesh wire sheets plugged into ground to protect from stray EMF. [...] If a hot wire from, say, a washing machine, suddenly shorts to its chassis, doesn't that route to ground, and isn't our happy "earther" suddenly now part of a deadly circuit involving the hot wire?

Basically, yes. As pointed out in Olins answer, all or most devices with a conducting chassis have this grounded for safety reasons. In these cases, it should make little difference if the person is grounded.However ...

Let's look at another scenario: Your alarm clock is (not your cell phone but) an older model with an AC connection. You managed to damage the cable near where it enters the (plastic) chassis and touch the live wire when fumbling for the thing one early morning.

Case 1) You are not grounded in any special way, but lying on a cotton sheet on some mattress on a wooden bed. Resistance for electric current to the ground will be very high. Electrically, you are - grossly simplified - now a capacitor connected to an alternating current via a 1k$\Omega$ resistor (your arm).

Case 2) Same as before but you lie on a grounded mesh. This time you are a 1k$\Omega$ resistor between the live wire and ground. Far more current will flow.

High resistance towards grounding plays a minor role in safety around eletricity. The normal case is that a device is built safely as described. For work on electrical equipment, there's 5 basic rules:

  • switch the power supply to the device you work on off
  • secure it against switching on,
  • confirm by measurement that there's indeed no voltage
  • first ground then short circuit the live wires so if the device is switched on the circuit breaker will engage
  • cover nearby devices, if still connected to power supply

So you consider how not to touch a life wire in the first place, not about where the current will go when you do or what the resistance is. The only instance I know of where this was given serious consideration is safety shoes, these need a high resistance according to the relevant industry codes.

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  • $\begingroup$ Mart, case #2 is actually an eye opener and (pardon the pun) I am shocked it has not been raised before. If our earther is grounded and happens to accidentally touch a hot wire anywhere, he/she is suddenly a path to ground, yes? True, it is not the original scenario I raised (a hot wire hitting the chassis of an appliance), but your case does seem to be a very valid safety concern in not tying yourself to ground. $\endgroup$ Feb 1 '16 at 13:32
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    $\begingroup$ exactly. Maybe I phrased it more complicated than need be, there will always be a shock since AC systems don't need a closed circuit strictly speaking, but far more severe when the person is grounded. If you (or someone else) feels the wording is unclear, please say so (or write what you think I meant) so I can correct myself. I want to clear on this. $\endgroup$
    – mart
    Feb 1 '16 at 13:44
  • $\begingroup$ I think your explanation is clear Mart, and perhaps I phrased my OP badly. I sensed a danger to the earther but couldn't put it into words very well--you did. $\endgroup$ Feb 2 '16 at 17:18
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As long as the resistance of the ground path is less than the resistance of the body of the person touching the wire, the electricity will flow through the ground path. This will always be the case for any normal electrical ground.

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    $\begingroup$ No - electricity or current does NOT take the path of least resistance. It travels via all available paths BUT the current divides in inverse proportion to the resistance of the path. So if eg the ground wire path has one unit of resistance and the path via your body has 99 units of resistance to ground then about 99% of the current will flow via the ground wire and 1% via your body. $\endgroup$ Jan 30 '16 at 15:26
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    $\begingroup$ Down voted for the same reason @RussellMcMahon commented - electricity doesn't evaluate all paths and then choose just one. Your power strip doesn't power your computer or your monitor. It tries everything at the same time, and current will flow through you if you make yourself part of the circuit. Common misconception, but possibly deadly consequences when you make statements like this to a question about whether mains voltage is safe if it's grounded. Please consider editing or deleting this answer. $\endgroup$
    – Chuck
    Jan 31 '16 at 0:23
  • $\begingroup$ I didn't downvote - but I suggest you remove the "path of least resistance" type comment and replace with something along the lines of my prior comment. $\endgroup$ Jan 31 '16 at 8:38

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