Single-Phase Pin and Three-Phase Socket

<...Recently, one of the workers (at site) inserted the 3 wires of a grinding machine(1 phase) into a 3 phase socket of a temporary supply board. He got fatal injuries....>

In the UK, this action in places of work is prohibited by Statute. All fatalities are reportable to the Health & Safety Executive. For that reason, all electrical activity in UK workplaces must be carried out by a competent person. The penalties for non-compliance are severe, and focus on prosecuting the "controlling mind", not the company in question.

<...what will happen if a worker accidentally connects a single phase (phase, neutral, earth - 3 pin top) into a 3 phase socket....>

The answer is stated in the second paragraph of the original post. The above grinding machine perhaps had an earth/ground wire connected to its case. When such a wire is incorrectly inserted into the outlet connection intended for a phase conductor, it will make the casing live. The operative completes the circuit to earth/ground, and the outcome is described.

It is highly inadvisable to attempt to run a single phase device off a 3 phase supply, as, quite apart from the safety implications for the operative above, the voltage applied to it could be too much by a factor of √3, presenting a threat both to the appliance and also its supply cable.

Ordinarily, 3-phase and single phase supplies to portable appliances will have different plug/socket arrangements, so that it is not possible to connect the appliance to the wrong one.

In the UK, portable appliances in industrial environments are ordinarily 110VAC centre-tapped to earth, so that the maximum voltage that can be experienced under fault conditions is 55VAC. Though unpleasant, a shock at 55VAC is rarely fatal, which is why it is used.

Beware of the arrangements in some South American countries. In Argentina, it is possible to find wall outlets of the same type used for two different voltages.

pwslack; i was under the belief that great Britain was 220 volt single phase from 220/380 , 230/400, 240/415 Wye,(star)volts, 50 HZ systems. do they use a step down 220/110v transformer, or autotransformer with the 110 center taped? thanks perry

In many locations, an installed centre-tapped 55-0-55V supply can be found.

Where only single phase 240V 50Hz sockets are provided to BS1363, a single phase supply is provided by using a portable step-down transformer.

In both cases, 110V sockets are the yellow IEC type.

http://en.wikipedia.org/wiki/Electrical_outlets

I agree with PWSlack completely. If your electrical system had of been wired properly, to any of the standards and codes available in the world, namely the CEC, NEC, IEC or the British Standard (whose name escapes me at the moment) or even the Indian one, this should never have happened.

The plug and receptacle configurations for the different voltages and phase counts are such that an error of this sort is impossible.

Someone has been criminally negligent!! I truly hope the responsible party is found and prosecuted to the full extent of the law in the jurisdiction in which this happened. This worker paid a heavy price for no reason at all other then because of someones greed or stupidity or perhaps both.

As a regulator charged with electrical safety in my jurisdiction, events such as this really make me mad and only reinforces the need for EVERYONE who works in our field to OWN the systems they deploy and maintain and to be fully aware of the state of the system at all times.

This was just plain wrong!

<...I agree with PWSlack completely....>

Username PWSlack does not give personal opinions or statements of policy, therefore any attempt to agree or disagree is abstruse.

I was agreeing with the points you raised, nothing more.

This has been the case of criminal negligence and the result are evident.

These are the reasons, we at CR4 have been advocating again and again please don't play with electricity, if you are not competent enough.

First quesstion- the 3 phase socket and the two phase plugs (even 3 pins) are not supposed to be fit-able and vice versa. Now did a smart electrician wired a 2 phase socket to 3 phase ?

Why did you not go ahead with standard sockets and plugs (eg 4 pins or five pis) for the 3 phase line?

Most of the systems are made foolproof against these. It is we who remove the safety features and kill others.

It will be worth finding who has done the wiring and take action.

And electrical portion is easy

It is Phase connected to phase.

Neutral - phase - so excessive voltage and also in quite a few machines and equipments, the neutral insulation is just a tiny bit weaker.

And then worse - Earth (connected to body of the equipment) to phase.

If there is no Earth fault relay - what has happened was bound to happen. Even if there was, there could be just that bit of arcing, and explosion before the isolation is done.

Dear sir,

you are correct. "the 3 phase socket and the two phase plugs (even 3 pins) are not supposed to be fit-able and vice versa." The worker inserted the 3 bare wires of single phase(230 V) into 3 phase (415 V) socket

prashanth

India

Let me get this correct, the dead worker took the three conductors of this portable appliance and shoved them into a three phase socket?

If that is true... perhaps a nomination for a "Darwin Award" for your worker and charges for the company for having no Safety System in place are called for.

That worker should be banish from this world for not consider the safety rules of electricity and make a hazed place to work with.

It is dangerous just to insert single wire into the socket and assuming that all the socket is 230V supply.

If he was an electrician he deserves a place on the following website.-

http://www.darwinawards.com/darwin/darwin2008-25.html

If he was not an electrician, what was he doing even touching this equipment?

If management was in any way involved, they should be put in prison for a long time.....

This is exactly the result that could happen when well meaning CR4 members answer questions from people who are obviously have totally inadequate training/knowledge of their question....or its possible consequences...

Remember what I always try and push through on CR4? "Safety First". Not answering some queries here is the only way NOT to be involved in possible injuries and deaths.

I am NOT saying that CR4 was involved here in this particular case, but it could have been......

So you are also a darwin fan?
I love that site.

This is a thing I have too often seen to be comfortable. Some guy puts a socket and connects three phases to it. The other guy has three wires in his hands and if it is thrr pin (not preferable, and not seen, but may be there) = presto 3 wires, 3 holes.

If 4 or five, then thinks a bit and may be as my children do, that Ringa Ringa roses.. or similar, randomly selects 3 of them and then the Boom.

In fact just to avoib that aspect, we refuse to have 3 phase sockets at our place. All connections, even temporary are from Switch-boards, And that ensures that it is the electrician who does it. It takes a few minute more, but may be worth it. At least we look at that way. The only plugs are the 3 pin single phase. period.

Connect a 3 phase load to it and nothing happens much, at the worst, the fuse blows off or the starter of the motor trips on the single phasing preventer.

I do some custom electrical device manufacturing and I have ran into this odd dilemma several times. Around here its very common in public places to find a 4 line 50 amp socket intended for high load applications.

Heres the problem I have been in many public places setting up temporary electrical distribution panels and found that in the same building and twice in the same room the 4 line socket is used for 240 volt three phase four line on one and 240 volt single phase four line on another. (Same socket style in each application)

If I wire the distribution box for single phase (two power, one common, one ground) and it gets plugged in to the three phase socket everything goes from 120 volts to 240 volts! The third phase is present where the 240 volt single phase common should be.

I was able to confront the building manager one time and ask why this is set up that way. He said its so people can use either system and get by with only one style of plug. I told him that three phase plugs are different from single phase plugs. He had no clue what I was talking about.

The sockets they are using for both systems are the standard 240 volt single phase 4 wire electric range type. To this day I always tie the common and the ground together in the custom distribution boxes so if they ever get plugged into a three phase socket they immediately pop a breaker. And this happens fairly often.

It may not be exactly code but it has saved loads of expensive electronic devices from being destroyed.

In a westernized country, the building manger could also face a prison sentence too.....

Here we have different plugs for different volatges and for 3 phase or single phase.

I am not trying to say that accidents never happen (that would be a lie) but at least there are a few rules that reduce the number of accidents dramatically.....

But true fools will not be stopped just because of not having the right connector or knowledge....as the Darwin Awards show!!

Natural selection working at its best......

If you connect 1 ph 230V equipment into 3 ph 400 V you will burn or explode the windings in the motor. When the winding melts three things can happen. one option is short circuit of the windings, in that case the amperage will go up and normally blow the fuse or take out the breaker. another option is open circuit, in that case the motor will not work and the fuse might not go out so you still have live 400 volt on the socket. Since the worker got injuries the third option is most likely, that is short circuit to the grounded part of the equipment fex if it is a metal houlsing equipment then the worker will get 400 v when he touches the housing.

Another possibility is that he directly connected the earth on the equipment directly to 400V in that case he was not so smart. One does not intentionally touch 400 V. In that case you have to count on earth leakage protection (ELCB).

of course, the earth connection would be lost and the equipment will become live, causing electrocution. Also, the full phase to phase voltage (400V? or more) will be applied across the terminals and this breaks down any insulation on the grinding machine. It's always good practice to check and verify power supply, install warning & caution notices on electrical equipment and avoid make shift connections.

The explosion is caused by the direct connection of L3 of the 3 phase supply to the ground wire of the single phase cord end. The connection between a hot wire fed by the 3 phase source directly to ground has very little resistance (only the resistance of the copper wire which is about 0.002 Ohms per foot of wire (for 12 gauge)). You can calculate the theoretical measure of current that produces the explosion using Ohm's Law, E=I*R (Units: Volts=Amps*Ohms).

Assuming you have a one leg of a 480V, 3 phase system shorted to a good ground (0.1 Ohm) through 100 Feet of 12 gauge wire , then the resulting current in the circuit is 277/(0.002/100+0.1) = 923 Amps. This amount of current is extremely dangerous, and would probably exceed the current ratings of the devices that supply the voltage including the distribution panel and breaker. If devices in the circuit survive it is only because the duration of the shock is very short because the point of connection melts away almost instantly.

Direction of current flow in a an AC circuit reverses polarity periodically, so assigning a direction is arbitrary. Direction of current flow in a DC circuit is something that Physicists like to argue about. Here is a good description of how DC current flows taken from an educational website:

You can think about current as the flow of electrons, which go from negative to positive, or as the flow of holes, which go the other way. If you are really into semi-conductor theory it makes a difference which one you use, but otherwise you aren't likely to care. We usually use hole flow because the direction agrees with the decision that the early scientists made when they had to pick a direction to use in their calculations. It's traditional.

From: http://www.mste.uiuc.edu/murphy/HoleFlow/HoleFlow.html

In other words, most diagrams show current flowing from the positive to negative (ground), but someone might argue with you no matter what convention you choose.

What has happened here, almost certainly is that the casualty found he had the wrong plug for the receptacle, removed his plug and used the bare wires wrapped around matchsticks or similar to effect a connection. If, as seems likely, he had no knowledge of electrics then he would be quite capable of connecting the earth wire to a phase. the result of course being the metal case of an industrial grinder becoming live at line voltage, 240V in India I believe. He would not, and could not, get a 415V shock unless he was holding the bare wires as he inserted them in to two phases. In all probability this incident could just as easily happened with a single phase socket of a different style to the appliance plug.

Mr Prashanth's concern with intensity and direction of current is irrelevant since currents in the order of 10mA are enough to cause a fatality and, since it was ac, the current went both ways! What he must be concerned with is the company's attitude to careless practices like this. Has no one noticed that this type of botch was being used? Why was a suitable adaptor or additional single phase sockets not provided? Is there a requirement for a socket to be protected with an earth leakage breaker? Was it so protected?

Chas

I'm leaving this pointless blog.

India never went for safety first since the British left.....some things have to be learnt the hard way it would seem.

Also laws are needed to protect people, but life is so cheap in India......sadly. Nobody really cares.....millions more where he came from....

He would probably have been fired from his job if he had asked for an electrician and the correct connector......

It might be interesting to ask what class of worker he was and whether he was a fully trained electrician.....

Byeeeeee

With due regards is it a typical colonial comment?

India never went for safety first since the British left

We too do know for the safety mechanisms, being practiced everywhere (of course courtesy globalisation of the news) and again a few first hand informations of visiting a few suppliers.

This type of comments are uncalled for.

Andy, your comment is ridiculous. Having worked on 5 continents, I'm confident that stupidity is a universal attribute. I have seen similar "short-cuts" in the US, Canada, Mexico, Britain, France, Germany, Spain, Argentina, Honduras, Kenya, Cote D'Ivoire, Thailand, and many other countries. It usually has very little to do with management or enforcement. Rather, some individuals have an inherent belief that they are so smart that the rules don't apply to them. Just a few examples:

• In Britain, a dock worker asked his crane operator mate to lift him onto the deck of a ship so he would not have to walk 30 meters to the gangway (he lost his grip & fell head-first to the concrete dock, killing him);
• In France, an electrician used a copper coin to make a 1200 ampere connector fit better (it exploded 30 seconds after energization);
• In Germany, a pipefitter vented a tank of liquid CO2 to chill his lunch (he was in an enclosed vessel & suffocated);
• In the US, a hotel guest tried to use a 13.2 KV live-front transformer as a stepping stone to go from one balcony to another (she survived, but was permanently paralyzed and horribly scarred).

All of these incidents occurred in developed countries with strong inspection and regulatory environments. In each case, the action was clearly wrong. If the individual had survived, they would probably be fired immediately. Unfortunately, design and regulations don't matter to some people. Every time you make something idiot-proof, the world creates a better idiot.