Two isolating transformers in touching distance in bathroom

[Chris N]

Just trying to get my head around this one.. discovered two shaver sockets in a bathroom, 1 in a cabinet, 1 wall mounted. Both sources from same circuit.

Scenario is.... plug shaver into one then plug shaver into other. There is a fault on both shavers... so because holding both shavers current flows through body but will never cause the circuit to disconnect because no earth path in isolating transformers.

Any come across this before... wo UK ld you class as a C2 or C3.

 

[DetlefSchmitz]

Since shaver sockets are specifically allowed, I don't see where the failure comes from. I'm not even convinced that in the unlikely scenario you detail, there would actually be the current you assume.

 

[Harry Bloomfield]

Scenario is.... plug shaver into one then plug shaver into other. There is a fault on both shavers... so because holding both shavers current flows through body but will never cause the circuit to disconnect because no earth path in isolating transformers.

They are isolating transformers, there is no voltage referenced to ground, nor between the two shavers, either pole of the output.

 

[JohnW2]

.... I'm not even convinced that in the unlikely scenario you detail, there would actually be the current you assume.

I think I'd go further than that and say that I'm pretty convinced that, unless there were faults in both transformers, as well as in both shavers (and we really need bernard to estimate the probability of those four simultaneous faults ), no current would flow between the two faulty shavers, through a person or otherwise.

Kind Regards, John

 

[Chris N]

I discussed with a lecturer on 18th edition course.... he said that there was a danger and although very unlikely the body would complete the circuit and depending on the resistance of skin (wet or dry) potentially prove fatal.

Could it be he was thinking 1 isolating transformer to 2 seperate outputs which is not allowed?

 

[JohnW2]

I discussed with a lecturer on 18th edition course.... he said that there was a danger and although very unlikely the body would complete the circuit and depending on the resistance of skin (wet or dry) potentially prove fatal.

I'm afraid that, lecturer or not, he does not know what he is talking about. As I recently wrote, in the absence of faults in both isolating transformers, as well as both shavers, there would be no path for current to flow through a person between the two faulty shavers.

Of course, even if there were only one transformer/socket (and one shaver), if there were simultaneous faults in both the one transformer and the one shaver could result in a (potentially fatal) shock if they touched the faulty shaver at the same time as touching something earthed - but that's nothing to do with the two sockets/transformers scenario you asked about.

Kind Regards, John

 

[Chris N]

Thanks John

 

[bernardgreen]

and we really need bernard to estimate the probability of those four simultaneous faults

I do not estimate the probability, I consider what would be necessary if ( when ) the improbable/impossible event (or combination of them ) happens.

A few months ago two improbable events happened a few hours apart. Both had been seen as probable and therefore plans were in place to deal with them. The first event was being dealt with when the second event happened. There would have been no problem if there had been two separate teams of trained people. But there weren't two teams.

There was a second team but it was not an official team so although they mobilised and sucessfully dealt with the second incident they were officially breaking all the rules.

The matter is being investigated so details cannot be put in a public domain.

 

[JohnW2]

A few months ago two improbable events happened a few hours apart. Both had been seen as probable and therefore plans were in place to deal with them.

That's a bit confusing - they can't have been "two improbable events" and "Both seen as probable"! If you mean that both events were regarded as probable but that the simultaneous occurrence of both was regarded as improbable, even that is a doubtful statement - in as much as the simultaneous occurrence of two 'probable' independent events is not all that improbable!

It is obviously in the nature of probability that, no matter how 'incredibly improbable' they are, events, or combinations of events, which are 'incredibly improbable' can, and do, sometimes occur. The issue is in deciding how probable a very unlikley event has to become for it to warrant consideration and attention.

In context, I would imagine that even you would probably agree that the probability of two shavers and two isolating transformers all simultaneously becoming faulty (with faults that, individually, would each be very improbable) would be too small to even think about, wouldn't you?

Kind Regards, John

 

[ericmark]

I discussed with a lecturer on 18th edition course.... he said that there was a danger and although very unlikely the body would complete the circuit and depending on the resistance of skin (wet or dry) potentially prove fatal.

Could it be he was thinking 1 isolating transformer to 2 seperate outputs which is not allowed?

Oh dear, and he is a lecturer? there are two types of wire wound transformers, one the primary and secondary are wound on top of each other, the other there are two independent windings on the same iron core, even when on top of each other there is often a earthed foil between both windings, but with the two independent winding type it is nearly impossible for the secondary and primary to ever connect together, it would need some physical damage not simply an overload.

So there is no problem having a row of 6 shaver sockets as long as each one has its own isolating transformer, the worry is that a person instructing did not know this, why is he giving a lecture when he is so out of touch with his subject?

Not the first, guess will not be last teacher or lecturer who does not know their subject, I remember my son coming home from school and telling me his science teacher had asked the question. "There are two types of transistor, can anyone in the class name them?" son (licensed radio amateur) answered "field effect and bipolar" teacher replied "no it's PNP and NPN" son laughed. OK in this case not quite so bad, but why was he teaching?

That evening parent teacher meeting, and he still had not realised his error, said oh is a field effect a new transistor, well no actually invented before bipolar however not perfected until a lot latter.

Next he will be saying James Watt invented the steam engine, but Hero built a model 1000's of years before.

What is wrong with admitting "I don't know"? rather than giving the wrong answer?

 

[JohnW2]

Oh dear, and he is a lecturer? ... the worry is that a person instructing did not know this, why is he giving a lecture when he is so out of touch with his subject? ... Not the first, guess will not be last teacher or lecturer who does not know their subject ....

Quite so. As I wrote ...

I'm afraid that, lecturer or not, he does not know what he is talking about. As I recently wrote ...

What is wrong with admitting "I don't know"? rather than giving the wrong answer?

The most worrying (and, in some contexts, most dangerous) people are those who "do not know what they do not know", and that could be the case here - i.e. that the guy in question actually sincerely believed that what he was saying was correct. I suppose that the really worrying thing in this case is that it's not simply a matter of incorrect beliefs about one specific thing (which probably applies to many/most of us!) but appears to indicate a lack of understanding of some of the crucial underlying basic principles.

Kind Regards, John

 

[Chris N]

Thank you all for the information. I was trying to get my head around the issue and hadn't thought about it before. I carry out many EICRs yearly and like to look primarily at safety. Although the circuit in question was installed in 2000 and under 16th edition regs no RCD was provided. I didn't see supplementary bonding at the radiator or behind the shaver point but will carry out a lead test between exposed pipework/ radiator and the cpc. At worst I can see it as a C3. Add to that no fan isolators. It's a rental property and there have been no checks carried out over 19yrs as the Landlord feels he can prove it's safe. (I think hes a Jedi knight). The previous tenants installed the cabinet next to the shaver point which has it's own shaver point,lights and demister pad. I believe new legislation next year will force the issue of having inspections carried out.

 

[ericmark]

In Wrexham near where I use to live, the local mines closed, the lecturers who did the courses on mining were not made redundant, but moved to teach other subjects, to be fair in most cases they did know what they were teaching, maths is maths does not really matter if used to build cars or mine shafts, OK may us i instead of j, but in the main it was OK, however there were times when they got it wrong, the mining electrician is use to industrial items, and to him a ring main is not the ring final used in domestic.

As to teaching 18th edition, he is showing one short cuts in memory so you can answer questions in allotted time, the exam shows you can read a book, and the standard questions I will admit with 16th and 17th did seem odd. Did one really need to know difference between skilled and competent, OK gone now, but that was a regular question, and other!!!

So in real terms it is a lecture how to remember, not how to do electrical work. Sure an English or History teacher could lead that course just as well as an electrician.

I remember doing it in primary school, chanting out one two is two, two twos are four, be it learning times table or BS7671 it is the same skill, when we got to 19 times we did not remember we worked it out or looked it up.

However I may be able to remember 25 x 25 is 625, but if asked 24 x 24 then would need to find out the hard way.

 

[bernardgreen]

re-written

A few months ago two improbable events happened a few hours apart. Both had been seen as improbable but possible and therefore plans were in place to deal with them just in case the improbable did happen.

 

[bernardgreen]

would each be very improbable) would be too small to even think about, wouldn't you?

but we are thinking about and even typing about it