Phase Identifier

[JohnW2]

.... appropriate labels of "400V between adjacent enclosures" sprinkled around the place where someone is likely to have multiphase connections open.

As I wrote earlier, what's the point? What precautions would you take if you knew there was a 400V pd between adjacent enclosures (or, indeed, a 400V pd within the same encloseure) that you wouldn't take if you knew that the maximum pd present was 'only' 230V?

Don't get me wrong, I can sympathise with you. I used to be pretty obsessional about "400V within enclosure" and "400V between adjacent encosures" labels - until, a year or two ago, folk here asked me the above questions (hence made the above point)!

Kind Regards, John

 

[Lectrician]

I wouldn't label the sockets with just the phase - that is of absolutely no use at all.

If you are going to label, do it as mentioned above. DB1-5/L2 for example.

Even with very early computers, different phases didn't make much odds, it was more different earthing systems that caused the problems.

Even the old Token Ring type coax networks didn't bat an eyelid at having different PC's/terminals/printers dotted around buildings on different phases.

 

[Iggifer]

If you are going to label, do it as mentioned above. DB1-5/L2 for example.

Particularly useful if there's multiple DB's in the install, and will be useful for the end user if anything trips

 

[Lectrician]

It's always done like that on well specced and executed commercial jobs. If the design is done well enough, you can order engraved sockets in advance too.

 

[OwainDIYer]

.... appropriate labels of "400V between adjacent enclosures" sprinkled around the place where someone is likely to have multiphase connections open.

As I wrote earlier, what's the point? What precautions would you take if you knew there was a 400V pd between adjacent enclosures (or, indeed, a 400V pd within the same encloseure) that you wouldn't take if you knew that the maximum pd present was 'only' 230V?

If I'm working live (which I never do, of course, but some professional electricians do) standing on my rubber mat, and I touch same phases with each hand, there is no pd and no across-the-torso shock.

On a multiphase then a shock is possible phase-phase across the torso not just phase-earth.

It's also a useful reminder to me that my 250V test meter is not going to be happy if it use it on 400V (I still think 415V...).

 

[JohnW2]

If I'm working live (which I never do, of course, but some professional electricians do) standing on my rubber mat, and I touch same phases with each hand, there is no pd and no across-the-torso shock. On a multiphase then a shock is possible phase-phase across the torso not just phase-earth.

That's all true, but given that there will nearly always be exposed neutral and/or earth, as well as L/phase, there is going to be an opportunity for a 230V 'across-the-torso' shock even when only one phase is present. If we're talking 'across-the-torso' shocks, then the difference between 230V and 400V (or between 240V and 415V) is really pretty irrelevant.

As I said, I used to think like you, but have been convinced that it's probably really not very helpful.

Kind Regards, John

 

[ban-all-sheds]

If we're talking 'across-the-torso' shocks, then the difference between 230V and 400V (or between 240V and 415V) is really pretty irrelevant.

It's not.

Given a light contact between conductors with skin that is dry, possibly a bit work-hardened, I can see how the difference between 230V and 400V could be the difference between "**** me" and arrest or some kind of fibrillation.

If I strapped you down and said "I am going to zap you across your torso for 200ms - do you want 230V and 30mA or 400V and 52mA?", would you say "I don't care, it makes no difference"?

 

[JohnW2]

If we're talking 'across-the-torso' shocks, then the difference between 230V and 400V (or between 240V and 415V) is really pretty irrelevant.

It's not. Given a light contact between conductors with skin that is dry, possibly a bit work-hardened, I can see how the difference between 230V and 400V could be the difference between "**** me" and arrest or some kind of fibrillation. If I strapped you down and said "I am going to zap you across your torso for 200ms - do you want 230V and 30mA or 400V and 52mA?", would you say "I don't care, it makes no difference"?

The point is that (particuarly without a satisfactorily-functioning RCD - and we know that they can 'fail'), 230V across the torso is more than enough to kill, so any sane person would be taking 'every precaution possible' to avoid receiving such a shock, even if no pds >230V were present. That would leave them with no 'extra precautions' to take if they were told that a pd of 400V was present - hence the dubious utility of 400V labels.

Kind Regards, John

 

[ban-all-sheds]

That's all true.

Labels used to be required - it had slipped my mind that they had been dropped - as you say it makes no difference to how you work.

I just don't think that IRL a 70-75% increase in the current that would flow through bits of you is irrelevant.

 

[JohnW2]

That's all true. Labels used to be required - it had slipped my mind that they had been dropped - as you say it makes no difference to how you work.

Indeed. As I keep saying, I used to be a supporter (and user) of such labels, basically because I had not thought it through properly. However, folk here convinced me that the labels really achieved nothing, and the IET now seem to agree.

I just don't think that IRL a 70-75% increase in the current that would flow through bits of you is irrelevant.

I understand what you're saying, but you're really just criticising my choice of words. If the impedance of the 'shock path' is such that 230V would result in more than enough current to kill, then an increase in current beyond that (due to a higher applied voltage) is of questionable 'relevance' - one can only die once!

It's also worth remembering that, with good skin contact, the currents which flow through the body are likely to be consdierably higher than the figures you mentioned (at either 230V or 400V). One's hope obviously is that an RCD will prevent death by limiting the duration of that very high current.

Kind Regards, John

 

[ban-all-sheds]

If the impedance of the 'shock path' is such that 230V would result in more than enough current to kill, then an increase in current beyond that (due to a higher applied voltage) is of questionable 'relevance' - one can only die once!

But what if at 230V it's not lethal, or has only transient effects, but at 400V it's more serious?

 

[JohnW2]

But what if at 230V it's not lethal, or has only transient effects, but at 400V it's more serious?

Yes, there are bound to be marginal situations (degrees of contact) in which 400V would kill (or do serious harm), but 230V wouldn't - so you're right that I probably should not have used the word 'irrelevant'.

However, I think we are agreed that this should not result in any relaxation of the degree of care and precautions one exercises when dealing with 'only 230V', so that the 400V labels, per se, are 'irrelevant' to safety.

I do continue to label when two or more phases are present in the same enclosure - but primarily as a reminder that care needs to be taken to achieve 'complete isolation' of the contents.

Kind Regards, John

 

[SimonH2]

Well there should never be a connection between a phase and any data lead - other than via the power supply of the equipment which should provide a suitable degree of isolation. For a data cable linking equipment on different phases to be a problem, you would need both items of equipment to, simultaneously, have a fault that connected the data circuit to phase without tripping any circuit protection.

There may be a cause for concern where all items in the group are of the "2 pin supply with no earth" variety which rely on insulation for safety. IN this case, each item will have a very weak pull-up to around 1/2 the phase-N voltage (120V), and that means around half the phase-phase voltage (207V) between items of equipment on different phases.
But it's such a weak pull-up that currents should be negligible (measured in µA).

 

[333rocky333]

when i was taught it, data cables were like a twin coax with b and c type connections, i was told that if a voltage inadvertantly appeared on the metal casing it could be transferred to the other appliance, although that voltage may have been significantly low to be dangerous , i suppose it could be higher when measured to the other phase supplying the other computer.
This was the early 80s a lots changed since then

Wheres securespark hes the 80s man

 

[SimonH2]

That would have been 10base2 ethernet, aka thin-net. Yes it's a 50ohm coax with BNC connectors which daisy chains down every device on the network. There were various products on offer that would make the user connections look more like a star connection but they all brought the cable out to the workstation and back to the wall to go on to the next one.
Great fun to diagnose a problem - if an end isn't terminated then the whole thing doesn't work. If you have a break in the cable then you get two segments with an unterminated end - so you can't just look at what's working to figure out where the break is because nothing works.

The coax is supposed to be isolated from each individual computer (to prevent earth loops and excess current in the screen), but earthed at one point. But this is still fairly irrelevant in terms of what phase the devices are connected to. For that to matter, you need a fault on one device that will make the cable live without blowing a fuse (so an open earth and a phase to chassis fault and the network cable linked to the chassis) in order to make the cable live; and then you need another combination of faults elsewhere.

IIRC the connection is transformer coupled on the network card (or transceiver if external) so no path for DC or low frequency signals onto the cable.

It's a few years since I've had any coax in my networks. I doubt if many of my colleagues have even seen it ! A while ago I wanted a bit of cable (and some cards or transceivers) for a talk and couldn't lay my hands on any.