3ph to Single Phase

[Harry Bloomfield]

The way I understand it, you'd want 1 phase core and neutral and earth for single phase.

That is correct.

However the frequency may be out of kilter. If your equipment is not sensitive to the frequency then this is acceptable.

Eh? UK mains single and three phase is 50Hz.

 

[Harry Bloomfield]

Yes but 3 phase is slightly different and the phases are different pulse widths.

Sorry, but no, it they are sinusidal rather than pulse and are 120 degree out of phase with each other and perfectly even. Easiest to imagine as a 3 cylinder, rotary engine with each conrod and ignition spread 120 degree, equally around the crank shaft.

 

[bernardgreen]

If the earth on a 3Ph item became faulty and a phase make contact with the metalwork, the metalwork will then be live and at a potential of 240v to earth. If two or three phase make contact, then the MCB will trip. Should two separate 1Ph items suffer that same fault and be adjacent to each other, then should you make contact with the metalwork of both items you would be across the much higher potential of 415v.

Many of the production lines I have experience of had bonding between adjacent machines. In some places it was referred to as auxiliary Earthing.

 

[SUNRAY]

Many of the production lines I have experience of had bonding between adjacent machines. In some places it was referred to as auxiliary Earthing.

Yep very common. and onto the cable management systen too.

 

[plugwash]

doh - already posted this on a previous page.

 

[plugwash]

That supplier has some rather..... interesting leads in his collection. One is a 32A 3P+N+E plug to 16A 3P+N+E in-line socket plus 16A 2P+E socket, without any inline protection. And the infamous 32A to 2 x 16A unfused splitter.

Is there actually a standard for such leads? There are standards for the plugs and cables of course, but is there a standard for the leads as a whole? and for how the responsibility to ensure a safe configuration divides between the person making a lead and the person using the lead?

I'm fairly sure I looked at IEC 60309 once, and I remember it having a bunch of detail on how the plugs/sockets should be manufactured, but I don't remember it having anything on how they should be used.

 

[SUNRAY]

Is there actually a standard for such leads? There are standards for the plugs and cables of course, but is there a standard for the leads as a whole? and for how the responsibility to ensure a safe configuration divides between the person making a lead and the person using the lead?

I'm fairly sure I looked at IEC 60309 once, and I remember it having a bunch of detail on how the plugs/sockets should be manufactured, but I don't remember it having anything on how they should be used.

In very simple terms the connector rating and the cable rating should be protected by a suitable over current protection device such as fuse or MCB, ie a 16A socket protected by a 16A device etc. (Let's not delve into BS7671 clauses for this explanation.)
On that basis one reasonally expects a 32A socket to be protected by a 32A device and therefore using a 32A plug to 16A socket adapter lead (or the popular 32A plug to 2x 16Asockets) will mean the socket and the following 16A extention lead etc is not correctly protected.

One of the problems with these types of connectors is they get used for temporary services such as public entertainment and building sites where 2 way splitters are very common and it becomes very easy to exceed 16A, in fact in such circumstances people would think nothing of using a 3KW kettle on top of the predicted load.

 

[SimonH2]

Hence why, from memory, you can find such leads with an inline housing for a (e.g.) 16A MCB which is the logical way to do it - but of course it makes the leads bulkier and more expensive. So an average "not well educated in the nuances of electrics and protection" person would look at the two and wonder why on earth he should pay so much - before going with the cheaper option.
And of course, for most of the time, for most situations, it all works out OK.

Mind you, some years ago I was staying in a hotel, and at breakfast they had two toasters and two coffee machines on a table. I had a look round the back and found them all plugged into one 4way extension lead running off one 13A socket Clearly it had been done that way for some time and they'd not burned the place down ...

 

[SUNRAY]

Mind you, some years ago I was staying in a hotel, and at breakfast they had two toasters and two coffee machines on a table. I had a look round the back and found them all plugged into one 4way extension lead running off one 13A socket Clearly it had been done that way for some time and they'd not burned the place down ...

This is a situation I come acrosss on a very regular basis, Village/school fetes seem tobe the worst where a line of borrowed 'domestic' extention leads are pluged in to each other and on the final cassette type lead with 4 sockets we find all 4 filled with: urns, toasters, kettles, candyfloss machines etc and they have absolutely no idea why they have such difficulties.
One village church in particular got into the habit of hiring a ~10KW generator at considerable expense relative to the amount raised {which came with a (3ph) cable with 3x DSSO's} to overcome the problem. For the next 3 years I provided correct extention leads from the church for the event at a fraction of the price.
One of the offices I visited had the unmistakeable smell of 'warm cable', they had 9 blocks of 3 desks, each with a 6way lead powering 3 pc/monitor. However all 37 positions were powered from a single 13A socket and they were very aware they had to power each station one by one to avoid blowing the fuse. There was only the one 20A radial in the room.

 

[JohnW2]

Mind you, some years ago I was staying in a hotel, and at breakfast they had two toasters and two coffee machines on a table. I had a look round the back and found them all plugged into one 4way extension lead running off one 13A socket Clearly it had been done that way for some time and they'd not burned the place down ...

A common sight.

However, is this not why we have regulations? If the circuit's OPD gives adequate protection to the circuit's fixed wiring, and if the (I imagine 13A) fuse in the extension lead's plug gave adequate protection to the lead of the extension, then there surely should be no risk of "the place burning down", unless the regs are incorrect in what they tell us about CCCs, would there?

Even the plug of the extension lead itself is, I presume, deemed to be safe from thermal damage (due to overcurrent) if fitted with a ≤13A fuse.

Kind Regards, John

 

[Harry Bloomfield]

Even the plug of the extension lead itself is, I presume, deemed to be safe from thermal damage (due to overcurrent) if fitted with a ≤13A fuse.

Trouble is, that 13amp plugs and sockets do often suffer, if under a continuous 13amp load and a 13amp fuse requires much more than a 13amps steady loading before they react.

 

[JohnW2]

Trouble is, that 13amp plugs and sockets do often suffer, if under a continuous 13amp load and a 13amp fuse requires much more than a 13amps steady loading before they react.

True - a 13A BS1362 fuse can allow up to about 22A to flow 'indefinitely'.

However, if BS1363 does not require a plug to be able to safely cope with a current that a 13A BS1362 fuse could allow to flow, then I would say that the Standard was not 'fit for purpose' !

Kind Regards, John

 

[Harry Bloomfield]

However, if BS1363 does not require a plug to be able to safely cope with a current that a 13A BS1362 fuse could allow to flow, then I would say that the Standard was not 'fit for purpose' !

I have long ago said exactly that, judged by the number of burned out 13amp plugs and sockets. They are mostly fine for todays modern low current appliances. For things rated at 3Kw, good quality plugs and sockets are needed to sustain such loads, or as with 3kw water heaters and storage heater - wired through a 20amp DP isolator.

 

[JohnW2]

I have long ago said exactly that, judged by the number of burned out 13amp plugs and sockets. They are mostly fine for todays modern low current appliances. For things rated at 3Kw, good quality plugs and sockets are needed to sustain such loads, or as with 3kw water heaters and storage heater - wired through a 20amp DP isolator.

I'm glad you agree - particularly, of course, since I was referring to a problem (seemingly with the requirements of the Standard) much 'worse' than the one you describe.

Although it's something I've personally very rarely experienced, as you imply, people seem to sometimes have problems with a BS1363 plug/socket carrying a sustained current of 13A (and certainly 2x13A with two plugs and a double socket) - but, as I said, the Standard surely really ought to require that the plugs (and sockets) could safely handle the current that a 13A BS1362 fuse could allow to flow (about 22A or whatever).

Kind Regards, John

 

[Harry Bloomfield]

Although it's something I've personally very rarely experienced, as you imply, people seem to sometimes have problems with a BS1363 plug/socket carrying a sustained current of 13A (and certainly 2x13A with two plugs and a double socket) - but, as I said, the Standard surely really ought to require that the plugs (and sockets) could safely handle the current that a 13A BS1362 fuse could allow to flow (about 22A or whatever).

It seems much more common now, than I think it used to be. I think standards in manufacturing of both sockets and plugs have declined - they might meet spec., but do they meet spec. long term?

I think the 13amp fuse only helps by blowing when there is a short, rather than a bit of overload, even then - more often than not in the case of a short, it's the MCB which trips rather than the 13amp fuse.