Unearthed IEC lead.

[John Rumm]

Could be instructive to do some sums...

If one takes the max ELI for a circuit protected by a B32 MCB as 1.44 ohms (that's the 17th edition figure before it was slightly reduced by the Cmin reductions in amendment 3).

Also lets assume the resistance of a 0.7mm^2 cable is in the order of 26 mOhms/m (1.0mm^2 CSA has a tabulated value of 18.10 mOhm/m). We can add a further 46 mOhms to the circuit total.

That gets us a ELI with a fault at the end of the lead of 1.49 Ohms.

Our prospective fault current will therefore be 230 / 1.49 = 154A

That is slightly shy of the 160A needed for a "instant" trip on the MCB,

so let's look at the fuse:

That looks well below the 0.1 sec time on that. So lets take a pessimistic worst case of 0.1 secs.

So the remaining question is what size conductor is required to carry

154A for 0.1 sec? If we assume PVC insulation hence a k factor of 115 we get:

sqrt( 154^2 x 0.1 ) / 115 = 0.42 mm^2

So we can conclude that the flex will withstand that current for long enough to blow the plug fuse.

[John Rumm]

It would fail PAT.

Probably expecting a little too much from your average user!

[Dave Plowman (News)]

Oddly, had a plug fuse blow the other day due to a short (don't ask) ;-) Took the MCB too.

[John Rumm]

Even with that borderline example its close to the instant trip current on the MCB. A shorter circuit, and it could easily get >160A of PSCC

The interesting ones are when it takes out the MCB but not the fuse, or as ISTR Adam posting one, taking out the main incomer fuse, but not the

13A fuse, or the MCB!

[whisky-dave]

That isn't our problem it's why we only buy such things from reputable suppliers and why ebay is avioded. And we don't normlly buy second hand either or sell our equipment on, we don't even like giving it away to schools, when we have in the past we've always had it PAT tested before giving it away.

[whisky-dave]

I don't think that would be allowed under H&S you shouldn't have live pins like that on any unit. Well there wasnt; in the PAT testers I've see, what they do have is apadpters that you use on the IEC socket on the PAT tester.

[Andy Burns]

It's an inlet, if it was the opposite gender, the trailing lead would have to have live pins ...

[whisky-dave]

Yes and inlet the 3 pin socket is used to plug in an IEC lead the socket end of that lead plugs into a socket on the PAT tester.

The Pins DO NOT/should NOT supply voltage in a IEC lead and I don;t see such things being called fixed plugs and that is why I asked what a fixed plug is.

[charles]

They aren't LIVE pins, they're where the live free socket is plugged in to.

[Andy Burns]

Presumably the PAT tester supplies voltage to a 13A socket, and a

13A->C13 lead under test is 'looped' back to the C14 inlet, so the tester can check continuity?

Presumably to avoid confusion where plugs are usually male and sockets are usually female? The C13 lead is overall "male" because it plugs inside the female C14 socket, but the individual terminals are female in the lead and male in the inlet?

[whisky-dave]

That's what I assumed and from what I;ve seen done here with PAT.

I just didn't know what a fixed plug was.

[Terry Casey]

No, no, no, no ,no!

The sole purpose of the fuse in the plug is to protect the flexible cable connected to it and should, therefore, be rated accordingly.

If you fit a 13A fuse to a plug fitted with flex rated at 3A and another idiot connects the other end to a 3kW load, what do you think might happen?

I hope you knpw where the nearest fire exot is and, of course, that the overheated cable isn't between you and it ...

[whisky-dave]

Yes and earth resistance and perhaps breakdown voltage depending on the test applied.

As these IEC/kettle leads are the most common, I'd expect a dedicated lead for testing the figure of 8 leads can be tested and an earth wire which can be connected to the case of the insturment under test (if they're not just testing leads.)

Did it work then did it stop confusion if that's the aim.

but C13 is usually female not male.

and C14 is normally male.

Maybe yours are transgendered.

[whisky-dave]

That person will be promted to manager.

Well presently we have an illuminated fire exit sign that points in the opp ersite direction to the actual fire exit, it points to an old fire exit now removed and a window has been installed rather than a door, and the stairs leading to it as a fire exit have been removed. It's been like this for over a month now but they think they'll be able to sort it out by 19th september although they haven't confirmed the year yet.

I offered to cover the sign with black tape, but the 'managment' have assur ed me they will sort it out.

[Dave Plowman (News)]

But have you seen anything these days with a 13 amp plug where the flex would suffer damage with a 13 amp fuse and short circuit?

You certainly used to. Rather like two core IEC leads. But not now.

Difference between a flex being capable of blowing a fuse in event of a short and handling 13 amps continuously without overheating.

[tabbypurr]

I found just such a thing years ago. The flex was under a pile of junk too. It had been running without incident for many years - it ran very hot & was floppy, but undamaged.

NT

[whisky-dave]

The point is that IEC is the connector not the cable. The fuse is there to protect the cable. Which is one reason we shouldn't replace the fuse without the lead being 't ested' but because it's managment making the rules they haven't a clue what is required they get a company in to decide for them which they think will make them blameless if an accident should accure.

We still have those figure 8 cables in use, I'd be very suprised if I found one with a 13amp fuse in the plug if I did I'd replace the fuse with a 5am p.

flexes aren't meant to blow fuses.

but if some idiot has put a 13amp fuse in an IEC lead that is only rated at 5amps then perhaps the flex will get how and perhaps catch fire long befor e teh fuse blows.

[Dave Plowman (News)]

How many IEC leads have you seen where the two aren't moulded together? In the same way as most 13 amp plugs are too?

[whisky-dave]

Enough, but most of our leads with an IEC connector on have a 5amp fuse in the 13amp plug, and virtually all have 5 or 6 amp spec'd cable connecting teh 13amp plug to the 6 or 10 amp IEC socket. Some have a 3amp fuse, those are mostly C13 to C14 for connecting the monitor to the back of a PC. I leave about 100 of theses sorts of cables in the lab in a box for easy access.

I have a couple of these somewhere in case we need them.

10amp IEC Cable Plug.

Most 13amps plugs are too what exactly ?

[John Rumm]

Actually, these days yes...

But note we are talking about the specific case of a short circuit, not a continuous overload.

(refer to the adiabatic calculation I did a couple of posts back - the minimum fault withstand cable CSA was less than 0.5mm which is typically the smallest flex size in common use these days. However all best are off if the flex is on the end of a long extension lead)

It would get very hot... the insulation may fail to the point where it then shorts and the fuse blows.