PAT testing

[Big_Stu]

[quote name='flyfisher' timestamp='1392415852' post='2368645']
Interesting suggestion. What sort of massive current do y ou estimate would be required to cause an M8 steel bolt to become red hot?[/quote]

Amazing that you know it was steel, I couldn't tell you whether it was steel, aluminium or brass. Unless you're now talking about a hypothetical M(edit)[i]6[/i] steel bolt in an electric fire's melting plug.

Edited February 14, 2014 by Big_Stu

[flyfisher]

Where did I say I 'knew' it was steel? I just suggested steel for the basis of the discussion with TimR just to make some rough approximations to see if some sense can be made of the whole thing.

[TimR]

[quote name='flyfisher' timestamp='1392417169' post='2368672']
Where did I say I 'knew' it was steel? I just suggested steel for the basis of the discussion with TimR just to make some rough approximations to see if some sense can be made of the whole thing.
[/quote]

Really you don't need to make sense of it. Today we replaced a fused spur at work that had caught fire with a 13amp fuse in it. That was due to a faulty electric thyristor on a heater. Everything else was in order. The fuse will only ever blow if enough current flows for long enough.

A pat will open the plug and check the size and condition of the fuse and hopefully spot any charring or discolouration early.

Edited February 14, 2014 by TimR

[flyfisher]

[quote name='TimR' timestamp='1392417355' post='2368674']
Really you don't need to make sense of it. Today we replaced a fused spur at work that had caught fire with a 13amp fuse in it. That was due to a faulty electric thyristor on a heater. Everything else was in order. The fuse will only ever blow if enough current flows for long enough.
[/quote]

Doesn't that sound like a case for suggesting that the fittings involved are not adequately protected by the rated fuse? I know that a 13A fuse will not blow as soon as 14A flows through it, but so do the people that define all the wiring regs, so you'd think they'd take account of that sort of thing wouldn't they?


[quote name='TimR' timestamp='1392417355' post='2368674']
A pat will open the plug and check the size and condition of the fuse and hopefully spot any charring or discolouration early.
[/quote]

'Hopefully' sounds a bit vague for a H&S procedure to me!

[TimR]

[quote name='flyfisher' timestamp='1392418001' post='2368682']


Doesn't that sound like a case for suggesting that the fittings involved are not adequately protected by the rated fuse? I know that a 13A fuse will not blow as soon as 14A flows through it, but so do the people that define all the wiring regs, so you'd think they'd take account of that sort of thing wouldn't they?




'Hopefully' sounds a bit vague for a H&S procedure to me!
[/quote]

What can you take account of? You can only cover so many scenarios. Sometimes as big Stu says 'sh*t happens'. That's why we have regular checks, sprinkler systems, fire alarms, fire brigade and so on.

By 'hopefully' I mean that the evidence of overheating is present when the PAT is done and not after. You can't catch everything, you can just try to catch them.

What did you say your business did? You're asking some very strange questions for a director of an electrical design company.

[Big_Stu]

[quote name='flyfisher' timestamp='1392417169' post='2368672']
Where did I say I 'knew' it was steel?[/quote]

Where you stated that it was steel, without qualifying that it might be another metal as I did. Unless of course - as I said - you're talking about another hypothetical bolt in another plug, rather than the one that I brought up.
The one that you - while admitting you're not an expert as TimR does genuinely appear to be - are having such a hard time believing did glow red hot without tripping the house fuse.

FWIW The house was a council owned, I know that much. It was long enough ago that it may have been one of the old fuse-wire boxes - in which case the guy maybe put something else in that too, instead of the proper fuse wire.
IMHO there are too many possible variables to be able to know why something didn't stop the bolt in the plug, whatever it was made of - from glowing red-hot.

[flyfisher]

@TimR - Industrial datacomms equipment.

Why are my questions strange? And even if you think they are, why not try answering them? The volts drop across the bolt for example?

I'm asking it because your post estimated 6kW "through the bolt and fire system combined", which is fine, but I'm sure you understand that the amount of that power that is actually dissipated [i]within[/u] that bolt and therefore acting to heat it up, will be largely dependent on the voltage across that bolt. Which is why I asked the question. Is that really so strange?

Edited February 14, 2014 by flyfisher

[flyfisher]

[quote name='Big_Stu' timestamp='1392418825' post='2368690']
Where you stated that it was steel, without qualifying that it might be another metal as I did. Unless of course - as I said - you're talking about another hypothetical bolt in another plug, rather than the one that I brought up.
The one that you - while admitting you're not an expert as TimR does genuinely appear to be - are having such a hard time believing did glow red hot without tripping the house fuse.
[/quote]

And where, exactly, [u]did[/u] I state it was steel?

If you re-read the thread carefully I think you'll find it was TimR who first mentioned steel. Carbon steel actually. My first mention of steel was "[i]What sort of massive current do you estimate would be required to cause an M8 steel bolt to become red hot?[/i]", which reads very much like a question rather than a statement to me.


[quote name='Big_Stu' timestamp='1392418825' post='2368690']
FWIW The house was a council owned, I know that much. It was long enough ago that it may have been one of the old fuse-wire boxes - in which case the guy maybe put something else in that too, instead of the proper fuse wire.
[b]IMHO there are too many possible variables to be able to know why something didn't stop the bolt in the plug, whatever it was made of - from glowing red-hot.[/b]
[/quote]

Now you're talking some sense, and I entirely agree with you, which is why I was very care to write "[i]I also find it hard to believe that a metal bolt could be glowing red hot[b] while the consumer unit fuse had not blown [/b]or even the house wiring cabling to the socket had not burned through first.[/i]"

I really think you're being a tad over-sensitve about all this and have jumped to conclusions. If I'd wanted to call you a liar I would have done so straight away without bothering to qualify my comments, but that would have been ridiculous and is why I didn't. I'm sorry if what I wrote upset you but I that wasn't my intention and I can't predict how someone might misinterpret something.

[TimR]

[quote name='flyfisher' timestamp='1392419261' post='2368698']
@TimR - Industrial datacomms equipment.

Why are my questions strange? And even if you think they are, why not try answering them? The volts drop across the bolt for example?

I'm asking it because your post estimated 6kW "through the bolt and fire system combined", which is fine, but I'm sure you understand that the amount of that power that is actually dissipated [i]within[/u] that bolt and therefore acting to heat it up, will be largely dependent on the voltage across that bolt. Which is why I asked the question. Is that really so strange?
[/quote]

No. It's the constant questions when you get an answer you question that as well.

It gets worse because the fuse at the DB would be a 30amp and probably capable of 40-50 amps for a couple of minutes. The bolt (if carbon steel) would have to have 10times the cross sectional area of the copper to have the same resistance. Then we also have to look at contact area and resistance of the bolt with the holder.

As big Stu implies unless you do a forensic examination of the whole thing it's all educated guesses. Fires do happen due to faulty electrical equipment that's protected correctly and tested and checked regularly but they happen more often to equipment that isn't.

Check your gear regularly and don't cut corners because it's not expensive. It makes sense.

[TimR]

So a 6mm bolt has a cross sectional area of 28mm2 which is close to 10x 2.5mm2.

But that's of passing coincidental interest. Lol.

[flyfisher]

[quote name='TimR' timestamp='1392420317' post='2368713']
No. It's the constant questions when you get an answer you question that as well.

It gets worse because the fuse at the DB would be a 30amp and probably capable of 40-50 amps for a couple of minutes. The bolt (if carbon steel) would have to have 10times the cross sectional area of the copper to have the same resistance. Then we also have to look at contact area and resistance of the bolt with the holder.

As big Stu implies [b]unless you do a forensic examination of the whole thing it's all educated guesses.[/b] Fires do happen due to faulty electrical equipment that's protected correctly and tested and checked regularly but they happen more often to equipment that isn't.

Check your gear regularly and don't cut corners because it's not expensive. It makes sense.
[/quote]

Yes, of course it's all educated guesses, which is why I was asking for yours to see if it made any more sense of things.

But no matter.

I'm just a little surprised at how relaxed you seem to be about electrical fires in 'properly protected' equipment. No wonder Sh1t happens.

[Big_Stu]

[quote name='flyfisher' timestamp='1392420205' post='2368712']Now you're talking some sense[/quote]
[b]I[/b] always was - by merely relating an incident as it happened, with nothing added,
You're the one who's spent pages trying to argue many points and resorting to pedantry when you're shown to be wrong.

[quote name='flyfisher' timestamp='1392420205' post='2368712']If I'd wanted to call you a liar I would have done so straight away without bothering to qualify my comments, but that would have been ridiculous and is why I didn't. I'm sorry if what I wrote upset you but I that wasn't my intention and I can't predict how someone might misinterpret something.[/quote]

I don't think you would, that's why you rely on little so much, such as
[quote name='flyfisher' timestamp='1392296698' post='2366888']I also find it hard to believe that a metal bolt could be glowing red hot while the consumer unit fuse had not blown or even the house wiring cabling to the socket had not burned through first. [b]But these sort of anecdotal stories abound[/b]. [/quote]
or
[quote name='flyfisher' timestamp='1392395045' post='2368209'] I said I find it hard to believe, .................I can only go on the information you provided. [/quote]
when you refuse to concede that you're wrong.

Edited February 14, 2014 by Big_Stu

[flyfisher]

[quote name='Big_Stu' timestamp='1392420825' post='2368722']
[b]I[/b] always was - by merely relating an incident as it happened, with nothing added,
[/quote]

So if you related an incident about seeing a ghost, you'd get all indignant that someone might question it because they find it hard to believe?


So what have we all learned from this discussion?

1. You've seen a bolt (of unknown metal) glowing red hot in a 13A plug fuse holder while connected to an electric fire

2. I find it hard to believe how that can happen

3. Discussions with TimR, the forum electrical expert, yield no conclusions about how the required amount of power to turn a small section of bolt (of unknown metal) could practically be dissipated within said bolt (of unknown metal) and cause it to be heated to a red hot temperature

4. You're upset because you think I've called you a liar

5. Both you and TimR think sh1t happens

6. I'm bemused by the whole thing and will try to curb my curiosity in future.

Edited February 14, 2014 by flyfisher

[Big_Stu]

[quote name='flyfisher' timestamp='1392421764' post='2368729']
So if you related an incident about seeing a ghost, you'd get all indignant that someone might question it because they find it hard to believe?[/quote]

Seriously that's a serious post? I mean - I don't see any s this time - from a "director" in
[quote name='flyfisher' timestamp='1392418542' post='2368687']Industrial datacomms equipment.[/quote]
??
I find that impossible to believe. Maybe you were thinking anecdotally.

Edited February 15, 2014 by Big_Stu

[flyfisher]

[attachment=155214:facepalm.jpg]

[tauzero]

[quote name='TimR' timestamp='1392420545' post='2368718']
So a 6mm bolt has a cross sectional area of 28mm2 which is close to 10x 2.5mm2.

But that's of passing coincidental interest. Lol.
[/quote]

At the risk of perpetuating this yet further, the other thing to consider is contact area. While a fuse has a big flat contact area to go into the big flat [1] fuseholder, the threaded bit of a bolt provides a series of teeny-tiny contact lines. That's going to be the major factor in considering the current-carrying area as a fuse has a considerably larger contact area than conductive cross-sectional area, while for a threaded bolt the reverse is true.

[1] Well, curved, but an even surface

[Dad3353]

[quote name='tauzero' timestamp='1392424601' post='2368759']... the threaded bit of a bolt provides a series of teeny-tiny contact lines...[/quote]

Are we talking Whitworth here, or BA..? Could be Metric, I suppose, or even AF. Hmm... So many variables...

[TimR]

I'm going to wire up a bolt next week and see what happens.

[TimR]

[quote name='tauzero' timestamp='1392424601' post='2368759']


At the risk of perpetuating this yet further, the other thing to consider is contact area. While a fuse has a big flat contact area to go into the big flat [1] fuseholder, the threaded bit of a bolt provides a series of teeny-tiny contact lines. That's going to be the major factor in considering the current-carrying area as a fuse has a considerably larger contact area than conductive cross-sectional area, while for a threaded bolt the reverse is true.

[1] Well, curved, but an even surface
[/quote]

And does the bolt fit the holder or is it rattling around, expanding and contracting with the heat.

[Dad3353]

[quote name='TimR' timestamp='1392426319' post='2368779']
I'm going to wire up a bolt next week and see what happens.
[/quote]

I'll bolt up a wire if you do..!

[flyfisher]

[quote name='tauzero' timestamp='1392424601' post='2368759']
At the risk of perpetuating this yet further, the other thing to consider is contact area. While a fuse has a big flat contact area to go into the big flat [1] fuseholder, the threaded bit of a bolt provides a series of teeny-tiny contact lines. That's going to be the major factor in considering the current-carrying area as a fuse has a considerably larger contact area than conductive cross-sectional area, while for a threaded bolt the reverse is true.

[1] Well, curved, but an even surface
[/quote]

Now that's the most constructive post so far in terms of better understanding this whole thing. Interesting.

[TimR]

[quote name='flyfisher' timestamp='1392465808' post='2369033']


Now that's the most constructive post so far in terms of better understanding this whole thing. Interesting.
[/quote]

I mentioned that earlier and you even quoted it. It will form part of my experiment.

[flyfisher]

I've re-read this discussion and can't see where you mentioned anything about the threads of a bolt affecting things. You alluded to contact resistance but then so did I in my specific question about the volts drop across the bolt, which you avoided. Tauzero, in a single post, has clearly explained his suggestion in an easily understandable way that requires no second guessing about what he actually means. Perhaps that's because, like me, he's trying to understand things rather than just personalise them?

[TimR]

It's personalised because I know you are/were a company director and I can't believe you are so ignorant of your responsibilities under the health and safety at work regulations. This leads me to feel once again you are playing devil's advocate and presenting straw man proposals deliberately to prolong discussion.

I may be wrong and you may be completely ignorant of your responsibilities, which is an entirely different debate.

[flyfisher]

You're so wrong, which is the danger with making assumptions. Let's try to stick to some facts shall we, which is what questions try to elicit, and leave the personal stuff out it please?