Picture of the week!™

[333rocky333]

If that contact area was poor or the torque not great enough, continuity may not be satisfactory.

What's the contact area with traditionally threaded conduit?

In the set up on the video possibly less than the grubscrew set up. most of the contact is the box butting up to the end of the thread where it meets the unthreaded pipe, however to get 3 boxes sitting flat to a wall, theres a good chance you could not over tighten the thread too much, thus reducing that contact

 

[ban-all-sheds]

Indeed.

 

[Adam_151]

In the set up on the video possibly less than the grubscrew set up. most of the contact is the box butting up to the end of the thread where it meets the unthreaded pipe, however to get 3 boxes sitting flat to a wall, theres a good chance you could not over tighten the thread too much, thus reducing that contact

I would also imagine in a correctly tightened conduit system, that there is also significant contact through the threaded surfaces as when the box is tightened down at the end of the thread there is a force in the direction of the conduit pushing against the box which causes the threads to be pushed against one another.

I don't see why the conduit system should not be tight just because the three boxes are against the wall, its just a case of trying them to see where they tighten to when they are hand tight, estimating how far out they are, and putting a bit more thread on which is a little shy of that then when they are tightened and forced to lie flat against the way, they are about as tight as they'll go.

Though I don't doubt that there are folk out there who just back the threads off a bit to get them to sit right. I guess that is why everyone specifies separate CPCs to be drawn in. Well that, combined with the fact that there isn't a way to test the integrity of the conduit anymore

 

[PBC_1966]

Well that, combined with the fact that there isn't a way to test the integrity of the conduit anymore

Why not?

 

[flameport]

The high current test equipment isn't made any more.

Modern continuity testers only use 200mA test current, feeble in the extreme and will show continuity even if just a thin whisker of wire is connected. Old ones such as the Clare V339 applied 25A or more, sufficient to destroy any substandard connections completely and cause wiring to rattle around inside the conduit due to the magnetic forces created.

 

[Echo the husky]

It's a shame proper conduit is going out of fashion, It's been a while since I have installed the larger sizes of conduit. I will have to pester the boss to order some more in, the last time I needed 2" conduit I had to put in 2"x2" trunking which was a not nice, a bit of 2" conduit with 2 bends would have looked much better and would have been easier to install.

 

[PBC_1966]

The high current test equipment isn't made any more.

Use older equipment? Or build your own - Not exactly a complex piece of equipment for an electrician to put together.

Modern continuity testers only use 200mA test current, feeble in the extreme and will show continuity even if just a thin whisker of wire is connected. Old ones such as the Clare V339 applied 25A or more, sufficient to destroy any substandard connections completely and cause wiring to rattle around inside the conduit due to the magnetic forces created.

If the connection is substandard, isn't it better that the test current does destroy it and show an open circuit than to be so small as to make everything look all right when in the event of a fault it won't be?

 

[ban-all-sheds]

The high current test equipment isn't made any more.

Modern continuity testers only use 200mA test current, feeble in the extreme and will show continuity even if just a thin whisker of wire is connected. Old ones such as the Clare V339 applied 25A or more, sufficient to destroy any substandard connections completely and cause wiring to rattle around inside the conduit due to the magnetic forces created.

Did the high current tests just drift out of fashion, or did they actually get deprecated? I thought the latter, but happy to be corrected.

 

[flameport]

BS7671 states 'not less than 200mA' now. The 15th edition and earlier had an appendix which suggested 1.5x design current but not more than 25A.
Not clear when that appendix was deleted.

 

[PBC_1966]

And I have to wonder whose bright idea that change was.......

 

[SimonH2]

The high current test equipment isn't made any more.

I suspect it is, but it's somewhat specialist.
Ah, a quick search for a term I recall from my days as an apprentice in the shipyard (they'd "ductor" the shore supply cable connections after hooking them up) comes up with this :
http://www.test-meter.co.uk/micro-ohmmeters-ductors/
"models capable of providing test currents up to 600A"

 

[RF Lighting]

I've got some conlok bits to experiment with now. I'll test them with the welder and thermal imager, and repeat with old fashioned threaded conduit when I get a spare hour.

 

[securespark]

BS7671 states 'not less than 200mA' now. The 15th edition and earlier had an appendix which suggested 1.5x design current but not more than 25A.
Not clear when that appendix was deleted.

Trying to look this up, but can't find the reference in the Appendices in the 15th or 16th. Can you remember where they are?

 

[stillp]

And I have to wonder whose bright idea that change was.......

What does the NEC require?

 

[flameport]

Trying to look this up, but can't find the reference in the Appendices in the 15th or 16th. Can you remember where they are?

In the red 1981 edition it's Appendix 15, section 3 on page 186.