Show us your Conduit!

[Engineer54]

That's what he's saying dpelctricalltd, Ductor testing is basically injecting high current accross a joint or contact test area, measuring the resistance. Flash testing involves injecting high voltage, 2.5 to 4KV, for testing insulation properties of panels and the like, and measures any weaknesses in mA....

 

[Engineer54]

I was involved on a large hotel build a few years ago and one Friday evening got asked to check why the power was going up and down erratically on one part of the build .
To cut along story short i found that one of the 1200 kva ( i think it was this size but it was a few years ago and we do not tend to deal with this size normally ) incomers fed into a floor standing panel the size of a large mini bus , had got a loose bus bar which had all but melted away .
The switch gear supplier would not take responsibility for it so our old timer Foreman asked for the flash test results to prove continuity at the factory and they backed down .
From memory he said the test involved firing 10000 volts with high current through it to bring out any loose joints but nobody does it any more because i quote " it tends to blow the s""t out of what you wanted to test in the first place "
I would love to know more about this and if it was indeed true , as of yet i have not come across anything like again .
Many thanks Dave

Tests of this type carried out at the factory, normally in the presence of a representative of the client, would in all likelihood be a high-pot test. There are many different test voltage formulas for this test, but generally if testing with DC voltage it's 3x rated voltage plus a 1000. (11KV tested at 34kv) This testing is normally only conducted after verification tests with a 5KV insulation test kit that can measure in the Tg ohm range. These High-Pot tests, in AC or DC are classified as destructive tests, so initial factory testing is quite often limited to 1 to 3 minutes, whereas final commissioning testing prior to be putting into service can be upto 15 minutes, and sometimes at an increased voltage.
Leakage levels are measured and recorded in mA....

Obviously there's an awful lot more to these tests than i've outlined, but should give a general idea...

EDIT....

By the way, Ductor tests would have also been applied to the Bus Bar joints and connections, sometimes these are conducted in the presence of the clients representative, but normally only as a sample on maybe 2 or 3 of the them, and readings compared with the factory test report. Also remember that these panels are then split down for transportation to site, so any bus bar joints connecting the panel sections together at site is the responsibility of the installer, ...Not the manufacturer!!! These bus bar joints will then require Ductor testing before sealing/closing the bus bar chambers to each panel section....

 

[Knobhead]

The tests that can do major damage are short circuit withstand. They are usually done on a sample panel for type approval. I for one wouldn’t be happy to take delivery of a new panel knowing some loony has shoved 50KA for 3 seconds through it.
Years ago I saw a film by GEC showing a withstand test failure. I don’t know about the purchaser witnessing the test, I wouldn’t want to be in the same county.

HiPot testing is fun, I’ve only done them up to 5000V myself. But have had to be the company representative during testing of 11KV gear. It wasn’t new stuff so the tests were down rated to 17KV to earth.

The highlight of testing was the interfering manager. I’d set up barriers warning, notices, etc. while I was doing 1 minute 2.5KV tests to earth on a 1.7KV cable. I was quite happily sat in the sub watching the figures rising in to gig ohms when suddenly the reading flicked down accompanied by a squeal from outside. Turned the test off and went to investigate. The idiot had climbed over the barrier to have a look at the termination I’d done and of course he couldn’t resist touching J Pity he didn’t arrive later when I was doing the 5KV phase – phase tests.
He’s nursing a sore arm while I’m nursing sore ribs from laughing.

 

[rocker]

What a bloody idiot! Don't you just wish we could put all the managers on a big old boat and send them off to sea to see how they 'manage'?

 

[Engineer54]

HiPot testing is fun, I’ve only done them up to 5000V myself. But have had to be the company representative during testing of 11KV gear. It wasn’t new stuff so the tests were down rated to 17KV to earth.

Very true, rarely if ever will you test at those higher levels, after the initial putting into service testing has been conducted. Which is why it's very important to keep up to date records of all such tests on cables and equipments. This especially in the case of multi cored cables, where both KV and times will need to be reduced quite significantly depending on age and length of cable runs (joints etc) Though i've never tested at quite so low a figure as 17KV normally the lower figures would be around 2 X rated voltage, but times would be around 5 to 8 minutes max, again depending on charging up times of long cables....

 

[Knobhead]

Very true, rarely if ever will you test at those higher levels, after the initial putting into service testing has been conducted. Which is why it's very important to keep up to date records of all such tests on cables and equipments. This especially in the case of multi cored cables, where both KV and times will need to be reduced quite significantly depending on age and length of cable runs (joints etc) Though i've never tested at quite so low a figure as 17KV normally the lower figures would be around 2 X rated voltage, but times would be around 5 to 8 minutes max, again depending on charging up times of long cables....

Some of the gear was over 50 years old, so we were very ginger about testing it. We’d extended a panel of old Ferguson Pallin switches with new GEC gear. The new gear was tested as normal then a reduced test when the bus-bars were connected through.

GEC bought FP out about 1960, what amazed me was how easy the two panels mated up. I was expecting a bit of messing about but it was all plain sailing.

 

[Engineer54]

Some of the gear was over 50 years old, so we were very ginger about testing it. We’d extended a panel of old Ferguson Pallin switches with new GEC gear. The new gear was tested as normal then a reduced test when the bus-bars were connected through.

GEC bought FP out about 1960, what amazed me was how easy the two panels mated up. I was expecting a bit of messing about but it was all plain sailing.

In that case ''Fair Comment'' ...Think i'd be a bit ginger about hi-pot testing it any higher too ...lol!!!