it seems my megger isn't up to this task.......

Status
Not open for further replies.
Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
here's my problem...... as i see it anyway....

i have a fluke megger. works fine on reasonable runs.....
say, 4/0 a few hundred feet long......

i have to megger three sets of 750 mcm copper thwn,
in parallel, that are 750' long... so that's 2,100' per
leg, and my little meter just won't pull it.

so, i need to go get a "real" megger that i can put
1kv on this beast, and see where the insulation value
is at.

the readings i'm getting, are not good, and i suspect
the dielectric load is exceeding the little fluke's ability
to perform.

what megger should i go looking to rent?
 
You really need to be able to check each of the paralleled conductors individually for damage anyway, so isolating them might bring it within the range of your megger.
 
I agree with Golddigger, is it not possible to pull them off the lugs at the ends? Poor readings would have you unlugging and isolating them anyhow.

What brought on this megger test to begin with? What's this feed?

I can't imagine what they spent on the original install, that's a lot of copper!!
 
Cow said:
I agree with Golddigger, is it not possible to pull them off the lugs at the ends? Poor readings would have you unlugging and isolating them anyhow.

What brought on this megger test to begin with? What's this feed?

I can't imagine what they spent on the original install, that's a lot of copper!!
Click to expand...

it's been sitting there unused for fifteen years.
they want to put it back in service.

i can pull them off the underground pull section at the load end,
and then unland them at the breaker and go onsie at a time,
but i've found a test equipment firm in LA that has a bunch of
5kv biddle units of various flavors..... so i'm thinking if i get a
megger with a bit more punch, and megger at 500 volts and
soak it for a while, and see what the numbers look like.

none of these runs would even let the fluke charge up to 1050,
which is it's open circuit voltage.... 350~700 is all they would
let it pull to, with resistance of .9, 2.1, and .1 megohms, phase
to phase.

so, they aren't ALL bad... i doubt i could even megger two in
the same pipe and get a reading i'd hang my hat on, so i'll
scurry out tomorrow and get something with more beans to it.

and i'm not just "kicking the tires and lighting the fire".
the 800 amp breaker feeding these is 50k interrupting rating,
and the gear is 3,000 amp bus, right nest to the utility xfmr.

not a good place to test drive the 40 calorie suit.
 
What Fluke meter are you using? I just had the company buy a Megger MIT410 and it's an excellent hand-held megger. IMO, it's vastly superior to the Fluke 1587.

Like the Fluke 1587, the MIT410 can test at 50V, 100V, 250V, 500V, and 1000V. But it?s a much more capable insulation resistance tester: whereas the Fluke 1587 can only measure up to 2G Ohms, the MIT410 can measure up to 100G Ohms. And the MIT410 has a real-time simulated analog ?needle? on the LCD display (in addition to numeric values). The MIT410 can automatically perform timed tests, including calculated Polarization Index (PI) and Dielectric Absorption Ratio (DAR) tests. And in addition to regular test probes (with various tips), Megger also includes a remote switch probe that has a button for starting the test built into the probe handle. And it comes with a hard-sided carrying case. All for just $496, new at Amazon.com:

http://www.amazon.com/exec/obidos/asin/B005S3JGUY/globalacces0b-20

Rather than trying to test the parallel runs as a set, I would un-lug everything at both ends and isolate each conductor individually for testing (while bonding all the other conductors with jumpers to ground).
 
Last edited:
Jon456 said:
What Fluke meter are you using? I just had the company buy a Megger MIT410 and it's an excellent hand-held megger. IMO, it's vastly superior to the Fluke 1587.

Like the Fluke 1587, the MIT410 can test at 50V, 100V, 250V, 500V, and 1000V. But it?s a much more capable insulation resistance tester: whereas the Fluke 1587 can only measure up to 2G Ohms, the MIT410 can measure up to 100G Ohms. And the MIT410 has a real-time simulated analog ?needle? on the LCD display (in addition to numeric values). The MIT410 can automatically perform timed tests, including calculated Polarization Index (PI) and Dielectric Absorption Ratio (DAR) tests. And in addition to regular test probes (with various tips), Megger also includes a remote switch probe that has a button for starting the test built into the probe handle. And it comes with a hard-sided carrying case. All for just $496, new at Amazon.com:

http://www.amazon.com/exec/obidos/asin/B005S3JGUY/globalacces0b-20

Rather than trying to test the parallel runs as a set, I would un-lug everything at both ends and isolate each conductor individually for testing (while bonding all the other conductors with jumpers to ground).
Click to expand...

i agree, it's a better piece of kit than the fluke....

i went and rented a phenix pm-5a megger that will do PI's as well.... it looks straight out of 1977,
and isn't battery powered, and has a printer that uses adding machine tape built into it.

and comes with a certificate of calibration... so it'll do the job... but i like that megger... and it
was less than the price of the fluke.... fluke has lost their connection to the real world, it seems.
a new product a month, an exorbitant price, and then a newer better replacement, a week later.
it's planned obsolescence, on crank, it seems to me.

i also got a TDR, to see what is going on, if it gets to that.

i'm gonna unlug everything from the destination gear, and then megger
from the supply. i can lift stuff if i need to, but i'm gonna see how it does
before i pull everything off.... it's pretty cozy, the make up is... and before
i rip it all apart.... i have a feeling it's more likely the breaker at the far end,
rather than the cables. that's been sitting 60' from the ocean turned off,
for almost a decade... condensation, etc.

which is fine. i can just order a new piece of gear with an underground pull section,
turn the gear 90 degrees, repour the housekeeping pad, and have dirt to trench from.
as the breaker section will now stick out over the edge of the existing housekeeping pad.

can't get in there till saturday, anyway. more will be revealed...
 
Fulthrotl said:
can't get in there till saturday, anyway. more will be revealed...
Click to expand...

couldn't make it till sunday.... it's been a bit busy.....

here are the readings i'm getting on each of the nine cables,
and by groupings.

individual tests were by tying every other cable to the low
side of the tester, and the one cable being tested was to
the high side.

pvc conduits are 6' ~ 7' deep, and this is right next to the ocean.
the gear where these terminate is about 25' from the water.

what it's looking like at this time, to me anyway, is that the
cables were damaged during pulling, and would be ok, except
that the pipes are flooding, and they always do, but this time
with salt water, and that is a pretty good electrolyte.

i've got a couple things i'm thinking about, one of which is
there are three cables out of the nine that look serviceable.

three 750's would be good for 530 amps, if i believe my phone
app. the runs are about 600', and if you calc the voltage drop
on 530 amps at 480 volts 3 phase 3 wire, it comes out under
2%.

and i only need 440 amps 3 phase, 3 wire.

each conduit has its own ground, and the pvc won't induction
heat. what if i used the three good legs to feed the panel, and
resized the overcurrent protection to be correct for a single
set of 750's... ?

two of them would be in one conduit, and one of them would
be by itself.

i'm gonna run the test again tomorrow... and do some more
head scratching.

whatchoo guys think? anyone got any experience with reviving
funky cables, or about using cable distributed across multiple
conduits? the cables are the same length within a few feet,
so that isn't an issue.

BTW, the conduit is most likely not usable at all, as in pulling
this stuff out, and repulling pipe. the wires have dried yellow
77 on them. lots of it. looks like they just poured a pail into the
pipe, and let it lube itself.

i can pull the stuff out, if i have to, including the switchgear pad
that the conduit comes thru, for that matter. there are several
cranes on site, the largest of which is 400 tons. that should do.

 
Unless you somehow combine the separate conduits into a PVC box at either end and go from that into your gear, you still run the risk of induction heating where the conduits enter your steel gear at both ends. My gut's telling me you should pull the old stuff out, check the conduits to find a good one and repull if possible.

Assuming 4" PVC and a 600' run, you'd only need about 391 gallons of lube to displace the seawater and make pulling a breeze. Call your local lube distributor and have them deliver. ;)
 
PetrosA said:
Unless you somehow combine the separate conduits into a PVC box at either end and go from that into your gear, you still run the risk of induction heating where the conduits enter your steel gear at both ends. My gut's telling me you should pull the old stuff out, check the conduits to find a good one and repull if possible.

Assuming 4" PVC and a 600' run, you'd only need about 391 gallons of lube to displace the seawater and make pulling a breeze. Call your local lube distributor and have them deliver. ;)
Click to expand...

both ends of the conduits come up into the bottom of gear,
thru concrete, and are not surrounded by metal where they
enter the gear, so it's two plastic pipes next to each other
in concrete, so there is sheet metal above the pipes, but
not encircling the pipes.
 
Fulthrotl said:
here are the readings i'm getting on each of the nine cables,
and by groupings.
Click to expand...
All those readings look too low to me. What you really need are historical insulation resistance (IR) tests to compare against to see how much -- and how quickly -- the wires are degrading.

We have a 700 foot run of (3) 500 MCM CU-XHHW feeders that were installed new 18 months ago. We recently had the installation contractor conduct an IR test on them (using a Fluke 1587) and measured two of the feeders at over 2G ohms (i.e., greater than the meter's maximum), and one at 615M ohms. That 615M ohm reading would be considered a "passing" value by commonly accepted rule-of-thumb, but is it really a "good" value when compared against the >2G ohm measurements of the other two wires? This set of feeders has already shorted out and tripped the upstream OCPD four or five times. So even though that one wire tests at an apparently "acceptable" 615M ohms, it's clearly damaged to the point of causing faults.

Fulthrotl said:
pvc conduits are 6' ~ 7' deep, and this is right next to the ocean.
the gear where these terminate is about 25' from the water. what it's looking like at this time, to me anyway, is that the cables were damaged during pulling, and would be ok, except that the pipes are flooding, and they always do, but this time with salt water, and that is a pretty good electrolyte.
Click to expand...
Even "fresh" ground water is fairly a good electrolyte. Here is a photo of an aluminum conductor with damaged insulation that was pulled out of a buried PVC conduit flooded with ground water. The leakage of electricity through the broken insulation and into the water accelerated the oxidation of the aluminum, causing it to swell to about 3 times in diameter and almost completely separate.

IMAG1516.jpg


Copper is much more resistant to corrosion than aluminum, but it too will dissolve when subjected to electrolysis.

Fulthrotl said:
BTW, the conduit is most likely not usable at all, as in pulling this stuff out, and repulling pipe. the wires have dried yellow 77 on them. lots of it. looks like they just poured a pail into the pipe, and let it lube itself.
Click to expand...
Why do you believe the conduit is not usable? The old lube, water, and whatever else can be removed by pulling through a wire brush followed by a flexible rubber disc mandrel. If you do re-pull through that conduit, you might want to get a visual inspection, at least of the entry/exit sweeps. Btw, what is the diameter of the conduit?

My recommendation would be to pull out the old wires, sell them to salvage to offset the cost of the new wire, and pull in new. Be sure to seal the ends of the wires before pulling in to prevent salt water from ingressing and wicking between the strands.
 
Jon456 said:
A
Why do you believe the conduit is not usable? The old lube, water, and whatever else can be removed by pulling through a wire brush followed by a flexible rubber disc mandrel. If you do re-pull through that conduit, you might want to get a visual inspection, at least of the entry/exit sweeps. Btw, what is the diameter of the conduit?

My recommendation would be to pull out the old wires, sell them to salvage to offset the cost of the new wire, and pull in new. Be sure to seal the ends of the wires before pulling in to prevent salt water from ingressing and wicking between the strands.
Click to expand...

well.... this area about 10 years ago, had severe loading of car sized rocks.
the ground was compacted enough to break a 6" PVC pressurized sewer line, 5' deep.
the folks operating it said there was over 100,000 tons of rock in two piles.

i've also seen the plot of how this conduit was run. more crooked than a dogs hind leg.

i've got a course of action on this one. i'm gonna retest the cables, take the three that
are serviceable, and land them on the bus in the load center, then take the three cables
and put them on the main breaker where they were before, one per phase.

then, i'm gonna light them up, and let them sit for a week.

then, i'm gonna tap off that bus, and set a 100 amp fused disconnect within 10',
and feed a 75 kva xfmr with it, and provide temp power for the build out of this
project, thru a 200 amp panel with suitable connections.

after the project is done, will pull out the feeders, all of them, scrap them, and send
a nice check to the owner of the property.

so, it's gonna make a hell of an extension cord.

for the project itself? i'm setting new gear, piping into main distribution with 4" OCAL,
and putting everything in fresh. 1,200 amp 480 gear, fed off a 800 amp breaker,
and we are good to go. i'll probably get the site layout and can start designing it, and
then get it into plan check shortly.

as long as i have this steam powered PI tester, i'm gonna use it on all my feeders
i'm pulling next week, if the wire supplier can get their act together, and supply
simpull. they sent some samples of some cheeze whiz wire that i'd never pull dry.
so, it's out for resourcing at this moment.
 
Status
Not open for further replies.
Top