direct buried cable in trench grouped??

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ritelec

ritelec

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Jersey
I saw the solor guys feeding the inverters with direct burial cable...
the feed is ....not sure 100 or 150 amp... but its 3 phase 4 wire with ground.

they have 2 groups of 3 wire laying in the trench. (I'm guessing one group is used for 3 phases the other group is neutral and ground and spare)

Is this right ??
 
ritelec said:
I saw the solor guys feeding the inverters with direct burial cable...
the feed is ....not sure 100 or 150 amp... but its 3 phase 4 wire with ground.

they have 2 groups of 3 wire laying in the trench. (I'm guessing one group is used for 3 phases the other group is neutral and ground and spare)

Is this right ??
Click to expand...
I would guess not, but how far apart are the groupings? Not that I can tell you what is “too far”.

Would it be much different if they were using cable tray?
 
My thoughts on direct burial ampacity: We are supposed to maintain spacing or derate for number of current carrying conductors. But at same time most people disregard ambient temp correction for underground - which typically will be a + adjustment instead of a - adjustment - so that does offset the need for number of conductors adjustment to some extent.

Most anytime I have done or seen direct burial with multiple conductors/cables maintaining spacing is never achieved, though the larger the conductor/cable the more it naturally sort of occurs anyway.
 
I wasn't worried about the spacing of the conductors for temperature correction. My thoughts were more on how the spacing would affect the current flow under fault conditions. The closer the better from what I understand.

My one and only failure:roll: :happysad:had to do with a temporary feeder we buried with no thoughts of spacing or bundling. VD was calculated for FLA. A year or two later a bolted line to ground fault at the far end would not blow the 60 amp fuses. Voltage would dip low enough to drop out the control first.
 
ptonsparky said:
I wasn't worried about the spacing of the conductors for temperature correction. My thoughts were more on how the spacing would affect the current flow under fault conditions. The closer the better from what I understand.

My one and only failure:roll: :happysad:had to do with a temporary feeder we buried with no thoughts of spacing or bundling. VD was calculated for FLA. A year or two later a bolted line to ground fault at the far end would not blow the 60 amp fuses. Voltage would dip low enough to drop out the control first.
Click to expand...
If you are talking irrigation applications - multiplexed conductors is about as good as you are going to get, but the distance we sometimes deal with you still see 60 amp fuse that won't blow or takes a long time to blow because of resistance of the run. But yes closer proximity reduces inductive/capacitive effects. We have a fair amount of old irrigation services that were originally corner ground delta - only three wires were buried. Then in mid to late 1980's POCO decided they don't want corner ground delta systems anymore so they came out and trenched in a fourth wire (which became the neutral), but put it about 5 feet minimum away from existing lines just to make sure they didn't dig into existing lines. Not sure that was all that wise of a decision.
 
kwired said:
If you are talking irrigation applications - multiplexed conductors is about as good as you are going to get, but the distance we sometimes deal with you still see 60 amp fuse that won't blow or takes a long time to blow because of resistance of the run. But yes closer proximity reduces inductive/capacitive effects. We have a fair amount of old irrigation services that were originally corner ground delta - only three wires were buried. Then in mid to late 1980's POCO decided they don't want corner ground delta systems anymore so they came out and trenched in a fourth wire (which became the neutral), but put it about 5 feet minimum away from existing lines just to make sure they didn't dig into existing lines. Not sure that was all that wise of a decision.
Click to expand...


I did that just once. Didn’t like it then either.
 
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