Paralell conductors ran in tray then conduits.

[francis.key19]

Hi,

I have a contractor who is running paralell feeders (3/0) for us on site. The service is for a 600HP drive, 3 phase, 4 wire. The route is to use the first 120ft of an existing ladder tray, then the remaining 30ft will be 4" conduits. They ran 2 (two) 4" conduits, instead of 3. Several questions concerning this installation. Contractors said the installation is proper and followed codes.

1. Should there have been 3 conduits where in each one, we should have A,B,C, N and Ground conductors?
2. I only see one ground 3/0. Contractors said only need one since most the distance are in the tray. What if there is a short in the conduit?
3. Since the cables will be in open air on tray then in conduits, how should the conductors be derated?

Lastly, this contractor took 7 days for the installation with 3 people. This seems a little bit much for this work. The tray is existing, and conduits are ran in open area 16ft elevation. Any idea how long this work should typically take?

Thanks.

Francis.

 

[Dennis Alwon]

Hi,

I have a contractor who is running paralell feeders (3/0) for us on site. The service is for a 600HP drive, 3 phase, 4 wire. The route is to use the first 120ft of an existing ladder tray, then the remaining 30ft will be 4" conduits. They ran 2 (two) 4" conduits, instead of 3. Several questions concerning this installation. Contractors said the installation is proper and followed codes.

1. Should there have been 3 conduits where in each one, we should have A,B,C, N and Ground conductors?

What is the voltage of these drives and what is the amperage? 3/0 is good for 200 amps at 75C so parallel would be 400 amps. Is a neutral needed?

2. I only see one ground 3/0. Contractors said only need one since most the distance are in the tray. What if there is a short in the conduit?

Are you talking equipment grounding conductor or neutral (grounded conductor). EQUIPMENT GROUNDING CONDUCTOR should be in each conduit unless the conduit is used as a equipment grounding conductor.

3. Since the cables will be in open air on tray then in conduits, how should the conductors be derated?

The conductors should be rated for the weakest link which is the conduit.

Lastly, this contractor took 7 days for the installation with 3 people. This seems a little bit much for this work. The tray is existing, and conduits are ran in open area 16ft elevation. Any idea how long this work should typically take?

I am not getting into that.

There are too many questions and something seems odd. 4" conduit for 3/0 conductors? Are there 2 runs in each conduit so that you have 4 parallel runs. Has this been inspected?

 

[infinity]

What's the input current rating of the drive?

 

[Fulthrotl]

Hi,

I have a contractor who is running paralell feeders (3/0) for us on site. The service is for a 600HP drive, 3 phase, 4 wire. The route is to use the first 120ft of an existing ladder tray, then the remaining 30ft will be 4" conduits. They ran 2 (two) 4" conduits, instead of 3. Several questions concerning this installation. Contractors said the installation is proper and followed codes.

1. Should there have been 3 conduits where in each one, we should have A,B,C, N and Ground conductors?
2. I only see one ground 3/0. Contractors said only need one since most the distance are in the tray. What if there is a short in the conduit?
3. Since the cables will be in open air on tray then in conduits, how should the conductors be derated?

Lastly, this contractor took 7 days for the installation with 3 people. This seems a little bit much for this work. The tray is existing, and conduits are ran in open area 16ft elevation. Any idea how long this work should typically take?

Thanks.

Francis.

ok. this is 480, correct? out at 600 hp, 4160 or 5kv is very common.

how many conductors in parallell?

neutral, on a 600 hp drive? what on earth for?

now, you have to derate if you have more than 3 ungrounded conductors
in a conduit. cable tray is unaffected, but you still have a 40% fill limit.

you should have one of each ungrounded phase per conduit.

customarily, you would run a separate conduit for each parallell feeder.

as to grounding, it's customary in a lot of tray installs to run a bare
ground cable sized for the ampacity of the gear, outside of the
tray, with korn clamps or something similar, to bond everything.
then you will place ground bushings on each end of the conduits,
tying to the ground cable on the tray, and the equipment ground
bus on the drive.

with all of this snoodling, i'd a just ran a 12" gutter from overhead
down to the drive, assuming it wasn't subject to damage, popped
two chase nipples with ground bushings in the side of the existing
chase, and been done with it.

as for the time necessary to perform the install.... it seems you
didn't get a flat rate, but went T&M instead? bummer. -2 points.

i did parallell 500 mcm's 800' in a refinery, thru cable tray except
for the last 60'. how long did it take? 4 guys, two weeks, pipe,
pull, and termination.

how hard can it be to pull thru cable tray? try it some time.
it's not as easy as it looks... what you are asking us to do is to
tell you how to parallell park your car, over a phone, while you
are telling us what you see in the rear view mirror.

 

[francis.key19]

More information

More information

Hello,

The drive amperage per phase is 666A, 480VAC , 3 wire. Currently, we have in each of two conduits, 2 (qty 2) 3/0 conductors for each A, B, C and a 3/0 Ground or total of 7. Total of 14 wires in both conduits. The disconnect at the drive is rated for 1000A.

Thanks.

Francis.

 

[infinity]

Your line side conductors need to be sized at 125% of the drive input rating or 666*125%=832 amps. {430.122(A)}

Your parallel #3/0's (4*200=800 amps) are only near that even before you account for derating of the two sets in each conduit.

225*2*80%=360 amps per conduit or 720 amps total

 

[Dennis Alwon]

Your line side conductors need to be sized at 125% of the drive input rating or 666*125%=832 amps. {430.122(A)}

Your parallel #3/0's (4*200=800 amps) are only near that even before you account for derating of the two sets in each conduit.

225*2*80%=360 amps per conduit or 720 amps total

I bet the contractor used the 90C rating and probably didn't derate for fill. or he/she didn't figure in the 125%

Still don't know why a neutral is needed. Do these VFD need a noodle?

 

[infinity]

I bet the contractor used the 90C rating and probably didn't derate for fill. or he/she didn't figure in the 125%

Still don't know why a neutral is needed. Do these VFD need a noodle?

He updated the info in post#5 no more neutral.

 

[Dennis Alwon]

I assume we are talking copper wire here???

 

[Fulthrotl]

Hello,

The drive amperage per phase is 666A, 480VAC , 3 wire. Currently, we have in each of two conduits, 2 (qty 2) 3/0 conductors for each A, B, C and a 3/0 Ground or total of 7. Total of 14 wires in both conduits. The disconnect at the drive is rated for 1000A.

Thanks.

Francis.

with two pipes, as mentioned by others... you are hosed.
you have two solutions that i can see... add two more conduits,
or pull out the conduits, and put in a 12" wide piece of cable tray,
or gutter. i'd go with correctly sized gutter, myself. easier and cheaper.

the derating of more than three in a pipe kills the deal. that was my first thought.

 

[roger]

That 666 number is aways a problem

Roger

 

[Fulthrotl]

I bet the contractor used the 90C rating and probably didn't derate for fill.

well, if the terminations on each end are rated for 90C, he can....
i always find out that the breaker i have to tie onto has 60C lugs,
or some such day ruiner.

 

[Fulthrotl]

That 666 number is aways a problem

Roger

the devil is in the details....

 

[infinity]

with two pipes, as mentioned by others... you are hosed.
you have two solutions that i can see... add two more conduits,
or pull out the conduits, and put in a 12" wide piece of cable tray,
or gutter. i'd go with correctly sized gutter, myself. easier and cheaper.

the derating of more than three in a pipe kills the deal. that was my first thought.

Even without derating using 4 conduits only gets you 800 amps with #3/0 Cu conductors.

 

[don_resqcapt19]

with two pipes, as mentioned by others... you are hosed.
you have two solutions that i can see... add two more conduits,
or pull out the conduits, and put in a 12" wide piece of cable tray,
or gutter. i'd go with correctly sized gutter, myself. easier and cheaper.

the derating of more than three in a pipe kills the deal. that was my first thought.

The OP said the conduits are 4". You can install two sets of 250kcmil in each conduit and have enough ampacity on the conductors.

 

[weressl]

Your line side conductors need to be sized at 125% of the drive input rating or 666*125%=832 amps. {430.122(A)}

Your parallel #3/0's (4*200=800 amps) are only near that even before you account for derating of the two sets in each conduit.

225*2*80%=360 amps per conduit or 720 amps total

Why bother with the conduit in the first place? He needs 3 sets of 300kCMil, before even ambient temperature adjustment and should use special tray cable with higher insulation rating for the inverter duty and evenly spaced triplen grounding conductors in EACH cable.

The installer may have tried to read the NEC, but did he read the drive manual?

 

[Smart $]

The OP said the conduits are 4". You can install two sets of 250kcmil in each conduit and have enough ampacity on the conductors.

In the interest of saving money, splice over in the tray near the conduit junction [392.56]. Copper 3/0 is good for 350A at 90?C in tray... but then the question arises of what the terminations and wiring method are at the supply end. May have to splice on 250's at that end too (side note: always wonder whther 310.15(A)(2) Exception applies to that end).

 

[weressl]

In the interest of saving money, splice over in the tray near the conduit junction [392.56]. Copper 3/0 is good for 350A at 90?C in tray... but then the question arises of what the terminations and wiring method are at the supply end. May have to splice on 250's at that end too (side note: always wonder whther 310.15(A)(2) Exception applies to that end).

Splice in a new installation? Not in our plants........Not unless it is a MV and complex run that just simply can not be done in a single pull. Avoid it like the plague......

 

[francis.key19]

Thank you all for your help, input and guidance.

Thank you all for your help, input and guidance.

Thank you so much everyone. It seems the contractor used table 310.15B(17) . Single conductor in free air to calculate the Amperage instead of 310.15B1(16). What does in free air mean? would this be a table to be used if single conductor is pulled on an empty cable tray or conduit? I am sorry to ask these basic questions, but I am new to electrical and am only one in the plant.

Regards,

Francis.

 

[Smart $]

Thank you so much everyone. It seems the contractor used table 310.15B(17) . Single conductor in free air to calculate the Amperage instead of 310.15B1(16). What does in free air mean? would this be a table to be used if single conductor is pulled on an empty cable tray or conduit? I am sorry to ask these basic questions, but I am new to electrical and am only one in the plant.

Regards,

Francis.

"In free air" means not enclosed within a raceway, cable armor or jacket, and such. Cable tray is a support system, not a raceway. The ampacity rules of 392.80 tell you which table is appropriate, and whether any derating is required... which is something I forgot to include in my previous post's ampacity value.... it likely has to be derated to 65% (which is only 227A per 3/0)... so disregard the splice suggestion.