4" CONDUIT FILL

RLMJR

Member
Location
British Indian Ocean Territory (Diego Garcia)
Occupation
Electrical Engineer
Is two sets of 500MCM THHN/THWN CABLE (4 WIRE SYSTEM) TOTAL OF 8 CONDUCTORS ALLOWED in a single 4" PVC/RSC conduit? In consideration for both -- code compliance per NEC and actual experience with regards to cable pulling these 8 conductors 500mcm plus 2-EA 2awg TW GRND.

Thank you in advance for the answers.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Two issues
1) only one equipment grounding conductor is needed in the conduit
2) max number of 500 kcm in 4" Pvc is 7 conductors without the equipment grounding conductor.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired) DINOSAUR
What is the length of the conduit.
(as Dennis points out the fill will not be to Code unless it's a nipple)
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Yes as per nec table upto 7 is allowed. Are we counting the number of current carrying or all conductors including the neutral in a three phase 4 wire system?
No, you count all the wires physically in the conduit, since the restriction is about installability in the conduit, not about heat generation.

But do you need a full size neutral? If not, you might be able to fit (6) 500 mcm conductors for the ungrounded conductors, and smaller conductors for the neutral and EGC/SSBJ. You'd have to do some calculations.

Cheers, Wayne
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
the feeders are protected by a 600 AT ECB sitting next to the 500kva xformer, isn't that the max load of a 500kva xformer 480/277 Y secondary is around 600amps only at 100 percent and limited by the code to 80% = 480 amps only.
So the secondary feeds a 600 amp OCPD? Your earlier post mentioned 800 amps. Can you explain the installation from beginning to end including the secondary conductor length?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired) DINOSAUR
Are these the secondary conductors of the transformer feeding the 600 amp (setting) OCPD ??
(If so, your "GRND" (post #1) is undersized as a #2 )
 

kwired

Electron manager
Location
NE Nebraska
He earlier said an 800 amp breaker. If that is correct final conductor ampacity must be no less than 800 amps (next size up rule no longer applies once you hit 800 amps)

Also I don't think anyone mentioned yet is you would need to adjust ampacity because there is more than three current carrying conductors in same raceway, which ultimately will also mean increase in conductor size is needed.
 

Tulsa Electrician

Senior Member
Location
Tulsa
Occupation
Electrician
Are these the secondary conductors of the transformer feeding the 600 amp (setting) OCPD ??
(If so, your "GRND" (post #1) is undersized as a #2 )

Then your 500's are too small (760 amps+ derating) and the SSBJ is also undersized.

RLM JR
What you call " GRND" on the secondary is a SSBJ. Size it from the correct table.
No, you count all the wires physically in the conduit, since the restriction is about installability in the conduit, not about heat generation.

But do you need a full size neutral? If not, you might be able to fit (6) 500 mcm conductors for the ungrounded conductors, and smaller conductors for the neutral and EGC/SSBJ. You'd have to do some calculations.

Cheers, Wayne

The SSBJ also serves as an EGC. However size from the SSBJ table.

Not sure what table fell free to ask.
SSBJ= supply side bonding jumper.

Then you can size the minimum netural size based on imbalanced load and correct minimum SSBJ required.

You had mentioned PVC. Is the transformer outside?
Is your 600 amp secondarys OCD inside.
The installation needs to be re-engineered. The wire and conduit sizes won't work.
Also be sure specify CU or Al in your one line.

So the secondary feeds a 600 amp OCPD? Your earlier post mentioned 800 amps. Can you explain the installation from beginning to end including the secondary conductor length?
 

Tulsa Electrician

Senior Member
Location
Tulsa
Occupation
Electrician
He earlier said an 800 amp breaker. If that is correct final conductor ampacity must be no less than 800 amps (next size up rule no longer applies once you hit 800 amps)

Also I don't think anyone mentioned yet is you would need to adjust ampacity because there is more than three current carrying conductors in same raceway, which ultimately will also mean increase in conductor size is needed.
I thought it over 800.
 

kwired

Electron manager
Location
NE Nebraska
I thought it over 800.
Never mind, must be too early yet?

Ampacity adjustment still necessary with more than three current carrying conductors, so assuming 90C conductors OP would need maximum of 700 amp OCPD and couldn't have actual load more than 688 amps, or would need to increase conductor size, which is already too big to fit as mentioned in 4 inch.
 
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