CapitalEng
Member
- Location
- Reno, NV
- Occupation
- Engineer
Hello!
First time here; sorry if this is covered somewhere else. Hoping to determine if a suggested feeder configuration would be allowed or not.
Situation:
An existing switchboard will be used to serve an existing panelboard. An existing cable tray system presently holds several triplex conductor bundles; the relevant cables are: one triplex cable of 500 kcmil conductors and one triplex cable of 350 kcmil conductors.
Because the panelboard is 480Y/277 Volt, 3-Phase, 4-Wire, and the triplex 500 kcmil cable doesn't include a neutral, we're looking at adding a neutral.
Contractor suggested (really, kicked over for consideration) that we use two of the 350 kcmil conductors contained in the 350 kcmil cable and splice them into a 500 kcmil conductor to serve as neutral (the third 350 kcmil conductor effectively abandoned in place).
In other words: A conduit with (4)-500 kcmil individual conductors (plus ground) leaves the switchboard and hits a splice box at cable tray level. Inside the splice box, the 500 kcmil phase conductors are spliced into the 500 kcmil triplex cable conductors and the 500 kcmil neutral is spliced to two of the 350 kcmil conductors in the 350 kcmil triplex cable. This forces the neutral into a parallel configuration for the length of the cable tray. At the panelboard end of the cable tray (again inside a splice box at cable tray level) the 500 kcmil phase conductors (triplex bundle) are spliced to 500 kcmil individual conductors and the two 350 kcmil conductors (parallel neutral) are spliced into a single 500 kcmil neutral. The (now) (4)-500 kcmil conductors enter a conduit and travel down to the panelboard.
I'm struggling to find any code articles which address this specifically. I know there are several code articles which touch on the topics of parallel conductors, splices, etc., but I haven't found anything prohibiting or permitting this specific configuration.
Theoretically, the paralleled portion of the neutral (the parallel 350 kcmil conductors in the cable tray) would exceed the rating of the 500 kcmil neutral (which is used in the conduit portions between switchboard and cable tray, and between cable tray and panelboard.
I hope this is clearly explained. Anyway, anybody know of any restrictions against this? Should I require a new feeder entirely be installed?
First time here; sorry if this is covered somewhere else. Hoping to determine if a suggested feeder configuration would be allowed or not.
Situation:
An existing switchboard will be used to serve an existing panelboard. An existing cable tray system presently holds several triplex conductor bundles; the relevant cables are: one triplex cable of 500 kcmil conductors and one triplex cable of 350 kcmil conductors.
Because the panelboard is 480Y/277 Volt, 3-Phase, 4-Wire, and the triplex 500 kcmil cable doesn't include a neutral, we're looking at adding a neutral.
Contractor suggested (really, kicked over for consideration) that we use two of the 350 kcmil conductors contained in the 350 kcmil cable and splice them into a 500 kcmil conductor to serve as neutral (the third 350 kcmil conductor effectively abandoned in place).
In other words: A conduit with (4)-500 kcmil individual conductors (plus ground) leaves the switchboard and hits a splice box at cable tray level. Inside the splice box, the 500 kcmil phase conductors are spliced into the 500 kcmil triplex cable conductors and the 500 kcmil neutral is spliced to two of the 350 kcmil conductors in the 350 kcmil triplex cable. This forces the neutral into a parallel configuration for the length of the cable tray. At the panelboard end of the cable tray (again inside a splice box at cable tray level) the 500 kcmil phase conductors (triplex bundle) are spliced to 500 kcmil individual conductors and the two 350 kcmil conductors (parallel neutral) are spliced into a single 500 kcmil neutral. The (now) (4)-500 kcmil conductors enter a conduit and travel down to the panelboard.
I'm struggling to find any code articles which address this specifically. I know there are several code articles which touch on the topics of parallel conductors, splices, etc., but I haven't found anything prohibiting or permitting this specific configuration.
Theoretically, the paralleled portion of the neutral (the parallel 350 kcmil conductors in the cable tray) would exceed the rating of the 500 kcmil neutral (which is used in the conduit portions between switchboard and cable tray, and between cable tray and panelboard.
I hope this is clearly explained. Anyway, anybody know of any restrictions against this? Should I require a new feeder entirely be installed?
