200 ampere sub panel for a building and underground aluminum feeder

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Jpflex

Jpflex

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Electrician commercial and residential
My boss has decided to have me install a 200 ampere sub pannel to a building, which I have completed along with all necessary branch circuits and breakers.

However, he has decided to feed the sub panel fed from a service disconnect panel. The run is 300 feet and he is using aluminum # 2 AWG conductor (specific type of insulation unknown but I will look for the conductor type and post it here when I find it).

He has also decided to use pvc (schedule 40? at 1 and 1/4 inch which will fit the conductors and equipment ground conductor to be within 40 percent of conductor fill

My questions are:

The #2 AWG wire will have an ampacity before correction at 115 amperes at 75 degrees Celsius and will be too small for the 200 ampere sub pannel even considering any possible 85% reduction demand factors for feeders similar to services and if relevant to feeders or allowed

Are not feeders supposed to be sized either to accommodate the largest load or be sized to 125 percent of continuous loads plus 100 percent of non continuous loads or final option to be sized for ampacity after temperature correction and conductor derating?

NEC says Aluminum is not to be within 18 inches of dirt or in wet locations such as underground conduit but NEC code contradicts this by also saying NEC 300.6 B

Aluminum in apparatus embedded in concrete or direct contact with earth must have supplemental corrosion protection?
 
Correction I used the wron table column aluminum conductor is rated less than 115 ampere but closer to 90 amperes at 75 degrees Celsius
 
Your #2 Al is a 90 amp conductor so you need a 90 amp or smaller OCPD at the origin of the feeder or at the separate structure as a tap if it all outdoors.
 
Just because the panel is rated 200 amps doesn't mean you have to use 200 amp wire. If you install a 90 amp breaker, for the #2 Al at the main panel, then you are protected even if the panel has a 200 amp main.

What is going to be in the 2nd building
 
Dennis Alwon said:
Just because the panel is rated 200 amps doesn't mean you have to use 200 amp wire. If you install a 90 amp breaker, for the #2 Al at the main panel, then you are protected even if the panel has a 200 amp main.

What is going to be in the 2nd building
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So it’s code compliant to place a 90 ampere breaker at the service panel and line side of feeder and terminate at a 200 ampere sub pannel?

I thought the boss was using a 200 sub panel because he was expecting to reach 200 amperes of loads but I see your point

Also what about the feeder being aluminum and underground or not 18 inches above the ground?
 
Jpflex said:
So it’s code compliant to place a 90 ampere breaker at the service panel and line side of feeder and terminate at a 200 ampere sub pannel?
Click to expand...
Yes the feeder is properly protected. Does the sub-panel have a main? You'll need some sort of disconnecting means at the separate structure.
 
infinity said:
Yes the feeder is properly protected. Does the sub-panel have a main? You'll need some sort of disconnecting means at the separate structure.
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The sub pannel has a main 2 pole breaker of 200 ampere before branch circuit breakers

Does this not also qualify as the feeder disconnect?
 
Update:

The feeder is an XL triplex cable with XLPE insulation but my NEC book does NOT list this under the cable table or conductor table and the manufacture claims this cable is rated for 185 amperes when buried and terminated at 75 degrees celcius

The conductor is aluminum but apparently is listed for underground

Why does not NEC have this cable listed?

See picture
 

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The cable on the cut sheet you show primarily a utility distribution cable and not covered by the NEC (similar to URD cable) however it seems to indicate it is also USE csble. IMO, you could use it as a USE cable at the ampacities listed for USE in Table 310.15(B)(16), 90 amps.

{I do have concern as, from what you say, the cable is not marked as required by 310.120}
 
augie47 said:
The cable on the cut sheet you show primarily a utility distribution cable and not covered by the NEC (similar to URD cable) however it seems to indicate it is also USE csble. IMO, you could use it as a USE cable at the ampacities listed for USE in Table 310.15(B)(16), 90 amps.

{I do have concern as, from what you say, the cable is not marked as required by 310.120}
Click to expand...
But the manufacture chart says this cable is
Dennis Alwon said:
Just because the panel is rated 200 amps doesn't mean you have to use 200 amp wire. If you install a 90 amp breaker, for the #2 Al at the main panel, then you are protected even if the panel has a 200 amp main.

What is going to be in the 2nd building
Click to expand...
this makes perfect sense to the point of connecting a 90 ampere breaker at the line side of the feeder but not so much for the load end or “overload” opposite end of the feeder termination.

There are 1000s of NEC codes and my concern would be that there would be a code disallowing any size breaker such as 400 amp to be used on load end even if protected properly on line side. I get that this practice works and would be perfectly safe but could an inspector fail it anyway?
 
augie47 said:
The cable on the cut sheet you show primarily a utility distribution cable and not covered by the NEC (similar to URD cable) however it seems to indicate it is also USE csble. IMO, you could use it as a USE cable at the ampacities listed for USE in Table 310.15(B)(16), 90 amps.

{I do have concern as, from what you say, the cable is not marked as required by 310.120}
Click to expand...
I’m confused because the manufacture chart shows the # 2 AWG cable ampacity at 185 amperes but does t make it clear if this is at 60 or 75 degrees? But you say use NEC chart 310 which puts it at 90 ampere? Code says use listed instructions but what if they conflict with nec
 
I will try again....

Individual Conductors used in a NEC installations must be NEC recognized and are shown in 310.104.
The cut-sheet you have shows a cable that is primarily a POCO cable and not listed in the NEC so the ampacities shown on the sheet are not relevant to a NEC installation
There is a note that the conductor is also rated as a USE in which base it could be used as a NEC listed condiuctor as USE under ampacities shown for USE (75°).
If it's an inspected job I would confirm it's acceptabilty with the AHJ due to it not be marked.
 
Jpflex said:
But the manufacture chart says this cable is

this makes perfect sense to the point of connecting a 90 ampere breaker at the line side of the feeder but not so much for the load end or “overload” opposite end of the feeder termination.

There are 1000s of NEC codes and my concern would be that there would be a code disallowing any size breaker such as 400 amp to be used on load end even if protected properly on line side. I get that this practice works and would be perfectly safe but could an inspector fail it anyway?
Click to expand...
As long as the feeder is adequately protected by the OCPD at the supply end of the feeder I do not think there is a problem with the main breaker in the subpanel at the load end of the feeder having a higher rating. It is just a switch.
 
Jpflex said:
But the manufacture chart says this cable is

this makes perfect sense to the point of connecting a 90 ampere breaker at the line side of the feeder but not so much for the load end or “overload” opposite end of the feeder termination.

There are 1000s of NEC codes and my concern would be that there would be a code disallowing any size breaker such as 400 amp to be used on load end even if protected properly on line side. I get that this practice works and would be perfectly safe but could an inspector fail it anyway?
Click to expand...
If you have proper overcurrent protection on the supply side the device on load end essentially becomes a disconnecting means. Could be 800 amp panel and it still wouldn't matter as the supply end will eventually trip if you are drawing more than 90 amps.

Another possible way to do this install is via an outdoor "feeder tap" from anything that is 100 amps or more. If you were doing that then the overcurrent device at the load end of the tap would have to be no more than the ampacity of the conductor which is 90 amps.
 
augie47 said:
I will try again....

Individual Conductors used in a NEC installations must be NEC recognized and are shown in 310.104.
The cut-sheet you have shows a cable that is primarily a POCO cable and not listed in the NEC so the ampacities shown on the sheet are not relevant to a NEC installation
There is a note that the conductor is also rated as a USE in which base it could be used as a NEC listed condiuctor as USE under ampacities shown for USE (75°).
If it's an inspected job I would confirm it's acceptabilty with the AHJ due to it not be marked.
Click to expand...
Also a conductor that has only a USE rating can not enter any building.
 
Jpflex said:
Update:

The feeder is an XL triplex cable with XLPE insulation but my NEC book does NOT list this under the cable table or conductor table and the manufacture claims this cable is rated for 185 amperes when buried and terminated at 75 degrees celcius
Click to expand...
You need 3 conductors plus a ground for a sub panel, so a triplex is not suitable.
 
Yes
kwired said:
If you have proper overcurrent protection on the supply side the device on load end essentially becomes a disconnecting means. Could be 800 amp panel and it still wouldn't matter as the supply end will eventually trip if you are drawing more than 90 amps.

Another possible way to do this install is via an outdoor "feeder tap" from anything that is 100 amps or more. If you were doing that then the overcurrent device at the load end of the tap would have to be no more than the ampacity of the conductor which is 90 amps.
Click to expand...
I understood all this but my concern was regarding if code would allow terminating onto a larger breaker (but not whether it would cause excessive current and heat for conductor) than conductor 60 to 75 degree terminating ampacity. Code can always overrule something that works and not allow it just because it’s a code.
 
I th
VirutalElectrician said:
You need 3 conductors plus a ground for a sub panel, so a triplex is not suitable.
Click to expand...
They are only supplying two hots and a neutral but no equipment grounding conductor between service enclosure and sub panel enclosure so we’ll have to run another cable as before

If the conductors were sized with an over sized OCPD due to manufacture listed instructions 185 amperes at 75 degrees underground then the equipment grounding conductor would be sized wrong either to table 250.122 for 185 ampere service breaker or not sized larger than largest ungrounded conductor at #2 AWG.

Another person posted to use ampacity table 310 but this is a cable so shouldn’t I use ampacity table 400 for cables (even if not listed?)
 
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