MI Cable to EMT With THHN Cu

[mstrlucky74]

Would you use the same size wire when switching from MI Cable to pipe and wire(thhn)? According to this pic and the 200A breaker and ATS seems like I can use smaller wire than 3/0 it's showing for the MI Cable. Even with voltage drops it looks like I can use 1/0 or 2/0 not 3/0 as shown with the MI cable.

Distance is about 160' away.

Thanks.

 

[Smart $]

You can't go smaller than 3/0 when powered by a 200A breaker (except for the exceptions, of course ).

 

[mstrlucky74]

You can't go smaller than 3/0 when powered by a 200A breaker (except for the exceptions, of course ).

Right so why is the MI cable 3/0? does it have a different current carrying capacity than MI? thanks

 

[gadfly56]

Right so why is the MI cable 3/0? does it have a different current carrying capacity than MI? thanks

I remember a blurb on one of the manufacturer's web sites that explains you can use smaller sizes of MI for the same ampacity. Yep, here you go. You can use the free air ampacity for MI.

 

[don_resqcapt19]

I remember a blurb on one of the manufacturer's web sites that explains you can use smaller sizes of MI for the same ampacity. Yep, here you go. You can use the free air ampacity for MI.

That is fine, but you can't terminate it on equipment using the free air ampacity. Terminations are based on the ampacities in Table 310.15(B)(16). See 110.14(C)(1).

 

[don_resqcapt19]

Right so why is the MI cable 3/0? does it have a different current carrying capacity than MI? thanks

3/0 is the smallest size you would use with a 200 amp OCPD based on Table 310.15(B)(16).

 

[Smart $]

3/0 is the smallest size you would use with a 200 amp OCPD based on 75°C terminations [110.14(C) and Table 310.15(B)(16)].

FIFY.

 

[gadfly56]

That is fine, but you can't terminate it on equipment using the free air ampacity. Terminations are based on the ampacities in Table 310.15(B)(16). See 110.14(C)(1).

You use the manufacturer's termination kits. See the same reference above. And for this application you could use 1/0.

 

[gadfly56]

3/0 is the smallest size you would use with a 200 amp OCPD based on Table 310.15(B)(16).

Try 310.15(B)(17), since that's where MI cable lives.

 

[Smart $]

You use the manufacturer's termination kits. See the same reference above. And for this application you could use 1/0.

I do not believe termination kits change the terminal temperature rating of the connected equipment. Termination temperature limitations are not solely based on the conductor terminal temperature rating.

 

[Smart $]

Try 310.15(B)(17), since that's where MI cable lives.

No. Don is correct for what he is referring to (incompletely as it seems to be). See 110.14(C).

 

[GoldDigger]

I do not believe termination kits change the terminal temperature rating of the connected equipment. Termination temperature limitations are not solely based on the conductor terminal temperature rating.

Maybe not, but if you terminate the MI into an MI connector to which you attach a larger gauge THHN jumper that connects to the equipment terminal you can probably make it acceptable.

 

[Smart $]

Maybe not, but if you terminate the MI into an MI connector to which you attach a larger gauge THHN jumper that connects to the equipment terminal you can probably make it acceptable.

Only if it is in an enclosure remote to the equipment terminal compartment. Some say at least 4 feet of the larger conductor is required too, from spec's on UL terminal temperature testing standard... or was that testing panelboards... recall not that great at the moment.

 

[GoldDigger]

Only if it is in an enclosure remote to the equipment terminal compartment. Some say at least 4 feet of the larger conductor is required too, from spec's on UL terminal temperature testing standard... or was that testing panelboards... recall not that great at the moment.

I think that was when testing breakers and their terminal temperature rating, IIRC.

 

[Smart $]

I think that was when testing breakers and their terminal temperature rating, IIRC.

Regardless, the heat sink principle behind a required distance still applies. And as far as the NEC is concerned, it can't happen within the enclosure of the 75°C-rated equipment.

 

[gadfly56]

No. Don is correct for what he is referring to (incompletely as it seems to be). See 110.14(C).

I think it depends if it is a cable assembly or 4 single conductors grouped together. If the latter, 332.80(B) applies and the correct table is (B)17, not (B)16 if you meet the requirements of 332.80(B).

 

[Smart $]

I think it depends if it is a cable assembly or 4 single conductors grouped together. If the latter, 332.80(B) applies and the correct table is (B)17, not (B)16 if you meet the requirements of 332.80(B).

That has nothing to do with correlating the minimum conductor size with termination temperature limitations of the connected equipment. 100.14(C) terminal temperature limitations use only Table 310.15(B)(16) for the minimum conductor size determination.

 

[gadfly56]

That has nothing to do with correlating the minimum conductor size with termination temperature limitations of the connected equipment. 100.14(C) terminal temperature limitations use only Table 310.15(B)(16) for the minimum conductor size determination.

If you're using the listed connectors, doesn't 100.14(C)(2) apply? Assuming that the equipment is listed for 90C.

 

[don_resqcapt19]

If you're using the listed connectors, doesn't 100.14(C)(2) apply? Assuming that the equipment is listed for 90C.

I don't see (C)(2) as changing anything.
If the equipment is listed for 90°C ampacities, then you can use those ampacities from Table 310.15(B)(16). There is not much equipment out there that is marked for use with 90° terminations.

 

[Smart $]

If you're using the listed connectors, doesn't 100.14(C)(2) apply? Assuming that the equipment is listed for 90C.

AFAIK, there is no listed enclosed distribution equipment with a 90°C temperature rating. As I understand it, UL listing requirements simply do not require testing to that temperature.