MI Cable to EMT With THHN Cu

[mstrlucky74]

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

Are you referring to the 75 degree column?

 

[mstrlucky74]

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

Thanks. According to 310.17 looks like they could use 1/0 MI for 200A but they are showing 3/0? Maybe the 150' VD is the reason for upsizing.

EDIT: So now reading through thread again I'm confused. Why look at 310.17 at all if you have to go by the temperature rating on 310.16? That's what Don, or NEC 110, is saying, correct?

 

[Smart $]

Are you referring to the 75 degree column?

He is.

Thanks. According to 310.17 looks like they could use 1/0 MI for 200A but they are showing 3/0? Maybe the 150' VD is the reason for upsizing.

EDIT: So now reading through thread again I'm confused. Why look at 310.17 at all if you have to go by the temperature rating on 310.16? That's what Don, or NEC 110, is saying, correct?

You have to go by 110.14(C), which says you have to use 310.15(B)(16) to correlate the minimum conductor size with the terminal temperature limitation, and the size used sets the maximum circuit ampacity.

You use 310.15(B)(17) and other aspects of 310.15, such as adjustment for the number of current-carrying conductors and correction for ambient temperature, to establish conductor ampacity for the conditions of use between terminal enclosures. The actual circuit ampacity is the smaller of the maximum circuit ampacity determined in preceding paragraph and the result of the conductor ampacity determination in this paragraph.

 

[don_resqcapt19]

Are you referring to the 75 degree column?

Yes, as it is extremely rare to find equipment that operates below 1,000 volts that is also listed for use with conductors operating at 90°C.

 

[mstrlucky74]

So when MI is calling for 4#350 isn't that 3H,1N. Where is the ground. If I'm switching to pipe and wire wouldn't I have to run 5 conductors. 3H,1N & 1G? Thanks.

 

[Smart $]

So when MI is calling for 4#350 isn't that 3H,1N. Where is the ground. If I'm switching to pipe and wire wouldn't I have to run 5 conductors. 3H,1N & 1G? Thanks.

MI cable is either copper or alloy steel sheathed. The copper sheathed variety is typically used, and the sheath qualifies as an EGC under 250.118, item (9).

 

[mstrlucky74]

MI cable is either copper or alloy steel sheathed. The copper sheathed variety is typically used, and the sheath qualifies as an EGC under 250.118, item (9).

Thanks. So if we were to switch to pipe and wire we could use the EMT as an EGC. Was asking because I always seem the engineer calling for a separate ground in the larger feeders.

 

[Smart $]

Thanks. So if we were to switch to pipe and wire we could use the EMT as an EGC. Was asking because I always seem the engineer calling for a separate ground in the larger feeders.

The very same engineeer is less likely to require a separate ground with MI cable because the sheath is continuous between terminations, much the same as running a wire-type EGC. Using EMT as the sole EGC is less reliable in the minds of many, but it is Code compliant when installed properly and maintained.

 

[don_resqcapt19]

Thanks. So if we were to switch to pipe and wire we could use the EMT as an EGC. Was asking because I always seem the engineer calling for a separate ground in the larger feeders.

When you switch from MI to EMT and standard conductors, don't forget about 300.20.

Most engineered jobs I see, require an EGC, even where the conductors are installed in a raceway that is permitted to be the EGC.

 

[mstrlucky74]

The very same engineeer is less likely to require a separate ground with MI cable because the sheath is continuous between terminations, much the same as running a wire-type EGC. Using EMT as the sole EGC is less reliable in the minds of many, but it is Code compliant when installed properly and maintained.

Thanks..interesting.

 

[mstrlucky74]

When you switch from MI to EMT and standard conductors, don't forget about 300.20.

Most engineered jobs I see, require an EGC, even where the conductors are installed in a raceway that is permitted to be the EGC.

Exactly why I asked. Thanks a lot.

 

[mstrlucky74]

Exactly why I asked. Thanks a lot.

So guys in my initial post/pic where it shows 3/0 MI it looks like I can still use 3/0 DRAKA according to attachment.

 

[mstrlucky74]

Doesn't look like I can use the same # of sets & Draka wire for this as they show for the MI. Need to upsize? About 200' away. Thanks

 

[don_resqcapt19]

Doesn't look like I can use the same # of sets & Draka wire for this as they show for the MI. Need to upsize? About 200' away. Thanks

I don't see why you can't use the same size conductors as you are using with the MI cable. However in your last post, I have no idea why they are using four sets of 350 kcmil on a 700 amp fuse. The four sets would give you 1240 amps of conductor.

 

[mstrlucky74]

I don't see why you can't use the same size conductors as you are using with the MI cable. However in your last post, I have no idea why they are using four sets of 350 kcmil on a 700 amp fuse. The four sets would give you 1240 amps of conductor.

Ill check into it in the morning. Thanks

edit: want to be very clear so I'm reference the correct tables for MI ampacity. Ultimately you have to reference 310.16 due to terminal temp ratings(110.14?)correct? So why even reference 310.17?

 

[mstrlucky74]

OK dumb question. In the attachment,and in any case, the fuse is 700A and the load(ats) is 800s. What do you size conductors to...load or fuse?

 

[Smart $]

OK dumb question. In the attachment,and in any case, the fuse is 700A and the load(ats) is 800s. What do you size conductors to...load or fuse?

ATS: Automatic Transfer Switch

800A is its current rating, not the load.

Conductor minimum size is based on load but can't be any smaller than protected by ocpd (fuse), which when not more than 800A, permits ampacity-load down to not smaller than next lower standard ocpd rating. Not knowing the actual calculated load, size to fuse rating.

 

[mstrlucky74]

ATS: Automatic Transfer Switch

800A is its current rating, not the load.

Conductor minimum size is based on load but can't be any smaller than protected by ocpd (fuse), which when not more than 800A, permits ampacity-load down to not smaller than next lower standard ocpd rating. Not knowing the actual calculated load, size to fuse rating.

Thanks, know what ATS stands for:happyyes:

Thanks for sizing info.

 

[don_resqcapt19]

These appear to be engineered design drawings. In general, you have to bid and install what is on the drawings. You don't get to make changes without involving the design engineer.