Motor Calc

[Alwayslearningelec]

Am I looking at this right?

Motor HP 22.8 per schedule
Per 430.250 I use 25 HP and it says 74.8 amps. Multiply that by 125% and it gives me 93.5 amps.

Schedule is calling for #2's but #3's would actually be ok??? Figuring what they show but I'm curious.

 

[infinity]

Yes #3 THHN is rated for 100 amps at 75° C.

 

[Alwayslearningelec]

Yes #3 THHN is rated for 100 amps at 75° C.

Thanks, but the way I figured the calculation was correct?

 

[d0nut]

Yes #3 THHN is rated for 100 amps at 75° C.

But it is only rated at 85A using the 60 degree column while the #2s would be 95A. If the terminals aren't marked otherwise, that is the column you would have to use per 110.14(C).

 

[Alwayslearningelec]

But it is only rated at 85A using the 60 degree column while the #2s would be 95A. If the terminals aren't marked otherwise, that is the column you would have to use per 110.14(C).

Oh, I do believe recalling that anything rated 100A or less you must use 60 degree column.

So that brings me to my other question. Panel terminal are most definite rate 75 degree so that leave the motor terminals. I guess I could check the unit cut sheet online or call them. Imagine it has to be listed somewhere.

 

[don_resqcapt19]

Oh, I do believe recalling that anything rated 100A or less you must use 60 degree column.

So that brings me to my other question. Panel terminal are most definite rate 75 degree so that leave the motor terminals. I guess I could check the unit cut sheet online or call them. Imagine it has to be listed somewhere.

Only if not marked otherwise. Most equipment that you would be able to purchase for this application will be marked for 75°C.
The rule in 110.14(C)(1)(a)(4) says most motors are permitted to use 75°C conductors.

 

[infinity]

Oh, I do believe recalling that anything rated 100A or less you must use 60 degree column.

So that brings me to my other question. Panel terminal are most definite rate 75 degree so that leave the motor terminals. I guess I could check the unit cut sheet online or call them. Imagine it has to be listed somewhere.

For any modern commercial equipment you can forget about the possibility of a 60° C terminal.

 

[Alwayslearningelec]

For any modern commercial equipment you can forget about the possibility of a 60° C terminal.

Agree.

 

[infinity]

Agree.

If this were a test question then what dOnut said would be applicable. Real world, it is not an issue.

 

[Alwayslearningelec]

I understand you bid what's shown but you could try and submit showing # 3 and see of the engineer approves correct? but then you face credit situation.

 

[infinity]

I understand you bid what's shown but you could try and submit showing # 3 and see of the engineer approves correct? but then you face credit situation.

We would bid #2 and pull #3. Most of the time no one will notice and the job is still code compliant. Even give backs are profitable.

 

[David Castor]

We would bid #2 and pull #3.

Seriously?

 

[infinity]

Seriously?

Value engineering. Our company does it all of the time. Sometimes the client asks for a credit often they don't but we'll give them something else for free.