Electrician Talk banner
1 - 17 of 17 Posts

·
Registered
Joined
·
68 Posts
Discussion Starter · #1 ·
Hello,
I need to find the wire size & ocpd of supply feed to 75 hp, 208 v motorized, pressure wash boot in an indust. place
(feeder running through 75 degree invironment, indoor, regular temparture)

Per Code book: 75 hp @ 208v is 211 FLA


Can I use 4/0 thhn, cu @ 90 deg. or
should I use 300 mcm, cu @ 75deg. ??????

Thank you
 

·
animal lover /rat bastard
Joined
·
13,547 Posts
ignore the 90 column, unless you are derating.

use the 75 column, unless you are running 300 romex in a house.
 
  • Like
Reactions: JRaef

·
Bilge Rat
motors and controls.........
Joined
·
8,486 Posts
110.14(C)(1)(a)(4) states that motors use the 75º column.

430.6(A)(1) states that the values listed in the tables are used to determine current, not the nameplate.

430.22(A) states that the wire for a single motor needs to be 125% of the value listed in the tables.
 

·
Registered
Joined
·
5,523 Posts
what column you look, 75 deg. or 90 deg
ignore the 90 column, unless you are derating.

use the 75 column, unless you are running 300 romex in a house.
110.14(C)(1)(a)(4) states that motors use the 75º column.

430.6(A)(1) states that the values listed in the tables are used to determine current, not the nameplate.

430.22(A) states that the wire for a single motor needs to be 125% of the value listed in the tables.
Shorter version of the above...

RTFC.
Read The :censored: Code
 

·
Registered
Joined
·
27 Posts
I've always been told as a general rule to ignore the 90-degree column when determining ampacity as most of the connections your conductor will face will not be 90-degree rated. Usually 75 on mechanical lugs, etc. Is my logic correct?

Sent from my SCH-I535 using electriciantalk.com mobile app
 

·
Bilge Rat
motors and controls.........
Joined
·
8,486 Posts
I've always been told as a general rule to ignore the 90-degree column when determining ampacity as most of the connections your conductor will face will not be 90-degree rated. Usually 75 on mechanical lugs, etc. Is my logic correct?

Sent from my SCH-I535 using electriciantalk.com mobile app
Generally speaking, true. 90C is mainly for derating for multiple conductors.

For NM, use the 60C column.
 

·
Bilge Rat
motors and controls.........
Joined
·
8,486 Posts
How does a licensed electrical contractor not know how to size wire for a motor?
It's actually more complicated than it seems. To do it properly, you need to look in at least 4 different articles.

For example, the 75ºC requirement is found in article 110. There is no reference to 110 in 430. Why would you look in 110 for motors when 430 exists?

I would be willing to bet a lot that half the people here on ET would not be able to select the wire size for the OPs motor.

Doesn't mean they're dumb, it means one of two things....or both

1) The typical work they do does not involve big motors

2) The code is far too complicated to be used as a reference for just about anything. Too much pertinent information hidden in unrelated articles. For example, 430 should contain everything needed to properly install a motor. It doesn't. And even worse, it doesn't even refer you to the other articles needed for the installation.

How many inspectors would fail a 1 HP single phase motor operating at 115 volts using #14s landed under a 40 amp breaker, even though it is a perfectly compliant installation? And how many people would be able to prove that the installation is indeed, compliant?
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #13 ·
It's actually more complicated than it seems. To do it properly, you need to look in at least 4 different articles.

For example, the 75ºC requirement is found in article 110. There is no reference to 110 in 430. Why would you look in 110 for motors when 430 exists?

I would be willing to bet a lot that half the people here on ET would not be able to select the wire size for the OPs motor.

Doesn't mean they're dumb, it means one of two things....or both

1) The typical work they do does not involve big motors

2) The code is far too complicated to be used as a reference for just about anything. Too much pertinent information hidden in unrelated articles. For example, 430 should contain everything needed to properly install a motor. It doesn't. And even worse, it doesn't even refer you to the other articles needed for the installation.

How many inspectors would fail a 1 HP single phase motor operating at 115 volts using #14s landed under a 40 amp breaker, even though it is a perfectly compliant installation? And how many people would be able to prove that the installation is indeed, compliant?
Send this reply to sstluise of Texas please
 

·
Registered
Joined
·
752 Posts
micromind said:
It's actually more complicated than it seems. To do it properly, you need to look in at least 4 different articles. For example, the 75ºC requirement is found in article 110. There is no reference to 110 in 430. Why would you look in 110 for motors when 430 exists? I would be willing to bet a lot that half the people here on ET would not be able to select the wire size for the OPs motor. Doesn't mean they're dumb, it means one of two things....or both 1) The typical work they do does not involve big motors 2) The code is far too complicated to be used as a reference for just about anything. Too much pertinent information hidden in unrelated articles. For example, 430 should contain everything needed to properly install a motor. It doesn't. And even worse, it doesn't even refer you to the other articles needed for the installation. How many inspectors would fail a 1 HP single phase motor operating at 115 volts using #14s landed under a 40 amp breaker, even though it is a perfectly compliant installation? And how many people would be able to prove that the installation is indeed, compliant?
I can see your point, my point is that if you are a "CONTRACTOR", which his profile says he is, that you should know more than the average ET user, even more than the average journeyman. That means here in Texas that you have passed a journeymans exam and a masters exam to be able to get your TECL license. By that point I would think you could size any motor big or small.
 

·
Registered
Joined
·
1,665 Posts
All of you make great points, but this member is not looking for an answer. He has been given it many times, and has ignored it each time! :mad:

Sizing cables for motor feeds, even in hot environments, is not difficult! ;)

In the 2012 CEC you use tables 2 or 4, depending on your choice of conductor. If need be, you use table 5A if derating due to temperature. If the 90 degree cable derated is better than the ampacity column of the lowest connection point, you are good to go. Simple! :no:

I'm sure I will be ignored! :laughing:

Thanks, Borgi
 
1 - 17 of 17 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top