can you figure this question out..?

[sparky723]

I am in Mikes NEC Exam Prep book on page 162. It has a question wanting to find branch conductor size. In step 1 of the problem solving, it shows 22A. Does Anybody know where this 22A came from?
The whole question is b.c and ocd for a 7.5,230v,three phase motor. I cant even get past the first part of the question. somebody please help. PM's would be great.

 

[charlie b]

The 22 amps is straight out of table 430.250. We are supposed to use that table to get running amps, rather than use anything on the nameplate.

 

[sparky723]

Thanks C.B.
I may be back on with more ques.
I am studying for my Masters and I am a bit rusty with all the tables and such. Been away from my passion to long...

 

[sparky723]

same question shows I.T.breaker in the answer from 430.52

I cant figure why though.

 

[billsnuff]

430.52

430.52

Maximum rating or setting of motor-branch circuit short-circuit and ground fault protective devices ..........gives you the % of full load current for each type OCPD.

single phase motor and non-delay time fuse = 300% of FLC, us IT Breaker and it is 800%.

 

[charlie b]

I don't have that book, so I have no context for the question. I would need to know more about (1) what information they gave you and (2) what information they are asking you to figure out.

 

[sparky723]

tap conductors

tap conductors

i have a "dumb" question:

what is the definition of a Tap?

 

[charlie b]

I have a "dumb" question:

No you don?t. No such thing exists.

What is the definition of a Tap?

I don?t think it has a formal definition. The basic concept is that every wire has to be protected against overcurrent, that it has to be protected on the basis of its ampacity, and that the protective device has to be located where the wire gets its source of power. Taps are exceptions to that basic notion. The ?Tap Rules? in 240.21 give us specific cases where we can protect a wire at the end of the run, rather than at the beginning. The common examples are when you have a large wire with a large overcurrent device, and you connect a smaller wire somewhere in the middle. The smaller wire could not be protected by the upstream breaker, since it is sized for the larger wire. But we are allowed to put the overcurrent protection for the smaller wire at the end of the run, if we follow the specific requirements of the applicable paragraph. Take a look through 240.21, and you?ll see what I mean.

 

[zog]

No you don’t. No such thing exists.

Oh yes it does, I used to say the same thing but after 15 years of teaching I changed my tune. Example, discussing fall protection requirements, specifically the 6 foot rule requiring fall protection.

Student "Is that measured from your head or your feet to the ground?"
Me: "How tall are you?"
Student : "6'2"", ah ha!! I get it now"

That being said the tap question is a good one, to me it is a setting of the primary to seconday turns of transformer windings. Means different stuff to different people.

 

[sparky723]

what size tap cond. for a 150A c.b. if continuous load is 100A?

I did 100x1.25, getting 125. A 1 AWG is 130A, but book says 1/0 at 150A.

AAUUGGHH!!!

 

[sparky723]

forget it. i figured it out.

 

[don_resqcapt19]

240.2 Tap Conductors. As used in this article, a tap conductor is defined as a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.