Questions NEC

[Samuel87]

Hi guys I am studying to take my test as residential electrician and I have some question where I don't find the reference in the NEC.

1) If an ungrounded #4 or larger conductor enters a raceway in a pull box, it shall meet which of the following requirements:
A. Be encased in concrete
B. Be protected by an insulated bushing
C. Carry less than 600v
D. None of the above

I got this reference 314.28 and 314.17(B)( 3), but I'm not sure.

2) In a 200A, 120/240v single family dwelling service entrance, with a calculated demand load of 150A, the minimum type THWN aluminum conductor size allowed is:
A.1/0 AWG
B. 3/0 AWG
C. 2/0 AWG
D. 4/0 AWG

For this I took table 310.16 and my answer was B but they said that is 4/0

Thanks.

 

[Tulsa Electrician]

Hi guys I am studying to take my test as residential electrician and I have some question where I don't find the reference in the NEC.

1) If an ungrounded #4 or larger conductor enters a raceway in a pull box, it shall meet which of the following requirements:
A. Be encased in concrete
B. Be protected by an insulated bushing
C. Carry less than 600v
D. None of the above

I got this reference 314.28 and 314.17(B)( 3), but I'm not sure.

2) In a 200A, 120/240v single family dwelling service entrance, with a calculated demand load of 150A, the minimum type THWN aluminum conductor size allowed is:
A.1/0 AWG
B. 3/0 AWG
C. 2/0 AWG
D. 4/0 AWG

For this I took table 310.16 and my answer was B but they said that is 4/0

Thanks.

(1) Your on the right track.
Key word #4 or larger. One of the articles will redirect you to another article. There your answer will be.

(2) Read again at what is asking for based on service size using an AL conductor.
Read a different artical then use table.

 

[Samuel87]

(1) Your on the right track.
Key word #4 or larger. One of the articles will redirect you to another article. There your answer will be.

(2) Read again at what is asking for based on service size using an AL conductor.
Read a different artical then use table.

Q1 is 300.4(G) Fittings
Q2 is Table is 310.12, for this when we read "Service or feeder rating - ampere " that means breaker amps?

Thanks.

 

[infinity]

Q1 is 300.4(G) Fittings
Q2 is Table is 310.12, for this when we read "Service or feeder rating - ampere " that means breaker amps?

Yes for question 1 the answer is bushing. What code cycle are you using? For 2020 you can use T310.12 and for 200 amps the answer is #4/0 aluminum. The fact that they mentioned 150 amps in the question is irrelevant.

 

[Dennis Alwon]

2) In a 200A, 120/240v single family dwelling service entrance, with a calculated demand load of 150A, the minimum type THWN aluminum conductor size allowed is:
A.1/0 AWG
B. 3/0 AWG
C. 2/0 AWG
D. 4/0 AWG

For this I took table 310.16 and my answer was B but they said that is 4/0

Thanks.

Did you use the 90C column or the 75C column? The 75C column is almost always used except when using nm cable and some other cases.

Look at 110.14(C) and then ask questions if you don't understand

 

[infinity]

Did you use the 90C column or the 75C column? The 75C column is almost always used except when using nm cable and some other cases.

I'm guessing that he looked up the conductor ampacity for 150 amps. #3/0 Al @ 75° C is 155 amps. His mistake was not using T310.12 or the 83% rule.

 

[Tulsa Electrician]

Q1 is 300.4(G) Fittings
Q2 is Table is 310.12, for this when we read "Service or feeder rating - ampere " that means breaker amps?

Thanks.

In this case yes and no. More on the no side.

2) In a 200A, 120/240v single family dwelling service entrance, with a calculated demand load of 150A, the minimum type THWN aluminum conductor size allowed is:
A.1/0 AWG
B. 3/0 AWG
C. 2/0 AWG
D. 4/0 AWG

I would break down the question to help understand what it's ask for.
The info in the first sentence before the comma.
"2) In a 200A, 120/240v single family dwelling service entrance,"
It does not say breaker. It says service entrance.
What your looking for is a 200 amp service entrance rated conductor.


It also provides information as where to look.
"120/240 v single family dewelling service."
This will tell you where to start.
Key words in bold. This is step one to solve.

Once you know this you move on to sizing.
As covered above is says 200 amp service entrance.
Key word 200 amp.

Then the trip, I call this a trip for this question because it can lead you astray.
", with a calculated demand load of 150A,"
You will notice another comma. Take read breaks every time you see one so pause then start again.
One working toward a master's this is important information. For a journeyman not so much test related or is it.
In case your working on a master's. Reminder this; The conductor must always carry the load. In the field the conductor must always carry the load.
Now can see the importance of the information, calculated demand load of 150 amp .
The conductor had to be sized for this load.
You will also notice the structure of the question. 200 above 150.
A way to look at it is 200 amp breaker and wire for 150 amp load.
If it was worded the other way it's a bad design. 150 amp breaker and wire for 200 amp load. See the trip, conductor must always carry load.
A tip, on your scratch paper always write down info as you read it one under another.

200? I'm this case, 200 amp wire
120/240 single phase
Single family dewelling
150 load
Then the rest.

After your second pause you get.
"the minimum type THWN aluminum conductor size allowed is'
Now where into the meat of the question.
They want conductor size.

200? I'm this case, 200 amp wire
120/240 single phase
Single family dewelling
150 load
Answer for size using type?
Type: THWN AL
Now you can see the relevance of the trip and why the conductor must always carry the load.
Now we have the conductor (wire) type to size the conductor from the table.
Look at the table.
The table is structured to read left to right.
Service or feeder rating,conductor.
Now look at your notes:
200
? Size of AL conductor
Code, left to right and top to bottom.
I did see residential exam.
So maybe keep it simple.
Residential service table 310.12 and note in book.

Good luck on your exam.

 

[Tulsa Electrician]

I would like to add. If your not on 2020 book and test let us know and we can walk you through the 83% and using different table.

 

[Samuel87]

In this case yes and no. More on the no side.

I would break down the question to help understand what it's ask for.
The info in the first sentence before the comma.
"2) In a 200A, 120/240v single family dwelling service entrance,"
It does not say breaker. It says service entrance.
What your looking for is a 200 amp service entrance rated conductor.


It also provides information as where to look.
"120/240 v single family dewelling service."
This will tell you where to start.
Key words in bold. This is step one to solve.

Once you know this you move on to sizing.
As covered above is says 200 amp service entrance.
Key word 200 amp.

Then the trip, I call this a trip for this question because it can lead you astray.
", with a calculated demand load of 150A,"
You will notice another comma. Take read breaks every time you see one so pause then start again.
One working toward a master's this is important information. For a journeyman not so much test related or is it.
In case your working on a master's. Reminder this; The conductor must always carry the load. In the field the conductor must always carry the load.
Now can see the importance of the information, calculated demand load of 150 amp .
The conductor had to be sized for this load.
You will also notice the structure of the question. 200 above 150.
A way to look at it is 200 amp breaker and wire for 150 amp load.
If it was worded the other way it's a bad design. 150 amp breaker and wire for 200 amp load. See the trip, conductor must always carry load.
A tip, on your scratch paper always write down info as you read it one under another.

200? I'm this case, 200 amp wire
120/240 single phase
Single family dewelling
150 load
Then the rest.

After your second pause you get.
"the minimum type THWN aluminum conductor size allowed is'
Now where into the meat of the question.
They want conductor size.

200? I'm this case, 200 amp wire
120/240 single phase
Single family dewelling
150 load
Answer for size using type?
Type: THWN AL
Now you can see the relevance of the trip and why the conductor must always carry the load.
Now we have the conductor (wire) type to size the conductor from the table. View attachment 2564138
Look at the table.
The table is structured to read left to right.
Service or feeder rating,conductor.
Now look at your notes:
200
? Size of AL conductor
Code, left to right and top to bottom.
I did see residential exam.
So maybe keep it simple.
Residential service table 310.12 and note in book.

Good luck on your exam.

I'm going to take the exam for residential in CA, and I'm studying by myself with NEC 2020 and sometimes I'm lost like this question. So it's correct to say that Table 310.16 is for branch circuits? Thanks for your help.

 

[Samuel87]

I would like to add. If your not on 2020 book and test let us know and we can walk you through the 83% and using different table.

I got NEC 2020 thanks.

 

[Samuel87]

Did you use the 90C column or the 75C column? The 75C column is almost always used except when using nm cable and some other cases.

Look at 110.14(C) and then ask questions if you don't understand

When I read that it's so confusing to me, special 110.14(C). I know the current flow produces heat in the conductor and we have terminations where they have a temperature rating. So the condition is that the ampacity of a conductor must be less than the temperature rating of termination, because if the ampacity is high we are going to produce much heat that is resisted for the termination, and the termination can cause an accident. We have two options: < 1000A with 14 - 1 AWG, and > 1000A with 1AWG higher. But I don't know when to use 75C or 90C? If you can help me with this one I'll be thankful.

 

[roger]

I got NEC 2020 thanks.

But is that what the test will be based on? If not you may be spinning your wheels.

 

[Dennis Alwon]

When I read that it's so confusing to me, special 110.14(C). I know the current flow produces heat in the conductor and we have terminations where they have a temperature rating. So the condition is that the ampacity of a conductor must be less than the temperature rating of termination, because if the ampacity is high we are going to produce much heat that is resisted for the termination, and the termination can cause an accident. We have two options: < 1000A with 14 - 1 AWG, and > 1000A with 1AWG higher. But I don't know when to use 75C or 90C? If you can help me with this one I'll be thankful.

First it is 100 amps, not 1000 amps. lol

90° is only used for de-rating because 90° equipment is pretty much non-existent. Even if the lugs are 90° rated the equipment that they are mounted in are only 75°. So we are basically looking at a bunch of ropes put together and the end result is our rope will only be as strong as the weakest link in the chain of ropes.

It is the same with wire-- we may have 90C wire with 75C equipment so the conductor must be rated at the 75C. Throw Nm cable in the mix and now our final ampacity is stuck at 60C since nm cable is rated 60C

The 100 amps > and less than only applies when we don't know the temperature rating of the equipment. If a panel isn't labeled then we must assume it is 60C if it is 100 amps or less and accordingly if the conductors terminate on terminals greater than 100 amps then we can assume 75C.

Just remember we have to look at all links in the chain and use the weakest link for our final ampacity.