jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Sure, just that sum means addition
So, add the negative since they are voltage drops.
Code Ques.
- Thread starter Flight987
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So, add the negative since they are voltage drops.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Sure, just that sum means addition
Looked it up, I was right when I said sum.
http://www.allaboutcircuits.com/vol_1/chpt_6/2.html
97catintenn
Senior Member
- Location
- Columbia, TN
Sorry man, you're right. I took Mike Holt's study material and learned it this way, "The sum of the voltage drops equals the applied voltage."
from Mike Holts electrical nec exam prep 2005 pg 51
from Mike Holts electrical nec exam prep 2005 pg 51
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Means the same exact thing. BTW I got the same book.
kwired
Electron manager
- Location
- NE Nebraska
You were expecting it to be more complicated than it is and had some kind of mind block keeping you from seeing how easy it was.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
True, but I still recommend a basic algebra course.
For example: take the the power circle chart.
I only need to memorize 2 equations and I can solve questions regarding all 12 through substitution.
E= I*R and P=E*I
kwired
Electron manager
- Location
- NE Nebraska
Really depends on what you call algebra, or an algebra class.True, but I still recommend a basic algebra course.
For example: take the the power circle chart.
I only need to memorize 2 equations and I can solve questions regarding all 12 through substitution.
E= I*R and P=E*I
Many young kids maybe 4th or 5th grade can solve for a missing element in most of those equations (maybe not ones using exponents or square root functions). Some of the very basics of algebra is taught in elementary grade level math classes before they even know the term "algebra". 5 - y = 2 is a very basic algebra equation.
A Ques.
A Ques.
A slash rated breaker, rated 277/480 volt,is permitted to be installed in an ungrounded, 480 volt,
three-phase, three-wire panelboard. Key answer False.
I get confused in the wording of 240.85. Went to Art. 100. When they say grounded or ungrounded,
what are they saying by that? Panel's are allway's grounded for protection, not? Then they talk of
nominal voltage, which is the one to consider? Little confused.
A Ques.
A slash rated breaker, rated 277/480 volt,is permitted to be installed in an ungrounded, 480 volt,
three-phase, three-wire panelboard. Key answer False.
I get confused in the wording of 240.85. Went to Art. 100. When they say grounded or ungrounded,
what are they saying by that? Panel's are allway's grounded for protection, not? Then they talk of
nominal voltage, which is the one to consider? Little confused.
Ques. 2
Ques. 2
Which of the following wiring methods are not permitted when exposed to physical damage?
Key Answ. E
A. Busway
B. EMT
C. IMC
D. RMC
E. LFMC
F. All of the above are permitted.
In the uses not Prem., some say ( physical damage) and some say ( severe physical damage).
I looked in Art 100. So far there Answ. are correct. It took you guy's to show me how they
come up with answer before, so this one has me confused. We all run EMT out of the ground.
Now we get to 300.50 and it say's more. We all run #80 PVC out of the ground.
Interesting.
Ques. 2
Which of the following wiring methods are not permitted when exposed to physical damage?
Key Answ. E
A. Busway
B. EMT
C. IMC
D. RMC
E. LFMC
F. All of the above are permitted.
In the uses not Prem., some say ( physical damage) and some say ( severe physical damage).
I looked in Art 100. So far there Answ. are correct. It took you guy's to show me how they
come up with answer before, so this one has me confused. We all run EMT out of the ground.
Now we get to 300.50 and it say's more. We all run #80 PVC out of the ground.
Interesting.
kwired
Electron manager
- Location
- NE Nebraska
Ungrounded systems do exist, and are many ways the same as grounded systems but do have some differences. You still have to install grounding electrode system and bond all non current carrying parts together just like you do for a grounded system - this is so that there will not be differences of potential between any of these items - just like a grounded system is supposed to be. You do have to install equipment that detects faults to ground, and then this will notify the operator that there is a problem but will not shut down a critical process or assembly line, but instead allows for orderly shut down - that is the main reason ungrounded systems do exist - there is also a high impedance grounded system that has similar detection and orderly shutdown capabilities. Now back to the question - if you have 277/480 you can't have an ungrounded system - this system has a neutral and the neutral must be grounded (but it can be impedance grounded as mentioned before). So to be able to have an ungrounded system there will be no neutral - if no neutral the 277/480 breaker can not be used it must be straight 480 volt rated.
I dislike physical damage questions - physical damage is subject to interpretation. It is possible to have 4 inch RMC that is subject to physical damage - it takes a lot more than EMT to damage it but it is not indestructable either.
Code Ques.
What minimum size main bonding jumper is required for an 1200 ampere service, supplied by six 3/0
XHHW-2 conductors paralleled per phaes?
A. #2
B. 1/0
C. 3/0
D. 250 kcmil
E. None of these.
Key Answ. C ,Ref. 250.28
I read 250.28, and that is fine. 250.28 talk's about the 12 1/2 percent on the sizing. Now, I went to
to table 250.122 to get the result's. I don't get the 12 1/2 percent, and how we rate it. Mike's
DVD's didn't have much on this.
What minimum size main bonding jumper is required for an 1200 ampere service, supplied by six 3/0
XHHW-2 conductors paralleled per phaes?
A. #2
B. 1/0
C. 3/0
D. 250 kcmil
E. None of these.
Key Answ. C ,Ref. 250.28
I read 250.28, and that is fine. 250.28 talk's about the 12 1/2 percent on the sizing. Now, I went to
to table 250.122 to get the result's. I don't get the 12 1/2 percent, and how we rate it. Mike's
DVD's didn't have much on this.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Is answer C, 2/0 or 3/0?
kwired
Electron manager
- Location
- NE Nebraska
First thing table 250.122 does not apply, table 250.66 does and is even mentioned in 250.28.
If you have six parallel 3/0 you have less than 1100KCMIL as mentioned in 250.28 and therefore the 12.5% part does not come into play. (go to Ch9 table 8 and get the area of a 3/0 conductor and multiply that by 6 to get your total area of the paralleled conductors)
If the conductors were 6 # 4/0 12.5% still requires a 3/0 MBJ, but if there were 6 - 250kcmil conductors 12.5% would require at least a 4/0 MBJ.
Code Ques.
On the last Ques. of the bonding jumper size, I can't seem to find it Mikes work book? Maybe it was in
DVD'S that he talked about it.
Chap. 9,table 8 show's .173 for area of 3/0. .173x6=1.038. I did that step before I even posted the
thread. Now I am looking at this and saying to myself, I know what to do, but it is not comming to
me. I don't know why I have a mind block on this deal? When I went throught the DVD,S it worked.
On the last Ques. of the bonding jumper size, I can't seem to find it Mikes work book? Maybe it was in
DVD'S that he talked about it.
Chap. 9,table 8 show's .173 for area of 3/0. .173x6=1.038. I did that step before I even posted the
thread. Now I am looking at this and saying to myself, I know what to do, but it is not comming to
me. I don't know why I have a mind block on this deal? When I went throught the DVD,S it worked.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Chapter 9 table 8 is for bare conductors. You need to look in the table for the conductor type you are using. Which in your case is XHHW-2, then look under the 3/0. That would be 0.2642.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
The conductor insulation type would be irrelevant for this question.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
So, what size single conductor would have the equivilent area?
I came up with a 1000kcmil and a 2/0 jumper size from T250.66.
Here is a link for future study.
http://www.iaei.org/magazine/1998/11/service-main-bonding-jumpers/
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