whadda ya think?

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crtrrhnd

Member
Location
Louisiana
When 20 12 AWG copper THHN current carrying conductors are installed in one 25' run of 2" EMT, what is the ampacity rating of each conductor?

Article?, Section?

What is the ampacity rating of each THHN copper conductor when installing five 10/2 with ground MC cables bundled together for a length of four feet?

Article?, Section?

If no overcurrent protection is provided on the secondary of a 480 volt 3 phase 5KVA transformer, what is the maximum primary overcurrent protection allowed?

Article?, Section?

In general, when installing a motor in one location and the motor controller in another location that are NOT within sight of eac other, the minimum number of disconnecting means required is?

Article?, Section? :mad:

[ February 22, 2003, 03:00 AM: Message edited by: crtrrhnd ]
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Re: whadda ya think?

1) 310.15(B)(2)(a) and Table 310.16, 90?C column

2) Same as above. If you don't think that the derating applies to bundled AC and MC cables, then why does Exception #5 to 310.15(B)(2)(a) exist?

3) Assuming that the primary voltage of this transformer is 480, the primary rated amps is about 6 amps. Table 450.3(B) permits the primary OCPD to be 167% of primary current. This is 10.055 amps. There is no provision to round up in this column so the maximum primary OCPD where there is no secondary OCPD is 10 amps. Note that the rules in Article 450 only cover the protection for the transformer itself. See 240.21(C) for required secondary conductor protection.

4) In general the answer is 2, there are exceptions that will permit one. See 430.102(A) and (B)

Don
 

crtrrhnd

Member
Location
Louisiana
Re: whadda ya think?

What is the minimum size eqipment ground for a 5 hp, 3 phase 208 volt motor with 20 ampere overload protection and short-circuit protection of 30 amperes?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Re: whadda ya think?

We really have to know the size of the motor circuit conductors and the type of overcurrent protective device for the motor branch circuit to be sure. If the branch circuit OCPD is an instantaneous trip circuit breaker or a motor short-circuit protector, then we size based on the motor overload rating. In this case that results in a #12. If the OCPD other than an instantaneous trip circuit breaker or a motor short-circuit protector, then we size based on the rating of this device, but we can apply 250.122(A) which says the EGC is not required to be larger that the circuit conductors. In this case, if the motor conductors are sized per the code minimum, then they would be #12s and the EGC would also be #12. If for some reason the motor circuit conductors were #10 and the branch circuit OCPD was a 30 amp fuse, then the EGC would have to be #10.
Don
 

kilowatt

Member
Location
Louisiana
Re: whadda ya think?

In this case I think 310.15 would imply that the neutral of the 10/2 MC be counted in the adjustment factor. Is this correct?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Re: whadda ya think?

kilowatt,
10-2 MC does not have a "neutral" conductor. It has two hots or one hot and a grounded conductor. In either case they are both current carrying conductors. To have a neutral, you must have a multiwire circuit and that requires a minimum of 3 conductors.
Don
 

-marty

Senior Member
Location
Alaska
Re: whadda ya think?

Graybar in AK doesn't carry 10-2 mc. But they carry 12-2mc. It has one ungrounded, one neutral, and one grounded. Is 10-2 different??? (except being 10 awg)
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Re: whadda ya think?

Marty,
10-2 and 12-2 MC cables have one hot, one grounded and one grounding conductor. The grounded conductor is commonly called the neutral, but you can't have a neutral with only one hot.
Don
 

jonaslc

Member
Location
Utah
Re: whadda ya think?

I am using NEC 1999 codebook and I do not see an exception 5 for 310-15(b)(2)(a). Could someone please tell me what that exception is
 

-marty

Senior Member
Location
Alaska
Re: whadda ya think?

Don,
Right, I stand corrected, I should have wrote grouding and not grounded.

But, I'm still confused.
"10-2 MC does not have a "neutral" conductor"
and
"but you can't have a neutral with only one hot.
"
Are you saying it's not called a neutral but rather a grounded conductor if there is only one hot wire?
 

-marty

Senior Member
Location
Alaska
Re: whadda ya think?

Don,
Right, I stand corrected, I should have wrote grouding and not grounded.

But, I'm still confused.
"10-2 MC does not have a "neutral" conductor"
and
"but you can't have a neutral with only one hot.
"
Are you saying it's not called a neutral but rather a grounded conductor if there is only one hot wire?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Re: whadda ya think?

Marty,
While most of us always call the white wire a neutral, it is not a neutral when there is only one hot wire. It is the grounded conductor. This is important when applying the derating rules for more than three current carrying conductors in a raceway or cable. A grounded conductor is always a current carrying conductor. A neutral is not always a current carrying conductor.
Don
 
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