simple calculation

[Mustwin351]

Just to double check there is not a problem with running 4 circuits (total 8 current carrying) #12 thhn through a 1/2” conduit to separate individual outlets. (All dedicated).

8 ccc reduces my ampacity to .70

#12 is at 90 degrees for derating and 30 amps

40X.7=21I

so in this case I should be able to pull 8 ccc and 1 equipment grounding conductor all within a 1/2” conduit if my calculations are correct?

thoughts?

 

[roger]

Just to double check there is not a problem with running 4 circuits (total 8 current carrying) #12 thhn through a 1/2” conduit to separate individual outlets. (All dedicated).

8 ccc reduces my ampacity to .70

#12 is at 90 degrees for derating and 30 amps

40X.7=21I

so in this case I should be able to pull 8 ccc and 1 equipment grounding conductor all within a 1/2” conduit if my calculations are correct?

thoughts?

You have a typo, but yes you can do as you plan.

Roger

 

[charlie b]

Agreed. The rule of thumb is that you can have 9 CCCs in a conduit, #12 THHN, and still use a 20 amp breaker. The limit for #10 THHN and a 30 amp breaker is 6 CCCs. Both can be confirmed using the simple calculation that you posted.

 

[Sierrasparky]

1/2 in conduit is going to be a tight pull. Just saying from Experience.

 

[ActionDave]

1/2 in conduit is going to be a tight pull. Just saying from Experience.

I've been pulling full boats of #12 in 1/2 emt since I started and never had a problem.

 

[kwired]

1/2 in conduit is going to be a tight pull. Just saying from Experience.

Depends on the installation. Straight run, stranded conductors, pretty easy compared to shorter run but with three 90's.

 

[infinity]

I find that with modern conductors like THHN or Sim-pull, 360° and 40% fill still isn't very hard to pull especially if you use all stranded conductors.

 

[ramsy]

8 ccc reduces my ampacity to .70

#12 is at 90 degrees for derating and 30 amps

40X.7=21

A 20A fuse does not make a compliant #12 wire.

There are a few places where this fails:

1) No capacity remains for other adjustments, such as continuous loads, or ambient temperatures > 30°C.
That means no attics, outdoors, unconditioned spaces, or if anything runs > 3hrs, this install overheats.

2) #12 adjusted for 8 ccc's operates in the 75°C column.
NEC 110.14(C) prohibits 75°C with 60° equipment, default for 100A or less, and anything missing 75° labels.

..a) For Maint. & Commercial guys lots of existing equipment is missing 75°C labels/listings. Default is 60°C
..b) For Residential guys that means no stripping 60°C NM cable for un-labeled conductors stuffed in conduit.

3) Most electricians smart enough to get 110.14(C), Ambient, and Continuous adjustments, will miss 220.18(A).

..a) After bending over backward to get all adjustments, they see the light shinning past tonsils.
..b) With head so far up butt, they always forget 120% for motor loads? Regardless of 20A HACR breaker that holds, this wire overheats.

 

[ActionDave]

A 20A fuse does not make a compliant #12 wire.

There are a few places where this fails:

1) No capacity remains for other adjustments, such as continuous loads, or ambient temperatures > 30°C.
That means no attics, outdoors, or unconditioned spaces. Anything runs > 3hrs, and this install overheats.

2) #12 adjusted for 8 ccc's operates in the 75°C column.
NEC 110.14(C) prohibits 75°C with 60° equipment, default for 100A or less, and anything missing 75° labels.

..a) For Maint. & Commercial guys lots of existing equipment is missing 75°C labels/listings. Default is 60°C
..b) For Residential guys that means no stripping 60°C NM cable for un-labeled conductors stuffed in conduit.

3) Most electricians smart enough to get 110.14(C), Ambient, and Continuous adjustments, will miss 220.18(A).

..a) After bending over backward to get all adjustments, they see the light shinning past tonsils.
..b) With head so far up butt, they always forget 120% for motor loads? Regardless of 20A HACR breaker that holds, this wire overheats.

Whatever point you are trying to make would would be easier to understand if what you said made any sense.

 

[infinity]

A 20A fuse does not make a compliant #12 wire.

There are a few places where this fails:
2) #12 adjusted for 8 ccc's operates in the 75°C column.
NEC 110.14(C) prohibits 75°C with 60° equipment, default for 100A or less, and anything missing 75° labels.

The calculation is simple 30amps*70%=21 amps. a 20 OCPD is code compliant.

 

[kwired]

A 20A fuse does not make a compliant #12 wire.

There are a few places where this fails:

1) No capacity remains for other adjustments, such as continuous loads, or ambient temperatures > 30°C.
That means no attics, outdoors, unconditioned spaces, or if anything runs > 3hrs, this install overheats.

2) #12 adjusted for 8 ccc's operates in the 75°C column.
NEC 110.14(C) prohibits 75°C with 60° equipment, default for 100A or less, and anything missing 75° labels.

..a) For Maint. & Commercial guys lots of existing equipment is missing 75°C labels/listings. Default is 60°C
..b) For Residential guys that means no stripping 60°C NM cable for un-labeled conductors stuffed in conduit.

3) Most electricians smart enough to get 110.14(C), Ambient, and Continuous adjustments, will miss 220.18(A).

..a) After bending over backward to get all adjustments, they see the light shinning past tonsils.
..b) With head so far up butt, they always forget 120% for motor loads? Regardless of 20A HACR breaker that holds, this wire overheats.

The fail is not determining what adjustments all apply, or knowing what your minimum requried ampacity is to start with. Continuous loads or most motor loads require you to multiply by 125% before you start to select conductors.

Ambient temp can increase the ampacity in some cases.

Not a lot of equipment in past 30 years that doesn't have 75C terminals - so if new you can almost be assured it will be 75C.
All general purpose conductors for 30+ years have been 90C. Exception has always been NM cable and sometimes SE cable must still be selected from 60C ampacity columns, everything else pretty much has 90C insulation if it is new. You do need to know how to handle existing conductors if they don't have 90 C insulation though.

 

[ramsy]

The calculation is simple 30amps*70%=21 amps. a 20 OCPD is code compliant.

The branch circuit also violates most State Energy Codes by exceeding a 3% Voltage Drop, at relatively short distances.

277v 18-amp load are limited to ~115ft, and 10-amp loads are limited to ~230ft before exceeding 3%.
120v 18-amp loads are limited to ~50ft, 10-amp loads are limited to ~100ft before exceeding 3%.

While no expert calculator is provided by the NEC, approved formulas for checking adjusted-voltage drop, or adjusted-conductor temperatures are referenced in NEC Table 8-9 Notes. The results of these NEC referenced formulas can be shown at once, for same circuit or raceway.

If the goal is to avoid overheated enclosures, nuisance tripping, under voltage, or to install with room for future expansion, there are better alternatives to Derating after max conduit fill.

In the Op's case, adding MC cable may be the lesser evil, especially at distance or ampacity, but the NEC tables by themselves don't warn about adjustments that exceed temperature limits or voltage drop, much less consider capacity for inductive loads as required per 220.18(A).

A calculator that shows all the formula results at once is needed to see what happens after the table adjustments.

 

[kwired]

The branch circuit also violates most State Energy Codes by exceeding a 3% Voltage Drop, at relatively short distances.

Did some looking apparently there is a state energy code here - never seen or heard of any place where it was enforced, not even sure who would enforce it or how they would enforce it. Probably on the law books to make Fed's happy and that is about the extent of it, especially when it comes to electrical energy efficiency items.

 

[ramsy]

Did some looking apparently there is a state energy code here..

Original Plans checked by licensed PE or EE or City Planning would be responsible for any Voltage Drops required by State Energy Code.
1) Later "As-Built" drawings could max conduit fill, if approved by on-site inspectors, and original Voltage Drops may not be enforced.
2) Changes by Maintenance personnel that max conduit fill could also alter previous Voltage Drops.

One solution to this problem is putting a calculator in the journeyman's hands.

 

[infinity]

The calculation is simple 30amps*70%=21 amps. a 20 OCPD is code compliant.

The branch circuit also violates most State Energy Codes by exceeding a 3% Voltage Drop, at relatively short distances.

277v 18-amp load are limited to ~115ft, and 10-amp loads are limited to ~230ft before exceeding 3%.
120v 18-amp loads are limited to ~50ft, 10-amp loads are limited to ~100ft before exceeding 3%.

While no expert calculator is provided by the NEC, approved formulas for checking adjusted-voltage drop, or adjusted-conductor temperatures are referenced in NEC Table 8-9 Notes. The results of these NEC referenced formulas can be shown at once, for same circuit or raceway.

If the goal is to avoid overheated enclosures, nuisance tripping, under voltage, or to install with room for future expansion, there are better alternatives to Derating after max conduit fill.

In the Op's case, adding MC cable may be the lesser evil, especially at distance or ampacity, but the NEC tables by themselves don't warn about adjustments that exceed temperature limits or voltage drop, much less consider capacity for inductive loads as required per 220.18(A).

A calculator that shows all the formula results at once is needed to see what happens after the table adjustments.

Your response has nothing to do with the OP's question. Where does it say how long the run is or that VD is an issue?

 

[kwired]

Original Plans checked by licensed PE or EE or City Planning would be responsible for any Voltage Drops required by State Energy Code.
1) Later "As-Built" drawings could max conduit fill, if approved by on-site inspectors, and original Voltage Drops may not be enforced.
2) Changes by Maintenance personnel that max conduit fill could also alter previous Voltage Drops.

One solution to this problem is putting a calculator in the journeyman's hands.

Around here you would be asked what is plans check?

Jobs that have engineer plans - they almost never give that kind of detail on branch circuits. You have a panel schedule and indication of what general purpose outlets are on same circuit - but how you get lines to them is totally up to installer in many cases.

But the jobs I do where long circuit length is more likely to be an issue - I am usually the electrical designer and installer.

 

[ramsy]

Your response has nothing to do with the OP's question. Where does it say how long the run is or that VD is an issue?

Is ignoring Temperature rise or Voltage drop, caused by max-conduit fill, alleged negligence?

Anyone who becomes involved in a construction lawsuit based at least in part on alleged negligence may wish to consult with a lawyer who specializes in construction law for an evaluation of the case and an assessment of both joint and several exposure for damages.

Failures from new electrical installations remain prolific enough to sustain a cottage industry for thermal-camera imaging, expert-fire investigators, and litigators that prosecute contractors. If enclosures are too hot, or voltage is measured below nameplate during production interruptions, contractor negligence is not hard to prove.

This epidemic ignorance of Voltage Drop & Temp.Rise, after NFPA ampacity-table adjustments, is addressed by Public policy.

The legal doctrine of Joint & Several Liability.
1% responsibility = 100% liability. You Touch it, Your responsible.

William J. Ferguson, General Council, Babcock Power, describes legal liability:
Taken from ECM Video - Fast FWD to 44min mark

 

[ActionDave]

Is ignoring Temperature rise or Voltage drop, caused by max-conduit fill, alleged negligence?

Anyone who becomes involved in a construction lawsuit based at least in part on alleged negligence may wish to consult with a lawyer who specializes in construction law for an evaluation of the case and an assessment of both joint and several exposure for damages.

Failures from new electrical installations remain prolific enough to sustain a cottage industry for thermal-camera imaging, expert-fire investigators, and litigators that prosecute contractors. If enclosures are too hot, or voltage is measured below nameplate during production interruptions, contractor negligence is not hard to prove.

This epidemic ignorance of Voltage Drop & Temp.Rise, after NFPA ampacity-table adjustments, is addressed by Public policy.

The legal doctrine of Joint & Several Liability.
1% responsibility = 100% liability. You Touch it, Your responsible.

William J. Ferguson, General Council, Babcock Power, describes legal liability:
Taken from ECM Video - Fast FWD to 44min mark

I have no idea what you are talking about. There are hundreds of millions of feet of 12AWG THHN in 1/2 EMT at max fill in service across the continent and nothing is blowing up and nobody is getting sued.

8 Current Carrying Conductors in a 1/2" EMT is gonna be just fine.