feeders ampacity

[Treg the electrician]

Im working on a project in a detatched garage with a sub panel being fed by #4 thhn , i want to upsize the existing breaker in the house panel to its maximum allowance . am i to use table 310.12a ?

 

[ptonsparky]

Is this the entire load for a single family residence?

No, you cannot.

 

[ptonsparky]

Do a load calculation for the building.
EV charger added?

 

[paullmullen]

@Treg the electrician, which "breaker" do you want to upsize? The main disconnect in the house's panel, or the breaker that feeds the branch circuit going to the panel in the detached garage?

 

[ptonsparky]

@Treg the electrician, which "breaker" do you want to upsize? The main disconnect in the house's panel, or the breaker that feeds the branch circuit going to the panel in the detached garage?

Well now you went and confused me. I assumed he meant the feeder breaker to the garage.

 

[tom baker]

A drawing would help
What size is the house service?
Is there a sub panel off the service that feeds the garage?
How much load are you adding and is the dwelling all electric, or gas, etc

 

[Treg the electrician]

200 amp at house panel , garage sub is fed with #4 copper currently fused at 60 a from the house . my question is can i upsize breaker at house panel to 100 a in accordance with allowable ampacities based on 310.12a for services and feeders or am i stuck with 310.16. the load currently at garage is almost nothing , a door opener , 2 plugs and a light. and yes its for a EV charger .

 

[ptonsparky]

200 amp at house panel , garage sub is fed with #4 copper currently fused at 60 a from the house . my question is can i upsize breaker at house panel to 100 a in accordance with allowable ampacities based on 310.12a for services and feeders or am i stuck with 310.16. the load currently at garage is almost nothing , a door opener , 2 plugs and a light. and yes its for a EV charger .

No.

What is the current draw for the charger?

 

[Treg the electrician]

i was asked to provide a standard nema 14-50 recpt. i think it is 48 amps

 

[infinity]

200 amp at house panel , garage sub is fed with #4 copper currently fused at 60 a from the house . my question is can i upsize breaker at house panel to 100 a in accordance with allowable ampacities based on 310.12a for services and feeders or am i stuck with 310.16. the load currently at garage is almost nothing , a door opener , 2 plugs and a light. and yes its for a EV charger .

#4 THHN is rated at 85 amps @75° C. Next size up would be 90 amp OCPD.

 

[paullmullen]

Just an attempt at a full checklist:
1) Do you have the right Overcurrent Protection Device in the house panel? (Thanks @infinity )
2) Do you have have the correct main disconnect OCPD in the garage?
3) Does the feeder ampacity need to be corrected for the conduit? (probably not with three or less current carrying conductors).
4) Verify that ground and neutral are separated except in the main panel.
5) Verify grounding system at the garage is in place (rods, plate, ufer, whatever).
6) Are there any local modifications to the NEC required by AHJ?

What else am I missing?

 

[Treg the electrician]

ok thank you

 

[retirede]

i was asked to provide a standard nema 14-50 recpt. i think it is 48 amps

An EVSE that plugs into a 14-50 will have a rating of 40A or less. That’s if it’s NRTL listed! If it’s some of the Amazon junk, all bets are off.

 

[Treg the electrician]

#4 THHN is rated at 85 amps @75° C. Next size up would be 90 amp OCPD.

yes but is it considered a feeder because its feeding a sub panel? and if so can i use 310.12a witch has #4 copper rated to 100 a

 

[ptonsparky]

yes but is it considered a feeder because its feeding a sub panel? and if so can i use 310.12a witch has #4 copper rated to 100 a

Read the first sentence in both 310.12 (A) and (B). Note the words... entire load associated with an individual dwelling unit...
Your entire load is served by the SE conductors, not the feeder to the garage

 

[Treg the electrician]

Read the first sentence in both 310.12 (A) and (B). Note the words... entire load associated with an individual dwelling unit...
Your entire load is served by the SE conductors, not the feeder to the garage

thats it ! thank you i totally missed that . i will go back to 310.16

 

[infinity]

yes but is it considered a feeder because its feeding a sub panel? and if so can i use 310.12a witch has #4 copper rated to 100 a

Pton gave you the answer due to the entire load requirement. Answer to your question is in post #10.