OH service for new panel detached garage (multi residential)

[AreGee]

Hello members,

In the spirit of the recent thread supplying Electrical Service to Detached Garage I, too, would like your comments for a project that I will be submitting to our city building dept.


I am preparing plans to install a new 200 A metered / load panel on our detached garages (owned by the Homeowners Assoc) .
PoCo will commit to a 200 A service drop.
Since this panel is installed on a detached garage, it seems that I need to account for temperature correction in the riser. In other words, a 2/0 is not acceptable.

Is the following calculation overly conservative?

3/0 awg ampacity derate, correction / adjustment factors
(1) 90°F Rating of Conductor (T-310.15(8)(16)) for 3/0 awg XHHW = 225 A
(2) 90°F Temp Correction Factor (T-310.15(B)(2)(a)) with RMT wall mounted = 0.91
(3) Conduit Fill Factor (T-310.15(B)(3)(a)) two current-carrying conductors = 1.0
3/0 awg ampacity derate = (1) x (2) x (3) = 225 A x 0.91 x 1.0 = 204 A
Ampacity derate > panel main breaker rating: 204 A > 200 A (acceptable)

 

[LarryFine]

Welcome to the forum.

What's your calculated load?

 

[AreGee]

Welcome to the forum.

What's your calculated load?

Thank you for the welcome.

The panel is solely for EV charging.
At the moment, continuous current is 40A x 2 NEMA 6-50R ... so 80 A
However, would like to add receptacles in the future.
Do I have to stop at 160 A ?

The panel is rated continuous 200A

 

[electrofelon]

I don't understand at all what you are doing, you lost me. There is no derating for temp or fill or current carrying conductors or anything for this application. Basically you use the 75 degree ampacity column plus next size up rule for the OCPD (if load calc allows). Yes it is just that simple.

 

[AreGee]

 

[AreGee]

 

[electrofelon]

Looks ok to me, assuming the 3/0 XHHW is Cooper not aluminum. Is CU XHHW common there? Here it would be special order and would be stocked in THHN. 4/0 AL has an ampacity of 180A which you can next size up to 200 amps for the breaker. 2/0 CU is 175 which is a standard size so you have to go 3/0 for 200. Personally, I I would use aluminum as it is cheaper and much easier to work with.

How tall is the riser? Might want to just use rigid as once you figure in the rain tight EMT fittings it might not be that much more for rigid.

 

[AreGee]

Looks ok to me, assuming the 3/0 XHHW is Cooper not aluminum. Is CU XHHW common there?

How tall is the riser? Might want to just use rigid as once you figure in the rain tight EMT fittings it might not be that much more for rigid.

Planning for all conductors to be Cu. Have not ck'd on XHHW availability.
Riser (and mast) is 7 ft. max

 

[AreGee]

...There is no derating for temp or fill or current carrying conductors or anything for this application. Basically you use the 75 degree ampacity column plus next size up rule for the OCPD (if load calc allows). Yes it is just that simple.

I understand now. You're referring to 110.14(c)(1)(b)

 

[electrofelon]

I understand now. You're referring to 110.14(c)(1)(b)

Partly. Basically 110.14 is mostly academic as pretty much all terminations are rated 75 degree C (even if under 100A) and conductors will be 90 degrees C.

Note that there is no such thing as conduit fill derating. There is derating for number of current carrying conductors, but that just about never is a factor for a single circuit or feeder (would have to be three phase with the neutral counting as a CCC which is very rare).

Ambient temperature derating is extremely rare (dont forget about 310.15(A)(2) exception). I dont recall ever derating for temp in 20 plus years as a sparky.

 

[AreGee]

Partly. Basically 110.14 is mostly academic as pretty much all terminations are rated 75 degree C (even if under 100A) and conductors will be 90 degrees C.

Note that there is no such thing as conduit fill derating. There is derating for number of current carrying conductors, but that just about never is a factor for a single circuit or feeder (would have to be three phase with the neutral counting as a CCC which is very rare).

Ambient temperature derating is extremely rare (dont forget about 310.15(A)(2) exception). I dont recall ever derating for temp in 20 plus years as a sparky.

Roger that ... so proper conductor sizing should be i.a.w. the 75°C table. However, I can use conductors under the 90°C table provided that the sizing is not smaller than the 75°C table because the terminals / equipment were tested to 75°C , which accounts for the appropriate heat dissipation.

Conduit fill factor s/b labeled "CCC derate" . Do you think it'd be an easier on the touch labor to install two 1/2" emt versus one 1" ?

 

[AreGee]

I think I can reduce the runs to the receptacles to #8 based on the 75°C table . 50A x 0.8 = 40 A then upsize to a 50 A breaker per 240.4(B) rnd up rule

 

[electrofelon]

I think I can reduce the runs to the receptacles to #8 based on the 75°C table . 50A x 0.8 = 40 A then upsize to a 50 A breaker per 240.4(B) rnd up rule

Yes you can use #8 for the receps. Also you can use a #10 EGC. When you derate you start from the 90 degree column, so 55Ax.8=44, next size up is 50. You can put that in a single 3/4.