ampacity of #2 rhw2 to detached garage.

[p real]

hello all, so recently completed installation of 100 amp panel to detached garage. Now to clarify, garage panel is fed from outdoor mdp that is also servicing the house associated with aforementioned garage. Ran #2 aluminum urd (dual rated rhw,rhw2) in pvc 1 1/4 conduit that went into an underground trench to the garage and proper egc. Put 100 amp breaker at mdp and on garage panel, separate grd rods and so forth. The inspector failed me because he says that rhw2 is only good for 90 amps under those conditions. I understand where he is getting that from because even tho the wire is rated for 90 degrees the breakers areonly good for 75 degrees but how is it that this garage is not being considered a separate building and the wires going to it should be considered residential feeders under 310.15b(7) and table 310.15b(7) am i wrong?

 

[infinity]

A detached garage is not a dwelling unit.

Welcome to the Forum.

310.15(B)(7) 120/240-Volt, 3-Wire, Single-Phase Dwelling Ser-
vices and Feeders. For individual dwelling units of one-
family, two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(7), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance con-
ductors, service-lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unit
and are installed in raceway or cable with or without an
equipment grounding conductor. For application of this sec-
tion, the main power feeder shall be the feeder between the
main disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit. The feeder conductors
to a dwelling unit shall not be required to have an allowable
ampacity rating greater than their service-entrance conduc-
tors. The grounded conductor shall be permitted to be
smaller than the ungrounded conductors, provided the re-
quirements of 215.2, 220.61, and 230.42 are met.

 

[p real]

bummer...

bummer...

thankyou for your help! damn...kinda figured i was grasping fpr straws there, Guess im pulling new wire. did that ampacity change this edition of the code? I dont have my 2008 book anymore, it had an unfortunate incident with some antifreeze...

 

[roger]

Why not put a 90 amp breaker on it?

Roger

 

[p real]

A great thought, and one i wish i cou,d employ, but the gentleman paid fpr a 100 amp service to his garage. Not his fault i screwed up. 100 amps it shall be. The 200bucks it will cost to replace the wire i pulled will probably empower me to check my tables closer next time.

 

[Dennis Alwon]

A great thought, and one i wish i cou,d employ, but the gentleman paid fpr a 100 amp service to his garage. Not his fault i screwed up. 100 amps it shall be. The 200bucks it will cost to replace the wire i pulled will probably empower me to check my tables closer next time.

That is very noble of you but I would explain to the owner the situation and chances are he won't ever need more than 90 amps. Perhaps even offer him the cost difference

 

[ActionDave]

I agree with Dennis. I would at least ask the owner what he wanted. See if he is okay with 90A give him a bit of rebate.

 

[suemarkp]

This rule has always been in the code, but the interpretations of 310.15(B)(6) (old versions of code, or 310.15(B)(7) in 2011) is all over the map. The consensus is it applies only to complete dwellings, not half a dwelling and not parts like a detached garage or shop. I think it should, as the diversity in many cases is the same and you have a 100A floor in that table. But until the code panel changes it (I think there was yet another mod in 2014) we're stuck with it.

Some local jurisdictions may allow that table to be applied to garages, shops, or feed each set of conductors in a dual panel setup like twin 200A's for a 400A service. But the NEC does not.

 

[roger]

That is very noble of you but I would explain to the owner the situation and chances are he won't ever need more than 90 amps. Perhaps even offer him the cost difference

I agree with Dennis. I would at least ask the owner what he wanted. See if he is okay with 90A give him a bit of rebate.

This rule has always been in the code, but the interpretations of 310.15(B)(6) (old versions of code, or 310.15(B)(7) in 2011) is all over the map. The consensus is it applies only to complete dwellings, not half a dwelling and not parts like a detached garage or shop. I think it should, as the diversity in many cases is the same and you have a 100A floor in that table. But until the code panel changes it (I think there was yet another mod in 2014) we're stuck with it.

I agree with all of the others.

Roger

 

[iwire]

I agree with all of the others.

Roger

Add another in agreement

 

[ActionDave]

This rule has always been in the code, but the interpretations of 310.15(B)(6) (old versions of code, or 310.15(B)(7) in 2011) is all over the map. The consensus is it applies only to complete dwellings, not half a dwelling and not parts like a detached garage or shop. I think it should, as the diversity in many cases is the same and you have a 100A floor in that table. But until the code panel changes it (I think there was yet another mod in 2014) we're stuck with it.

I agree with this too. We didn't always need 90A breakers

 

[iwire]

I agree with this too. We didn't always need 90A breakers

Well you did but nobody knew it.

 

[p real]

thank you all for your input, appreciate all of your time very much. I will approach the 90 amp issue witb the homeowner, he is a friend, who i have done much work for, he has already paid me however, and lives out of state so i will most likely be replacing them with the proper copper since i wont get any bigger aluminum down that pipe. Thankyou all for the input and for setting that straight, have always been confused on what exactly to call a detached garage, especially when it has its own panel, derived from a main panel, and yet sharing a service. Technically a subpanel, but not quite since a subpanel normally installed in a dwelling dpes not need its own ground rods, yet for a subpanel in a detached garage you have 2 rods and an egc that is connected to tbe main panel. are there any sections of the code that shed more light on this? Is the egc just meant as a redundant ground in case the connection to the rods fail? Essentially i dont understand why they want a detached building grounded in the same way that we treat a service to a dwelling unit but for the sake of powering it the wires coming to it are not considered feeders. Seems like a difficult to interpret section of the code, anybody know what exactly to term a panel in a detached garage in this situation?

 

[p real]

plus hey come on, we all know dudes that live in garages!

 

[Smart $]

... anybody know what exactly to term a panel in a detached garage in this situation?

Garage Panel :slaphead:

 

[infinity]

Technically a subpanel, but not quite since a subpanel normally installed in a dwelling dpes not need its own ground rods, yet for a subpanel in a detached garage you have 2 rods and an egc that is connected to tbe main panel. are there any sections of the code that shed more light on this? Is the egc just meant as a redundant ground in case the connection to the rods fail? Essentially i dont understand why they want a detached building grounded in the same way that we treat a service to a dwelling unit but for the sake of powering it the wires coming to it are not considered feeders. Seems like a difficult to interpret section of the code, anybody know what exactly to term a panel in a detached garage in this situation?

Actually there are not the same since a service disconnect/panelboard you would bond the neutral and EGC together. In a remote panel in a detached structure you would still have a GES (grounding electrode system) but it would isolated from the neutral. Take a look at 250.32.