MKlas
New User
- Location
- Raleigh, NC
- Occupation
- Engineer
I am new to this forum, so I apologize up front for being long winded or any other rules that may be broken. First, full disclosure, I am not a contractor, I am an Engineer. The particular code/common practice question I have is in regards to a 100amp Subpanel located in a detached garage and connected to my 200 amp service panel (source of first disconnect).
The short story leading up to my current situation is my original contractor (approved by the inspector somehow) ran 4-4-4-6 UF individual AL conductors underground to the panel. He left the panel bonded (neutral/ground bar connected), connected the Hots and Neutral at the Sub and main, connected the EGC at the main (bonded), but left it loose in the subpanel - no connection. He did not run a GEC to soil. Needless to say, I have issues. Last week, I lost power to this subpanel. Took some Voltage and Ohm readings and discovered that I had a large voltage drop across one hot (about 20 volts with power being supplied to sub but all sub breakers off. It dropped to 0v with all sub circuits on) and no continuity. Clearly, there is a break in the wire underground that is arcing. I don't know if this was simply a defect or small cut in the coating that soaked up water and soil over time - or a result of the power outage that happened. There was an outage in the neighborhood (not storm related nor was it near my home) that effected 1600 homes. Unclear as to what happened; however, it was off for only 30 minutes and no breakers tripped in either panel. My main panel is fine. The reason I suggest it may simply be coincidental, and not related is because I really do not know for sure when the panel went down. I used those circuits on the previous Sunday, the outage happened on Wednesday and I did not notice the issue until Friday. Anyway, I checked all the breakers for physical damage and continuity. All seem fine.
I want to do the following:
1. Leave all 4 existing conductors in ground, remove from both panels and cut below grade.
2. Route new Conductors above ground in Schedule 40 PVD Conduit (I now have a deck that bridges my main house to my Garage/addition. I can mount to the underneath side and tie to joists to keep concealed). I will use 1 1/2". This run will include about 40' total with 2 90s (1 at either end), 1 small offset in middle and terminate into LBs leading into panels. I did check the fill chart and any combination of wire I plan on choosing will fit with a max of 33.5% fill. If I used schedule 80, that would change, but none of this conduit will be coming from grade or in an area subject to physical damage.
3. Before anyone asks, I am aware of 310.15(B)(7) and even if that applied to this application, I would not adhere to that. It does not apply. My property is zoned as a single family dwelling with a detached structure. My garage/addition is not considered a single family dwelling and the sub panel is not the main power feeder. I will follow 310.15(B)(16).
4. I have already un-bonded the neutral bar in the subpanel, added a ground bar, connected all the ground leads to the ground bar, and added an 8' ground rod with #6 bare solid copper GEC.
My contractor wants to do the following:
1. Run AL 1-1-1-4 XHHW-2 individual conductors. (I do prefer XHHW over THWN)
NOTE: Both breakers (feeder at main and 100 amp on sub panel) are clearly marked with a 75C rating. So, I understand that we can use the 75C column to determine size of ungrounded conductors.
In watching Mike Holt's Youtube videos and reading some of comments on the forum threads (really good "stuff"), I understand that the NEC code says that any equipment 100Amps or Less are to use the 60C column unless the equipment is clearly marked otherwise. Several have made it a point that: The ratings on the terminals aren't necessarily the only "equipment" you have to consider and also, there may be other installation considerations that take priority when sizing. While the length of run and ambient conditions in my area do not require a deration calc., I do have concerns over running exterior above ground conduit (about 25' under deck). It does get hot in the conduit. Is there a consideration there - either due to code violations or "best practices"?
My questions are - based on Code or best practices:
1. Should I be using 1/0 AL for both hots and neutral?
2. Should I keep my Neutral at 1AWG AL regardless? (I have not done an unbalanced load calc and don't really want to pick sizing based on that for possible added circuits.)
3. Based on the answer to the above, should the EGC remain at 4Gauge AL or go to #2?
4. Does ease of pull through 1 1/2" come into play here?
Thanks in advance for any expertise.
The short story leading up to my current situation is my original contractor (approved by the inspector somehow) ran 4-4-4-6 UF individual AL conductors underground to the panel. He left the panel bonded (neutral/ground bar connected), connected the Hots and Neutral at the Sub and main, connected the EGC at the main (bonded), but left it loose in the subpanel - no connection. He did not run a GEC to soil. Needless to say, I have issues. Last week, I lost power to this subpanel. Took some Voltage and Ohm readings and discovered that I had a large voltage drop across one hot (about 20 volts with power being supplied to sub but all sub breakers off. It dropped to 0v with all sub circuits on) and no continuity. Clearly, there is a break in the wire underground that is arcing. I don't know if this was simply a defect or small cut in the coating that soaked up water and soil over time - or a result of the power outage that happened. There was an outage in the neighborhood (not storm related nor was it near my home) that effected 1600 homes. Unclear as to what happened; however, it was off for only 30 minutes and no breakers tripped in either panel. My main panel is fine. The reason I suggest it may simply be coincidental, and not related is because I really do not know for sure when the panel went down. I used those circuits on the previous Sunday, the outage happened on Wednesday and I did not notice the issue until Friday. Anyway, I checked all the breakers for physical damage and continuity. All seem fine.
I want to do the following:
1. Leave all 4 existing conductors in ground, remove from both panels and cut below grade.
2. Route new Conductors above ground in Schedule 40 PVD Conduit (I now have a deck that bridges my main house to my Garage/addition. I can mount to the underneath side and tie to joists to keep concealed). I will use 1 1/2". This run will include about 40' total with 2 90s (1 at either end), 1 small offset in middle and terminate into LBs leading into panels. I did check the fill chart and any combination of wire I plan on choosing will fit with a max of 33.5% fill. If I used schedule 80, that would change, but none of this conduit will be coming from grade or in an area subject to physical damage.
3. Before anyone asks, I am aware of 310.15(B)(7) and even if that applied to this application, I would not adhere to that. It does not apply. My property is zoned as a single family dwelling with a detached structure. My garage/addition is not considered a single family dwelling and the sub panel is not the main power feeder. I will follow 310.15(B)(16).
4. I have already un-bonded the neutral bar in the subpanel, added a ground bar, connected all the ground leads to the ground bar, and added an 8' ground rod with #6 bare solid copper GEC.
My contractor wants to do the following:
1. Run AL 1-1-1-4 XHHW-2 individual conductors. (I do prefer XHHW over THWN)
NOTE: Both breakers (feeder at main and 100 amp on sub panel) are clearly marked with a 75C rating. So, I understand that we can use the 75C column to determine size of ungrounded conductors.
In watching Mike Holt's Youtube videos and reading some of comments on the forum threads (really good "stuff"), I understand that the NEC code says that any equipment 100Amps or Less are to use the 60C column unless the equipment is clearly marked otherwise. Several have made it a point that: The ratings on the terminals aren't necessarily the only "equipment" you have to consider and also, there may be other installation considerations that take priority when sizing. While the length of run and ambient conditions in my area do not require a deration calc., I do have concerns over running exterior above ground conduit (about 25' under deck). It does get hot in the conduit. Is there a consideration there - either due to code violations or "best practices"?
My questions are - based on Code or best practices:
1. Should I be using 1/0 AL for both hots and neutral?
2. Should I keep my Neutral at 1AWG AL regardless? (I have not done an unbalanced load calc and don't really want to pick sizing based on that for possible added circuits.)
3. Based on the answer to the above, should the EGC remain at 4Gauge AL or go to #2?
4. Does ease of pull through 1 1/2" come into play here?
Thanks in advance for any expertise.
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