I think my General Contractors Electrician is wrong !

[Smokinjoe32]

First let me say thanks to all of you on the board. - I am new here, but am on several of the automotive forums. - I have read, researched, searched and found numerous conflicting information, so I was hoping some of you may help clarify.

I bought a foreclosed house in need of many repairs and I hired a General Contractor to oversee everything. One of the items was the house had aluminum wiring with many new copper "taps" that had been added over the years. - I chose to install a new panel and rewire the house in copper - One of my planned additions was a detached shop.

The electrician installed a new 200 Amp panel for the house and everything looks good, but I requested ( and paid for ) a 100 amp breaker with a direct run to the edge of the house to feed the future shop. The electrician used copper NMB AWG 4-3 with 8 ground. The wire is currently running about 70' thru my attic and down the exterior wall to a weather rated outdoor disconnect.

Originally when it was inspected, the electrician had a 60 Amp breaker installed for the shop and when I became aware of it, he said it was a mistake and replaced it with a 100A ( which was also the last I saw of him ). -

Now here we are a year and a 1/2 later, my shop is now up and the General Contractor and electricians are long gone and I need to meet with the city inspector for electrical for the shop. In reading thru the NEC Tables, one table shows the #4 should be good to 95A, and 310.15(b)(7) , shows that #4 wire should be rated to 100A if used as a feeder, but when I look up NMB, AWG 4-3, it shows as a 30 degree Celsius and lists it as 70A.

I was originally planning on running a 100A breaker to the shop, but now I'm thinking maybe I need to downsize to 60A to meet code ? - I was planning on running 3 individual #4 wires and a #8 insulated ground thru a 1-1/4" conduit 18" below grade for the 70' to the shop and will be setting up an appointment with the city inspector in the coming weeks.


Any thoughts or input would be greatly appreciated, so I can switch the 100A breaker back to 60 if that's what it should be. - The electrician assured me the wires were correct #4 wires were ok for the 100A, but now I'm not so sure.


Thanks for all you do for us Noobs !


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[JoeFin]

Its fine for 100 a feeder

Your not going to be continually pulling 100A across it anyway

 

[rockwithjason]

is the wire copper or aluminum? i am going to guess it's aluminum. table 310.16 shows that aluminum of the common insulation types as being good for 65 amps. i would guess that is why the "electrician" put a 2p60 breaker there. you are not going to be legal unless you run at 65a or below. if you want the full 100 a you will have to upsize the wire.

 

[Smokinjoe32]

Hello Joe and Jason, - Thanks for the posts. -

Joe, I appreciate it, I didn't want the inspector to come out and see the 60A breaker had been incorrectly replaced with a 100A. - And yes, there will probably never even be close to 40 amps. I just wanted to run it once and be done with it in case I ever need to run an Arc-Plasma-Reactor out there or something.

Jason, I thought I was being thorough in the original post, but I did forget to mention the NMB 4-3 was copper. - Any thoughts about the situation using copper in mind instead ?

Thanks - I really appreciate it.

 

[Stuff]

310.15(b)(7) is only if the feed is for the entire "dwelling" - commonly ignored. Also doesn't apply to NM cable.

 

[Aceman]

Its fine for 100 a feeder

No, it's not.

4-3 copper nm cable is good for 70 amps.

 

[JoeFin]

No, it's not.

4-3 copper nm cable is good for 70 amps.

Obviously they are going by article 310-15

 

[theoldwizard1]

4-3 copper nm cable is good for 70 amps.

That depends on the total length of the run, but based on the voltage drop chart I consulted, you will have less than a 3% voltgae drop at 70A and 140'

It would probably be cheaper to run 2-2-2-4 MHF from the outside disconnect to the panel in the garage. MHF is aluminum so you have to be certain the terminals in the disconnect box are rated for aluminum and use all other precautionary measures. MHF is rated for direct bury, but it must be in conduit above ground or inside of a building.

The size of "main" breaker in the garage has very little to do with this situation. It primary purpose is to provide a disconnect so that branch circuits in the garage can be installed/serviced. It is "legal" to have a 70A breaker in the house panel and a 100A "main" breaker the garage. Overloading the garage panel will result in tripping the breaker in the house, admittedly an inconvenience to have to go to another building to rest it.

 

[Smokinjoe32]

Hello Everyone and thanks for the input. - It's sounding like the NM cable was a bad choice on the electrician's part and it also looks like I got "taken" by the General Contractor as this was sold to me as a 100A service. - It also sounds like it was an unsafe move on the electricians part to swap the 100A breaker in, ( and possibly even an intentional move by waiting until after it passed the inspection ).

I appreciate all the input. - I guess I will swap out the breaker in the house panel to a 70A and will go with a 60A in the garage, on the odd chance I do trip it, it'll be a shorter walk . - ( The 100A was going to be overkill, but I figured it was better to do it upfront than trying to retrofit 10 years from now ).

Old Wizard, I appreciate the post. I'll look into the MHF as running #4 copper was quite pricey for the length I need, and I trust there is a lot better stuff available today to help keep the Aluminum and Copper junctions safer.

Thanks for all the input and I'd be glad to learn more if anyone has anything to add !

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[sands35]

It's probably too late for any sort of claw back from the GC or the electrician and probably not worth the hassle if it was possible.

But if you asked for a 100 amp service to a sub-panel (hopefully in writing) and you only got a 60 amp, I'd certainly tell the GC about it and then tell all your friends to never hire that electrician.

 

[sccutler]

It's probably too late for any sort of claw back from the GC or the electrician and probably not worth the hassle if it was possible.

But if you asked for a 100 amp service to a sub-panel (hopefully in writing) and you only got a 60 amp, I'd certainly tell the GC about it and then tell all your friends to never hire that electrician.

Do we know what the GC told the sparky to do? He may have followed the directions just fine.

 

[Smokinjoe32]

Hello Sands and Sccutler,

As unsurprising as it may seem, my General Contractor and I were not on good terms by the end of the job. - So much so that it's would drum up more than the $400 worth of anger by tracking him down. -

I do know that both he and the electrician were aware of the 100A service and they did lay a larger cable, which in retrospect, I am glad at least he did that, because if not, I would be stuck with a NMB #6 in there right now and would be limited to 50A and would be furious.

Thanks again - Can anyone post why the NMB rating is so much less than a THHN ?

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[pattenp]

THHN is run in conduit and always has air space around it. NM in a lot of cases is run in a wall and is within insulation so heat is not transferred very well. So the NEC has seen fit to restrict the temp to 60C.

 

[Smokinjoe32]

Great !!


Thanks for all your help everyone. It is appreciated.

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[BillK]

Joe,
Keep one thing in mind ....... none of the answers given here matter if your local inspector does not approve. I would talk with him, tell him the entire story and the truth, and do what he wants because he is the one that has to approve it

 

[Smokinjoe32]

Good Advice Bill. Thanks. - I have decided to just put a 60A breaker back in there and call it a day. - I didn't want the inspector coming back out and wondering why he passed a 100A breaker on an NMB #4 and I really don't need anything more than that. The 60A should be plenty, but should the time ever arrive that I start tripping it, I can reassess the situation at that time.

Thanks again to all !

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[Smokinjoe32]

Hello again everyone, Thanks for all the input and in helping me understand what I currently have. - I certainly appreciate all the posts and have a new plan for moving forward, Now I am hopeful someone might chime in to let me know if I am on a good course.

Given the 70A rating of the copper NMB #4 that is installed and running to the outdoor disconnect, could I install a 60A fused disconnect where the NMB #4 stops and then run THHN #6 for the 70' run to the shop with a 60A load center in the shop ?

I had planned on running THHN #4 to the shop but given the 95A rating on that, it seems overkill if the wires in the attic are only rated to 70A, so if I am correct, it would be a bit cheaper with no loss of functionality using lower rated wire to the shop.


I'd just like to have an acceptable plan in mind when I go speak with the city.




Thanks again !

Joe

 

[pattenp]

#6 THHN/THWN is 65A, so just splice the #6 to the #4 NMb in a junction box and put a 70A breaker on the #4 in the main service panel and feed it straight through to a 100A panel in the shop. It's okay to up size the breaker on the #6 the next standard sized breaker which is a 70A.

Edit: You could also use #4 aluminum THHN/THWN which is 65A to the shop.

 

[Smokinjoe32]

Awesome PattenP...., That's what I was hoping to hear. - I'll plan on incorporating a 60A fusible disconnect where the #4 and #6 wires meet in the event something catastrophic happens. The junction box is right outside my bedroom window, so I'd rather torch a fuse than my room

Thanks to all of the board for your help.

Joe