Sub panel wire size questions.

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Old 05-07-19, 09:17 AM
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Sub panel wire size questions.

I bought a house and the inspector tagged the wiring to the sub panel in the attached garage.

The main box (200 amp) is on the back of the house and conduit runs from a 50amp breaker from the there around the soffit and into the garage (about 30ft)

The wire used is THHN 8 AWG (two hot, two neutral, one ground.

Ive read that this is okay for 50amp service. Is that true?
 
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Old 05-07-19, 09:19 AM
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The breaker in the main box used to feed this subpanel needs to be 40 amps or less for 8 gauge wire in cable or conduit. The breaker (if any) at the top of the subpanel can stay as-is.

If the conduit can get wet (like outside or buried) then the wire in it has to be water resisting, like THWN or THWN/THHN.
 
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Old 05-07-19, 09:22 AM
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Depends on the wiring method. If the #8 THHN is continuous through conduit it is acceptable at 50A. If it switches to a cable like NM or UF then it should be reduced to 40A. THHN in conduit has a higher temperature rating and therefore is rated for greater ampacity than cable assemblies.
 
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Old 05-07-19, 10:08 AM
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Also, #8 is approved for a 50 amp breaker as long as this breaker and the panel it connects to are marked that they're rated for 75 deg C. Modern breakers and panels usually are 75 deg C rated, but older ones may not be. If unmarked, the 60 deg C wire ampacity must be used.
 
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Old 05-07-19, 01:15 PM
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Would I be able use 6/3 romex (in conduit) instead of the 8 awg THHN

 
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Old 05-07-19, 01:48 PM
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No, romex (nm-b) is not rated for outdoor use.

6 ga THWN is the answer.
 
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Old 05-07-19, 02:34 PM
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Was this a home inspector? Get him to tell you exactly why he tagged it.
 
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Old 05-07-19, 02:45 PM
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It was a hope inspector. He stated on the report that the breaker was oversized. 50amp breaker with 8awg.
 
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Old 05-08-19, 06:18 AM
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If that is what he meant by "tagged" then change the breaker to a 40amp from a 50amp which will help (but that only solves half your issue). Again, if the conductors are THHN and not THWN you will still have an issue since the conductors are in conduit. Google the difference between the two.

Also you stated above that there are two hots, two neutrals, and a ground. Why two neutrals - or was that a typo?
 
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Old 05-08-19, 03:01 PM
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No typo, there’s 2 blacks (hots going to the supply), 2 whites (going to a buss bar on the left), and a green ground going to a bar on the right. I wish I know how to post a pic on here lol.
 
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Old 05-08-19, 03:37 PM
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I wish I know how to post a pic
How to Insert pictures ...........................................................
 
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Old 05-08-19, 05:45 PM
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If it's #8 THHN/THWN in conduit from panel to panel then as mentioned earlier a 50A breaker is okay as long as the devices(breakers) and panel connections are rated at 75 deg.C., if rated at only 60 deg.C then a 40A breaker is needed.
 
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Old 05-09-19, 06:55 AM
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You really don't have to do anything per code, but if all that's holding up the sale is a $10 breaker; change to 40A and never think about it again.
 
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Old 05-09-19, 09:41 AM
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It was a hope inspector.

Assuming that is a typo and you meant "Home Inspector", I am not really too surprised. There are a few good independent home inspectors out there, but very few that know and are good at inspecting electrical systems.

I agree with ibpooks when he said:

You really don't have to do anything per code, but if all that's holding up the sale is a $10 breaker; change to 40A and never think about it again.
 
 

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