30A Generator on 40A Breaker

Little Bill

Little Bill

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Tennessee NEC:2017
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Semi-Retired Electrician
Do you see anything wrong with connecting a portable generator, with interlock and inlet, that is a 30A generator but using a 40A breaker in the panel?
Conductors are #8, and the generator has it's own 30A breaker.
 
Little Bill said:
Do you see anything wrong with connecting a portable generator, with interlock and inlet, that is a 30A generator but using a 40A breaker in the panel?
Conductors are #8, and the generator has it's own 30A breaker.
Click to expand...
2023 NEC
I do not recommend that.
It may violate the MFG's instruction or warranty.
If the generator is rated for 30 amps, use a 30 circuit breaker.
The conductors are suitable for 30 amps.

TX+MASTER#4544
 
If generator has its own 30A breaker, I see no issue with a larger one in the panel, especially if the wires are upsized to match it. I did this with mine using a 60A at the panel and the generator has a 50A. The generator breaker may have a more generous trip curve and going with a larger breaker in the panel let's you take advantage of that.
 
My generator was hooked up hat way. 30 amp generator and I had a spare 60 of the correct manufacturer as my panel.
Akin to folks asking if they can feed a 200 amp subpanel with a 100 amp feed,
 
TX+ MASTER#4544 said:
2023 NEC
I do not recommend that.
It may violate the MFG's instruction or warranty.
If the generator is rated for 30 amps, use a 30 circuit breaker.
The conductors are suitable for 30 amps.

TX+MASTER#4544
Click to expand...
There is no issue. The generator has a 30 amp breaker so the generator is protected. There is no issue using larger conductors from the 30 amp breaker in the generator to a 40 amp breaker at a remote location. The conductors between the two breakers can be any size as long as their ampacity is at least 30 amps.
 
My house was like this for years until I went whole house. My portable generator had a 30, and fed a 200A main.
 
My cousin had a 30-amp generator that her husband was back feeding a welder circuit in the garage. After he passed on, she had a 200-amp panel which I left and added a sub panel with a manual interlock with the emergency circuits in the sub panel and wired a generator inlet.

30 amp breaker in the gen 30 amp back feed in the sub panel and 30 amp wire. It is amazing how much that thing will run. Honda make a great generator.
 
nizak said:
Good for 800A I’m guessing😥
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electrofelon said:
I did this today, similar thing. Supply house was short one.....
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125 amp 😂

Looks like a 125 amp load center buss.
Maybe 125*1.20 (buss plus 1.20) depending on what it feeds. 🤣
High leg delta optional calc.🤣😂
Just funing around for the new year.



On a serious note with a question.

Would the breaker added to the panel for generator require a hold down kit if plug on buss type.
 
Tulsa Electrician said:
Would the breaker added to the panel for generator require a hold down kit if plug on buss type.
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Yes
Interlock kits come with one, but I don't think they are listed. Matter of fact, it is just two tie wraps/zip ties joined together. You put them around the generator breaker and the two adjoining breakers on opposite side.
 
Tulsa Electrician said:
125 amp 😂

Looks like a 125 amp load center buss.
Maybe 125*1.20 (buss plus 1.20) depending on what it feeds. 🤣
High leg delta optional calc.🤣😂
Just funing around for the new year.



On a serious note with a question.

Would the breaker added to the panel for generator require a hold down kit if plug on buss type.
Click to expand...
Yeah fuse kept blowing and couldn't for the life of me find a fuse increaser 🤣

I'd have to refresh myself on the exact code wording, but I think yes a generator back Fed breaker would need a hold down
 
Little Bill said:
Yes
Interlock kits come with one, but I don't think they are listed. Matter of fact, it is just two tie wraps/zip ties joined together. You put them around the generator breaker and the two adjoining breakers on opposite side.
Click to expand...
While interlock kits have been a common practice, the 2026 code, assuming the first draft language stands, will be the first to actually permit the use of interlock kits.
702.5 (A) General.
Interconnection, interlocking device, or transfer equipment shall be required for all standby systems subject to the requirements of this article. Equipment shall be suitable for the intended use and shall be listed, designed, and installed so as to prevent the inadvertent interconnection of all sources of supply in any operation of the equipment.
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UL Guide Information for the Installation, Use, and Marking of Panelboards (QEUY) says the following about interlock kits.
Some panelboards, constructed with interlocked main switching and overcurrent protective devices, have been investigated for use in optional standby systems in accordance with Article 702 of the NEC and are marked "Suitable for use in accordance with Article 702 of the National Electrical Code ANSI/NFPA 70," or, if provided within kit form, "Suitable for use in accordance with Article 702 of the National Electrical Code ANSI/NFPA 70 when provided with interlock kit Cat No. ____.
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So, the application of 110.3(B) will require the interlock kit to be specifically identified for use with the panel.
 
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