200 amp CB feeding 200 amp disconnect with 150 fuses.

[kevinsparks]

We Installed a new trane RTU (hvac) that had a max amp rating of 150 amps.
We used the original conductors & breaker in the building and used a 200amp disconnect with 150 amp fuses to lower the amperage.

The new building inspector for the town said we have to change the breaker in the building to 150amp breaker unless we could show her something from the NEC book that allows you to use fuses to lower amperage.

It seems like common sense to me.
But I went digging into the 2020 NEC book anyway and,
I cannot find anything & I'm running out of time, she gave us till EOD to come up with something.

Any idea

 

[infinity]

What size are the conductors between the breaker and the fuses?

 

[kevinsparks]

3/0 cu

 

[LarryFine]

Welcome to the forum.

You have a compliant installation.

The inspector needs to cite a violation.

 

[don_resqcapt19]

The only rules that apply are that the conductors be protected at their ampacity and that the AC unit be protected in accordance with its nameplate. The 3/0 copper conductors are properly protected and the 150 amp fuses at the load end protect the equipment. There is no code issue.

 

[kevinsparks]

I'm sorry it's 4/0 between cb & disco then 3/0 from disco to rtu
Thhn copper on 3/0

 

[augie47]

Agree with Larry

 

[wwhitney]

The 3/0 copper conductors

What 3/0 copper conductors? There are no conductor sizes in the OP.

We need more details. There are scenarios where the described change causes a code violation, and scenarios where it doesn't. Here's one where it does:

The old unit had an MOCP of 200A and an MCA of 130A (to make up numbers). The old install was 200A breaker to #1 Cu (75C ampacity = 130A) to a disconnect. The new unit has an MOCP of 150A and an MCA of 105A. Based on the new lower MOCP/MCA we have lost the permission to protect the 130A conductors at 200A.

Here's a grey area:

The old unit had an MOCP of 200A and an MCA of 150A, so 1/0 Cu with a 75C ampacity of 150A was used. The new unit has an MOCP of 150A and MCA of 100A. Now if the 1/0 Cu were to supply the new unit plus a 50A non-motor load, then the motor feeder rules would permit that with a 200A OCPD. But there is no actual 50A non-motor load present; is the feeder protection at 200A still allowed due to a "phantom" or "future" 50A load?

Cheers, Wayne

 

[kevinsparks]

The only rules that apply are that the conductors be protected at their ampacity and that the AC unit be protected in accordance with its nameplate. The 3/0 copper conductors are properly protected and the 150 amp fuses at the load end protect the equipment. There is no code issue.

That is what I said She also did not give us a sheet telling us what codes we violated, she verbally told us we violated the code regarding the Amps listed on the name plate VS the Amps on the breaker in the basement She does not believe you can use fuses in a circuit to lower the Amperage of the circuit.

She is a nice lady but new on the job despite being older. Not sure how she got the job of lead building inspector. The project is the townhall as well so it's not like I can tell the customer the inspector doesn't know what's what. Lol

Im trying not to spend the $1600 on a 150amp breaker.
But looks like I'm going to

 

[infinity]

That is what I said She also did not give us a sheet telling us what codes we violated, she verbally told us we violated the code regarding the Amps listed on the name plate VS the Amps on the breaker in the basement She does not believe you can use fuses in a circuit to lower the Amperage of the circuit.

She is a nice lady but new on the job despite being older. Not sure how she got the job of lead building inspector.

Sorry to say but you're dealing with someone who is basically incompetent.

 

[rc/retired]

That is what I said She also did not give us a sheet telling us what codes we violated, she verbally told us we violated the code regarding the Amps listed on the name plate VS the Amps on the breaker in the basement She does not believe you can use fuses in a circuit to lower the Amperage of the circuit.

She is a nice lady but new on the job despite being older. Not sure how she got the job of lead building inspector. The project is the townhall as well so it's not like I can tell the customer the inspector doesn't know what's what. Lol

Im trying not to spend the $1600 on a 150amp breaker.
But looks like I'm going to

Fight it. She is flat out wrong! Print this thread and show her.
Good luck.

Ron

 

[kevinsparks]

Thanks for all the help guys, we passed our inspection, I called another building department & they called and straightened her out for us.

 

[wwhitney]

What 3/0 copper conductors?

Wow, for some reason all of "kevinsparks" posts other than the OP were not showing up for me until now, although everyone else's posts were. So obviously ignore my first post.

Cheers, Wayne

 

[wwhitney]

The new building inspector for the town said we have to change the breaker in the building to 150amp breaker unless we could show her something from the NEC book that allows you to use fuses to lower amperage.

I think all you need to do is demonstrate that the fuses you are using are UL listed as branch circuit protection, rather than just supplemental protection.

Cheers, Wayne

 

[wwhitney]

Wow, for some reason all of "kevinsparks" posts other than the OP were not showing up for me until now, although everyone else's posts were.

It just happened again with post #12, it did not show at the time I made my last two posts.

Is there some website oddity happening? Maybe a new user's posts need to be approved before being visible to everyone, but the moderators get to see them immediately? Meaning a moderator may respond to a post that is still invisible to everyone else, which would obviously be very confusing to non-moderators.

Cheers, Wayne

 

[don_resqcapt19]

What 3/0 copper conductors? There are no conductor sizes in the OP.

post #3

 

[wwhitney]

post #3

Indeed. Please see posts #13 and #15. Any thoughts on why this occurred?

Thanks,
Wayne

 

[infinity]

Is there some website oddity happening? Maybe a new user's posts need to be approved before being visible to everyone, but the moderators get to see them immediately? Meaning a moderator may respond to a post that is still invisible to everyone else, which would obviously be very confusing to non-moderators.

No oddity here. The first few posts of a new user are required to be approved by a moderator but a mod can read them prior to approval. They typically get approved before a mod posts for the reason you've mentioned that is because to everyone else they're invisible. Not sure what happened in this thread. I approved the OP prior to posting.

 

[wwhitney]

They typically get approved before a mod posts for the reason you've mentioned that is because to everyone else they're invisible.

Ah, so my guess was correct; that's definitely an oddity for everyone else when it doesn't happen as you described. Maybe there's a way to automate or interlock this process so it doesn't rely on the moderator remembering to do things in the correct order?

Edit: or, if in the user interface that moderators have the "non-approved" status is somewhat subtle, maybe make it really obvious somehow, like an orange background for the any non-approved posts?

Cheers, Wayne

 

[Little Bill]

Ah, so my guess was correct; that's definitely an oddity for everyone else when it doesn't happen as you described. Maybe there's a way to automate or interlock this process so it doesn't rely on the moderator remembering to do things in the correct order?

Edit: or, if in the user interface that moderators have the "non-approved" status is somewhat subtle, maybe make it really obvious somehow, like an orange background for the any non-approved posts?

Cheers, Wayne

We don't reply/post in a post awaiting approval. It's clearly different and even says "awaiting moderator approval". I don't know what problem you had. Perhaps your screen didn't refresh after you had read or replied.