Adding Main Disconnect Switch for MLO Panel

V

Volt-Amps

Member
Location
Indianapolis
Hello,
I have a project where the main panel is rated 400A, 3-phase, 4 wire, 240V. I needed additional panel space so I added a 200A breaker in the 400A panel and fed a new MLO panel from it. The two panels are adjacent to each other, so the 200A main breaker is accessible and within line of sight. The inspector is asking for a disconnect switch to be added for the 200A panel. Anyone knows why I would need a disconnect switch if the main breaker that feeds this panel is readily accessible and within line of sight?
Thank You
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
did you address available fault current ad AIC rating of the breakers in the MLO panel
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
There is no requirement that a panel have a disconnect or main breaker in it, and not even a requirement that the OCPD for the panel be within sight of the panel.
The only rule that would apply is.
408.36 Overcurrent Protection.
In addition to the requirement of 408.30, a panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panelboard.
Click to expand...
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
augie47 said:
did you address available fault current ad AIC rating of the breakers in the MLO panel
Click to expand...
Good idea, that could be what the inspector was getting at in a round about way, or we're not getting the exact language he used. If the new panel is a different brand there will not be a series rating. I have provided a main breaker in a panel board before when it's only purpose was to get a series rating to allow the to use of regular 10K branches.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Volt-Amps said:
Could you please help me better understand the series rating requirement?
Click to expand...
Say you have 65000 amps of fault current available at your service. A tested combination of breakers in series can protect the lowest rated breaker from rapid disassembly when subjected to a fault. My residential grade panel lists various breaker and/or fuse combinations to accomplish this.

You may have 10,000 AIC breakers that could be exposed to much higher currents. Simply putting in an additional breaker or disconnect may not solve the problem. The combination of breakers must have been tested for the purpose.

Adding conductor length would help, but you will need to do the math.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
try this link for the math.
www.mikeholt.com

Mike Holt Enterprises - The leader in electrical training.

Mike Holt worked his way up through the electrical trade from apprentice electrician through electrical contractor, to become one of the most recognized experts in the world as it relates to electrical power installations. He was a Journeyman Electrician, Master Electrician, and Electrical...
www.mikeholt.com
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
In your situation with the new panel right next to the other the reduction in available current will not be reduced much by wire size/length.
Still a guess at why your inspector wants a fusible disconnect but IF you have a fault current problem and you can't series rate to your existing panel (this would definitely be the case if the panels are of different manufacturer), you might be able to series rate the new breakers to a fuse.
First you need to see why hr wants the disconnect...if it;'s not for AIC ratings the I know of no valid reaason.
 
V

Volt-Amps

Member
Location
Indianapolis
AIC rating of the main breaker in the main panel that feeds my subpanel is not clear from the survey photos. the branch circuit breakers in the main panel are rated 10k-AIC. The panel I spec'd is rated 22K-AIC, my specs call for fully rated panel (although not needed to be fully rated).
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
same manufacturer ?? (existing panel & new panel)
 
Last edited:
V

Volt-Amps

Member
Location
Indianapolis
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Maybe as simple as thinking a 110.22 violation. Even if within site it should be marked as location of the disconnecting means if not within the enclosure.
 
T

Tulsa Electrician

Senior Member
Location
Tulsa
Occupation
Electrician
What I noticed from the OP.
240 volt three phase 4 wire.

He added a 200 amp ?
Single phase or three phase?

So I wonder if the AHJ is seeing something we don't.
Like a load center for single or three phase or some two or three pole breakers slash rated in the panels.

Granted the fused disc between has me at a loss unless the main panel and feeder breaker has a AIC listing greater the the listing on the sub panel adjacent.

Maybe just a typo(240).

Maybe a little more information will help.

FYI, slash rated would have nothing to do with the disc he is asking for.

After all it could be a non fused disc from what was in the OP. There was no mention of a fused disc. In that case the 200 amp breaker on the feeder would be all you need.

Maybe get a few more details from the inspector on what and why. Then we can provide a much better ansawer.
 
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