Stormy01
New member
- Location
- Bayfield, Co, USA
Can you, according to the NEC, feed a 200 amp main breaker panel with a 100 amp breaker from another MCC? If so please provide NEC references.
200 amp panel with 100 amp breaker
- Thread starter Stormy01
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- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Yes. There is no real NEC provision that would prohibit this so it's allowed. The 200 amp CB is simply being used as a disconnect if the feeder is protected by a 100 amp OCPD at it's origin.
Welcome to the Forum.
Welcome to the Forum.
kwired
Electron manager
- Location
- NE Nebraska
Supply it with a 15 amp breaker if you so desire - as long as the connected load is less than 15.
7EA
Member
- Location
- California
It's a good question and one thats come up before with me. It's commonplace to use a panelboard or loadcenter that is rated for more than the feeder, ie, 200a 42 ckt MLO panel feed by a 100a feed. Personally, I've never thought it's a good idea to have a main breaker in that panel that is oversized simply to avoid confusion. 408.30 and 36 give some guidelines but it's not prohibited that I know of.
kwired
Electron manager
- Location
- NE Nebraska
You have some explaining to do before most of us will buy that theory. Like I said you could supply that panel with a 15 amp breaker if the connected load is less than 15 amps. There is probably better and less expensive ways if that is the case but is otherwise NEC compliant.
What I mean, is if your feeder is rated at 100Amps, you can not have a 200Amp main breaker in the sub panel.
You can have a 100Amp feeder that has 100A OCPD that will feed a 200A subpanel.
kwired
Electron manager
- Location
- NE Nebraska
I think I understood, you still haven't told us why you make that claim. If the supply is protected by a lower level overcurrent device what harm is there having the higher rated device?
You could even replace that main breaker with a molded case switch with no internal overcurrent protection if you wanted, as the 100 amp feeder device is providing the protection, or even convert to a main lug panel if a disconnecting means isn't required (say a separate building application). If there is an overload the 100 amp feeder is tripping. If there is a ground fault, it could be a crapshoot as to which responds first, all depends on the trip curves of each breaker and how much current flows during the fault event.
I went back and read what i wrote. I agree, what i said in post #5 does not make any sense. :ashamed1::ashamed1::lol:
GerryB
Senior Member
- Location
- woodbridge, ct. USA
I saw that a few years ago, someone changed out a fuse box with a 200a MB panel but left the 100a fused disco in place. When the HO called me to upgrade the service I was able to feed the new panel so in that case it worked out well.
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
You also have to remember to treat the 2nd panel as a sub-panel and not bond the EGC's and neutral together (just in case that wasn't understood).
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
The relevant code article is 408.36. It says that there must be overcurrent protection that is not greater than the rating of the panelboard. It does not say the OCPD must be equal to the rating of the panelboard. So a 100 amp upstream breaker and a 100 amp feeder can be used to supply a 200 amp panelboard, even if the panelboard has a 200 amp main breaker.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
The article that confirms this statement is 408.30.
mjf
Senior Member
Is there a code requiring the connected load to be less than 15?
(I do realize that common sense and not wanting the breaker to constantly trip apply)
kwired
Electron manager
- Location
- NE Nebraska
Is there a code requiring the connected load to be less than 15?
(I do realize that common sense and not wanting the breaker to constantly trip apply)
Yes, 210.20(A) - but that is for branch circuits, 215.3 says about the same thing and would apply to feeders. I don't see similar language in art 230 for services though.
230.23(A), 230.31(A), 230.42(A) for conductors. 230.90(A) for ocp.
kwired
Electron manager
- Location
- NE Nebraska
Conductors must be able to carry the load, just like feeders or branch circuits. But the requirements for OCP in 230.90 is not worded like it is for feeders or branch circuits. It just says not higher than the allowable ampacity of the conductor and never mentions an overcurrent device needing to be not less than 100% non continuous/ 125% continuous load like the sections covering feeders and branch circuits says.
I don't see that a 15 amp service overcurrent device is in violation of any code being connected to a 20 amp load. Not a good design though. The conductors need to be 20 amp conductors, but nothing says the overcurrent device needs to be a minimum rating, just that it can not exceed the conductor ampacity. Or did I miss it somewhere?
Last edited:
No, you did not miss it. I had looked at it as you describe before... but it got lost somewhere up top.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Is there a general agreement that the mandate of a minimum service size for a residence does not require a matching minimum size main breaker?
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By not requiring that the downstream OCPD to be lower in size than the upstream OCPD, the NEC does not seem to care about the coordination between protective devices operation. Such lapse, if it really exists in the code, may not be tolerated by stating that NEC is not a design manual, IMO.
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