27hillcrest
Senior Member
When is it okey to install a Main Lug only panel? When is it not okey to install a Main Lug only panel?
Main Lug only Panel?
- Thread starter 27hillcrest
- Start date
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- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I do not believe you will ever find a code requirement that the 'main protective device' actually be inside of the panel.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If you read Jim's response you'll see that your questions are so broad that there isn't really an answer. Do you have some specifics in mind as far as the type of installation? One example would be, you can use a MLO panel if there is an OCPD ahead of the feeder and in the same building. One could install a MLO on the 10 floor of a building with the OCPD ahead of the feeder in the basement service equipment.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I take the OP to be asking more of when do you need a main breaker/disconnect at or in the panel, and when can you leave the feeder breaker in the switchboard, MCC, panelboard, or wherever it is fed from and just use a MLO.
Perhaps some clarification on the specific project set-up is in order.
Perhaps some clarification on the specific project set-up is in order.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Because of how vague the question is, the only viable generalized answer in my opinion is that it is NOT OK to install an MLO panel when there is no other suitable OCPD in the circuit. Everything else is subject to specifics of the installation.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
A service panel must be service rated and can have up to 6 throws-- dp breaker is one throw-- of the hand to disconnect the structure. So , in a sense, you never need a main breaker. Often there is a main breaker at the service panel and then main lug panels after that. The exception would be a sub panel in a detached structure that may also have a main breaker panel but the 6 throw rule applies there also.
27hillcrest
Senior Member
Sorry to be so vague guys. I wanted to know when do have to have a main breaker in a sub panel that is in the same building? From some of the responses it seems like NEVER if it is in the same building as long as the OCP is installed on the feeder.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
No apologies necessary.
Yes, that's correct, sort of. Even if an OCPD were required at the panel it wouldn't need to be a main CB it could be a fused switch or other OCPD located adjacent to the panel.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I would think more along the lines of convenience. Is it required, maybe not, but would it be nice to have from a maintenance perspective, maybe. If it is located in a large building where it might take a while to track down somebody down and locate the right OCPD then probably would be nice. Industrial where you have lockout/tag-out requirements and everything is well labeled, and only the plant electricians touch the stuff, then probably not.
Remember NEC is MINIMUM safety requirements; it is not a practical design guide.
Remember NEC is MINIMUM safety requirements; it is not a practical design guide.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Also be aware, that a requirement for a disconnecting means (i.e. LOTO at an out building) does not mean it must be an overcurrent protective device like a 'main breaker'.
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