Service entrance conductors are the run between the utility connection and the main disconnect, and they have no overcurrent device at their supply end. Everything downstream of the main breaker is protected; the service conductors themselves are not. That single fact drives the rules about where they may run, how far they may go inside a building, and why the top of a panel stays live with the main off.
Protection sits at the far end, not the near end
On a branch circuit, protection is at the origin, so a fault anywhere along the run is interrupted. Service conductors are the opposite: the protective device is at the load end, at the service disconnect. A fault in the service conductors themselves can only be cleared by the utility protection upstream, which is coarse and slow by design. The available fault current from a distribution transformer is very large. That combination is why service conductor installations are constrained tightly, and why the rule limits how far service conductors may run inside a building before reaching the disconnect.
The main breaker does not kill the whole panel
This is the fact that matters most to anyone opening a panel cover. Switching off the main disconnect de-energises the bus and every branch breaker. It does not de-energise the service conductors landing on the main lugs, which remain live from the utility. In many residential panels those lugs are exposed once the cover is off, sometimes only inches from the breakers. Anyone working in a panel has to know exactly which terminals stay energised and treat that area as live. If work requires those conductors to be dead, that means a utility disconnect or a meter pull, arranged through the utility.
Why the run inside the building is limited
Because unprotected conductors inside a structure are a fire risk, the rules push the disconnect close to where the service enters. That is the reason meters and main disconnects are usually on an exterior wall or immediately inside it, and why running unprotected service conductors across a basement to a panel at the far end is not acceptable. Where a longer run is needed, the usual solution is a service disconnect near the entry point and a feeder from there to the panel, since the feeder is protected and can travel. Local utility rules add further requirements about meter location, clearances and access.
Grounded conductor and bonding at the service
The service is also the one place where the grounded conductor and the equipment grounding system are deliberately connected, through the main bonding jumper. Downstream of that point they stay separate. Getting this right at the service is what makes fault clearing work everywhere else in the building, and getting it wrong, or repeating it at a subpanel, puts normal neutral current onto the grounding system and onto metal enclosures. The grounding electrode conductor also connects at the service, tying the system to the electrode system.
Overhead and underground arrangements
Overhead services bring their own requirements about clearances over roofs, driveways and walkways, and about the drip loop where conductors enter the weatherhead. Underground services involve burial depth, conduit, and protection where conductors emerge. In both cases the utility owns part of the installation and the property owner owns part, and the dividing line differs by utility. Before planning anything involving a service, talk to the utility about what they supply, what they connect, what clearances they require and what notice they need. Service work is not a homeowner project, and in most jurisdictions it requires a licensed contractor and a permit.
What to check before you act
- Assume the main lugs and service conductors stay live with the main breaker off.
- Keep unprotected service conductors inside the building to the minimum permitted.
- Verify the main bonding jumper is present at the service and nowhere downstream.
- Contact the utility before any work affecting the service or the meter.
Common questions
Why is there no breaker before the meter?
Service conductors are protected at their load end by the service disconnect. Upstream protection is provided by the utility system, which is not part of the premises wiring.
Can I work in my panel with the main off?
Only if you know precisely which parts remain energised and are equipped to work near them. The line side of the main disconnect stays live.
The practical takeaway
Service conductors are unprotected at their origin, which is why they must reach a disconnect quickly and why the panel is never fully dead with the main off. Treat the line side as live at all times, and involve the utility for anything upstream of the disconnect.
References and further reading
- OSHA: wiring design and protection, including services and overcurrent protection
- NFPA: National Electrical Code overview covering services and service equipment
- CDC NIOSH: electrical hazards and safe work practices around energised equipment
Numerical scenarios are illustrative unless identified otherwise. Follow the exact product instructions; component ratings and local installation requirements can differ.
