A commonly held misperception is that you can’t splice service-entrance conductors. Actually, you can [230.46] and sometimes you should. It’s an engineering decision, not an NEC-based decision.
A few reasons to avoid splicing service-entrance conductors are you add connections that:
- Are potential points of failure.
- Must be inspected and maintained.
- Develop a resistance.
- Are most likely difficult to get to for maintenance.
- May require coordination with the utility for maintenance.
Of course, those first three issues are true of all connections. That last two are somewhat moot because those conductors should undergo periodic insulation resistance testing anyhow. You can test the AC resistance across the connections while the conductors are de-energized.
Still, the challenges of working on these particular conductors mean you want to avoid splicing them if it’s practical to do so.
If you do splice service-entrance conductors, comply with these specific NEC requirements:
- 110.14. This has extensive requirements. A key point is you must use splicing devices identified for the use.
- 300.13. Basically, the splice must maintain mechanical and electrical continuity.
- 300.15. This also has extensive requirements. A key point is you can use connectors only with the specific wiring methods for which they are designed and listed. Bad assumptions here lead to spectacular fireworks displays.