National Electrical Code 2011
Chapter 3 Wiring Methods and Materials
Article 312 Cabinets, Cutout Boxes, and Meter Socket Enclosures
I. Installation
312.8 Switch and Overcurrent Device Enclosures with Splices, Taps, and Feed- Through Conductors. The wiring space of enclosures for switches or overcurrent devices shall be permitted for conductors feeding through, spliced, or tapping off to other enclosures, switches, or overcurrent devices where all of the following conditions are met:
(1) The total of all conductors installed at any cross section of the wiring space does not exceed 40 percent of the cross-sectional area of that space.
(2) The total area of all conductors, splices, and taps installed at any cross section of the wiring space does not exceed 75 percent of the cross-sectional area of that space.
(3) A warning label is applied to the enclosure that identifies the closest disconnecting means for any feed-through conductors.
Esta é a seção de código aplicável. Costumava dizer que não eram permitidas emendas a menos que houvesse espaço suficiente. Isso levou muitas pessoas a simplesmente dizer "NÃO é permitido fazer emendas". Eles estavam errados. Você ficaria espantado com o que seria fisicamente necessário para atingir esse número de preenchimento de 75%.
Então basicamente sim, as emendas são FINE em um painel de disjuntores.