OM3 (Optical Multimode 3) is a type of multimode optical fiber commonly used for high-speed data transmission in data center environments. The maximum distance that OM3 fiber can support for 40 Gigabit Ethernet (40GB) connections depends on the type of transceivers used and the specific standard or protocol being employed. The most common transceiver for 40GB over OM3 is the QSFP+ (Quad Small Form-factor Pluggable).

Here are some general guidelines for OM3 fiber with 40GB using QSFP+ transceivers:

1. Short Range (SR): QSFP+ SR modules for 40GB over OM3 typically support distances up to 100 meters (about 328 feet).

2. Extended Range (ER): There are some QSFP+ ER modules that can support longer distances, typically up to 300 meters (about 984 feet).

It's important to note that these are general guidelines, and the actual achievable distance can depend on various factors including the quality of the fiber, connectors, and the specific transceiver used. Additionally, advancements in technology may result in new transceivers that support longer distances over OM3 fiber.

Always refer to the datasheets and specifications provided by the manufacturers of the OM3 fiber and the QSFP+ transceivers for the most accurate and up-to-date information on distance capabilities.