Transition Splices (50ft rule) FREE cabling and networking Helpdesk
 Question by Brent Goodbread posted 26 Sep 2007
 Transition Splices (50ft rule)
What is the deciding factor in the 50ft rule of entering a building?
Is it the fire rateing of the sheath or the electrical properties of the copper pairs and sheilding or both?
If it is just the sheath, why do they not make an indoor/outdoor copper cable.
Another question is do all OSP copper cables (like PE-89), regardless of the distance outside need transition splices and protection on both ends?
 Answer by Dmitri Abaimov posted 15 Feb 2008
Dear Brent ,

The 50ft rule being a NEC rule is strictly fire-related, based on the amount of the fuel material (polyethilene, water blocking grease) you'll have on a cable that's 50ft long.

The need for protection is defined by the length of the run outside of the area protected from lightning by the buildings themselves. There is no exact formula, please browse our site for more info about lightning protection.

But, going back to your first question, no matter how long or short is the piece of cable outside, if it is longer than 50ft inside, you have to splice it to a rated indoor cable.

Dmitri Abaimov, RCDD

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