NEC Handbook 50 ft rule for BLX or similar cable

[eric dupree]

Exhibit 800.5 An example of applications of listed communications cables.

REF 800.5 in 2005 NEC Handbook.

Can anyone explain the arbitrary number of 50' feet on this drawing?

It is stated in the diagram that the "outside plant cable (not to exceed 50' within building", but I don't find where they establish why it is 50'.

I understand the intent it is probably due to the type of insulation jacketing on the cable (*Type BLX for instance) and the fire spread hazard, but I would like to understand more of where the 50' rule came from.

Any help is appreciated.

Eric

 

[W6SJK]

I think it's a BICSI standard, but I'm not at work so I can't look it up.

 

[celtic]

It is stated in the diagram that the "outside plant cable (not to exceed 50' within building", but I don't find where they establish why it is 50'.

Have you read the commentary/s following 800.100 ('05 NECH)..and following the FPN?

In part:

However,a specific length is not specified in the Code because such
a length limitation may not be practical in some installations.

The picture is an example and not to be taken as "code". The NEC does not contain a limit on lenght for an occupancy OTHER than 1 & 2 unit dwelling units(800.100(A)(4)).
The number "50" seems to be arbitrary as detailed in the commentary/s.

 

[don_resqcapt19]

800.113 requires the use of listed communication cables within the building. Outside plant cables are not listed. Execption #2 is where the 50' limit is found as without the exception the non-listed cable would not be permitted in the building.

Exception No. 2: Listing and marking shall not be required where the length of the cable within the building, measured from its point of entrance, does not exceed 15 m (50 ft) and the cable enters the building from the outside and is terminated in an enclosure or on a listed primary protector.

As far as why this rule exists, I am not sure, but assume it has to do with fire spread and smoke production in the event of a fire.
Don

 

[tom baker]

In our state electrical rules, we only allow the Outside Cable Plant to extend 12" past the point of entry to the building. This is an FCC rule.