TELECOM Digest OnLine - Sorted: Re: Power and Cable TV Outages

Re: Power and Cable TV Outages

Neal McLain (
Thu, 21 Jun 2007 23:27:05 -0500 wrote:

> I know the cable TV system in my area depends on commercial power
> and stays out even after power is restored (I guess they have to
> reset it). That scares me if I dependended on cable TV for telephone
> service.

They don't "reset" it. A cable TV network will continue to operate as
long as it's physically intact and has operating power available. At
any given customer location, it's entirely possible for the power to
be off, but cable TV to be operating normally.

Virtually all cable TV facilities are now protected by backup power:

- Headends are protected by on-site standby generators. Some headends
also have batteries to cover transitions between utility power and
generator power.

- Nodes are protected by batteries capable of maintaining service for
several hours. They are equipped with power input connectors and
transfer switches to accept power from vehicle-mounted generators
(similar to telco DLC cabinets).

- Pole-mounted power supplies are also protected by batteries. During
extended outages, they can be connected to vehicle-mounted generators
(standard off-the-Home-Depot-shelf generators work fine).

A more likely reason for simultaneous power-and-cable TV outages is
plant damage. If a poleline is damaged (falling tree, drunk driver,
house fire) it's likely to affect everything on the on the line:
power, cable TV, and landline telephone. In such situations, the
power company always gets its repair work done first; cable and telco
crews can't get near the line until power has finished its work and
declares the area safe.

All of which means that cable TV indeed "stays out" until after power
is restored. But it doesn't necessarily mean that the same customers
are affected. Depending on the topology of the cable network
vis-a-vis the power network, it's possible for the cable signal and
electric power to be running in opposite directions along the same
poleline. In such situations, a damaged poleline would affect
different sets of customers. A house fire at a critical intersection
could knock out power on the north side of town, cable TV service on
the west side, and landline telco service on the south side.

Neal McLain

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