Lightning rod directly over aerial cables

[patrick0]

I've got a question for anyone who knows anything about lightning strikes & conductor rods:

I live in a four storey council block (around 100 flats in building) in London. Recently the council hired contractors to install around 20 lightning conductors from the roof down to the ground (it's a long narrow building).

The thick copper conducting rod is covered with a wooden box at ground level. From 2.5m upwards it's just the copper rod with no insulation.

Above each floor there are 10-20 cable tv wires that are bunched together that run the length of the building. They've placed the copper rod directly over these on each floor without any insulation or air gap (obviously there's a v thin rubber layer on each aerial cable).

In the unlikely event of a lightning strike, I'm wondering if the rubber would be melted and at least some of the strike hit TVs in our flats (potential fire risk)? I'm asking as I suspect the rod should be insulated where it passes over the aerial cables - but trying to get the council officers to look into the issue is pretty difficult.

 

[bugsy]

The energy released on a strike would not only melt the insulation it would take out the connect equipment (in my opinion ) there are guidelines and a B.S.6651 which they should adhere to

 

[patrick0]

I asked for a response from the contractors involved and received the below. They are saying that the rods come in contact with the communal TV cables but that they are bonded (I can't see any evidence of that). The rods also pass over satellite TV cables and electrical cables.

Some photos: Conducting rods - a set on Flickr

Does the response make sense and does it appear unsafe to anyone? I just want to check as us leaseholders are being charged thousands for the work and it affects many flats over about 15 buildings, so I'd like to kick up a fuss now if there are any potential issues.

RESPONSE 1:
“Our specialist lightening protection sub-contractor has confirmed that the conducting rods are sheathed and in places do pass over communal IRS systems and in some instances individual cables where residents have installed their own satellite dishes.
The correct bonding and protection has been provided to the communal IRS system and is protected and therefore is not an issue. It was, however, not possible to divert the lightening conductor rods around private unauthorised satellite cables which could be termed at risk. We would recommend that these residents are informed that their cables either need to be removed or redirected to avoid these lightening protection installations. It is not possible to redirect the lightening conductor rods as these are positioned to protect the building”


RESPONSE 2:
“Our LPS Specialists have confirmed that the communal aerials on all LHC3 roofs (where owned by Lambeth) have been bonded in accordance with the BSEN.

Private unauthorized aerials or dishes have not been bonded as these are not the responsibility of the Client. Furthermore, to do so would legitimize their existence and invite potential claims for damage etc to the residents’ illegal installations.

Our specialists have confirmed that the risk of a strike “flashing” to the coaxial cables is very low indeed. Current from a lightning strike follows the route of lowest impedance - coaxial cables have a typical impedance in excess of 4W, often much higher. The downtapes used on the LPS installations on site have an impedance of less than 1W. The system is designed so that the lightning would therefore always take the easiest route to earth (ie through the downtapes) and would not run down the coaxial cables.

The installation of the surge protection units at the electrical intakes protect the electrical appliances in the block from a strike through the LPS.

One further point to note is that the pvc coating on the downtapes is purely for aesthetic purposes only and is not intended to act as an insulating material.

Finally, it should be noted that the principle of an LPS installation is to reduce the risk of damage to the structure. The existence of an LPS on a block will not guarantee that damage will not occur in the event of a strike.