earthing sky dish

[mackers]

hi all
just been asked to price for earthing a communal sky system.

SKY have asked for a 4mm earth to be run back to the MET from there equipment.

there are 4 dishes positioned around the blocks of flats 2 storey high

there in no landlords db so where do they want me to connec t it?

anyone come across this before ?
never had much to do with tv's

cheers

 

[Ian B]

I can't publish them here as they are copyrighted documents, but COP-3 is available from here: CAI Publications

 

[Ian B]

I should add that the purpose of the mast/dish connection to the same MET earth reference that the headend is connected to, is mainly to reduce the potential for eddy currents in the screen of the signal connections to the headend, should the LPS be connected to the mast/dish at some point, and obviously not for Lightening Protection!

 

[Engineer54]

Well that link isn't going to tell me much ..lol

I'm only talking about the situation where a LP system is in place. Any dish or antenna's framework, will need to be connected to that LP system, as they will both extend beyond the protected flat areas and be acting as an ''air conductor'', there is no if's or but's about that!!

Now if your saying that a separate 4mm CPC should also be taken from these dish frames/structures to the MET direct, you are effectively cross connecting and negating the LP systems protection and allowing a lightning strike passage direct to the installations MET!! ...Rather you than me ...lol!!

All your head and other hardware stuff can be effectively protected in such LP systems by the inclusion of surge arresters...

Let me assure you that in the hundreds of LP systems i've been involved with, i have never connected or seen any dish/antenna frames directly connected to a MET, where it is protected by the LP system. It is if you like a conflict of interest between the two earthing systems..

 

[Ian B]

Well that link isn't going to tell me much ..lol

I'm only talking about the situation where a LP system is in place. Any dish or antenna's framework, will need to be connected to that LP system, as they will both extend beyond the protected flat areas and be acting as an ''air conductor'', there is no if's or but's about that!!

Assuming they are above the flat areas absolutely.

Now if your saying that a separate 4mm CPC should also be taken from these dish frames/structures to the MET direct, you are effectively cross connecting and negating the LP systems protection and allowing a lightning strike passage direct to the installations MET!! ...Rather you than me ...lol!!

No I'm saying the CAI COP states that the dish/mast should be connected to the MET via the equipotential bonding system at the headend using 4mm conductor if the building has a LPS fitted, whether or not the LPS is connected to the mast/dish.

All your head and other hardware stuff can be effectively protected in such LP systems by the inclusion of surge arresters...

Agreed, the purpose of the 4mm connection is not for LPS.

Let me assure you that in the hundreds of LP systems i've been involved with, i have never connected or seen any dish/antenna frames directly connected to a MET, where it is protected by the LP system. It is if you like a conflict of interest between the two earthing systems..

There's no 'conflict'. The LPS will provide an 'easier' path to ground for LP, and the equipotential bonding will prevent circulating earth currents in the signal cabling, however feel free to take it up with the CAI if you wish.

:cool4:

 

[RISElectrical]

This is possibly true as in the BS it states that LPS systems should now be connected to the MET, a practice that I really don't agree.

 

[Engineer54]

Assuming they are above the flat areas absolutely.

No I'm saying the CAI COP states that the dish/mast should be connected to the MET via the equipotential bonding system at the head end using 4mm conductor if the building has aLPS fitted, whether or not the ALPS is connected to the mast/dish.


Agreed, the purpose of the 4mm connection is not for LPS.


There's no 'conflict'. The LPS will provide an 'easier' path to ground for LP, and the equipotential bonding will prevent circulating earth currents in the signal cabling, however feel free to take it up with the CAI if you wish.

:cool4:

Why would you bond a mast or dish to the equipotential system, it's not going to be extraneous is it, sitting on top of a roof?? But it will act as a very good air conductor for a LP system....

The LP system ''IS'' connected to the MET via a 50mm cable link from one of the down conductor earth electrodes or from a ring link of the down conductor electrodes, so why would you run a 4mm link from a LP protected mast/dish to the MET??

As i said, if you can let me see the relevant code paragraph(s) your referring too, i might be able to make a little more sense of it...

 

[Engineer54]

This is possibly true as in the BS it states that LPS systems should now be connected to the MET, a practice that I really don't agree.

The idea is to bring the two earthing arrangements/systems to the same potential during the short duration of a lightning strike. Thus negating dangerous flash overs between the two earthing arrangements. Installations of delicate equipment etc, are protected from such strikes by the inclusion of surge arrester arrangements... As now outlined in BS7671 Amendment 1