Hi everybody.

I have a question regarding earthing system for LPS and for protection.

Should these be connected together?

BR

411.3.1.2 would seem to say yes (unless BS EN 62305 contains any exceptions).
- Andy.

Depends on the class of the LPS system - if it's an isolated LPS then no - if not, then connection to the LV MET is normal - if you are putting in a lot of ground network for the LPS you may be able to share that with the HV but it depends on if you have a hot or cold site at HV and can predict what the ROEP will be around the area.

Not helpful I appreciate - but this is a piece of string job

regards

OMS

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Failure is always an option

Thank you very much!!!

Just to add on, whilst BS EN 62305 doesn't forbid the installation of an (electrically) isolated LPS it does recommend a single integrated structure earth termination system for lightning, power systems AND telecoms. This is the case in the old BS 6651 which recommended for a "common earth termination network" and the American NFPA 780.

The standards also requires you to ensure that no sparking (flashover) will occur in the structure so unless you've used insulation of the required grade or adequate air separation between any earthed part of the structure and LPS conductors they must be bonded to the MET anyway.

Even an "isolated external LPS" can be equipotentially bonded at ground level. The term "isolated" is referring to the physical isolation of the air terminals and down conductors from the structure to be protected and not necessarily the electrical isolation (at ground level).

So unless you really done the detailed engineering bond the systems together. If you want to protect telecoms or data equipment you need to incorporate zoning and surge protective devices - isolation isn't the answer.

There's a nice series of diagrams here from IEC 61000-5-2 that I show to people who rave on about "clean earths" and "dedicated LPS earths" (common in my office ).

As OMS said though it get more complicated if you're got on-site transformers and have HV and LV earths are seperated.

Regards, Tim

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Everyone loves a fireman - but hates the fire inspector.

Thank you Tim, many engineers doesn't agree about this.