What is an example of functional earth?

[WilliamAtkin]

Doing some college work atm and come across a question asking me to provide an example of functional earth. I asked my boss at work but he doesn't even know what it is. The regs says " Earthing of a point or points in a system or in an electrical installation or in equipment for purposes other than electrical safety, such as for proper functioning of electrical equipment "
With a quick google to find some examples I've come across Tv / internet cables but not really sure as found no specific examples online

 

[Pretty Mouth]

Some RCDs and RCBOs have a functional earth, a lot of the older ones seem to

 

[plugsandsparks]

Always think of my early days when "earth calling" was standard practice for phone lines..

EXCHANGE LINE TYPES - LOOP CALLING - EARTH CALLING - DASS2 - DISA - DDI

UK Line Types

www.britishtelephones.com

 

[nicebutdim]

This is a question I've never felt able to give a decent answer to when it has come up in coursework. The best I can describe is an earth provided for the correct functioning of equipment, rather than for safety.

I have a suspicion that @pc1966 addressed this at one time, but a quick search of the forum isn't turning up anything from him.

 

[WilliamAtkin]

This is a question I've never felt able to give a decent answer to when it has come up in coursework. The best I can describe is an earth provided for the correct functioning of equipment, rather than for safety.

I have a suspicion that @pc1966 addressed this at one time, but a quick search of the forum isn't turning up anything from him.

I've read up that it gets used in IT - computer systems aswell as telecom so I've put that down. College work is annoying as I always think the boss or other qualified electricians at work will be able to help me and know the answers to my questions but 50% of the time they don't have a clue

 

[nicebutdim]

I've read up that it gets used in IT - computer systems aswell as telecom so I've put that down. College work is annoying as I always think the boss or other qualified electricians at work will be able to help me and know the answers to my questions but 50% of the time they don't have a clue

I think certain equipment IT equipment may be provided with a functional earth, but don't quote me.

I'd be inclined to provide more specific information if this is an answer in an assignment. Poor wording could lead to lost marks if they think you've confused functional earthing with high integrity earthing.

 

[pc1966]

The most common 'functional earth' I can think of are for the EMC filters used in SMPSU, which are common for IT equipment. A lot of traditional IT stuff is metal cases class I so need an earth for safety reasons (as in ADS) but for stuff like a laptop that may be isolated electrically to class II it might still have some 470pF - 1nF class Y capacitors L-E and N-E.

As @Pretty Mouth mentions you see some RCBO and RCD sockets that are connected to the CPC/earth for 'functional reasons' (in the sense they are not achieving load-fault ADS by that means) where if the N goes high in voltage due to an up-stream open N or reversed polarity the RCD will fire anyway.

 

[fatboyslim]

When I think of a 'functional earth' I mainly refer to DC component boards due to capacitors leaking current, as they leak a small amount of current down to earth to function, this is to avoid damage to certain electronics in the board.

Perhaps I'm wrong, please correct me.

 

[Avo Mk8]

How about this as a candidate for 'functional earth'?
It's common, well obligatory now, in the electronics manufacturing industries, to have static dissipative flooring, bench coverings, and personnel wrist straps etc. all of which require a connection to earth.
The earth is to discharge any static build-up on people, clothing etc due to their movement, which could otherwise harm some electronic components. There may be instances where the earth is a safety measure for people, eg in dusty/potentially explosive atmospheres, but normally it's for safety and reliability of the electronics being assembled or repaired.
(In most cases the earthing is via resistors for safety, if live equipment may be worked on!)

 

[pc1966]

The anti-static aspect is a good reason and as @Avo Mk8 says you normally have either a dedicated ~1M resistor or a partially conductive plastic strip used for connections. That also applies to some electronic stuff that you don't want charging up to a high voltage but you don't necessarily want a low impedance earth path that can result in significant AC current flowing in the cables "hum/earth loop".

Most electronics won't leak DC as the SMPSU, while rectifing the AC mains to ~340V DC, is usually well isolated from the (extra) low voltage side that would normally have any sort of CPC attached.