Earthing Air Conditioning Pipes

[RobFurn]

Do you have to provide a Main Equipotential Bonding conductor to Earth Air conditioning pipework?

413-02-02 (iv) (Brown Book) says so.

I would have thought the Earth in the Supply Cable is adequate as the Pipes in AC systems are linked to the earth in the outside units Circuit board.

Anyone have an opinion?

 

[Spark123]

Can they introduce a potential, generally earth potential into the location?
Unless the CPC is large enough to be used as a MEB (and the resistance low enough) it shouldn't be used for the purpose of a MEB.

 

[JohnD]

It is a metallic service entering the house from outside, so it needs to be main-bonded.

Same as gas, water and oil.

 

[Spark123]

If it is an air con unit mounted on the wall tho I'd question the need.

 

[mdbalson]

I would not have said that they would need bonded, as the pipes only run from the condenser & Compresser to the Evaporator, & are insulated.

 

[JohnD]

but It is a metallic service entering the house

 

[Spark123]

Can it introduce a potential into the equipotential zone? I doubt the wall mounted ones can, but if the compressor is sat on the floor or in a separate building then they possibly can.
I think it has to be assessed on a case by case basis.

 

[JohnD]

probably it won't, any more than a gas or water pipe which might be plastic when it's in the ground. but we still have to main bond them when they turn to metal at the meter or stopcock.

Who knows, maybe it will be struck by lightening or an overhead cable will fall on it. Or the wall will get wet or flooded.

 

[Spark123]

I don't really agree with having to bond the water/gas where the supply is poly but yes, we are told to do it.
Same with metal windowframes, should we MEB them?

 

[JohnD]

not a metallic service

 

[Spark123]

True, but they are at the same risk as the others. Doesn't really need to be a metalic service to be questioned if it is an extraneous conductive part.

 

[RobFurn]

I dont have a problem bonding the pipes but the compressor is 40m from the DB. Cant I just bond the pipes to the earth in the supply cable, or would you recommend using a seperate earth from the MET to bond the pipes. Supply cable is 6mm as is the Earth. Its also SWA so surely the SWA is large enough to satisfy the 10mm requirement of TNCS?

 

[Spark123]

MEB needs to connect from MET to where the service enters. 40m is pushing it resistance wise, what size service? 10mm is not necesserilly correct. The MEB needs to be sized minimum to table 54h which relates to the neutral of the supply - also consult the DNO as they can overrule this.

 

[luminaire]

Is it RCD protected?

 

[Spark123]

Why?
There is a risk where something else goes wrong within the premises and raises the potential of the MET and the service pipe remains at 0v, hence the reason for it to be main equipotential bonded.