Main gas bonding in commercial installations

awarner · May 17, 2009

Morning all
I've got a lot of work coming up doing main gas bonding but its mostly going to be in commercial and industrial situations. I'll give you the following scenario.
Main DB is in building number 1, gas main comes into building number 2 on the same site. Blg 2 is fed , electrically, via a submain from bldg 1 and has its own DB.
BS7671 says that main bonding has to be taken to the MET, but in a situation such as this, is the main earthing terminal at Building 2 alright to go to or have I got to go to the lengths of getting the cable back to the MET in building 1?
Also, if the bond can be made in building 2, should the size of the bond (as per section 544 of the regs) be worked out on the mains coming into DB1 or the size of the submain going to DB2?
I'm scratching my head on this one at the moment and thanks for any advice you can give me.

scotsparky · May 17, 2009

My understanding is
The Gas,water etc hat to be bonded where it enters the building so I would bond at each entry to both buildings sizing my bond from the main incommer to each building.

Basically i woul;d trat each building as a seperate installation.

hope that helps.

Guest123 · May 17, 2009

Hi.

It would all hinge on the size of the sub-main between building 1 and 2 and your earthing system.

damo · May 17, 2009

awarner said:
Morning all
I've got a lot of work coming up doing main gas bonding but its mostly going to be in commercial and industrial situations. I'll give you the following scenario.
Main DB is in building number 1, gas main comes into building number 2 on the same site. Blg 2 is fed , electrically, via a submain from bldg 1 and has its own DB.
BS7671 says that main bonding has to be taken to the MET, but in a situation such as this, is the main earthing terminal at Building 2 alright to go to or have I got to go to the lengths of getting the cable back to the MET in building 1?
Also, if the bond can be made in building 2, should the size of the bond (as per section 544 of the regs) be worked out on the mains coming into DB1 or the size of the submain going to DB2?
I'm scratching my head on this one at the moment and thanks for any advice you can give me.

hi,spooky ive just completed an exact same job.i had a 95mm main incomer with a 50mm main bonding but i took a seperate 35mm bonding in2 the seperate building to my mains gas even though that had a 25mm submain supplying that building.That is If the gas supply is supplying both buildings.otherwise like that guy says treat every installation as its own.My view is so long as you label everything up and even when you fill in your certs.Also maybe fill in on a seperate attatchment to your certs stating what you have done.
good luck