Bonding question with two supplies.

[Pat Tester]

I am doing some work for an engineering company who are taking over the unit next door. I have put in new 80A fused isolator feeding 3 phase board, this is supplying various 3 phase sockets, single phase lighting, 3 circuits along with 13A sockets. They have just had Propane heater installed, hanging from roof. I have put in separate 6A supply on fused switched spur as requested. I believe the 2” steel gas supply should be bonded as the tank is external, the problem is they have T’d the gas from the unit next door. Upon examining this other heater, installed 9 years ago I discover no bonding ! As both units have their own 3 phase supply with PME, My question is this: If I bond the new heater how will this impact the other unit ?
Is there an issue with potential differences using two neutrals ? I have not come across this problem before and would appreciate any assistance or advice from anyone with more experience in this field.

 

[Deleted member 26818]

Consider metallic sevices in a house. Would you not bond, because next door is bonded?

 

[IQ Electrical]

The common pipework (gas supply) must be bonded at its entry to each building, if you have Guidance Note 8 then figure 5.14 shows this detail.

I assume you are talking about main protective bonding to the gas service even though you mention 'bonding the new heater'

 

[Pat Tester]

Yes, main protective bonding of gas service. I will check out Guidance note 8, thank you.
So from what you have both written I run an earth from earth point of supply to gas pipe at entry for each unit, bonding the pipe twice, from two different earth points ?

 

[IQ Electrical]

Yes, each building will be an equipotential zone so a bond is required from each main earth terminal to the point of entry to the building.

So 2 buildings, 2 main protective bonds.

 

[Pat Tester]

Many thanks IQ,
2 buildings, 2 main protective bonds but gas pipe joins both so do the bonds not create one equipotential zone with two supplies ?

 

[IQ Electrical]

The pipework can introduce a potential from the building it exited to the building it enters-either earth or earth-fault so you need to create equipotential in each building.

 

[Pat Tester]

Many thanks for your help IQ, sorry if it sounded like I doubted your posts, I just wanted to ensure I
had not been ambiguous in my wording.
Thanks again
Pat

 

[IQ Electrical]

No problem but don't forget that 'thanks' button!