Discuss Bonding between two buildings in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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brizospark

Working in a factory at the moment

One half of the building is fed from one street, the other from a different supply in a different street

Should the bonding be connected together or kept separate?
 
Are there two separate sets of services?.Presumably it used to be two separate buildings?...if so I would bond each service to the applicable incoming supply......Sounds like an Isolation nightmare though.....lots of warning notices at DB's would be appropriate me thinks.
If the supplies overlap within the buildings I would suggest a link between the two MET's would be a good idea to avoid any potential difference between the two earthing systems.
 
i would have thought they would be 3 phase supplies. still could come from separate subs. though.
 
they do not overlap as far as im aware but i suppose the potential for them to overlap is there
 
You could run in a separate bonding conductor from one MET (say from the original factory supply) to the second supply via a detachable/removable link at the second supply MET. Leave the link open until such time that the supplies start overlapping between the two factories.
Then it's just a case of labeling this link connection at both ends....

This is fairly standard practice where two or more buildings are supplied from separate supplies, that through necessity supply various plant in two or more of those buildings
 
The only danger is in the event of a fault in one of the buildings. When the cpc will have one of the phases present from the other building. In that scenario you may have more than one phase present at a time (in unexpected circumstances .. you'd normally label all likely places). That's assuming that the delivery of each building is in phase sync (which it probably is anyway and) in the worst case would be taking two phases as 180deg out of phase (purely theoretical) ... hence the at worst case double it scenario.
 
If it is now one building then the structural steel would probs all be linked throughout so my gut feeling would be all the bonding should be linked.
 
If it is now one building then the structural steel would probs all be linked throughout so my gut feeling would be all the bonding should be linked.

If you try getting continuity between adjacent steel structures you'll find a very high resistance (coz the steel is in concrete usually).
 
If you try getting continuity between adjacent steel structures you'll find a very high resistance (coz the steel is in concrete usually).

Was thinking of big RSJs but i suppose it's probs silly of me to to comment on the building stucture when i haven't even seen lol (it could be brick and wood for all i know)
 
Agreed mate. With separate buildings if you come along after build (and 1st/2nd fix electrics) and do a test you'll find a degree of continuity (IE low(ish) resistance ... because of the bonding). If you do it during construction (once the concrete has gone off) you'll find the resistance so high it ain't worth considering.

Warehouses are a whole different ball game as, as you mention, they often share some common conductive structure (same with office blocks).

In reality, I guess, the risk is only (potentially) marginally worse than any 3 phase fault, where phases are used individually (IE fault on one phase appearing physically close to another phases line). The risk then is that the cpc (on one phase) can now be in physical proximity to another phase (not sure I'd wanna be there).
 
If you try getting continuity between adjacent steel structures you'll find a very high resistance (coz the steel is in concrete usually).

That shouldn't be the case at all!! As steel framed buildings should be effectively grounded at time of construction, that has been in force for as far back as i remember. Obviously the more up market the building is, the better the grounding scheme employed. Modern day steel frames that i've seen can have the vertical structural steelwork actually set in conductive mortar. But more usual is, ground mats, rods, or perimeter bare copper ring/loop...

Even modern concrete structures, will have re-bar break out points, so that the mass of connected reinforcement steel, can also effectivley provide lightning protection to the building.
 
Try reading the post just before the one you've posted (bonding)! I wouldn't disagree with what you've said at all.

I'd be interested to hear your reflections on the bond versus don't bond question though ;)
 
Topquark,

I was basically only replying to your post highlighted in my post in this instance....

As to your question on the bonding issue, many of the the adjacent buildings and even some more remote buildings on projects i've worked on had bonding links between them. All of which were connected via removable links on the respective Main earth Bar arrangements.

On one particular project in Saudi, a medical city (as it was called) had a 185mm insulated conductor that connected every medical and service buildings Main Earth Bar on the project. It Also had a 240mm bare copper ring from a substantial ground field, that also connected to the Main Earth Bar of each building, again via removable links on the earth bar.... I've had very few conflicts during times of testing these systems, individually or as a whole....
 
Further to your question on my reflections on bonding between buildings. I have read your points on this matter and can agree on in principle on what you say. The thing is, when your dealing with many industrial facilities that have huge amounts of interconnecting metal plant and pipework, or say hospitals that again have several metallic systems, and various pipework systems. ...It becomes almost academic, as it's almost impossible to isolate any particular system from another, so parallel earth paths are going to always be a fact of life that we are going to have to deal with and accept i'm afraid!!! In small factory premises and the like it is far easier to manage, (if that's the right word) but your never going to get away from those parallel paths in reality. So better to effectively bond than not too....
 

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