Bonding bother.

[GBDamo]

The present small job is in a unit, one of 40, in a single story Victorian mill.

The construction is cast pillars and beams in a roughly 6 meter grid

I cannot find any evidence of the steel being bonded, the site is huge and it seems unreasonable to spend days sorting this for a few sockets.

Where tested all the steel returns a result of 0.0MOhms (IR 500V) between the test spot and CPC of the incoming distribution circuit, a 5 core 25mm SWA, all parallel paths omitted.

So it is either bonded or Extraneous.

Is there an issue with just running a 25mm bond to the nearest steel, check continuity at various places, and being done.

Or is there a concern, that if the steel is not bonded, that fault currents from elsewhere on site will effectively flow through 'my' DB?

Hope this makes sense.

 

[pc1966]

Can you do a continuity check between two of the pillars?

If they are low R (say in the region of 0.1 ohm or less) you could reasonably assume they are all part of one structure and bond just one of them to the supply's CPC.

 

[Strima]

Do you have access to the main intake/plant room or contact with the site owner?

 

[ipf]

Does the unit have an individual supply or is it a sub main? I would suspect a sub main, which would mean a switch room of some sort.
The steel construction should be bonded from the main incomer to the building, in the switch room?....Access required, I'd say.

 

[Lucien Nunes]

0.0MOhms

With the limited resolution there (least significant digit is hundreds of kilohms) that could be 49kΩ, and if one allows the usual +/- one count (or more) it could be 149kΩ, not extraneous and in the order of half a million times higher than something that is bonded. I.e. this test range is not suitable (and I never did like the idea of poking 500V up a random piece of metal that someone else might be leaning on, just in case it isn't as well earthed as it looks.)

However, it's the structural frame of an old mill, in contact with masonry all over and is bound to be down in the few kΩ or less even without bonding. A continuity test that reads down to 0.1Ω to the DB will be a lot more revealing, although it would only take one machine isolator near the origin to be bolted to the metal to give a low enough reading that you won't be able to tell if it's bonded.

Prob need to eyeball it as suggested above.

 

[GBDamo]

Does the unit have an individual supply or is it a sub main? I would suspect a sub main, which would mean a switch room of some sort.
The steel construction should be bonded from the main incomer to the building, in the switch room?....Access required, I'd say.

It's a sub main from a switch room some 80meters away.

I'll have to make an appointment to gain access.

 

[radiohead]

I recently lost a job on similar issues. A large old warehouse type building divided into various units but with a single intake. Trying to gain access to areas to establish whether main bonding was in place was like trying to gain access to the kremlin. In the end they never got back to me and I'm certain they just got someone in who did the job and didn't bother with bonding and other niceties.

 

[ipf]

I recently lost a job on similar issues. A large old warehouse type building divided into various units but with a single intake. Trying to gain access to areas to establish whether main bonding was in place was like trying to gain access to the kremlin. In the end they never got back to me and I'm certain they just got someone in who did the job and didn't bother with bonding and other niceties.

Plenty of them over the years. Getting access, or details, is sometimes impossible. I'm talking about big buildings, some new. I find it's a case of noting 'no Access' on the certificate and detailing about lack of access on additional sheet.
On bigger jobs you can spend hours searching and asking. Hotels, football stadia, restaurants, shopping centres.....even an airport once.....had a 4hr induction for working in a shopping mall....how to duck a bleedin' plane on the runway but the H+S dipsticks had no switch room entry or details for electrical incomer and bonding.