Main Protective Bonding Conductor, Where To Connect

[WACKY1965]

We are testing a very large production plant with multiple Air Handling Systems with multiple ductings fed from each system, all systems are fed from the same sub-station package, would we have to connect to each ducting service to satisfy a "tick in the box" under services bonded, we have carried out a continuity test at various point on the system and they all are at the same potential to earth (below 0.02mohms)
Just wondering if anyone has come across this problem.

 

[Geoffsd]

Do you actually mean 0.02 Megaohms?

When you say 'to earth' do you mean the MET?

 

[Badged01]

Without knowing your exact circumstances and the practicality of doing it there is a bit of a stock answer on 'Bonding'.

Do an IR test between the 'metal' ducting and the MET (earth). If the reading is above 23KΩ then its not considered an extraneous-conductive part of the electrical installation and doesn't need bonding to the MET.

Less than 23KΩ bond it!

 

[guest119]

As I understand it, incoming services need main bondiing conductors at the incoming point.
In a domestic instance a heating flow and return are internal unless the boiler is in a lean to or outhouse in which case the f and r are incoming services.(aside from the frost stat issues)
That is no different from a ducting incomer from an AHU mounted externally. It can bring in a voltage.
The same can be said for a sprinkler incomer whether from street mains or from diesel/electric pumps, incoming service none the less.


Boydy

 

[Knobhead]

Without knowing your exact circumstances and the practicality of doing it there is a bit of a stock answer on 'Bonding'.

Do an IR test between the 'metal' ducting and the MET (earth). If the reading is above 23KΩ then its not considered an extraneous-conductive part of the electrical installation and doesn't need bonding to the MET.

Less than 23KΩ bond it!

So no consideration is to be given to static build up?

The value you give would build up a very good charge. A dusty environment and you’re looking at a big bang.

I do wish people wouldn’t try to apply stupid BS7671 rules of thumb to industrial situations. Air ducting should always be bonded, especially across inline joints.

 

[Engineer54]

So no consideration is to be given to static build up?

The value you give would build up a very good charge. A dusty environment and you’re looking at a big bang.

I do wish people wouldn’t try to apply stupid BS7671 rules of thumb to industrial situations. Air ducting should always be bonded, especially across inline joints.

Spot On!! I take it you mean flexible non metallic joints here

And anyone trying to check 23K ohms in an industrial set up will have a bloody hard job isolating all the parallel earths, of that i can assure you!!

 

[Silly Sausage]

Spot On!! I take it you mean flexible non metallic joints here

Well, during my thrilling evening tonight, I spotted that whilst perusing BS7430.

 

[Knobhead]

It’s even more fun to spent the night replacing explosion panels after some Pillock removed the earth bonds.

 

[Badged01]

So no consideration is to be given to static build up?

The value you give would build up a very good charge. A dusty environment and you’re looking at a big bang.

I do wish people wouldn’t try to apply stupid BS7671 rules of thumb to industrial situations. Air ducting should always be bonded, especially across inline joints.

The OP has alluded that the ducting is already 'earthed' but I guess what you are referring to is regs such as the likes of DSEAR, which specifically apply to atmospheres where explosions are likely, because of the environment being operated in. Yes, these give further requirements above and beyond BS7671 and open up a whole can of additional protection measures. Anti-static being just one of them required as part of the whole explosive risk reduction package!

I spent the greater part of my "career" designing on different top-tier COMAH sites with some very explosive environments. BS7671 in its various guises applied just the same as the DSEARs of this world and I don’t quite think the HSE would have thought of them as "stupid" and non-applicable in industry. Fortunately, I never crossed their path for failing to comply with BS7671 (or any other regs) so didn’t receive any enforcement notices potentially leading to production shutdown.

I would be hoping that the OP wasnt on here from such a risky explosive atmosphere (dusty or otherwise) where specific regs apply, asking for advice on design criteria. He would hopefully be CompEx trained as a minimum and know where to start but having seen some of the posting on the forum I could well be proved wrong ..…. yet again!!

 

[Engineer54]

Each commercial/industrial type AC ducting system from an AHU, should be bonded back to the MET, and bonded across (normally 2 flexible links diagonally opposed) any flexible joints within that air handlers ducting system. In fact the metal ducting (which can be quite extensive) from the AHU, will be isolated from the AHU body itself by a flexible joint.

 

[Knobhead]

The OP has alluded that the ducting is already 'earthed' but I guess what you are referring to is regs such as the likes of DSEAR, which specifically apply to atmospheres where explosions are likely, because of the environment being operated in. Yes, these give further requirements above and beyond BS7671 and open up a whole can of additional protection measures. Anti-static being just one of them required as part of the whole explosive risk reduction package!

I spent the greater part of my "career" designing on different top-tier COMAH sites with some very explosive environments. BS7671 in its various guises applied just the same as the DSEARs of this world and I don’t quite think the HSE would have thought of them as "stupid" and non-applicable in industry. Fortunately, I never crossed their path for failing to comply with BS7671 (or any other regs) so didn’t receive any enforcement notices potentially leading to production shutdown.

I would be hoping that the OP wasnt on here from such a risky explosive atmosphere (dusty or otherwise) where specific regs apply, asking for advice on design criteria. He would hopefully be CompEx trained as a minimum and know where to start but having seen some of the posting on the forum I could well be proved wrong ..…. yet again!!

One of the dangers often overlooked is the fact that some fairly innocuous dusts when airborne become flammable.

I spent most of my working life dealing with explosive gases and pulverised coal. I’ve had to deal with more duct explosions than I care to remember. But there again the plants were designed to handle internal explosions.

 

[Guest111]

One of the dangers often overlooked is the fact that some fairly innocuous dusts when airborne become flammable.

I spent most of my working life dealing with explosive gases and pulverised coal. I’ve had to deal with more duct explosions than I care to remember. But there again the plants were designed to handle internal explosions.

Some years ago I was working in the one of the factory's belonging to a well known curry maker,the design of the new plant was a lash up from start to finish.It was discovered that the washdown coating in the frying room was actually a combustible material,so the fire authority ordered it to be replaced,this meant relocating all the equipment to keep production going,the batch mix plant was installed by their own people who were brought over from India as they didn't want any risk of spys getting in.Anyway a fault occurred on a panel and they had no choice but to take me into the mixing room,the scene was beyond belief,all the pipework was 100mm steel,but at several points this was joined with flexible nylon (like hoover tube) and not an earth bond in sight!All the while the powdered spices were being pumped merrily along these pipes,there had been several complaints of staff getting static shocks off this setup,some quite severe.All hell broke loose when I decided to circumvent the normal procedure and went straight to the plant manager,who happened to be one of the owners,After explaining to him that the way things were he could quite likely be running the first curry factory in space the whole lot was handed to me and my team for remedial works,several hundred meters of 6mm later and the plant was safe and there was no more static shocks.

 

[Silly Sausage]

Good stuff Phil!
More importantly though, did you get any recipes???

 

[Guest111]

Good stuff Phil!
More importantly though, did you get any recipes???

I was sick of eating the stuff,and the smell got everywhere,When I left the wife washed my boilersuit and put it away in the cupboard,months later when I needed it again you could still smell the curry,no matter how many times they were washed it took ages to get the smell out.