Bonding to commercial properties on district heating

[smee]

Hello all, first post so apologies if it’s in the wrong forum.

I wonder if someone could help me to determine if the bonding on a commercial district heating system is correct.

The gas boilers are situated in their own boiler house approximately 1000 meters away from a block of 12 storey flats; the heating and hot water to the flats are fed by underground steel district heating pipework; which then feed each flat by steel risers, entering each flat with a flow/return pipework with isolation valves fitted on each house entry, (Inside the property).

There is currently a phase of work being done to replace old Elson storage heating tanks with heat exchangers and alteration of copper pipework to the heat exchanger; the programme also includes removing 2 motorised valves and replacing the old programmer for a newer model which operates a valve on the heat exchanger to provide heating when required.
No additional wiring is being installed so a minor works cert is being issued for each property stating that all bonding is ok and the consumerunit is to the 17[SUP]th[/SUP] edition.

However; a dispute has occurred because I have said the steel pipework on the flow and return should be bonded in 10mm and link to the flow or return; but others are saying, not so because it is bonded in the boiler house which I assume would be a dead test as the steel pipework goes into the ground and is earthed, plus each property is not protected because no bonding from the consumer unit is fitted.

They have also said that on testing and the reading is below a certain level then the bonding is not required. This is the stumbling block, it does seem to me that a lot of steel in the block of flats are not bonded?

The water mains entering each property are bonded so I think the flow and return should also be bonded to each property.

Am I right or wrong?

I would really appreciate some advice as this could be a massive issue if I am right.

Thanks all.

 

[Engineer54]

I agree with you, any extraneous metalwork entering a flat should be bonded to that flats MET (EMT). Whether it's been bonded as it enters the building or not!! The same should apply at the boiler house installation, both the flow and return pipes should be bonded as it leaves the building, to the Buildings MET!!

That heating system must be the most inefficient i've heard of!! Why have they located the boiler house, a kilometer away from the building it supplies?? lol!!

 

[Sintra]

HT I have undeleted this one as I think it is the only one left. I have deleted a few plus pm'd the OP about duplicate threads.

 

[Knobhead]

Contact the district heating company. There’s something niggling the back of my mind about this. The pipes underground are insulated steel. You could set up circulating currents through the system. It’s not like a normal service pipe entering a building.

 

[High Tower]

HT I have undeleted this one as I think it is the only one left. I have deleted a few plus pm'd the OP about duplicate threads.

Happy days!, i think i was fiddling with me buttons while you were sorting this.

 

[Sintra]

Happy days!, i think i was fiddling with me buttons while you were sorting this.

As long as that's all you were fiddling with. :46:

 

[Knobhead]

Whatever keeps you amused in the back office :artist:

 

[Engineer54]

Contact the district heating company. There’s something niggling the back of my mind about this. The pipes underground are insulated steel. You could set up circulating currents through the system. It’s not like a normal service pipe entering a building.

Nothing different to a boiler house supplying several buildings on a project, such as we have on my present project. We bond the pipes as they enter and leave each building, as we do with any other service that enters and leaves a building, be they wrapped insulated services or not.


Having said that, if circulating currents are found in steel pipes, then corrosion will quickly follow at joints etc, so would need to be subject to passive cathodic protection... Which in effect is a made connection to copper, magnesium or similar, earth rods...

 

[Knobhead]

True but you can ensure all intakes are earthed. District heating isn't quite as organised. Nottingham is total chaos!

 

[smee]

I agree with you, any extraneous metalwork entering a flat should be bonded to that flats MET (EMT). Whether it's been bonded as it enters the building or not!! The same should apply at the boiler house installation, both the flow and return pipes should be bonded as it leaves the building, to the Buildings MET!!

That heating system must be the most inefficient i've heard of!! Why have they located the boiler house, a kilometer away from the building it supplies?? lol!!

Lol yea sorry about thats is more like 500m. The heatings system is larger than a 1 storey flat but tried to make it as simple as possible to get an answer.

 

[smee]

Can I apologise for entering my question on so many threads, I got an email saying my messages has been removed due to duplication so I entered it again thinkng that all had been deleted.

Many thaks for all your replies, I am more gas related than electrical so thats why I posted the question, the heating system is more complex tan I stated but listing all the issues would ave confused the question so I tried to keep to simple.
One more question:

Would a meter test be carried out on completion of a minor elec cert, to determin if the bonding readings were within regs?

 

[Engineer54]

Would a meter test be carried out on completion of a minor elec cert, to determin if the bonding readings were within regs?​

​

Where a metallic service enters a building an IR test should always be conducted from the MET of that building to the metallic service pipe or whatever. If a value of 22/23000 ohms or over is seen, then no bonding is required!!