Surprised by todays readings

[jackhammerJIM]

Went to look at wiring a biomass boiler today ...

boiler and buffer tank located in a breeze block out building sat on concrete pad .

PME earthing system , existing supply to outbuilding in 25mm 3core swa .

ALL the pipework was in place (copper and steel pipe) connecting buffer tank and boiler .

Mains water also in place in nice blue plastic pipe .

Grabbed the wander lead and tester out of the van to test if the metal pipework was extraneous
and low and behold got a dead short . also dead short from unistrut on walls to earth (which is bizarre as
it is not in contact with anything metal) . :rolleyes4:

So does concrete conduct electricity ? this is the only plausible answer .

i meggared between the concrete pad and earth at 500v with 32Mo resistance , so not conducting well !.

the buffer tank is 3000 litre and has a large metal footprint sat on the concrete pad .


im going to bond the pipework but am gobsmacked as to how it has become an extraneous part .



your thoughts on this please .

 

[yellowvanman]

When you say 'dead short' was that on the insulation resistance range?

On my tester (Fluke) anything below 20K is shown as '0' on the insulation test range. Change to continuity test to see if it is really a dead short!

 

[Plonker 3]

Were the walls damp?

 

[jackhammerJIM]

yes on insulation resistance at 500v and 250v , hmmmm its a fluke 1653b aswell .

didnt know that yellowvanman , was showing 0.00 Mo but in the bottom right corner

of the tester shows the voltage gone through i think ? this was coming back as 1 volt ?

so im not sure whats going on with that ?

Changed over to continuity but cant seem to remember what the reading was , i will retest

tomoro and take my old megger .


i did notice the walls were damp DILLB but the pipe clips attached to the strut are insulated .


If it is below 20k it needs bonding

 

[Marvo]

If there's copper and steel pipework and I'm guessing mostly metallic boiler there might be motivation to bond to reduce corrosion regardless of whether the components test as extraneous conductive or just exposed conductive.

 

[jackhammerJIM]

wouldnt class them as an exposed conductive part marvo .

will do some more testing tomoro but will likely be bonding .

cant get my head around the earth path though .

 

[jaypp]

if there was steel in the concrete base that at edge was in contact to earth, maybe fixing on boiler touches steel mesh resulting in earth path to pipes?

 

[Lucien Nunes]

You mention the mains water was in plastic pipe but what about other outgoing pipe connections to the building it serves?

Moisture-laden concrete is conductive enough that if (say) a rawlbolt holding the tank framework is touching a rebar grid in the slab it could give you quite a low reading, due to the large area of metal in intimate contact with the concrete. You probably won't get any reading by probing the surface because the contact area is so tiny and the screed will probably be drier anyway.

 

[Engineer54]

wouldnt class them as an exposed conductive part marvo .

will do some more testing tomoro but will likely be bonding .

cant get my head around the earth path though .

Think about what a Ufer earth is, and you will see that concrete (depending on it's make-up) that incorporates a metal rebar grid can be a good conductor, especially when in contact with perpetually damp or wet ground....

 

[Guest111]

Concrete never actually dries out completely and is one of the best floor surfaces for conducting electricity which is one of the reasons they often put rubber matting in switch rooms,its actually one of the worst things you could stand on if you happen to get an electric shock.

 

[DPG]

Concrete never actually dries out completely and is one of the best floor surfaces for conducting electricity which is one of the reasons they often put rubber matting in switch rooms,its actually one of the worst things you could stand on if you happen to get an electric shock.

2nd worst, the worst thing to stand on would be one of Eng's earth rods! Daz

 

[jackhammerJIM]

You mention the mains water was in plastic pipe but what about other outgoing pipe connections to the building it serves?

hello Lucien . all outgoing district heating pipes are insulated plastic .

I see the logic behind the large surface area of the buffer tank in contact with the concrete .
Todays test with the low ohm meter came back at 1100 ohms .

I have bonded the pipework and may suggest a rubber matting or insulator on the next jobs .

:cool3:thankyou for everyones help .

 

[Lilyrose08]

I didn't think you could transport PME supply I have a few times as there is no registration to say you can't a load of old ###### to me.

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Regulation I meant predictive text for ya

 

[jaypp]

this is the kind of thing i joined for, can't put a price on this info!
also joined for this!....................

2nd worst, the worst thing to stand on would be one of Eng's earth rods! Daz

 

[Engineer54]

I didn't think you could transport PME supply I have a few times as there is no registration to say you can't a load of old ###### to me.

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Regulation I meant predictive text for ya

What are you actually trying to say here??