Bucket of water or not?!?!

[Trulyshocking]

Hi,
I'm lucky enough to have been charged with the responsibility for doing all the LPS testing at an MOD base that I work at :frown2:.
Having done the testing, I've had to fail a number of earth electrodes as they measure too high a resistance (in other words above the number of electrodes on the system x 10 ohms). The site includes explosive storage facilities so I want to get it right!!! The question i have is whether or not it is acceptable to douse the temporary test probes (am using a Fluke 1654B) with water to get a better reading. Obviously this cant be applied to the electrode under test!!! The surrounding ground is chalk which doesn't help, but am keen to avoid causing lots of cost in upgrading the buried earth ring if necessary!!
Cheers

 

[mayfair]

First Q that spring to mind is have you already tried this and did it improve the readings?

 

[Engineer54]

First off, you shouldn't be professionally testing a Lightning Protection system with a Fluke multi function tester!! More so, when your dealing with an explosive storage facility!!! You will need a purpose built Earth tester, be it a 3 or 4 pole test kit or a clamp on test kit....neither are cheap bits of kit. You will also need a good low ohm test kit like a ductor tester, to test joints and connection resistances.... (very important)

So.... tell us what is the ground earth network on your installation, individually connected ground rods from down conductors, or a linked rod earth ring??

 

[mayfair]

Missed the lightning bit m8 well spotted , reading to quick ...............or the wine.QUOTE=Engineer54;308825]First off, you shouldn't be professionally testing a Lightning Protection system with a Fluke multi function tester!! More so, when your dealing with an explosive storage facility!!! You will need a purpose built Earth tester, be it a 3 or 4 pole test kit or a clamp on test kit....neither are cheap bits of kit. You will also need a good low ohm test kit like a ductor tester, to test joints and connection resistances....

So.... tell us what is the ground earth network on your installation, individually connected ground rods from down conductors, or a linked rod earth ring??[/QUOTE]

 

[Trulyshocking]

The 1654B has a dedicated earth resistance function, and we have the specialized 3 lead kit to ensure correct distances of test probes!! I also have a good quality low reading ohm meter for the job (which has also failed many parts of the LPS installation!!)
There are various individual electrode per down conductor and buried earth ring configurations within the site. Sadly it's been neglected by various contractors over the years, meaning that i seem to have uncovered a can of worms now!!! The problem is, I know this is a specialized field but typical MOD wont pay for the relevant courses. Managed to get hold of an LPS training CD ROM which suggested dousing the relatively short temporary test probes with water to attain a better result!! Thought I would check to see if this is an accepted industry technique??!! Also swallowed the BS on LPS, but frankly there's naff all on maintenance and testing within it...
Haven't tried the water technique yet....

 

[Engineer54]

TS,

Correct, the inspection and testing of Lightning Protection systems is somewhat a specialised system. Now the thing is, that your fluke multi function meter is fine for testing say domestic commercial TT rods etc, but it is doubtful if it's % accuracy is low enough for this application, which should be in the order of 1% to 2%. I personally wouldn't use such a test kit for L/P systems. Same goes for the low ohm meter, as a minimum, it should be reading in the milliOhm ranges...


The thing is, with the differences of individual down conductor rods and a ground earth ring connected rod system, is that the ring connected rods should be cad-welded (exothermic weld) to the bare ring conductor (normally min 50mm hard drawn copper stranded cable)!! Usually there will will 2 test point positions for the building diagonally opposed, where the cable to rod connections will be of the bolted type. In other words the individual rods cannot be tested, they are tested in 2 sections. The down conductors from the protected building are also without test points apart from the two connected to the 2 test points.

What your describing is a mixture of both types of system, which is not a normal situation, and makes testing that much more involved. Do you have any previous documentation for this L/P system to guide you???

Both systems should have a maximum overall Ra of 10 ohms.


By the way, Yes it is common practise to soak the areas where the short test spikes are positioned, to help give a the test instruments injection current a decent path to read from...


The actual installed rods of the L/P system may need chemical treating, with specialised treatments to reduce the surrounding ground resistance to rods, but that's another detailed subject at this stage of the process...

 

[SW1970]

Engineer54, Fluke 1654B has milliohm earth resistance spec:

Range/Resolution:	200 Ω/0.1 Ω
Accuracy:	±(2% + 5 digits)
Range/Resolution:	2000 Ω/1 Ω
Accuracy:	±(3.5% + 10 digits)
Frequency:	128 Hz
Compliance Voltage:	+25 V

Seems ok.

 

[Trulyshocking]

Duly noted and appreciated E54!

To put it into context, I have no drawings for any of the 30+ storage and process buildings on site and only 1 set of previous test results which may actually have been filled out by chimp! Having looked at a recent set of results from a contractor which showed an electrode to earth reading of 0.01 ohms I took them over to retest alongside me and found they weren't even aware there had to be a set distance between test probes!! The actual reading was closer to 6 ohms!

I will be pushing for the appropriate test equipment and some training in the field as well. Meantime, if dousing the individual failed electrodes doesn't work (buried earth ring systems with designated test points all pass easily), I will probably go the Bentonite route so as to avoid changing the design of the system which I'm not prepared to do. Alternatively I guess I could just fiddle the results like everyone else has!! Just kidding!

 

[Engineer54]

Engineer54, Fluke 1654B has milliohm earth resistance spec:

Range/Resolution:	200 Ω/0.1 Ω
Accuracy:	±(2% + 5 digits)
Range/Resolution:	2000 Ω/1 Ω
Accuracy:	±(3.5% + 10 digits)
Frequency:	128 Hz
Compliance Voltage:	+25 V

Seems ok.

On paper, your right it does look impressive. I'm sure that it is more than acceptable in domestic and small commercial applications, when conditions are, lets say favourable!! But maybe be prone to interference when your dealing with strings of rods and/or when there is other buried electrical cables/services and the like in the area.

Noise elimination and voltage disturbance nulling are important features of any Earth Tester. You really need a selectable range of test frequencies. You also will often need the facility to conduct 4 point/pole tests, when needing to test very low earth resistances.

Not trying to be elitist here, but a good earth proprietary tester can often cost more than the multi function testers, so it's doubtful if a single range on such an instrument, is going to be able to compete with a proprietary earth tester..

Sorry my bad, i meant to say micro ohms ranges, which is what a ductor tester is basically used to measure. It is basically a connection/contact proving instrument. An L/P system stands or falls on it's low resistance path to earth with minimal to no damage to the L/P installation or the building it's protecting...

 

[Engineer54]

Duly noted and appreciated E54!

To put it into context, I have no drawings for any of the 30+ storage and process buildings on site and only 1 set of previous test results which may actually have been filled out by chimp! Having looked at a recent set of results from a contractor which showed an electrode to earth reading of 0.01 ohms I took them over to retest alongside me and found they weren't even aware there had to be a set distance between test probes!! The actual reading was closer to 6 ohms!

I will be pushing for the appropriate test equipment and some training in the field as well. Meantime, if dousing the individual failed electrodes doesn't work (buried earth ring systems with designated test points all pass easily), I will probably go the Bentonite route so as to avoid changing the design of the system which I'm not prepared to do. Alternatively I guess I could just fiddle the results like everyone else has!! Just kidding!

TS,

Yes, ...I know what you mean, it's a sad fact that many electricians don't have much of a clue when it comes to out of the normal testing procedures and requirements. They are often thrown in to conduct these tests, by just as clueless employers without any guidance or training. This is one of IQs observations, on test sheets that he's come accross when he has his testing hat on at work...lol!!!

Unfortunately, ....Bentonite and similar rod placement enhancers can only be used when placing new or replacement rods. They also can only be used when rod bore holes have been made. the bores are filled with the bentonite slurry and the rods then dropped into the bores. What you may need is propriety chemical ground enhancers, which will need to be applied at regular durations. Some are mildly corrosive to the electrode in there application, but no-where near as corrosive as the old treatments of yesteryear...lol!!!


Oh, ....and don't believe the old tales about peeing on the rod will lower the Ra, ...It Doesn't!! Not unless you can pee enough to soak a decent area around the rod, and down over a metre, ...even then i doubt it's any better than pouring water over the rod position...lol!!!

 

[adiewadie247]

Surely dousing the rods is a form of fiddling the results. Do you not need to test the worst case scenario, ie. dry ground and allow for corrosion.

 

[ringer]

Engineer54, Fluke 1654B has milliohm earth resistance spec:

Range/Resolution:	200 Ω/0.1 Ω
Accuracy:	±(2% + 5 digits)
Range/Resolution:	2000 Ω/1 Ω
Accuracy:	±(3.5% + 10 digits)
Frequency:	128 Hz
Compliance Voltage:	+25 V

Seems ok.

According to this spec the smallest reading possible on the tester would be 0.1 ohms and the accuracy is +/- 2%
That is not milliohm accuracy, unless I am misunderstanding the spec.
And E54 now states that micro-ohm capability is required.

 

[HandySparks]

Surely dousing the rods is a form of fiddling the results. Do you not need to test the worst case scenario, ie. dry ground and allow for corrosion.

They're talking about dousing the temporary test electrodes, not the system under test.