Lightning protection testing

[Kate]

Hi all,
was hoping someone could explain to me how I test/verify the lightning protection bonding.

im generally a domestic electrician as I work for myself, and I've never come across a property with this type of bonding. I'm subcontracting to a local electrician and do all his testing for him, this property is a 2million pound mansion new build, 3 phase, 3 storey....basically it's huge! From my understanding a specialist company was brought in to install the lightning protection but I have to include it in my test results.
The only way I can think of doing it is to make a trailing lead from one end up to the other and test between. But that's going to be well over 50m. Is there an easier way? I do not want to get up on the roof of this place.

Part of me is hoping/wondering if the electrician is taking the ****. I am extremely gullible and have fallen for many jokes. Shouldn't the company who installed it have certificated??

Any help would be appreciated, I think I'm back there testing this Thursday

 

[telectrix]

the lightning conductor must be connected to the MET. this can usually be checked visually.

 

[Kate]

You won't believe how many cables are connected at the mains, there isn't a specific MET, as all DB's are wired from a 3phase DB in the plant room at the main incomer. There's 3 DB's just in the main house; one on each floor, then there's a DB in the barn, 2 holiday apartments with a DB each, a plant room DB for all heating, stables has a DB, another DB in the transformer room (haven't seen this yet) and a DB in an out building supplying the back garden electrics. Some DB's have a 2nd separate earth running to them. There is no chance of knowing from a visual check which earth is which.

 

[ackbarthestar]

The lightening protection system should be covered and maintained by the who installed it.
Dependent upon the position of the lighting rods, electrodes and distance from the MET will depend on whether or not it should be connected to the MET.
I had to seek advice on this one and was told by the lightning company that due to the position of the various structures, electrodes that in this particular case it shouldn't be connected to the MET.
You are looking at something around 10 Ohms for the electrode resistance and if you want to test the continuity of the main protective bonding then a roll of 4mm2 will do the job.

 

[Kate]

Thank you, so my best case scenario the guy was winding me up and the installer should be certificating.
Worst case, if I had to get up there I was right in how I thought it should be done and now know to look for 10 ohms reading.

 

[MDJ]

When a lightning conductor is installed by a specialist they should provide the customer with a test certificate of the ohm readings and results, you should see at least one green and yellow at or very close to a pit where the tape enters the ground, on some systems several may be in, however if your unsure, get a wander lead and test to see if a connection to earth is evident, if there isn't evidence of a connection then just report your findings.

 

[Kate]

MDJ electrical in Gloucester, sounds fimiliar!
Thanks everyone, I'm going to check with the boss to see if the electrician was just winding me up, but if I have got to test it at least now I know for sure how to! Can save me some of my dignity!

 

[MarkieSparkie]

Hi Kate, Lightning protection systems for buildings and structures are covered by BS EN 62305 and the specialist who installed the system should have certified it as conforming to that standard. Your only duties in relation to the lightning protection system as the general electrician certifying the main electrical installation, are ensure that the certification in respect of BS EN 62305 exists and to confirm that the lightning protection system is connected to the Main Earth Terminal (MET) of the electrical installation. From your description one would expect the MET to be located in the plant room close to the 3 phase DB and incoming supply.

 

[Engineer54]

As i have read the OP, you have only been asked to test/verify the bonding connection between the LP system and the MET, which should be an easy task. You haven't been asked to test the LP system as a whole or in part. Test this bonding conductor as a TT system at the main intake position, as it will be solidly connected to the overall LP system. As long as you have an overall Ra value of 10 ohms, it's compliant. In reality it will be much lower than 10 ohms, depending on how many down conductors/rod positions have been installed on this large house/mansion. ...lol!!


The MET is where the main DNO supply (service cut-out/intake position) comes into the property. The other DB's you talk about, will be Sub-main distributions from the main intake position and their main earthing points will be deemed as EMT's... eg, Ze value is only taken at the MET, and Zs (Zdb) values are taken at the EMT's. ...!!
I'm assuming that none of these other buildings have a separate DNO service cut-outs supplying them...


Never seen a LP system of any size, that has NOT been connected to the protected buildings MET!!

 

[Kate]

I've never actually seen a lightning protection of any size! Yes you have it, each separate DB's Ze reading will actually be a Zs reading. All circuits in 'DB/1' in the plant room is a distribution circuit to another DB. So it all ties in.

There's only temporary single phase electric at the minute from a different property and it enters the house NOT the plant room. This is purely for the site office, some kettles and battery chargers. MEB are installing the three phase supply tomorrow so maybe it will be more obvious then, and hopefully not TT!

I just physically don't know where to get the reading from, do I have to get up on the roof?
Ive always R1+R2 my circuits. And in a normal house the main gas and water are close-ish to the mains.

 

[Kate]

Oh and yes all I have to do is verify not record a reading. It's for a domestic, niceic installation certificate. I'm pretty sure it just asks bonding cable material, size and then you have to tick the verified box.

 

[Engineer54]

The bonding cable from the LP system, will be from one of the earth electrode positions connected to one or more of the down conductors (depending on the earth electrode system used). So no, you don't have to get up on the roof, the LP bonding cable should already be the MET, exactly the same as should be the water/gas etc, bonding cables....

The test is exactly the same as for a TT system, loop test with the LP bonding cable.

 

[Guest55]

Never seen a LP system of any size, that has NOT been connected to the protected buildings MET!!

agreed.
the church im working on now has 5 spire lightning tapes , all terminating to their own earth rod ,
all linked together with a whopping 95mm earth cable which commences at the MET.

test it my arse lol , a poke around with a screwdriver will suffice.
;-)

 

[Engineer54]

agreed.
the church im working on now has 5 spire lightning tapes , all terminating to their own earth rod ,
all linked together with a whopping 95mm earth cable which commences at the MET.

test it my arse lol , a poke around with a screwdriver will suffice.
;-)

I hope it doesn't commence at the MET, that connection should only be a bond to the LP system. Haven't seen a 95mm on any LP system, normally it'll be bare 50mm or 70mm hard drawn copper cable linking the electrodes, only the bonding cable would be insulated. That's hard drawn stuff, isn't anywhere near as flexible as the normal soft copper cable.

If all the electrodes are linked by this 95mm cable, i take it there is only one down conductor with a test point installed??

Well Kate's OP did state ''test/verify'' !! lol!!

 

[Kate]

Definitely only verify, thought I had to do a test to do that screwdriver poke sounds good! Lol