One for the pro's

[ChrisR]

I fit central heating, boilers , and do Landlords Gas Safety Checks.

I am obliged to record a missing earth bond on a gas main incomer. I found one the other day where the clip had been removed, the pipe painted an the clip replaced! Even where things aren't as blatant, shouldn't I be saying that all earth bonding needs to be tested by a sparks?

Similarly, people are impressed with cross bonding loops beween all the 6 or 7 pipes going into the bottom of a combi. Even if half the piping is plastic elsewhere! Similar situation in bathrooms.

So, briefly, is there any point in my "OKing" a bit of earth bond, or indeed fitting it to a bit of pipe I haven't necessarily any knowledge of beyond the floorboards?

How do you check the effectiveness of bonding?

 

[Gees]

The only way to do it properly is with an earth loop impedance tester. Using a special lead that has the earth lead connected to a test prod. You can then plug it into a socket and test each earth in turn
http://www.bis.fm/bis/products/Avo_Megger_LT5.asp
as far as i know this is the only way to be Sure...
I must admit that lots of earth bondings look good but if the whole system is copper dont you need only one GOOD earth???

 

[breezer]

I must admit that lots of earth bondings look good but if the whole system is copper dont you need only one GOOD earth???

no, because there may be a palstic pipe somewhere unkown to you. better safe than sorry

The regulations are concerned with the continuity of the earth as well as the current carrying capacity, although say a 15mm pipe is 15mm, it can not carry as much current as a 6mm cable can, and what if, there was a fault, suppose one of the soldered joints melted, apart from no continuity there would be water every where

 

[Gees]

Breezer.. Have you ever tried to melt the solder on a joint that has water in it? It cant be done mate. yes I agree abt. the posibility of a plastic pipe but what if you are SURE its all copper? IE you installed it..!!?

 

[breezer]

Gees, good point.

for earth bonding see this

although the above is about bathrooms, you should cross bond almost everything. the main incoming water and gas pipes should be bonded as they enter the building (on the end users side), but the regs do not allow you to use the pipework as an earth conductor

 

[spark]

As far as the regs are concerned, in general there aren't any specific requirements for any supplementary bonding to be installed, provided that the conditions for automatic disconnection (in the event of a fault) are met, apart from what are defined as 'special locations', only one of which you are likely to encounter regularly as a heating engineer and that is bathrooms (well technically it's 'locations containing a bath or shower'). Generally if you ensure that the main equipotential bonding is in place and is mechanically and electrically sound (if it's been painted under the clamp it will almost certainly not be) and the bathroom has been bonded in accordance with BS7671:2001 (basically all metalic parts joined together with a conductor not less than 4sq.mm), then you're unlikely to have a problem. Main equipotential bonding should create an earthed equipotential 'zone' (the dwelling basicly), meaning that all exposed-conductive-parts ( basicly metallic parts of the electrical installation) and extraneous-conductive-parts (basicly metallic parts which are not part of the electrical installation such as pipework) within the installation (the building) are connected to the main earthing terminal. The supplementary bonding, as applied for example in bathrooms, is only required where it is necessary to ensure absolutely that all the metallic parts within that simaltaneously-accessible zone are to the same potential.

With regard to the plastic pipe issue, an extraneous conductive part as defined by the reg's is 'a conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation'. This is where you have a grey area and it's down to the descretion of those concerned with certifying the electrical or gas installation. A metallic window frame for example is not liable to introduce a potential (basicly meaning it's not liable to become live). In the case of a bathroom, you may have a metallic towel rail which is fed by two plastic pipes; the question is not just 'is it bonded?', but instead the question should be 'can it be described as an extraneous-conductive-part?'. I would argue that in most instances where it is supplied solely by plastic pipes then the answer is probably going to be no, in which case there is no need to bond it. If however a potential is likely to arise beteen that towel rail and another metallic part within that zone (if it has copper pipes for example), then it should certasinly be classed as an extraneous-conductive-part, and as such should be bonded.

Anyway...(deep breath!), coming back to your questions. People who are impressed to see cross bonding loops aross the boiler are almost certainly a little misguided. The chances are that if you removed those cross bonds between the pipes and tested between the pipes with a low-reading ohmmeter, the reading would probably be less than 0.05 ohms; so nothing has really been acheived by doing it, the pipes will proably already be at the same potential. The pipes may be connected together, but are they connected to the main earth terminal in any way? Maybe, maybe not but all that cross bonding is pointless unless it's actually doing a job. The best way to check if pipework is connected to the main earth terminal is with a low reading ohmmeter. Take a length of earth cable (4sq.mm will do fine), use your low reading ohmeter to measure it's resistance (remember it!), connect it to the main earth terminal and carry out resistance reading between to other endof your earth cable and your pipe. It can be easier to just carry a part used drum of 4mm earth around with you and just unroll it and roll it back on as you require, depending on how far the pipe is from the main earth terminal.

I wouldn't have thought though that would be within the scope of certifying a gas installation? I always thought that if the mainequipotential bonding conductor is all correct and present (present is one thing, but correct is another issue!) then you would have met your obligation of certifying the gas installation? Hope this has answered your questions and I may have made a few errors whilst typing so if you need any of my points clarified or if you need reg numbers let me know.

 

[corgiman]

I must admit that lots of earth bondings look good but if the whole system is copper dont you need only one GOOD earth???

no, because there may be a palstic pipe somewhere unkown to you. better safe than sorry

The regulations are concerned with the continuity of the earth as well as the current carrying capacity, although say a 15mm pipe is 15mm, it can not carry as much current as a 6mm cable can, and what if, there was a fault, suppose one of the soldered joints melted, apart from no continuity there would be water every where

to quote breezer, I am not and electrcian, but when youe see a earth to a gas pipe you had better hope to hell that the pipe has been installed in metal, copper, steel, or you will have more problems that just a lack of earth bonding

and as gee said no way on earth a soldered joint can melt unless the house was on fire and water would not reach high enough temp to melt it.

 

[ChrisR]

Thanks y'all, to "spark" particularly - I know how long it takes to type this stuff! Useful material I'll read again and digest later.

I think you're saying that if say you were doing a test on a whole house's instalation you'd do a PSCC test on any bonding you saw. Which means that if I do any bonding, I ought to be saying that it should be tested.

Some Reg Gas Installers always use one of:
Your bonding is missing - get it done by a niceic man, or
I can't test your bonding - get it tested by a niceic man
!

Supplementary Q - which I think you've answered: all radiators need their own earth bond, yes? Whether it's plastic pipe or not? Looks that way.
This is important to me at the mo because I'm quoting a semi-commercial job where I want to make sure things are done right. I must admit that in most domestic situations there's no way I'm going to bond all the rads!

 

[spark]

Not quite, a PSCC test is a live test which measures the potential magnitude of fault current that would flow between live and neutral in the event of a short circuit (can also be used to measure the earth fault loop impedance or calculate the PFC ). Tests for continuity should be done using a low-reading ohmeter. Low reading ohmeters are generally another function on an insulation resistance tester (also called a megger). This type of instrument is a 'dead' tester in that it does not require a circuit to be live to use it; it measures the circuit while it is dead. I think you may be confusing the PSCC test because someone mentioned using a loop tester to check the bonding. The auxillary clip on a loop tester is to measure the resistance of any paralell earth paths when carrying out a loop impedance tests. I would not recommend that you use a loop tester to carry out tests for the continuity of main equipotential bonding conductors because in the event that there is no bonding, then the pipework will become live for the duration of the test. This can potentially be very dangerous. The link refered to by Gees says that the instrument measures external earth continuity, this is what is known as the Ze, or extrfernal loop impedance and is totally different to continuity of bonding conductors.

Generally radiators do need to be connected to earth, but usually connecting an adequte main-equipotential-bonding conductor to the intake at the gas and water will satisfy this requirement. So no, they shouldn't each need their own earth bond.

I can go more in depth if you want, but I don't want to cause any unnecessary confusion.