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Zdb

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Just been read through this and it says:

How to determine if it’s an extraneous-conductive-part

For this, a simple measurement is undertaken. This is done by testing the resistance between the suspected extraneous-conductive-part and the MET or the nearest known connection to Earth, such as the circuit protective conductor (CPC) of a local circuit (so long as its connection to Earth has been verified).

Published guidance by the IET suggests that if the ohmic value between the suspected extraneous part and Earth is greater than 22 kΩ, then the part in question is considered as unable to introduce a shock risk and, as such, won’t require bonding.

To measure this sort of reading will require the use of the insulation resistance testing range (MΩ) where 22 kΩ will usually be displayed as 0.02 MΩ.

If the test reading indicates anything greater than 0.03 MΩ, then it may be concluded that the item in question isn’t likely to introduce a dangerous potential and therefore wouldn’t require bonding.


So does this mean that using a MFT set to insulation resistance, I can connect one lead to some cable basket and the other to a nearby socket using a plug (R2) adapter instead of the MET?
 
So does this mean that using a MFT set to insulation resistance, I can connect one lead to some cable basket and the other to a nearby socket using a plug (R2) adapter instead of the MET?


yes as longas you have verified that the socket earth is connected back to earth . this may be done with a simple R1 + R2.
 
Just been read through this and it says:

How to determine if it’s an extraneous-conductive-part

For this, a simple measurement is undertaken. This is done by testing the resistance between the suspected extraneous-conductive-part and the MET or the nearest known connection to Earth, such as the circuit protective conductor (CPC) of a local circuit (so long as its connection to Earth has been verified).

Published guidance by the IET suggests that if the ohmic value between the suspected extraneous part and Earth is greater than 22 kΩ, then the part in question is considered as unable to introduce a shock risk and, as such, won’t require bonding.

To measure this sort of reading will require the use of the insulation resistance testing range (MΩ) where 22 kΩ will usually be displayed as 0.02 MΩ.

If the test reading indicates anything greater than 0.03 MΩ, then it may be concluded that the item in question isn’t likely to introduce a dangerous potential and therefore wouldn’t require bonding.


So does this mean that using a MFT set to insulation resistance, I can connect one lead to some cable basket and the other to a nearby socket using a plug (R2) adapter instead of the MET?
No not really as all parallel paths would need to be removed. The test should be from the means of earthing or connection to the earthing conductor with all possible other connections to earth via different routes removed
 
No not really as all parallel paths would need to be removed. The test should be from the means of earthing or connection to the earthing conductor with all possible other connections to earth via different routes removed
Agree,near impossible in an energised installation with the parallel earths,& you really wouldn’t want to disconnect All those earths would you.
So if you think it needs Main bonding then ,Bond it.
 
Surely removing those parallel earth paths would for when testing Ze, for example.

In this case testing is to see whether a piece of metal is an extraneous conductive part, or is just a piece of metal. Those potential parallel earth paths, may have a deciding factor on whether it needs bounding or not.

The test procedure, as I've known it, is that highlighted in red by @Zdb. Otherwise, when the parallel earths, such as circuit CPC's are reconnected, that might alter the value obtained, and the requirement or not to bond.
 
This test is often almost impossible in practice. A copper pipe for example is quite likely to be mechanically connected to another extraneous part such as a gas service (via the boiler)or structural steel (from fixings). In reality the test is only conclusive where it can be visually ascertained that the metallic part is completely independent of other possible extraneous parts.
 
Surely removing those parallel earth paths would for when testing Ze, for example.

In this case testing is to see whether a piece of metal is an extraneous conductive part, or is just a piece of metal. Those potential parallel earth paths, may have a deciding factor on whether it needs bounding or not.

The test procedure, as I've known it, is that highlighted in red by @Zdb. Otherwise, when the parallel earths, such as circuit CPC's are reconnected, that might alter the value obtained, and the requirement or not to bond.
It requires parallel paths removed,for example the cpc connected to the boiler earthing which in turn is in contact with the copper gas pipe. If you do not disconnect the cpc if testing that the gas pipe requires bonding or it’s just an isolated piece of metal, then it will measure practically a dead short 0.00 Mohm on the instrument
 
It requires parallel paths removed,for example the cpc connected to the boiler earthing which in turn is in contact with the copper gas pipe. If you do not disconnect the cpc if testing that the gas pipe requires bonding or it’s just an isolated piece of metal, then it will measure practically a dead short 0.00 Mohm on the instrument

But that kinda defeats the object of the test. If it’s a dead short, because of its physical connection with the boiler, then cpc. What’s the point of deciding to bond, if the test result suggest it should be.

On the other hand, what if the physical connection is not great, and would give a value over 1667 ohms, but less than 0.02 MO. With the CPC disconnected, it then gives a value of over 0.02 MΩ.

I haven’t my Guidance notes to hand, but all references I can google for this test, are as said before; between extraneous part and MET or known earth, such as CPC. No mention of dis’ parallel earths. Does it say something different in the Guidance notes?
 
But that kinda defeats the object of the test. If it’s a dead short, because of its physical connection with the boiler, then cpc. What’s the point of deciding to bond, if the test result suggest it should be.

On the other hand, what if the physical connection is not great, and would give a value over 1667 ohms, but less than 0.02 MO. With the CPC disconnected, it then gives a value of over 0.02 MΩ.

I haven’t my Guidance notes to hand, but all references I can google for this test, are as said before; between extraneous part and MET or known earth, such as CPC. No mention of dis’ parallel earths. Does it say something different in the Guidance notes?
The test can’t be made where a conductive part say for example a conductive part like steel is to be tested but you have electrical items and say metallic containment like conduit connected to the steel by ways of fixings, bolts etc.
it would be impossible to test it as it’s in direct contact with exposed conductive parts that are connected together at points within the installation, so a test between a known cpc and said steel would be pointless unless you can remove the parallel paths created by the cpc’s or exposed conductive parts as you would essentially read 0.00 Mohms when trying to test.
same as a gas pipe connected to the boiler manifold / metallic housing, along with the cpc from the heating circuit, they are connected together so this connection must be removed.
By way of circumstance you always end up having metallic parts connected to earth that don’t need to be but bonding is entirely different to earthing.
 
The test can’t be made where a conductive part say for example a conductive part like steel is to be tested but you have electrical items and say metallic containment like conduit connected to the steel by ways of fixings, bolts etc.
it would be impossible to test it as it’s in direct contact with exposed conductive parts that are connected together at points within the installation, so a test between a known cpc and said steel would be pointless unless you can remove the parallel paths created by the cpc’s or exposed conductive parts as you would essentially read 0.00 Mohms when trying to test.
same as a gas pipe connected to the boiler manifold / metallic housing, along with the cpc from the heating circuit, they are connected together so this connection must be removed.
but in those cases, the "suspect" metal is already bonded due to it being bolted/welded/etc. to the bonded extraneous parts.
 
No it maybe earthed by being in contact with exposed parts but not necessarily bonded which is different
earthed if connected to exposed conductive parts, but bonded if connected to already bonded extraneous parts. :)
 
earthed if connected to exposed conductive parts, but bonded if connected to already bonded extraneous parts. :)
Something like that ha
I’ve always gone down the route of testing it with the installation isolated, earthing conductor disconnected from the earthing terminal in the CU but connected to the means of earthing,then from the disconnected earthing conductor to the suspect metal.
In practice tho I’ve only ever done this at a domestic level, a commercial or industrial installation already in service, I find is impossible to do the test.
 
earthed if connected to exposed conductive parts, but bonded if connected to already bonded extraneous parts. :)
Like in a factory, say, where you have the bonded main steel structure and take off a bond for any other required...
 
Here's something I've read, they might be wrong of course.
SO HOW DO WE MEASURE IT?

And Does Metallic Cable Tray Require Bonding? - https://professional-electrician.com/technical/bonding-time/
Yeah i would that’s fair enough as long as you haven’t earthed the tray by ways of fixing exposed conductive parts to it or say fixed the tray to steel which has metallic conduit fixed to it also, this would then earth all metallic parts concerned, so it wouldn’t be easy to test to see if it was extraneous ( which I can’t see how it would be in most circumstances)
 
Like in a factory, say, where you have the bonded main steel structure and take off a bond for any other required...
Egggsackly. free range. ( 3 friggin' words)
 
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Yeah i would that’s fair enough as long as you haven’t earthed the tray by ways of fixing exposed conductive parts to it or say fixed the tray to steel which has metallic conduit fixed to it also, this would then earth all metallic parts concerned, so it wouldn’t be easy to test to see if it was extraneous ( which I can’t see how it would be in most circumstances)
And the other one?
 

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