I have a stainless steel control cabinet located in the equipotential zone for a stunner.
This cabinet has a supply via the installation MEN earthing system and is earthed via the PEC of this final subcircuit.
Should this cabinet also be connected to the equipotential bonding system?
It doesn't seem right have a localized equipotential zone connected to its own earth electrode that could then end up at two different potentials, in fact it seems dangerous.
I can't see anything that restricts the connection of a bonding conductor to this cabinet in section 3.4 an although this adds another earth electrode to the installation I can't see this being worst than the possibility of two different potentials.
However table 2 number 7 in section 4 says "no directly wired connection from the equipotential bonding bar is connected to the MEN supply earth" and references 3.4.1.
Anyone able to clarify of shed some light around this for me? Should my cabinet be connected to the bonding network even though it has an earth from the MEN supply.
NZS6116:2006 Metal Enclosure in equipotential zone
Re: NZS6116:2006 Metal Enclosure in equipotential zone
Correct that the point of an equipotential Zone (EZ) is to avoid having simultaneously accessible metal at two different potentials. See definition in 1.4.
The wording of 3.4.1 is clear that specified types of metalwork must be bonded together, and the resulting EZ must be connected to a local electrode.
3.4.4 reinforces this requirement; such that ALL metalwork in the Zone (ie within 2.5 m of a stunning / stimulating appliance) must be connected to the EZ.
The test prescribed in Table 2 Row 7 means that there must be NO direct connection from the EZ bonding bar to the MEN system.
Such a connection could result in the EZ's potential being raised due to faults outside the EZ, including faults outside the installation.
I presume this is the reason for the specified test; but I agree that it could, and should, be clearer.
After all, 1.2 says that any alterations or modifications to "3000" are "specifically stated"; and "3000" normally requires a conductive enclosure for electrical equipment to be earthed to the installation's earthing system.
3.4.1 specifically requires bonding, but it doesn't specifically revoke the earthing requirement of "3000".
Table 2 appears to do so; but in my view it is not proper to impose a requirement via a test.
The revocation of the normal earthing requirement should have been done in 3.4.1.
Note that Table 7 only precludes a directly wired connection between the EZ's 'bonding bar" and the MEN supply earth.
Indirect connection is therefore permitted.
"equipotential bonding bar" is not defined, and also is not a required component of an EZ system.
It can be argued that your enclosure is not a bonding bar, so the specified test does not apply to it.
Given the room for argument, perhaps best to move the box out of the Zone?
The wording of 3.4.1 is clear that specified types of metalwork must be bonded together, and the resulting EZ must be connected to a local electrode.
3.4.4 reinforces this requirement; such that ALL metalwork in the Zone (ie within 2.5 m of a stunning / stimulating appliance) must be connected to the EZ.
The test prescribed in Table 2 Row 7 means that there must be NO direct connection from the EZ bonding bar to the MEN system.
Such a connection could result in the EZ's potential being raised due to faults outside the EZ, including faults outside the installation.
I presume this is the reason for the specified test; but I agree that it could, and should, be clearer.
After all, 1.2 says that any alterations or modifications to "3000" are "specifically stated"; and "3000" normally requires a conductive enclosure for electrical equipment to be earthed to the installation's earthing system.
3.4.1 specifically requires bonding, but it doesn't specifically revoke the earthing requirement of "3000".
Table 2 appears to do so; but in my view it is not proper to impose a requirement via a test.
The revocation of the normal earthing requirement should have been done in 3.4.1.
Note that Table 7 only precludes a directly wired connection between the EZ's 'bonding bar" and the MEN supply earth.
Indirect connection is therefore permitted.
"equipotential bonding bar" is not defined, and also is not a required component of an EZ system.
It can be argued that your enclosure is not a bonding bar, so the specified test does not apply to it.
Given the room for argument, perhaps best to move the box out of the Zone?
Re: NZS6116:2006 Metal Enclosure in equipotential zone
I did consider whether the box should or shouldn't be in the zone, more infact further enough from the zone as to prevent touching the two different earthing systems at the same time
Without moving the box I think the better option is to ensure a bonding conductor be connected to the box and believe that although the enclosure is connected via the MEN installation PEC and also connected via the bonding conductor maybe you could argue these two systems are not directly connected but indirectly through the enclosure. This seems like a better option than the potential for two different earthing systems at different potentials and the enclosure definitely not meeting the requirements of 3.4.4
Without moving the box I think the better option is to ensure a bonding conductor be connected to the box and believe that although the enclosure is connected via the MEN installation PEC and also connected via the bonding conductor maybe you could argue these two systems are not directly connected but indirectly through the enclosure. This seems like a better option than the potential for two different earthing systems at different potentials and the enclosure definitely not meeting the requirements of 3.4.4