Hi Tom. According to BS 7671 section 705, an electrical installation in a zoo has to follow certain rules (Special locations). You have measured that the metal cages are connected to the metal beams of the building, which makes them extraneous-conductive-parts. This means that the metal cages could bring a potential difference into the installation. This could create a dangerous difference in voltage between the metal cages and any exposed-conductive-parts in the area where the keepers work, such as the big pressure washer. This could cause a risk of electric shock to humans and animals who touch these parts. Therefore, it might make sense to bond the metal cages to the main earthing terminal (MET) to reduce this risk.

Thank you for your reply AMK .

Second paragraph reads awful ! Should perhaps read:

On one side of the enclosure is the area in which the animals shelter. This area contains no exposed conductive parts.

The two areas sit side by side.

Is there a buried grid (e.g. steel reinforcement rods in concrete floor) that could be included in the bonding scheme?

Large, "Long wheelbase" bare footed, and possibly wet nosed, animals are not a good combination for voltage differences - either between metallic parts or between a metallic parts and the general mass of the Earth.

Another possibility is to remove the risk associated with earth faults to exposed-conductive-parts in another way - e.g. going for an all-insulated installation (double/reinforced insulation throughout) or use of separated circuits.

   - Andy.

AMK said:

According to BS 7671 section 705

We do need to be a little careful here. I don't disagree it would be advantageous to use the guidance in Section 705 as a minimum, but generally zoo animals are not livestock (although some may be).

BS 7671 is not aimed at protecting all animals (livestock, however, is part of the aims). Further, it should be noted that the reference standards BS EN IEC 60479-series Effects of current on human beings and livestock which is generally taken into account by electrical safety standards has some limitations when it comes to animals in general.

Andy good question I am pleased you asked. No there is no buried grid and here is the other spin on this...
there is no bonding to the steel girders that make up this building and have their foundations deep in the earth. The cage structure is attached to these steel girders / beams.

As such I want to address (and I may have this incorrect) by looking to equalise potential on the keepers side under fault conditions on the animals side you risk creating a potential difference

It is true that zoo animals may differ from livestock in their physical and behavioural traits, and therefore the protection measures of section 705 may not suit their needs. What other sources of guidance or standards that are specific to zoo animals can we refer to?

AMK said:

What other sources of guidance or standards that are specific to zoo animals can we refer to?

Not a great deal at the moment, which is why I used the statement 'Section 705 as a minimum' ... I just don't want anyone to get the impression that it's 'Section 705, job done !'

There are a huge amount of issues that are unaddressed, not limited to differences in size and reach of different animals, but also for example, how do we deal with the electrical installation for a polar bear enclosure (IK ratings out of the window), or a seal / sea lion pool - I have no clue how those creatures respond to electric shock !

...or a Hippo enclosure with a pool.

Glen thank you for seeing the concerns. I was taking S. 705 as minimum and looking at lots of custom issues in what is an old installation. As such a platform like this to bounce thoughts and considerations is useful

As such I want to address (and I may have this incorrect) by looking to equalise potential on the keepers side under fault conditions on the animals side you risk creating a potential difference

Indeed. There seem to be two perineal problems with "equipotential zones" - firstly they're never quite equipotential (even bonding of a fraction of an Ohm will develop quite a significant voltage difference if the earth fault currents flowing through it can be large (which then often can be) - and then the problem of what happens at the edges - not too bad if you have insulating walls of a building to keep inside and outside apart, but  a lot trickier in many other situations.

   - Andy.

AJJewsbury said:

and then the problem of what happens at the edges

or outdoors, where the potential gradient away from metal posts and fences that are bonded can drop off relatively quickly. unless you are stood on ground that has a bonded grid (of dimensions and depth compatible with the potential fall) buried in it.