Connection to earth of computer rack drawers

Assuming the safety of the devices is not in question (each device having its own cpc), we are really only talking about EMC measures (as the parts in question are typically neither extraneous-conductive-parts not exposed-conductive-parts).


The standards in question (referenced from Section 444 of BS 7671) are:

• BS IEC 61000-5-2

• BS EN 50310

First "curly" or "not curly" - usually the recommendation is generally NOT curly, as the inductance is increased by both the length of the lead, and by the action of providing a coil. The object of earthing for EMC would be to conduct higher frequency currents away from the affected part (whether it's shielding radiated emissions or sinking conducted emissions).


Second, is the bonding to these parts actually required or not? Well, that depends. Reasons to do so include:

• Rack contains measurement instruments sensitive to high frequencies and radiated / conducted emissions.

• Rack contains a mixture of equipment with industrial emissions (or Class A for some product standards), and domestic/light industry immunity, and shelves/trays are used as part of the mitigation measures in the EMC control plan (although, there are orders of magnitude difference between the light industry immunity and the Class A emissions, so this is not always necessary)

• Someone is worried about mains cables breaking, and making contact, thus it's considered in that risk assessment as an exposed-conductive-part.

A way of avoiding lots of bonding conductors in a rack is to use internals made of substantially conductive materials that are protected against corrosion, such as zinc-plate colour-passivated, meaning each shelf fixing is electrically connected to the support rails, front panels etc. - in fact, some ranges of 19 " rack are specifically designed with this in mind, such as the Cooper-Bussmann EMC range. Even then, one could argue that the earthing of a pull-out drawer or shelf was only "fortuitous", but so long as it's not for safety (pull-out shelf or drawer is not an exposed-conductive-part), and we're not talking about SIL-level functional safety risks from EMC, then that shouldn't be too much of a problem.


The latest edition of BS EN 50310 goes down to rack earthing and bonding level, and is an interesting read ... but doesn't expressly contain the bullet list above.

Assuming the safety of the devices is not in question (each device having its own cpc), we are really only talking about EMC measures (as the parts in question are typically neither extraneous-conductive-parts not exposed-conductive-parts).


The standards in question (referenced from Section 444 of BS 7671) are:

• BS IEC 61000-5-2

• BS EN 50310

First "curly" or "not curly" - usually the recommendation is generally NOT curly, as the inductance is increased by both the length of the lead, and by the action of providing a coil. The object of earthing for EMC would be to conduct higher frequency currents away from the affected part (whether it's shielding radiated emissions or sinking conducted emissions).


Second, is the bonding to these parts actually required or not? Well, that depends. Reasons to do so include:

• Rack contains measurement instruments sensitive to high frequencies and radiated / conducted emissions.

• Rack contains a mixture of equipment with industrial emissions (or Class A for some product standards), and domestic/light industry immunity, and shelves/trays are used as part of the mitigation measures in the EMC control plan (although, there are orders of magnitude difference between the light industry immunity and the Class A emissions, so this is not always necessary)

• Someone is worried about mains cables breaking, and making contact, thus it's considered in that risk assessment as an exposed-conductive-part.

A way of avoiding lots of bonding conductors in a rack is to use internals made of substantially conductive materials that are protected against corrosion, such as zinc-plate colour-passivated, meaning each shelf fixing is electrically connected to the support rails, front panels etc. - in fact, some ranges of 19 " rack are specifically designed with this in mind, such as the Cooper-Bussmann EMC range. Even then, one could argue that the earthing of a pull-out drawer or shelf was only "fortuitous", but so long as it's not for safety (pull-out shelf or drawer is not an exposed-conductive-part), and we're not talking about SIL-level functional safety risks from EMC, then that shouldn't be too much of a problem.


The latest edition of BS EN 50310 goes down to rack earthing and bonding level, and is an interesting read ... but doesn't expressly contain the bullet list above.