Static Ground

[rlit]

We are currently installing a commercial project that requires a Static ground using a chemical ground. The engineers are telling me that the static ground cannot be tied to the electrical grounding system. This static ground will be utilized in the manner of wrist bands to prevent stray static voltage from contacting the PC boards when they handle them. There is also a static ground flooring that is tied to the building steel columns, not the static ground system, and imbedded in the floor. In my opinion this could create an unequal potential plane if there was ever to be a ground fault and breaker failure. This could be for only an instant but an instant could cause harm to personnel. I can't find in the codebook where there is an exception for this. My understanding is that all grounding systems need to be bonded together or does this fall under the classification of an auxiliary ground?

 

[K8MHZ]

We are currently installing a commercial project that requires a Static ground using a chemical ground. The engineers are telling me that the static ground cannot be tied to the electrical grounding system. This static ground will be utilized in the manner of wrist bands to prevent stray static voltage from contacting the PC boards when they handle them. There is also a static ground flooring that is tied to the building steel columns, not the static ground system, and imbedded in the floor. In my opinion this could create an unequal potential plane if there was ever to be a ground fault and breaker failure. This could be for only an instant but an instant could cause harm to personnel. I can't find in the codebook where there is an exception for this. My understanding is that all grounding systems need to be bonded together or does this fall under the classification of an auxiliary ground?

I was not aware of any exceptions. AFAIK, all systems on the same premises must be bonded together.

250.50

 

[rlit]

I am aware of 250.50. In my opinion electrical engineers should be required to know how to use the NEC. We have installed a jumper to tie the systems together per NEC but there is no telling what will happen after we leave.

 

[GoldDigger]

Any ground electrode that is not connected in any way to building wiring or loads would not, IMHO, be subject to the NEC and there would be no reason to interconnect it.
But if it is attached to any metal that is required by the NEC to be bonded to the EGC/GES, then it would not be possible to keep it isolated.

 

[starbolin]

We are currently installing a commercial project that requires a Static ground using a chemical ground. The engineers are telling me that the static ground cannot be tied to the electrical grounding system. This static ground will be utilized in the manner of wrist bands to prevent stray static voltage from contacting the PC boards when they handle them. There is also a static ground flooring that is tied to the building steel columns, not the static ground system, and imbedded in the floor. In my opinion this could create an unequal potential plane if there was ever to be a ground fault and breaker failure. This could be for only an instant but an instant could cause harm to personnel. I can't find in the codebook where there is an exception for this. My understanding is that all grounding systems need to be bonded together or does this fall under the classification of an auxiliary ground?

They are trying to meet ANSI/ESD S20.20. The isolated ground really is necessary for their production systems. No, they are not trying to electrocute anyone, the floor mats and wrist bands are required to be high impedance. In addition the system cannot present any bare metal that could be touched. Where I worked they had quarterly performance tests to assure the integrity of the series impedance.

NEC and ANSI have fought over this for decades. Being an EC and not an ESD installer you handled it as best you could. The responsibility falls to the plant engineer.

 

[K8MHZ]

Any ground electrode that is not connected in any way to building wiring or loads would not, IMHO, be subject to the NEC and there would be no reason to interconnect it.
But if it is attached to any metal that is required by the NEC to be bonded to the EGC/GES, then it would not be possible to keep it isolated.

I disagree. Chapter 8 requires the bonding of electrodes used for radio antennas. It doesn't matter if the radios are battery powered or not.

We now have special connectors designed to make the bonding of systems other than the premises mains wiring system almost fool proof.

 

[GoldDigger]

I disagree. Chapter 8 requires the bonding of electrodes used for radio antennas. It doesn't matter if the radios are battery powered or not.

We now have special connectors designed to make the bonding of systems other than the premises mains wiring system almost fool proof.

As starbolin noted, we have a conflict between two incompatible standards.
And unfortunately for the OP, the NEC usage of auxiliary ground electrodes still requires that they be bonded to an EGC even if they are not bonded directly as part of the GES.
An interesting question to ask here is whether 250.54 [2011] requires all electrodes to at least be connected to an EGC and loosens the other requirements for an auxiliary or simply tells us that if it does not connect to an EGC it is neither an auxiliary grounding electrode nor a standard electrode?

An isolated ground, running insulated all the way back to the service bonding point, may be the best compromise available, compatible with the NEC, although it may still not meet the ANSI ESD standard.

 

[jtinge]

"Grounds for Grounding", Joffe and Lock, IEEE Press, has a whole section regarding control of ESD in facilities (Section 10.3). This is an excerpt from 10.3.5 regarding connection of the ESD ground to the building safety ground.

Design and construction of ESD protected areas is commonly achieved through grounding ESD protective equipment in a two-step procedure. The first step is to en* sure that everything in the work space is maintained at a common electrical potential at all times during normal operation. This is achieved by grounding all components of the work area, including all BSD protective elements such as external parts, work surfaces, personnel, and electronic test equipment and power tools in an electronics production and test area, to the same electrical ground point called the common-point ground {31, 32]. This ESD common-point ground should be properly identified. Use of the symbol in Figure 10.31 is recommended to identify the common-point ground. Figure 10.32 shows a practical implementation of ESD common-point grounding [29].

The second step for achieving ESD protective grounding is to connect the common point ground to the local equipment electrical safety ground (ESG) or protective earth (PE) connection point. This is the preferred ESD ground connection because all electrical equipment on the site should already be connected to this point. Connecting the BSD control materials or equipment to the equipment electrical safety ground guarantees that all components in the work space are at the same electrical potential. If this were not the case, a possible electrical potential difference between the electrical safety ground (to which the ESDS item is connected) and an auxiliary ground (to which the work space surface containing the ESDS item was to be connected) could result in damage to the ESDS item, counteracting the purpose of the ESD ground and possibly even constituting a safety hazard for personnel if they come into electrical contact with both grounding systems simultaneously. Subsequently, any auxiliary ground structures (e.g., water pipe, building frame, or ground stake) present and used in the work space must be bonded to the equipment electrical safety ground in order to maintain the integrity of the connections from the common-point ground to this point and to. Minimize electrical potential differences between the two. The resistance between the two connections should be as low as possible, typically less than 1 ohm.

Figure 10.32. Implementation of ESD common point ground. (Image courtesy of M. Netzer.)