Instrument Grounding and Guide for the Right Setup

Purpose of This Note

This technical note is intended to help you better understand the term “grounding”. Many researchers take this topic too lightly. However, this can not only negatively impact your experiment but lead to hazardous situations for you and your surroundings. We will discuss the basic concept of grounding, its purpose, and explain how to correctly connect your Gamry device and measurement cell.

Introduction

When running electrochemical experiments, researchers mostly think of connecting the working, reference, and counter electrode. The ground connection at the cell cable or potentiostat are often ignored. Even though it may be best to just leave them disconnected, a proper ground connection may help reduce measurement noise seen in the measured signal and thus lead to better results.
However, a wrong ground connection can create a safety hazard which can not only damage the instrument but also lead to personal injury or death. This is especially critical if the measured cell is not isolated from earth ground which is not always obvious. Hence it is particularly important to know the experimental setup and the functionality of the potentiostat’s and cell cable’s ground connections.

Electric Power Distribution

Grounding builds the basis of our entire power system, beginning from its generation up to the end consumer. Figure 1 shows the general principle of the electric power distribution.

Figure 1: General principle of the electric power system.

Electricity generated by power plants is fed into the electric grid, a network of transformers and transmission lines which distribute the electricity to residential and industrial end consumers.

Electricity is transported via transmission towers over long distances. Here, power losses due to heat generation and power line resistance need to be minimized. Lowering the current (P=I^² R) or increasing the voltage respectively reduces these losses. Therefore, transformers step up the voltage level to voltages between 230 kV and 765 kV before being fed into the electric grid.

These voltage levels are too high though for residential or industrial use. For industrial use, transformers step down the voltage to mid voltage levels between 4 kV and 69 kV. For residential consumers, voltage is further stepped down to 120 V and 240 V respectively and distributed to each household via distribution lines. This low voltage is safe for use with electrical household equipment.

One of the biggest challenges in maintaining a stable power grid is to avoid large fluctuations of the electricity fed into the system. Large spikes due to outages in power generation, excessive infeed of electricity, or failures in the distribution system can disrupt the whole power grid and lead to blackouts. There are many different safety mechanisms to avoid these failures such as power banks, redirecting electricity to other networks, shutting down (or reactivating) power plants, and so on.

For the complete power grid to even function, ground connections are an indispensable part. There would be no possibility to safely handle these vast amounts of electricity without grounding which means having a common reference point for the voltage. This common reference point is Earth.

Stabilizing Voltage Levels

Per definition, voltage is the difference between two potentials. Without having a stable and well defined reference point, it is nearly impossible to maintain stable voltage levels or even know the magnitude of such levels. Earth is a convenient and (not surprisingly) global reference point we have access to. With its huge mass, it can basically absorb unlimited amounts of electric current without experiencing any voltage change. This makes it an ideal grounding point which we will refer to as “earth ground” or simply “earth”. Hence, earth ground is used as “zero-volt reference point”, meaning that its potential is zero volts. One could also refer to it as global reference electrode.

However, Earth itself is generally not the most effective conductor. You cannot simply run a wire from an instrument and stick it into the ground. In order for Earth to function as a zero volt reference point, we need to use material with reasonably high electrical conductivity (i.e., low resistance) and it has to be deeply anchored within the ground to provide a stable electrical connection. Typical example for good earth ground connections are:

• ground rods or ground rings
• metal underground water pipes
• concrete encased electrodes

Safety

Ground connections do not only provide a constant reference point but also serve as safety mechanism against electric shocks. If a ground connection is bad, “stray voltages” may appear. This means that an electrical potential between two objects can occur where there typically should be no voltage difference. As a result, electrical charge can build up, causing an increased electrical shock hazard when touching electrical equipment.

High impedances between conductor and earth ground also cause a large potential difference, for example by bad ground connection or fallen down power lines. The potential difference is highest at the contact point and decreases with increasing distance. This phenomenon is also called “earth potential rise” (EPR). The potential difference is registered by the human body and the distance between the feet (step potential). Normally, this difference is small enough for the body to not recognize it. But if large enough it can be deadly, for example by being close to a fallen down power line.

Electric Wiring

Figure 2 shows the standard 2 pin and 3 pin sockets that are used in North America (NEMA 5 15 socket) and parts of Europe (CEE 7/3 socket, “Schuko”). Note that not only the design varies by region but also the supply voltage. For example, in North America the standard voltage is 110 120 V, whereas it is 220 240 V in Europe.

Figure 2: Power plug types used in NA (left) and parts of Europe (right).

When plugging in a device, current flows from the “hot” wire for the initial power feed through the device and back to the “neutral” wire which is connected to earth ground as shown in Figure 3. Because “neutral” is connected to earth, it functions as the zero voltage reference point.

Figure 3: Wiring diagram for a 2 way (top) and 3 way outlet (bottom).

The third connection used in three pin sockets purely serves as fixed earth ground connection for the instrument’s chassis. This connection is relevant for devices which require additional safety features discussed in the next section. Depending on the instrument design, devices can be differentiated between three classes.

Instrument Classification

According to the international standard IEC 61010, Safety requirements for electrical equipment for measurement, control, and laboratory Use, electrical equipment has to be tested and must meet certain test requirements before it can be sold. Depending on the design and voltage levels being used, instruments can be categorized into three classes:

• Class I: Instruments require a combination of basic insulation and protective earthing to reduce the risk of electric shock. Class I power supplies have 3 pin receptacle, with its ground pin connected to the instrument’s chassis when plugged in. Two examples of Class 1 devices are Gamry’s Reference 30k Booster and the Interface Power Hub (IPH).
• Class II: Instruments do not need protective earthing but require a two level insulation (either by double or reinforced insulation). Class II devices use power supplies with a 2 pin receptacle, with only the “neutral” wire being grounded to earth. Instruments usually have a separate grounding connection for the chassis but it is not connected to earth ground. Each Gamry potentiostat such as the Interface 1010 or Reference 3000 belongs to this category.
• Class III: No extra protection is required and basic insulation is sufficient. Instruments are supplied by a separate extra low voltage (SELV) power supply and do not exceed extra low voltage (ELV) limits, i.e., 50 V rms, under normal conditions. Typical examples are laptops or mobile phones.

Grounding Terminology

Depending on the ground connection, different definitions for grounds are used:

• Earth ground: General term for a ground connection between the conductive part of an instrument and an external earthing system, e.g., by connecting a grounding cable between instrument and earth ground. Earth ground is depicted with following symbol:
  
• Protective earth ground: According to international standard IEC 61010, protective earth ground is defined as “bonded” (fixed) connection between conductive parts of the equipment and an external protective earthing system. This connection is made via the ground prong in the AC line cord. Instruments with protective earth ground are always grounded to earth when plugged in, as shown in Figure 3B.
  All Class I instruments require protective earth ground such as Gamry’s Reference 30k Booster and the Interface Power Hub. The symbol for protective earth ground is:
  
• Chassis ground: Ground connection point between the instrument’s enclosure and earth ground. Depending on the instrument design, it may or may not be also connected to the instrument’s circuitry. Note its different grounding symbol.
  
• System ground: Ground connection point of the instrument’s circuitry. It is not connected to the instrument’s chassis but only the circuitry. 
  
• Floating ground: Common ground point of an instrument that is not connected to an earth grounding system. Floating ground must be isolated from earth ground when testing earth-grounded systems! 
  

You may have noticed the use of the terms “grounding” and “earthing” throughout this tech note. Both terms are often used interchangeably but this is not entirely correct:

• “Grounding” an instrument means that the “neutral” wire of the cabling provides a connection between earth ground and the instrument’s inner circuitry. Its main purpose is to protect the equipment itself by balancing unwanted currents due to overloads or unbalanced loads.
• “Earthing” provides a connection between the instrument’s enclosure and earth ground. In contrast to grounding, it does not increase the system’s stability but protects the user from harmful electrical shocks. Charge build up in the enclosure is reduced by the direct connection to earth ground and therefore reduces the risk of electrical shocks.

Grounding your Gamry potentiostat

All of Gamry Instruments’ devices are capable of “floating operation”. As discussed above, this means that the potentiostat’s internal circuitry is not connected to earth ground and completely isolated, thus enabling experiments with earth grounded cells. However, the experimental setup might not just consist of a cell but also utilize auxiliary apparatus, a Faraday cage, or other devices. These can introduce ground connections which might not be always that obvious. In order to set up an experiment correctly and safely, you should check following points:

• What potentiostat type is being used?
• Is the cell earth grounded?
• Is a Faraday cage used?
• Are there any external auxiliary apparatus connected?

1. What ground connections are there?
   The first point to check is the type of potentiostat being used and what ground connections are available. Usually, the instrument’s Class type is stated in the operator’s manual. Class I type devices require a protective earth ground connection, i.e., a fixed ground connection between earth and the instrument’s chassis. This connection is done via the ground plug of the 3-pin AC line cord.

Gamry’s Reference 30k Booster is an example of a Class I type device. It has two ground connections on the rear panel called Protective Ground and System Ground, as shown Figure 4. Both binding posts are isolated from each other. Even if the protective earth binding post on the rear panel is not connected, protective ground connection is still maintained if appropriate cables are used.

If the measured cell is isolated from earth ground, both grounds can be connected using the provided ground strap. This may help reduce noise in the measurement.

Figure 4: Reference 30k Booster rear panel ground connectors.

If the cell is earth grounded, both grounds must be isolated and system ground must not be connected to earth ground.

The second connection point to the Booster’s system ground is the sense cable’s black lead. It is recommended to remove the ground lead’s alligator clip to avoid any accidental contact to earth ground, negating floating operation as shown in Figure 5. In most cases, you can leave it disconnected but it may be useful with a Faraday cage as discusses later.

Figure 5: Reference 3000 sense cable with the alligator clip of the black ground lead removed.

All other Gamry devices such as Interface and Reference family potentiostats, the RxE 10k rotator, or LPI1010 belong to the Class II category. They use a 2‑pin power plug and do not require a bonded grounding connection. There is only one ground plug on the rear panel, called Chassis Ground as shown in Figure 6.

Figure 6: Reference 3000 rear panel ground connector.

Chassis Ground is the common voltage reference point for the potentiostat’s circuitry and chassis. It floats with respect to earth ground and is not connected to any earth grounding system. The second connection point to chassis ground is the cell or sense cable’s black lead. It is recommended to remove the ground lead’s alligator clip to avoid any accidental contact to earth ground, negating floating operation as shown in Figure 5.

In either of these two cases, working in floating operation enables safe study of earth‑grounded measurement setups. This comes with a downside though as the instrument’s performance could be degraded.

Floating operation can be neglected if the measured cell setup is fully isolated from earth ground such as a sample in a glass cell or a battery in the UBH. Connecting system or chassis ground to earth may lower measurement noise seen in electrochemical tests.

2.  Is the cell earth‑grounded?

After clarifying what potentiostat type is being used, we can set our focus on the cell and check if it is earth‑grounded or not. Typically, electrochemical setups in a chemistry lab consist of a glass cell filled with an electrolyte and electrodes immersed (working electrode, reference electrode, counter electrode). This type of setup is generally not earth grounded. Batteries, capacitors, or solar cells are additional examples of isolated cells. Thus, floating operation is not required.

However, there are many cells that are earth‑grounded which may not even be that obvious at first glance. Below is a list of few examples for earth‑grounded systems:

• Autoclaves
  • In many cases, the autoclave’s earth-grounded wall is generally used as the counter electrode of the cell.
• Pipelines
  • Underground water pipelines are often earth‑grounded which might not be obvious at first. Due to their direct connection to earth, they make excellent grounding conductors. Hence exercise extra caution when performing corrosion tests in the field.
• Storage or fuel cell tanks
  • For safety purposes and to reduce electric shock hazards, fuel‑cell tanks are earth‑grounded.
• Electronic microscopy
  • To obtain good imagery, the working electrode is often connected to the microscope’s chassis which in turn is earth‑grounded.
• Flow‑based devices (e.g., fuel cells or electrolyzers)
  • Pressurized inlet or outlet lines using metal tubing can earth-ground collector plates.

3. Using a Faraday cage?

Using a Faraday cage such as Gamry’s Faraday Shield™ can help reduce noise when measuring small signals. By encasing your cell with a metal enclosure, both the effect of external electrical fields as well as electromagnetic radiation can be reduced.

4. Is an auxiliary apparatus connected?

Using any auxiliary apparatus such as oscilloscopes might accidentally ground the cell or the potentiostat. For example, connecting the Monitor BNC of a Reference 3000 potentiostat to an oscilloscope will earth‑ground the instrument. Thus, one have to be careful when connecting any external apparatus to the cell or potentiostat.

Another example is the LPI1010™ Load/Power Interface which uses an external power supply or electronic load for experiments with voltages of up to 1000 V. Because of these hazardous voltages and its complex setup, we will discuss the LPI1010 and its ground connection separately further below.

Refer to the flowcharts for Class I and Class II potentiostats shown in Figure 7 and Figure 8. Use them as guidelines for your measurement setup.

Figure 7: Grounding flowchart for a Class I potentiostat (Reference 30k Booster connected to a Reference 3000).

Figure 8: Grounding flowchart for a Class II potentiostat (e.g., Interface 1010).

Connecting an LPI1010 Load/Power Interface

Typical lab EIS systems cannot handle large voltages of up to 1000 V which are required to study large battery packs and fuel cell stacks. Gamry’s LPI1010™ was designed to gain access to such voltage levels without sacrificing any EIS performance. Three different models are available which handle these voltage ranges: 10 V, 100 V and 1000 V.
Figure 9 shows a typical system of an LPI1010. It consists of an Interface 1010E potentiostat in conjunction with an LPI1010.
The LPI1010 D sub module plugs into the Interface 1010 cell cable connector and is powered by the potentiostat’s User I/O connector. Two cables run from the D sub module. One is connected to the LPI Cable End module which handles voltage monitoring and down regulates voltages exceeding ±10 V. Two voltage sense cables connect it to the device under test (DUT). The second cable manages current control and monitoring. Via BNC connectors, it plugs directly into a Bipolar Power Supply (for battery studies) or an Electronic Load (for fuel cell studies). Both devices are again connected to the DUT.

Figure 9: Typical setup of an LPI1010.

 

The high voltage levels and the complex setup already show that correct grounding connections are even more crucial when using an LPI1010. Th LPI1010 itself is a Class II device and does not require protective earthing. It floats with respect to earth ground. The instrument’s chassis and internal circuitry common voltage reference point is Chassis Ground.

Most power supplies and electronic loads are connected to protective earth ground. Thus, it will also earth‑ground the LPI1010 after connecting both. This will negate its floating capability which can cause hazardous conditions when measuring earth‑grounded cells.

Use the flowchart in Figure 10 as guideline for your LPI1010 measurement setup.

 

Summary

Grounding is often ignored when setting up an experiment. But extra precaution is required if the tested cell is earth‑grounded. Wrong grounding connections can lead to hazardous conditions which may not just damage the instrument but also harm you and your surroundings.

Hence it is important to know your measurement setup. Always check what ground connections are available on your instrument. Verify if your cell is connected to earth ground which is in some cases is not always obvious. Additional instrumentation such as autoclaves or oscilloscopes can also earth‑ground cell or potentiostat.

Follow the flowcharts in this technical note and use them as guidelines to correctly ground your Gamry potentiostats or LPI1010.

 

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