CAT-IV Digital Multimeter and its Significance to user

If you are planning to travel on a bike or a car its necessary for your safety to wear the helmet or wear seat belt. Helmet will protect you from impacts and mechanical shocks. Seat belt saves your head from making impact on steering wheel. Air bags installed in car will be inflated in an accident situation.

What If you are taking voltage or current measurements in electrically hazardous environment? will you Just pick up any multimeter with any random specifications ? NO !!! you must not. Then what you should do to keep yourself safe. Lets first understand the working environment in which you are going to use the multimeter.

Your measurement area may vary from a simple battery voltage measurement, to the MCB or fuse protected sockets or at the utility incomer of your factory or house or you may be measuring directly on electrical pole.

Naturally a question may arise in your mind that voltage is a voltage, may it be  at my house hold socket or it is at electrical pole, what difference it makes to me, as multimeter is designed to measure voltages up to 1000V. How location of the measurement will affect me ? Can I select any multimeter to use at any locations described above. To find the answer of this question lets take a look at what makes these various locations or working environments, different than each other even though voltage levels may be the same.

The answer is energy levels i.e. ability to deliver the current at high voltages. As energy level increases, threat to life increases exponentially.  Your multimeter must be designed to protect you in that particular energy environments.  The energy levels at CAT IV are higher compared to CAT III or CAT II or CATI.

Depending upon the energy levels, these working environments are referred as Installation categories and are divided into  four categories i.e. CAT I, CAT II, CAT III, CAT IV. As energy level increases installation category increases hence the risk level also increases.

Below are the examples of installations categories.

1) CAT I : A battery or protected (by fuse or other means)electronic equipment or any high voltage low energy sources like 1000V in photocopier machine.

2) CAT II: The appliances connected to wall sockets.

3) CAT III: Installations, lighting loads in side the buildings. Loads separated from utility through at least one isolation transformer. Fixed or permanent installations directly connected to building mains supply.

4) CAT IV: Origin of installations, Panels at entry (source) level of the buildings, cables running between electrical pole to building. The connections to the meters at utility inputs.

Bus and feeders, distribution panels.

If you are working in CATIV environment high voltage and high energy transients or spikes caused by motors,lightening,variable frequency drives,discharging of capacitors etc can run through your multimeter without any warning. If your multimeter is not designed and tested for CATIV your life is at risk. CATIV 600V (or CATIII 1000V) multimeter should with stand 7.8kV transient, CAT III600V multimeter should withstand 6.1kV transient according to IEC-61010 safety standard. Other wise it can be dangerous to user’s life as shown below.

Lightening strike causes a transient on electrical line which can form an arc between input terminals of the multimeter. If proper clearance is not maintained during design or protection components are not used, this will lead to a high short circuit current in terms of few kilo Ampere for a momentary time. This can lead to the blast or burning of multimeter.Very high temperature will result from such arcs. This can cause burns to the user and cost his life.

One more reason for high current flow through multimeter is using multimeter in wrong way. For example an electrician is measuring current. For this he should insert the leads in mA or A sockets.

In A measurement mode input resistance is 10 mΩ. If now user want to measure voltage but forget to change the leads to V sockets even though the function selector knob is changed to Voltage function  then voltage source will be short circuited, leading to a heavy current flow. Here the high quality fuses will come into picture to protect the user. These fuses should be ultra fast acting so that before current exceeds dangerously high level fuse should blow.

Always choose the multimeters with proper category and voltage you are working in.

Tips to select right Multimeter for appropriate installation category:

• If you are working in CATIV environment having working voltage 440V AC choose CATIV 600V Multimeter.
• While choosing mulitmeter Category and voltage, always choose category first and then  voltage.
• For example: CAT IV 600V multimeter is safer than CAT II 1000V.
• Voltage ratings of the Fuses used should be equal to or greater than maximum voltage measured by multimeter.
• Fuses should be ultra fast acting.
• Multimeter housing and probes should be double insulated.

Rishabh Instruments provides Multimeters with additional safety feature to eliminate accidents due to wrong connections. This feature is called as ABS i.e. Automatic Blocking System. When you turn the function selector knob to voltage position mA and A sockets are blocked by ABS plate so that user can not insert test leads in wrong sockets. When function selector knob is placed on mA or A position, mA or A socket will be opened respectively and voltage socket will be blocked. So at any point of time only correct socket is available to insert the test leads.

Rishabh Instruments CATIV Multimeters and Clamp meters:

Rishabh Multimeters:  RISHABH 016,6015,6012 (USB and Bluetooth) / RISHABH 616,615,612 / Rish Multi 12s, 14s, 15s, 16s, 18s, 20 are CAT IV 600V multimeters

Clamp meters: Rish Clamp 1000 A/300A AC, 1000A/300A ACDC, Rish Clamp Power 1000A/400A ACDC are CAT IV 600V Clamp meters.

All the above mentioned multimeters and clamp meters are designed and tested to fulfill the safety requirements  according to IEC-61010 safety standard.

Protection devices like PTCs ,Surge resistors, VDRs, spark gap are used to keep you safe in electrically hazardous environment.

Fuses used in the multimeters are ultra fast acting with 1000V ratings and 30kA rupture capacity.

Housings are double insulated so that your hand remains electrically isolated in hazardous conditions.

Multimeters are provided with Automatic blocking system as described earlier to avoid accidental misuse.

Remember: Just knowing the safety is not enough, but practicing it is the key to total safety!!!

For more information
Web: http://www.rishabh.co.in