Technical description

Technical solution regards an device for an automated measurement of the continuity of the PEN conductor and a protective conductor PE in regards with a STN 33 2000-6.

Described technical solution considers two devices. The first one (PENCE) is designed to automatically measure the continuity of the PEN conductor from the source { a transformer } up to a point of distribution of the PEN conductor.

It is done through a transformer, which measures the current (MTP).

Second, an additional device (ENCE), automatically measures the continuity of the protective conductor PE from the PEN conductor's point of distribution in the switchbox up to the final current-using equipment in the electrical installations. This is done in the supplay net TNC-S.

Using these devices (PENCE) and (ENCE) at the same time safeguards the control of the continuity of the PEN conductor and protective conductor from the source of electric energy , the transformer, up to the current-using equipment.

Note: I. class objects are electrical objects with an obligatory protective clip and protective conductor to avoid the electric shock.

Current state of technics

Currently there isn't an device which would automatically measure the continuity of the protective conductor PEN a PE.

Out of IEC 60364-6: 2006 and a harmonising document HD 60364-6 a harmonised STN 33 2000-6 was taken. Part 6: Inspection, states in an art. 61.3.2 / common modification with an international norm / - Conductor continuity in a section a) It is obligatory to test the continuity of the protective conductors , including the conductors for protective bonding and conductors for supplementary bonding. Inspection technician can verify the continuity of the protective conductor PEN and PE. It can be done, for example, by measuring the impedance {resistance} of the protective conductor with a special measuring instrument or by measuring with basic measuring tools, which is technically demanding and sometimes unrealistic for the great distances.

Electrical equipment inspections are done when it is planned to use the equipment for the first time { initial inspection, or initial professional inspection and professional exam} and then repeatedly at pre-set times. The times depend on the type of object in which the electrical installation placed and on the external influences ranging from ¹ A to 5 years. In the time before the initial inspection (after the assembly ), repair, reconstruction, modernisation and between the repeated inspections, there can be a fault in the protective conductor PEN, which creates a dangerous state in the electrical installation, which can lead to an injury caused by an electric current, electric shock.

/ There were ocassions, when disconnection of the protectove conductor lead to a destroyal of the whole electrical equipment , or even to a death injury in the worst case. /

Fundamentals of the technical solution

The risk of electric shock is higher when there is a protective conductor fault.

This is because electrical equipment can still be in operation, however, the largest protection against electric shock is not working.

This considers mainly the objects, where the electric energy (electroinstalltion) is used by people without the electrotechnical qualification, laymen, which increases the risk of electric shock.

When the protective conductor PEN and PE faults, there is no protection against electric shock safeguarded by automatic disconnection of supply. The object's functions of supplementary protection - residual current device and surge protective device - are also at risk.

Described technical solution of the ENCE and PENCE device , see Picture No

4, are the devices , which contain electrical and electronic elements contained in particular parts of the device.

The device ENCE , see Picture No 1 , contains a supply NZE, pulse generator

GIE, measure moduls MBE, control unit RJE, alarm unit SJE.

The device PENCE, see Picture No 3, contains a breaker modul BI , rectifier U, supply NZ, standby supply A, measure circuits MO , help circuits of measure transformer of current POMTP, measurie transformer of current MTP, control unit RJ and an alarm unit SJ.

The device is designed to automatically control the continuity of the protective conductor PEN {equipment PENCE }and PE {equipment ENCE } in the

TN-C-S or TNS supply, in switchboxes and electrical circuts located in electric energy distribution.

To automatically measure the continuity of the protective conductor means, that it is possible to set the frequency of the continuity control {once a minute, hourly, daily, etc} depending on the time of using the objects, especiall of the

1st class objects .

ENCE device is made out of a supply NZE containing a standby supply - accumulator {with an autonomity according to the demand }, pulse generator GIE , two measure moduls MBEl and MBE2, control unit RJE {which contains mainly the comparators and a microprocessor} and an alarm unit SJE containing the alarm elements. The fundamentals of the automated control of the protective conductor PE continuity dwells in pulse transmition according to STN EN 61557 / IEC 61557/ through the protective conductor and a neutral conductor and in the identification of a direction from where the pulse returns. This happens through the measuring transformers of the current. The evaluation of these pulses is done in the microprocessor placed in the control unit RJE. After the pulse detection and the evaluation of the protective conductor condition through the microprocessor, the condition of the protective conductor continuity and protective bonding is signaled by the light of the green LED diode.

In the case of disconnected protective bonding , when the protective conductor is connected , the continuous red light of the LED diode will switch on , which will be accompanied by a continuous penetrating acoustic alarm signaling a threatening danger.

In the case of disconnected protective conductor, the red light of the LED diode will blink and the sound alarm will give out an interrupted penetrating acoustic alarm signalling the danger. This should warn the user and the work of the electrical equipment {1st class especially} should be stopped.

ENCE device is supplied in the three wire system through a single phase (see Pict. No. 1), in five wire system it can be through one or three phase ( see Pict. No.2). Three phase supply increases the reliability of the supply and provides the control of possible phase disconnection at the same time.

Control unit RJE contains a testing button ,,TT". TT launches the connectivity test of the protective conductor and a protective bonding at any time , mainly at the beginning of the 1st class electrical objects usage (e.g. washing machine, etc.). After the equipment does the test of conductor connectivity, it signals user whether the object is connected to the protective conductor and if it can be safely used.

We recommend to provide the ENCE protection against the overvoltage by surge protective device class D / IV/ .

We recommend to use the device ENCE directly in socket circiuts

{directly in the sockets} and mainly in the circuits of the current - using equipment { directly in the current / using equipments} of the 1st class , e.g. washing machies, dishwashers, fridges, freezers, electric heaters, water heatrs and irons in the households, fridges and freezers in the restaurants, computers in the offices, computers and drivers in the productions workings.

PENCE device contains of power supply NZ, which provides the supply of the control and supplementary circuits and an accumulator A charging. Accumulator A continuously charges while at operation. In the case of interruption in the supply or in the case of protective conductor PEN disconnection, it supplies the control and alarm unit. It is recommended to set the autonomity of the accumulator supply depending on its capacity and the type of operation/ premises , where the device is planned to be used. We recommend minimum of 6 hours. A power supply is designed as galvanicaly separated. For safety reasons it is possible to disconnect its primary neutral point through electronic high impedance switch circuit with the signal from the control unit, in the case of detected disconnection of the PEN conductor.

A way of PEN conductor connectivity evaluation is as follows:

Line -to-neutral volatge are one way rectified in the rectifier {AC/DC converter } U. Positive and negative half waves are evaluated separately. Through a measuring resistance voltage divider there runs a measuring current volatge connection (through electronic switch element ) (in accordance with STN EN 61557, IEC 61557), which creates a voltage drop in the resistance voltage divider, that is equalised by a smooth capacitor. This voltage is compared to a reference value in the comparator and an evaluated logical output of this operation is executed in the control unit RJ.

Measuring transformer of current MTP must be dimensioned according to the switchbox parameters , to which it is connected. In the secondary circuit of the POMTP measuring transformer, it is necessary to provide a sufficient resolution of the decoding circuit in the extent of the values and its own measuring current bonding of the PEN conductor {when the PEN conductor is not loaded} . This is so because of the need of the relatively small current evaluation. It is necessary for the circuit to bear a full load at the same time, while to differ and absolute value of the current is necessary only in the range needed for evaluation of the measuring current.

Measuring transformer of current MTP is used in the circuits for the needs of finding the path circuit of the measuring current from the supply:

1. PEN conductor to source of supply

2. to local earthing of the PEN conductor

3. to lead out PEN conductors.

For the correct operation of the device the MTP measuring transformer of current should be connected {from the view of way of supply, e.g. transformer } before the branching point and local earthing and connection of this device to the PEN conductor.

The control unit RJ ensures connecting of the measuring circuit at required intervals, decodes measuring current, its circuits path closure. In the case of detection of the PEN conductor disconnection and a fault in supply, it controls the alarm unit. A test button ,,TT" is a part of the control unit, which enables to launch a test of connectivity of the protective conductor and protective bonding at any required time.

The alarm unit SJ signals safe and fault conditions with an acoustic and light signalisation. In the case of uninterrupted PEN conductor , the green light of the LED diode is on. In the case of detected cutt - off PEN conductor , the red light of the LED diode blinks and there is a distinctive penetrating interrupted acoustic signal. In the case of a fault in a supply , the red light LED diode will be on continuously and there will be a continuous acoustic signal.

It is possible to set the time of how often should the connectivity of the PEN conductor be controlled {once a minute/ hour/ a day}, depending on the time of 1st class objects usage . This is called an automatic control of the PEN conductor connectivity.

The device PENCE is designed to be used in low-volatge electrical power supplies. TNC, or TNC-S, where it should do an automatic operational continuous control of the input PEN conductor continuity.

There is an increased risk of possible electric shock in the metal distribution/ switch boxes and in the fuse boxes of the distribution wiring system. This is because they are placed in public places and they are aceesible to people without an electrotechnical qualification. When the PEN conductor disconnects, there is no protection against electric shock by an automatic disconnection from a supply provided behind the place of disconnection. A line- to-neutral voltage can reach the exposed conductive part of the metal distribution and fuse boxes and the 1st class current-using equipment in the conncetd electrical installations.

We recommend to use the device PENCE directly in the switch boxes so that the signalisation of the PEN conductor condition is accessible {visible and audible}. One advantage of PENCE device , in operation with ENCE device, is that it provides the control of the PEN conductor continuity from a supply - transformer up to a current -using equipment, {see Pict No 4}

Another advantage of using the PENCE and ENCE devices is the division of the measurement of the PEN conductor continuity to two parts: from a supply up to a branching point and from a branching point to a current -using equipment. A conductor PE and N is used for measuring in the second part a so the supply of el. energy-transormer, is not overloaded by measuring impulses. Overloading the supply could cause problems if too many current -using equipments were involved.

Considering that both the devices ENCE and PENCE contain electronic elements, they have a self - consumption /assumed up to 2 W/ , which is their disadvantage. It can also be a a source of higher harmonics, as this design does not involve a higher harmonics filter. In the case of ENCE and PENCE devices usage in greater amounts, we recommend to facilitate the equipment with a higher harmonics filter. List of Pictures

Picture No.l - Block diagram of the ENCE device for an automatic measurement of the PE conductor continuity for a three-wires electrical installation.

Picture No.2 - Block diagram of the ENCE device for an automatic

measurement of the PE conductor continuity for a five-wires electrical installation.

Picture No.3 - Block diagram of the PENCE device for an automatic measurement of the PEN conductor continuity

Picture No.4 - An example of wiring the devices ENCE and PENCE for an automatic measurement of the PEN and PE conductor continuity

An example of technical solution realisation

A device for an automatic meaurement of the PE conductor continuity, ENCE , see Pict. No. 1, is a device made out of a supply NZE , containing standby supply - accumulator with autonomity according to the need {e.g. 12 hours}, impulse generator GIE, two measure moduls MBl a MB2 with measuring transformers of the current , control unit RJE containing mainly comparators, control microprocessor and a test button TT , and a alarm unit SJE containing green and red LED diode light signalisation and an acoustic signalisation with a penetrating acoustic signal.

The device is assembeld directly to the 1st class current-using equipment., e.g. washing machine, dishwasher, computer and etc. , where it will control and signal the condition of the PE conductor behind the branching point. It can also be assembled directly to the socket supplying the 1 st class current -using equipment.

Automatic measurement of the PE conductor continuity dwells in in pulse transmition from the impulse generator GIE through the protective conductor and a neutral conductor and in the identification of a direction from where the pulse returns . This happens through the measuring transformers of the current in the measure moduls MBEl a MBE2 . The evaluation of these pulses is done in the microprocessor placed in the control unit RJE.

After the pulse detection and the evaluation of the protective conductor condition through the microprocessor, the condition of the protective conductor continuity and protective bonding is signaled by the light of the green LED diode. In the case of disconnected protective bonding , when the protective conductor is connected , the continuous red light of the LED diode will switch on , which will be accompanied by a continuous penetrating acoustic alarm signaling a threatening danger.

In the case of disconnected protective conductor, the red light of the LED diode will blink and the sound alarm will give out an interrupted penetrating acoustic alarm signalling the danger. This should warn the user and the work of the electrical equipment { 1 st class especially} should be stopped.

At the same time there will be a device PENCE assembled to the entry of the switchbox , which will measure automatically the PEN conductor continuity. The device PENCE contains of power supply NZ, which provides the supply of the control and supplementary circuits and an accumulator A charging.

Accumulator A continuously charges while at operation. In the case of interruption in the supply or in the case of protective conductor PEN disconnection, it supplies the control and alarm unit. It is recommended to set the autonomity of the accumulator supply depending on its capacity and the type of operation/ premises , where the device is planned to be used. We recommend minimum of 6 hours. A power supply is designed as galvanicaly separated. For safety reasons it is possible to disconnect its primary neutral point through electronic high impedance switch circuit with the signal from the control unit, in the case of detected disconnection of the PEN conductor.

A way of PEN conductor connectivity evaluation is as follows:

Line -to-neutral volatge are one way rectified in the rectifier U. Positive and negative half waves are evaluated separately. Through a measuring module MOl, M02 there runs a measuring current volatge connection (through electronic switch element ) (in accordance with STN EN 61557, IEC 61557), which creates a voltage drop in the resistance voltage divider, that is equalised by a smooth capacitor. This voltage is compared to a reference value in the comparator and an evaluated logical output of this operation is executed in the control unit RJ.

Measuring transformer of current MTP must be dimensioned according to the switchbox parameters , to which it is connected. In the secondary circuit of the POMTP measuring transformer, it is necessary to provide a sufficient resolution of the decoding circuit in the extent of the values and its own measuring current bonding of the PEN conductor {when the PEN conductor is not loaded}. This is so because of the need of the relatively small current evaluation. It is necessary for the circuit to bear a full load at the same time, while to differ and absolute value of the current is necessary only in the range needed for evaluation of the measuring current.

Measuring transformer of current MTP is used in the circuits for the needs of finding the path circuit of the measuring current from the supply: 4. PEN conductor to source of supply

5. to local earthing of the PEN conductor

6. to lead out PEN conductors.

For the correct operation of the device the MTP measuring transformer of current should be connected { from the view of way of supply , e.g. transformer } before the branching point and local earthing and connection of this device to the PEN conductor.

The control unit RJ ensures connecting of the measuring circuit at required intervals, decodes measuring current, its circuits path closure. In the case of detection of the PEN conductor disconnection and a fault in supply, it controls the alarm unit. A test button ,,TT" is a part of the control unit, which enables to launch a test of connectivity of the protective conductor and protective bonding at any required time.

The alarm unit SJ signals safe and fault conditions with an acoustic and light signalisation. In the case of uninterrupted PEN conductor , the green light of the LED diode is on. In the case of detected cutt - off PEN conductor , the red light of the LED diode blinks and there is a distinctive penetrating interrupted acoustic signal. In the case of a fault in a supply , the red light LED diode will be on continuously and there will be a continuous acoustic signal.

List of marks used in the Pictures

NZE -one -phased supply with a standby accumulator, for safeguarding the operation in the case of diconnection or in the case of interrupted protective conductor

GIE - impulse generator , generates the measuring impulses to prevent the blinding of the protective devices from automatic continuity measuring instrument and to prevent harm the serviceman from harm

MBEl, MBE2 - measure modules containing measure transformers of the current for the pulse detection

RJE - control unit , contains control microprocessor, comparators and a test button TT

SJE - alarm unit , contains signaling LED diodes and an acoustic

signalisation

BI - breaker modul

U - rectifier

MOl, MO2 - measure modul NZ -supply, feeds the device

A - standby accumulator , feeds the device in the case of supply

disconnection or in the case of protective conductor disconnection

MTP - measuring transformer of the current

POMTP - supplementary circuits of the measuring transformer of the current

RJ - control unit , contains control microprocessor, comparators and a test button TT

SJ - alarm unit , contains signaling LED diodes and an acoustic signalisation

ENCE - a device for measuring the PE conductor continuity behind the branching point of the conductor PEN

PENCE - a device for measuring the PEN conductor continuity before the branching point of the conductor PEN