Socket & See PDL310 Technical Document - Stroma
Contents
1. PART P Loop Testing using the PDL 310 What IS the Loop and why must it be tested When a fault occurs in an electrical system the over current device must open the circuit to cut off current quickly In domestic circuits this device will be a miniature circuit breaker MCB or a fuse both of which operate when the current they carry exceeds the rated value The supply voltage drives this fault current the value of the current depending on this voltage and the resistance strictly the impedance of the circuit in which it flows A higher voltage or lower impedance will result in a greater current and a faster time of operation of the fuse or of the circuit breaker It is of the greatest importance that the circuit concerned is disconnected as quickly as possible to prevent dangers due to electric shock or to fire The supply voltage is fixed by the Supply Company so to achieve the greatest possible level of safety we must ensure that the impedance of the path taken by the fault current is low enough to ensure rapid operation of the protective device This path is called the earth fault loop or sometimes simply the loop This loop may be extensive going through the installation itself and all the way back to the Supply Company s transformer The PDL 310 measures the impedance of this loop and thus checks the safety of the system The lower the loop impedance the greater the fault current and the more quickly the circuit is discon2. Faulty E L N miswire After use the instrument should always be switched off to prevent unnecessary battery drain The instrument has a feature that Faulty L Emiswire automatically switches off after about two minutes if this is forgotten Zz fa Faulty L N E miswire A 2 A Faulty L N E miswire Faulty L N miswire Zz fa e e Zz A No Mains e Batteries The PDL 310 uses 4 x AA batteries and ideally good quality alkaline types should be used A new set of these batteries LED s will flash to indicate fault condition NC No Connection can be expected to complete more than 10 000 tests or the shelf life of the batteries amp 9EE Socket amp See Industrial A WOTE www socketandsee co uk Unit 4 Century Road High Carr Business Park This document is intended as a Guide to Loop Testing only and Newcastle Staffordshire UK ST5 7UG reference should be made to the PDL310 User Manual for full T 44 0 1782 567096 operating instructions before any tests are undertaken F 44 0 1782 567095
3. L 310 showing a measured value of prospective fault current This is an example only plugged into a 13A standard socket normally PFC would be measured at the distribution board origin of supply using fused test leads such as ITLS 400 The PDL 310 has a number of other features in its design Condition Wiring Supply LED that are useful to the user Number Condition Terminal Display N These are i Continuous Warble Warble Warble Warble Warble Warble Warble Warble Warble Warble Warble Warble Warble Warble Warble Warble 9 None Correct Operating temperature cut out L E reverse L N E miswire The instrument can warm up with repeated use and if a high temperature L N reverse is reached this could affect the accuracy of the readings obtained The PDL 310 has an automatic cut out to inhibit its L N E miswire Faulty N L E miswire use if such a temperature is reached and Faulty N E miswire Faulty N Faulty N L E reverse the thermometer symbol appears in the display to the left of the voltage display If this happens switch the instrument m rm ee Se ie ee 2 3 4 5 6 7 8 2 off when it has cooled down it will Ss Zz a Faulty E L N reverse Faulty E Faulty E N miswire automatically reset and test correctly al Zz ay Automatic switch off TU a eee ree ae e eal re J zZ a
4. can proceed 3 The PDL 310 showing correct connections and displaying the supply voltage Below these indicators the display screen will show the supply voltage In theory the nominal supply voltage for the UK is 230 V but in practice it is more usually around 240 V If the supply voltage is outside the permitted limits of 207 V to 253 V the tester will be automatically prevented from carrying out further tests In this unlikely event expert help probably from the customers Supply Company will be an urgent necessity Loop testing with the PDL 310 Leave the PDL 310 plugged into its socket or connected to the supply with the fused test lead set Check that the three LEDs in the triangle are all green and that the supply voltage is within the correct limits of 207 V to 253 V Now press the button below marked LOOP PFC TEST There will be a short series of flashing zeros on the display whilst the test is underway followed by a sharp beep sound During this period the wait symbol will also appear to the left of the display Then the value of the loop impedance will appear on the display for about five seconds If the reading is less than 1Q this is an excellent result a value we would expect from most installations fed from an underground supply which are known as TN systems see Figure 4 Possibly the only situation where this result would not comply with the Wiring Regulations is if it applies to a high current circuit su
5. ch as a cooker protected by a rewirable fuse This is unlikely in modern practice and could be rectified by changing the fuse for a suitable miniature circuit breaker MCB ing a measured value Should the reading be above 1Q but below 2Q this may well be acceptable First make sure that the plug pins and the socket contacts are clean by unplugging and re plugging the plug several times and then test again Another possible reason for the high reading is if the socket under test is distant from the incoming mains The longer the cables feeding the outlet the greater will be their resistance and the higher the loop reading will be However it is very unlikely that cables feeding an outlet are so long that they will have a major effect on the loop impedance There are cases where loop impedance readings as high as 10 Q are acceptable in installations fed from an underground supply TN systems but these apply only to circuits fed from very low rated fuses or circuit breakers usually 5 A or 6 A The installer who is not totally familiar in electrical installation theory would be well advised to treat 2Q as the maximum acceptable value of earth loop impedance for an electrical installation fed from an underground supply TN system In cases where the electrical supply is by overhead cables TT system it is very likely that high values of loop impedance will be encountered due to the high resistance of the earth electrode co
6. nected So what should the value be Loop impedance values There is no single simple answer to the question What is an acceptable value for fault loop impedance The answer is of course the impedance that will allow enough fault current to operate the fuse or circuit breaker quickly enough to prevent damage to the installation or to those using it But this impedance depends on the exact operating characteristics of the fuse or the circuit breaker concerned as well as on the rating of the device For example a rewireable fuse requires lower loop impedance than does a cartridge fuse whilst the acceptable value is higher for a miniature circuit breaker Again a 30 A fuse will require a much lower loop impedance value than will a 5 A fuse Exact maximum values for loop impedance are to be found in tables forming part of the IEE Wiring Regulations BS 7671 This publication can be difficult to interpret A little later a simplified explanation of the acceptable results will be given Setting up the PDL 310 You must first understand that the loop to be tested includes the supply system so the mains must be switched on to carry out a test Caution We strongly advise reading and understanding this guide before the instrument is used In particular note the safety issues that follow Although fully protected up to 600V AC this tester is for use on 230V AC circuits only Always check the tester on a known correctly wi
7. nnecting the system to earth In these cases electric shock protection cannot be provide by fuses or circuit breakers and the IEE Wiring Regulations require that residual current devices RCDs are fitted to provide this protection Residual Current Devices RCDs These safety devices have become common in many modern installations both those fed by underground supplies TN systems as well as overhead supplies TT systems They are intended to limit the time during which the electric shock received in the event of an earth fault to a value unlikely to case death They operate by constantly monitoring the electric currents in live phase and neutral conductors the difference between the two being current escaping the earth When this current reaches a preset level typically 30 mA which is thirty thousandths of an ampere they will switch off the circuit extremely rapidly See Figure 6 al current device 6 A typical resi A RCD in consumers unit B Plug in RCD for protection of single appliance C Socket outlet incorporating RCD To measure the impedance of the earth fault loop a current is deliberately passed through it in most cases tripping the RCD The PDL 310 however has special circuits to prevent this from happening thus removing the need to short out the RCD which is a skilled task and not recommended in current guidance notes Measuring Prospective Fault Current PFC Prospective fault curren
8. red live socket outlet before and after use Before use check your tester for any damage to the plug lead and cabinet Plug the tester into a socket on the circuit to be tested as shown in Figure 1 The PDL 310 connected ready for use Switch the socket on when the instrument will go through its pre test routine The three LEDs in the orange triangle on the tester will be a steady green accompanied by a series of bleeps while the instrument sets itself up into its operating condition If the LEDs are not all green indicating faulty wiring or connections the tester will automatically lock out to prevent further tests Should any of the LEDs in the triangle be lit or flashing as red or orange accompanied by a warbling tone this indicates a wiring fault the nature of which is shown by the list on the front of the instrument and in more detail by the table on the back of this Guide This extremely valuable test facility is built in to the PDL 310 Such faults may require assistance and advice to correct them In the event of a socket not being available the PDL 310 loop tester can be powered by connecting it to any suitable supply possibly at a consumers unit using a fused test lead set Care must be taken to ensure that the brown lead is connected to the phase live Note this picture shows using the Socket amp See ITLS 400 fused test lead set the blue neutral probe can be piggy backed into the green earth unit and
9. t is the electric current that will flow in the event of a short circuit from live phase to earth or neutral This is the current that operates the fuse or the circuit breaker in the event of an earth fault and which therefore provides protection All fuses and circuit breakers have an upper limit of current beyond which they cannot be relied upon to operate safely and the installation designer must choose protective devices that will deal safely with the maximum current possible in a particular case In order to do so he will calculate the maximum current that can flow and will need to verify this in the completed installation by measuring it The PDL 310 will carry out this measurement The voltage applied to any circuit drives the current flowing in it and the resistance or the impedance of the circuit limits this current The maximum fault current value therefore can be found by dividing the supply voltage by the impedance it meets In this case the PDL 310 measures both the supply voltage and the loop impedance and is programmed to carry out the calculation so that the prospective fault current can be displayed Pressing the PFC button after first having carried out the LOOP PFC test will calculate and display the prospective fault current value as shown in Figure 7 If the current does not exceed 999 A the value will be shown directly in amperes A whilst for higher currents it will be measured in kA thousands of amperes 7 The PD
10. then a croc clip attached to the front of the green unit Your tester is now a two wire testing device and measurement can be made between phase neutral or phase earth WARNING Always make the Neutral or Earth connection before connecting to Phase 2 The PDL 310 PLUS connected to a consumers unit using the fused test lead set supplied Please note the ITLS 400 test lead set is only included with PDL 310 PLUS It is an optional extra for standard PDL 310 Reversed Supply Polarity It is seldom appreciated that the supply to an installation can be misconnected so that the live phase and neutral earth supply conductors are reversed This state of affairs is extremely rare but very dangerous indeed because the live phase of the supply system will in many cases be connected directly to the earthing system so that all earthed metal will become live If this mistake has been made there will be no obvious sign with sockets and all equipment operating normally and most loop impedance testers will not show that a dangerous situation exists The supply polarity can be verified by applying firm thumb pressure onto the orange area at the bottom of the front panel of the tester which is labelled PRESS AND HOLD Note that this area does not depress as is the case with the ON OFF PFC and LOOP PFC TEST buttons above it If the three LEDs in the orange triangle remain green as shown in Figure 3 polarity is correct and the loop test
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