Re-take - Useful Information for 2394 :

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UsefulJunk : 41.3.

Maximum( Zs ) for . Circuit-breakers to . BS-EN-60898 - Overcurrent-characteristicsof . RCBO - BS-EN-61009-1 . for. ( Instantaneous-operating ) givencompliance with the . 0.4s & 5s . disconnection-times at . nominal-voltage . (Uo of 230V )

Characteristics- type - B . ( Zs- Ω ) for device of . rated-current . (In ) 46 / In .
Characteristics- type - C . ( Zs- Ω ) for device of . rated-current . (In ) 23 / In .
Characteristics- type - D . ( Zs- Ω ) for device of . rated-current . (In ) 11.5 / In .

 

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Circuit-breaker- BS-3871 . Still in Use. Obsolete to BS-7671:2011: standards

Whatis the . Maximum-value of ( Zs ) at anominal-voltage . Uo - 230V .
Type- 2 . circuit-breaker . BS-3871 . with a rated-current ( In -30A ) Maximum-value of ( Zs -230V ) is [ 32.8 / In = 32.86 / 30 = 1.1Ω ]

41.3: - 3A . 6A . 10 .
[ Type - B - right hand side of table - 41.3 ] making me . 46/ In

Your Example to work to . Scenario !!. Type - B. circuit-breaker . rated-current ( In ) of 8A .
Overcurrent- characteristic of . RCBO . Maximum-value of ( Zs ) - 230V is 46 / In = 46 / 8 = 5.75Ω . [ 46 ÷ 8 = 5.75Ω ]

 

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Maximum( Zs ) circuit-breakers - BS-3871 . Obsolete to BS-7671:2011: standards
for.( Instantaneous-operating ) givencompliance with the . 0.4s & 5s . disconnection-times at . nominal-voltage . (Uo of 230V )

Type- ( Zs - Ω ) for device of rated-current - ( In )
Type- 1 . 57.5 / In .
Type- 2 . 32.86 / In .
Type- 3 . 23 / In .
Type- 4 . 4.6 / In .

Type- B . 46/ In .
Type- C . 23/ In .
Type- D . 11.5/ In .

 

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Example: Basics .

Maximum-Earth-fault-loop-impedance. Overcurrent-protective-device .

(Zs ) can be found using the formula given . in Appendix - 3 - BS-7671: p.295 .Where :- [ Zs = Uo / Ia ]

Uo ) . is the nominal . a.c. - rms .Line-voltage to earth .
Ia) . is the current-causing-operation . of the protective-device within the specified-time. [ 0.4s or 5s ] obtained from the .manufactures-time / current-characteristics. for this particular-device-type & rating .

Example. manufactures-time / current-characteristics . for a 400A - fuse. to BS-88-2 . gives a value of . ( Ia - 2840A ) for a disconnection-time of 5s .
Usingthe above-formula . the maximum-value of ( Zs ) for a disconnection-time - 5s . & a nominal-voltage ( Uo - 230V ) Now - 230V ÷ 2840A = 0.08Ωs .

 

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Fig- 3A1 . p.296 . …. it is worth keeping the BS-7671:2008:

Fuses: 2008 : complying with these - withdrawn-standswill be found in . existing installations . for years to come .

BS-1361 is → BS-88-3 : fuse-system C .

Table- 41.2. - ( 0.4s ) BS-88-3 :
Table- 41.4. - ( 5s ) BS-88-3 :

Question. Maximum ( Zs ) value for . BS-88-3 . in 41.4 - (b) How these . maximum ( Zs ) values are obtained.
411.4.5.- Formula - ( Zs x Ia ≤ Uo )

Where:
Zs) . Earth-fault-loop-impedance in Ωs
Ia) . Current in amps . which causes the protective-device to operate . withinthe time-specified in table - 41.1. or
Ifappropriate . within the . 5s . disconnection-time-specified in . regulation -411.3.2.3. for TN-system(s)
Wherean RCD . is used . the current ( Ia ) isthe rated-residual-operating-current . which provides disconnection . within thetime specified in . table - 41.1. . or
Ifappropriate . within the . 5s . disconnection-time-specified in . regulation -411.3.2.3. for TN- system(s)

Uo) . Nominal-voltage to Earth . in Volts- 230V for standard . a.c. Single-phase & Three-phase-circuit(s)
Uo- 2011 ) Nominal . a.c. rms or d.c.line-voltage to Earth in volts - ( V )

Appendix- 3 :
Thevalue of ( Ia ) can be obtained by reference to the appropriate . time /current-characteristic of theprotective-devices & RCDs inAppendix - of BS-7671:2011:

20A- BS-88-3 fuses .
Assumewe have a . 230V - TN - a.c. system with. overcurrent-protection . provided by 20A - BS-88-3 . for a final-circuit - not exceeding 32A .
41.1.- requires that disconnection of the circuit . takes place within a .maximum-time of ( 0.4s )

Youron Calculations .
Maximum-earth-fault-loop-impedance - ( Zs ) which will ensure that . 20A - BS-33 fuses will . disconnect the circuit. within - 0.4s
411.4.5. shown above . but transpose . it to make . ( Uo the subject . this gives ) Uo . Zs ≤ Ia . Uo = 230V .

Toobtain ( Ia ) Fig - 3A1 . Appendix - 3 . time/ current-characteristic . for BS-88-3 . fuses .

Fig- 3A1 . I can’t draw a line .
3A1. representing the . 20A - fuse givesus the value of current . ( 113A ) mucheasier to use the table at the .top-right of the page . fromthis table we can see . that the value of current which causes . 20A - BS-88-3 . fuse to operate within. 0.4s is ( 113A ) back to your formula . ( Uo. Zs ≤ Ia 230V ) Zs ≤ 113 . Zs ≤ 2.04Ω .

Table- 41.2. (b) Maximum - Zs . 20A - BS-88-3. fuse is 2.04Ω

Maximum- ( Zs ) Table(s) & Appendix - 3 . relationship between . the current required to. operate the protective-device . & the earth-loop-impedance-values .

 

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Q). 2394 : ( T ) could you get this on Exams.
Documentationfor every electrical-installation . should include that required by . Regulation . ??

p.20. 132.13 .
Everyelectrical-installation . shall be provided with appropriate- documentation .including that required by . Regulation - 514.9. Part - 6 . & where applicable Part - 7 .

 

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Q). 2394 : ( T ) could you get this on Exams.
Documentationfor every electrical-installation . should include that required by . Regulation . ?? Sorry .All the Above - 132.13 .

 

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2394: Q ) . When automatic-disconnection of supply . is used as a measure of protection. additional-protection by RCD . shall be provided for . ??
Socket-outlets. with a rated-current not exceeding . 20A. that are for the use by . Ordinary-persons & are intended for .general-use. - 411.3.3.

 

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2394: Q ) . All circuits in a location .containing a bath or shower shall have . ??
Additional-protectionby . a 30mA - RCD - 701.411.3.3.

Q) . in Exams . this is to warm you up. -&-s
Maximum-disconnection-time. for a lighting-circuit in acommercial-premises . protected by a . TT- system . A) . 0.2s - table - 41.1

Q) . The maximum - ( Zs ) to ensure .30mA RCD operation is . A) . Table - 41.5. 30mA - 1667Ω

Q) . BS-EN-60898 - circuit-breaker can . be used for . Table - 53.2.
Isolation.
Emergency-switching.
Functional-switching.
All of the above

2394: As BS-7671:2011: makes a song & dance about it . “ Line-conductor “ please referto definition
Q) . A Line-conductor includes ?? .
Aconductor of an . a.c. system for the transmission of electrical-energy other than a .neutral . protective-conductors & PEN-conductor . definition

 

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Thiswas Posted to me . two-days ago . some reading required .

411.4.5. - Where an RCD is used for . Fault-protectionin a circuit TN-system . the condition ( Zs/ Ia ≤ Uo ) has to be met . just as it does when an. overcurrent-protective-device is used to provide . Fault-Protection . to meetthis condition where an RCD . is used . the earth-fault-loop-impedance ( Zs )in the circuit must not exceed the nominal-voltage of the supply ( Uo ) divided by the current ( Ia )causing-automatic-operation of the RCD within thespecified-maximum-disconnection-time .
Time not exceeding ( 0.4s ) has to beachieved using an RCD to BS-EN-61008-1 & BS-EN-61009-1 . of Non-delay-type. with a rated-operating-current ( IΔn) of 100mA

( a ) in a . circuit of nominal-voltage - 230V . it can be seen from table - 3A . in appendix -3 . BS7671:2011:
That a current of . 100mA is required to cause the RCD to operatewithin - 0.4s . Operation will actually-occur within . 300mS at 100mA .
Accordingly. the maximum-earth-fault-loop-impedance ( Zs ) thatcan be tolerated in the circuit is . 2300Ω - ( 230V ÷ 0.1A = 2300Ω ) …. 100mA ÷ 1000 = 0.1A

RCDs- IΔn - mA

Maximum-valuesof earth-loop-impedance ( Zs - Ω ) for RCDs for fault-protection - TN- systems . operating on 230V .
Earth-loop-impedance ( Zs - Ω ) Circuit-loop-impedance .

Note- ( G - RCDs ) (a)
BS-EN-61008-1:
BS-EN-61009-1: ( 0.4s )
30mA- 7667Ω
100mA - 2300Ω
300mA- 767Ω
500mA- 460Ω

a) . Measured-values of ( Zs) should be lower than those in the above table . as the earth-loop-path in a TN- system is entirelymetallic . The ( Zs - value ) in this table apply to TN- system only .

b) . RCD - time-delay ( S ) Maximum-permitted( Zs ) depends on the rated [ declared-time-delay ] of the RCD .
Todetermine . Maximum - ( Zs ) consultRCD-time-current-characteristics . & obtain ( Ia ) the current inamperes-causing-operation . within the required-disconnection-time-delay ( Zs ) must not exceed ( Uo / Ia )

RCD- time-delayed ( S )
100mA- (b) 0.4s . 1150 Ω .
300mA- (b) 0.4s . 383 Ω .
500mA- (b) 0.4s . 230 Ω .

RCD- time-delayed ( S )
100mA- (b) 5s. 2300Ω .
300mA- (b) 5s. 767Ω .
500mA- (b) 5s. 460Ω .

Forconvenience . it has been listed . the maximum-earth-fault-loop-impedance values( Zs ) for RCDs used for .fault-protection in TN-systems . it is important that the ( Zs) values achieved in the installationshould be much lower . than those given in the table . as the . earth-fault-loop-path. in a TN-system . it should also be noted thatthe . maximum-values of ( Zs ) in theabove relate only to a nominal-voltage of 230V .& should be multiplied by a factor-equal to . Uo / 230V . if othernominal-voltages are to be used .

RCD. is employed for . fault-protection . consideration must also be given to protection against Overcurrent .

 

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Usefuljunk . We want the current ( Ib ) to beless than . 10mA - 0.01A “amperes “
mA - milliamp or 1 / 1000 part of an Amp .

 

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Backto the past . BS-7671:2001 / 2004 . O.S.G.

1.1.Scope .
Thisguide is for electricians ( Skilled-persons) it covers the following-installations. (in these days you could ask the boss for a pay-rise )

1.1.Scope . 2011 :
Thisguide is for . installers ( forsimplicity , the term installer has been used for electricians& electrical-installers) it covers the following-installations.

 

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Usefuljunk

- Ampere or Amps - represents the amount of current in a circuit .
- Voltage- is defined scientifically as . the circuit-potential-difference . & can be seen as the amount of “ Pressure“ that drives electricity in a circuit .
- One-Watt- is equal to one volt . multiplied by one-amp .

Garden-hose.
Thewater-pressure in the hose . is like-voltage
Ampis like the . volume of water-flowing through the hose .
Wattagethen . is the total amount of water that comes out the hose . per unit of time .

Term- that helps tie . together the other three . is the ( Ohm ) which is a unit of ( Electrical-résistance ) going back to the garden-hose . has alarger-diameter . more water will be able to flow through .
- Circuitwith a high-résistance-value . expressed in ( Ωs ) isable to carry fewer-amps . than with lower-résistance . regardless of the voltage.
-High-voltage-encounters-high-résistance . the amount of possible-amps in thecircuit . will be very-low . not muchwater will get through a narrow-hose . no matter how high the pressure is .

 

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TT- Installations . “Protective-devices “

Disconnection-timeof ( 0.2s ) for TT- installation has beenintroduced in the . 17[SUP]th[/SUP] Edition . This makes the use of an . RCD or. Circuit-breaker with a . residual-element . virtually-essential .


RCDs- again
TT- installation . the earth-fault-loop-impedance is not usually-sufficiently lowto facilitate the operation of an (Overcurrent-protective-device ) within the required-disconnection-time .BS-7671:2011: as the disconnection-timefor . TT - systems is 0.2s .

TT - systems compared with the ( 0.4s ) required in the Previous-Edition . “how thing have Changed “

TT- installations require attention becausethey normally have a higher-impedance to earth via-an electrode buried in theground . high-earth-fault-impedancewould reduce an . earth-fault-current & slow down the tripping of acircuit-breaker . 2395 : “ RCDs “

Some-Facts: TN- systems have avery-low-earth-impedance . which in most-cases . circuit-breakers would meetrequirements should an earth-fault-occur .
BS-EN-60898 & BS-EN-61099-1- circuit-breakers . designed to trip - 0.1s . reason ( Instantaneously) . requirements for . fault of Low-impedance . between Live-conductors
TT- systems . which have ahigher earth-impedance . they do notreliably meet the requirements for disconnection-time . Backto RCDs again . so . 0.04s / 0.2s

2394: don’t get mixed up on TN- . TT- . Systems . 0.4s - 0.04s / 0.2s - 0.04s . ( If )
TN- low-earth-impedance . ( Zs ) circuit-loop-impedance .
TT- systems . which have ahigher earth-impedance . ( Zs ) circuit-loop-impedance .

 

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2394: Where an RCD is used . we have two-methods .
Addition-protection )
Fault-protection )

Wherean RCD is used for ( Fault-protection ) product of the rated-residual-current andthe sum of the resistances of theinstallation - Earth-Electrode . & Protective-conductor (s) connecting it to . exposed-conductive-parts ( R [SUP]A [/SUP]) is required to benot . greater than . 50V - regulation - 411.5.3.

(R [SUP]A [/SUP]) It isrecommended that an . Earth-Electrode-résistance. where possible not-exceed - 200Ω -411.5.3. Note -2

2394: TT - system . do comeinto the Equation . in Exams . ( R [SUP]A [/SUP]) I got this on Exams . 411.5.3. so that there’s no confusion .
P.38 . The sum of the résistance of the . earth-electrode& the protective-conductor .connecting . Etc

Fault-protection: ( ADS ) - TT - system .
TT- system there is no . direct-connection between the installation . MET &the earthed-supply-source - earthed-neutral or star-point . other than throughthe general-mass of the Earth . therefore . particular requirements are necessary- Regulation - 411.5.1.

 

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2394:
Dear Customer . RCD / RCBO . Have you tested by . Operation of thepushbutton at . frequent-intervals . Then I can stop using (Grecian-2000 )

Iwas taught to do the ( x5 - test ) first . &if the device didn’t trip . take that as evidence that the ( User )probably wasn’t exercising the device .at the recommended-periods . in thelast six-months I’ve use this method . it can free sticky RCDs . not always , Howdo you get through to your customer . “ RCD is important “
“Seize up “ Lubricant used on the .Latching-mechanism - would emulsify overa period of Time . Yeah . as we wouldsay . “ Push theButton “

N****. training-DVD - Inspection & Testing . does say that . Initial-pushbutton testto ( Pre-lubricate the mechanism ) No am not working for the other side .

 

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2394 : Known yourregulations .

Earth fault loop impedance (Z[SUB]s[/SUB]) ……. inour case - Circuit-loop-impedance

Regulation612.9 requiresthat, where protective measures are used which require a knowledge of the earthfault loop impedance (Z[SUB]s[/SUB]), the relevantimpedances are to be measured, or determined by an alternative method.

 

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Useful junk BS-951

Installing a clamp in an inaccessible position

Likeall types of electrical connection that are not excused by Regulation - 526.3of BS 7671, the electrical connections between a BS 951 clamp, the pipe (or other tube) to which it isattached, and the protective conductor connected to its terminal must beaccessible for inspection, testing and maintenance (Regulation 543.3.3 refers).
Failing to fit a warning label

It is adeparture from Regulation 514.13.1 of BS 7671 to fail toinstall a suitable ‘SAFETY ELECTRICAL CONNECTION - DO NOT REMOVE’ label in avisible position at the connection of an earthing-conductor to an earthelectrode or of a bonding conductor to an extraneous-conductive-part. Such alabel is normally supplied with each BS 951 clamp. Misuse of BS-951 clamps Casesof misuse of BS 951 clamps are occasionally found Fitting a BS-951 clamp to the armour or metallic sheath of a cable BS-951 states that clamps to this standard are notintended for connection to the armour or sheath of a cable and requires thepackaging of the clamp to include the warning “ Notintended for use on the sheath or armour of a cable ”. This is becausethe action of tightening the clamp is liable to damage the cable, for exampleby crushing the bedding or insulation or by causing the metal in a lead sheathto cold-flow. Such damage may result in high resistance and unreliability in theelectrical connection between the clamp and the armouring or metallic sheath,and may even result in an electrical fault within the cable, with thepossibility of serious injury to persons. Fitting a BS951 clamp to the armour or metallic sheath of a cable is thereforeunacceptable. Fitting a BS 951 clamp whichis unsuitable for the pipe diameter and/or cable size.

A BS 951 clamp must be correctly selected for both thesize of pipe or tube to which it is to be fitted and the size of cable. Fittinga clamp which is unsuitable in either of these respects is liable to be adeparture from the requirements of Regulations 526.1 and/or 526.2 of BS 7671 relating to durable electrical continuity,adequate mechanical strength, and appropriate selection of a means ofconnection.

 

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2394: As the RCBO . is here to stray . Somefacts . ( i )
Conventional-tripping-current. RCBO-61009-1.

Anovercurrent-protected-pole . is defined by BS-EN-61009-1 . as a pole provided with an overcurrent-release .

Rated-current ( In ) is the maximum-current which an RCBO . isdesigned to carry for long-periods . ata specified-reference air temperature . normallyof 30°C
Theterm ( Rated-current ) generallymeans the same as ( Current-setting ) asused in BS-7671 . in relation to protection against . Overcurrent .

Thepreferred-values of rated-current givenin BS-EN-61009-1 . 6A - In . up to 125A- In . BS -

Rated-residual-operating-current- ( IΔn ) of an RCBO . is the value of . residual-current . assigned to the RCBO by themanufacture . at which an RCBO-operatesunder specified-conditions .

The. Standard-value . of ( rated-residual-operating-current ) BS-EN-61009-1- 0.01A . 0.03A .0.1A . 0.3A . 0.5A .
Re-cap.
10mA ÷ 1000 = 0.01A . . Etc .
500mA ÷ 1000 = 0.5A .

Wherethe function of an . RCBO as a RCD . rather than as anOvercurrent-device . is used for . fault-protection as part of the . protective-measure . ( ADS ) fault-protection depends upon the .RCBOs - sensitivity . as a residual-current-device .

The - Lower the rated- residual-operating-current . the Greater the sensitivity . should the fault be of .non-negligible-impedance . There’s a However .
Ifan RCBO is selected with to . low arated-residual-operating-current . this may result in . unwanted-tripping .

 

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2394: As the RCBO . is here to stray . Somefacts . ( ii )

Conventional-tripping-current. RCBO-61009-1.

The conventional-tripping-current . of acircuit-breaker . is the characteristic relating to . protection of the circuitagainst overload . it is a . specified-value of the circuit-current . which causes the device to trip within a specified-time - known as the conventional-time . at the specified-reference-temperature .
Conventional-tripping-current. is usually expressed as a . multiple of the rated - ( nominal ) current - ( In) of the circuit-breaker .

RCBO- residual-current-breakers . conforming to BS-EN-61009-1 . all have a conventional-tripping-current of. ( 1.45 - In ) the related- conventional-time . is
(1 - Hour ) for circuit-breaker(s) of rated-currents ( In ) up to and including ( 63A )
(2 - Hours ) for circuit-breaker(s) of rated-currents . Greater than( 63A )

Symbolgenerally used for . conventional-tripping-current ( I[SUP]2 [/SUP] ) rather than ( I[SUP] t [/SUP] ) as is used in . circuit-breaker standard such as RCBO-61009-1.
This is because . conventional-tripping-current. means the same as the . term .current-causing-effective-operation ofthe . Overload-protective-device . used in - BS-7671 - in which the symbol ( I[SUP]2[/SUP] ) is used .