# Electricity in Buildings Cibse Code K

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Electrical Engineering

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• CIBSE AMENDMENT

Guide K: Electricity in Buildings

Page 8-3, Figure 8.3: Caption should read:

August 2005

• Page 3-1: the following replaces equation 3.1:

P = Uo I cos (3.1)where P is the active power (W), Uo is the phase-to-neutralvoltage (V), I is the current (A), is the angulardisplacement between the voltage and current waveformsand is known as the power factor angle; cos is known asthe power factor.

Page 3-1: the following replaces equation 3.2:

P = 3 U I cos (3.2)where U is the line (i.e. phase-to-phase) voltage (V).

Page 3-1: the following replaces equations 3.3 and 3.4:

For single-phase:

S = Uo I 103 (3.3)

For three-phase:

S = 3 U I 103 (3.4)where S is the apparent power (kVA).

Page 4-6: the following replaces equation 4.1 (wrongly numbered3.1 in the Guide):

Sa = 3 U Il 103 (4.1)where Sa is the rated kVA of the alternator (kVA), U is theline (i.e. phase-to-phase) voltage (V), and Il is the rated fullload line current (A).

Page 5-1: the following replaces equation 5.1:

PL = I2 Rc (5.1)

where PL is the power loss (W), I is the current carried inthe cable (A) and Rc is the resistance of the cable (). Byincreasing the voltage and, hence, reducing the current, thepower loss is reduced and the transmission efficiencyimproved.

Page 5-10: the following replaces equation 5.4:

KVAb Z lCable impedance (%) = 105 (5.4)V 2

where KVAb is the base kVA value (kVA), Z is the imped-ance per unit length of the cable (m1), l is the length of thecable (m) and V is the line (i.e. phase-to-phase) voltage (V).

Page 5-10: the following replaces equation 4.1:

MVAf 103

Isc = (5.7)3 V

Page 5-10: Example: fault level calculation: the followingreplaces the last equation in the example:

Hence, the maximum short circuit current is:

14.01 103Isc = = 20.22 kA3 400

Page 5-11: equation 5.8 is wrongly numbered 5.9 in the Guide;replace by:

HV fuse current LV device operation < (5.8)

0.05

Page 6-1: the following replaces equation 6.1:

S = Uo I 103 (6.1)

where S is the full load power (kVA), Uo is the ratedseondary (phase-to-neutral) voltage (V) and I is the ratedoutput current (A).

Page 6-2: the following replaces equations 6.2 to 6.6 and theaccompanying text:

For three-phase transformers, this is expressed as:

S = 3 U I 103 (6.2)The values for voltage and current in star- and delta-connected three-phase windings are as follows.

For star connection:

UPhase-to-neutral voltage = Uo = (6.3)3

For delta connection:

Phase voltage = line voltage = U = 3 Uo (6.4)The output current of the transformer in both cases isequal to:

S 103I = (6.5)

3 Uo

or:

S 103I = (6.6)3 U

Jan 2006

CIBSE Guide K: corrigenda GK01-1

• Page 6-5: the following replaces equation 6.7 (wrongly numbered6.3 in the Guide):

3-phase trans. rating (kVA) 100Fault level (kA) = (6.7)3 Uo impedance (%) where U is the secondary line (phase-to-phase) voltage (V).

Page 8-3: the following replaces the caption to Figure 8.3:

Figure 8.3 Basic radial final circuit; typical UK practice (Note: cablecolours will change from 2006, see section 8.4.1.4)

Page 10-3: in Figures 10.3(a) and 10.3(b), Uo should bereplaced by Uoc.

Page 10-3: the following replaces the caption to Figure 10.3:

Figure 10.3 Definition of earth loop impedance(9); (a) TN system, (b) TT system (Uoc is the no-load open circuit phase-to-earthed-neutralvoltage measured at the terminals of the transformer)

Page 10-7: the following replaces equation 10.4:

Ut = (Uoc Zp) / Zel (10.4)

where Ut is the touch voltage (V), Uoc is the no-load opencircuit supply phase-to-earthed-neutral voltage (V), Zp isthe return path impedance () and Zel is the earth faultloop impedance ().

Page 10-9: the following replaces equation 10.5:

If = Uoc / Zel (10.5)

where If is the earth fault current (A), Uoc is the no-loadopen circuit supply phase-to-earthed-neutral voltage (V)and Zel is the earth loop impedance ().

Page 10-10: in Figures 10.11 and 10.12, Uo should bereplaced by Uoc.

Page 10-10: the following replaces equation 10.13:

(Zp + Zpo)Ut = Uoc (10.13)Zel

where Uoc is the no-load open circuit phase-to-earthed-neutral voltage (V).

Page 10-10: the following replaces equation 10.14:

ZpUt = Uoc (10.14)Zel

Page 10-12: the following replaces Figure 10.14(b):

Main earthingterminal

Consumer'searth electrode

Generator

Supply from PES (REC)L1 L2 L3

L1 L2 L3 N E(b)

PEN

Jan 2006

CIBSE Guide K: corrigenda GK01-2