Acceptable value for earth resistan
Acceptable value for earth resistan
(OP)
Acceptable value for earth resistance
When measuring the resistance of the large earth electrode (earth mat) what is the acceptable values depending on soil resistivity.I also want to know the relevant SABS code that can be kept as reference for future earthing practise in my company.Please coment on the best methods I can use to measure earth resistance on substations.
When measuring the resistance of the large earth electrode (earth mat) what is the acceptable values depending on soil resistivity.I also want to know the relevant SABS code that can be kept as reference for future earthing practise in my company.Please coment on the best methods I can use to measure earth resistance on substations.






RE: Acceptable value for earth resistan
Use software (ETAP) or others to do this calculation.
Further suggest that you look in the Brown and Green books of IEEE. These may also help.
RE: Acceptable value for earth resistan
See IEEE Std 80, "IEEE Guide for Safety in AC Substations Grounding."
For measuring resistance, see IEEE Std 81, "IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System (Part 1)" and IEEE Std 81.2, "IEEE Guide for Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Grounding Systems (Part 2)."
RE: Acceptable value for earth resistan
http://www.cbi.co.za/papers/26/CBI4.pdf
http://www.promech.co.za/architect/archive.htm
(check with SA architects)
http://www.asosh.org/Standards/standards.htm
(check for standards)
RE: Acceptable value for earth resistan
RE: Acceptable value for earth resistan
The response to your question appears to have a wide range of variation depending of the accepted engineering practice, application, compliance with code and standard. The follow are some of the acceptable resistance value that I remember:
IEEE Std 80 & IEEE Std 142….…… <1 Ohm for large HV substation
` <5 Ohms for distribution substation.
IEEE Std 142 clause 4.1.2 ……. <1 Ohm for large Indust., HV sub & gen. st.
<5 Ohms for Indust. plant, & comm. facilities
Go Not Go Test (Typ. US Utilities)… <1 Ohm
Telecommunication facilities…………<5 Ohms
Lightning protection…………………....<1 Ohm
Ground Rod per NEC 250- 84. ……….<25 Ohms
And NESC (IEEE Std C2 096)
RR Pole grounding……………………...<25 Ohms
(f/stray current Corrosion Ctl)
RE: Acceptable value for earth resistan
RE: Acceptable value for earth resistan
1. Complete circuit for earth fault current return
2. Safety
Of which 2. is the most important. Providing ohm values as guideline values for earth grid safety ignores basic safety issues and is irresponsible.
Providing safe ground resistivity values ignores the fact that most safety criteria equations result in lower limits for lower ground resistivity.
Touch and step voltages depend on fault current magnitude, a fact that ohm guidelines ignore. In addition, safety criteria usually depend on fault duration.
To provide a safe earthing design you must use a standard that addresses touch and step potentials. Satisfy yourself that a standard has a sound theoretical basis before using it.
RE: Acceptable value for earth resistan
RE: Acceptable value for earth resistan