tryinghard
Senior Member
- Location
- California
All electricians do not ground for the same reasons. There are different types of electricians with each having specific skills and trades like:
1 High voltage (lineman, transmission & utility service)
2 Data/communication/signal (Communication & System Installer/Technician)
3 Premises wiring of 600 volts and less (journeyman inside wireman).
Even the label ?electrician? is too broad and not descriptive enough causing confusion regarding installations especially grounding and bonding. These different electrical trades DO ground commonly to control lightning and transformer failures but that?s it, they do NOT share common reasons for ground fault control (equipment ground conductors & effective ground fault path) or even unbalance load return path, the grounded conductor (neutral).
It is most important to have a low impedance path that enables the highest amperes to instantaneously open a ground fault; ohms law (I=E/R) can help us understand this through some examples below.
1 High voltage: a ground fault to a reasonably low impedance ground will enable high current that will blow fuses or activate relays that open circuitry. High voltage will also install mid-point electrodes to lower impedance intentionally creating a parallel unbalanced load (neutral) return path.
A- 800A=22KV/25ohms*(electrode system ohms are environmentally controlled, unknown moment by moment, therefore so is the current)
B- 680A=17KV/25*
As you can see these circuits will open even with 650A protection all the more insured to open with lower ampere protection!
2 Premises wiring of 600 volts and less: Unlike high voltage 600 volts or less grounding to earth is not effective to open a circuit that has ground fault, in fact it usually allows circuitry to remain activated.
A- 4.4A=110V/25*
B- 11A=277/25*
C- 19A=480/25*
As you can see these circuits will NOT open even with 15 & 20A protection, respectively!
3 But an effective ground fault path ? EGC as qualified in 250-118 ? IS EXTREMLY EFFECTIVE to open a circuit in ground fault usually instantaneously!
A- 55A=110V/2ohms **(2 ohms is conservatively fixed with correct installation and not environmentally controlled)
B- 139A=277/2**
C- 240A=480/2**
As you can see these circuits WILL open instantaneously with protection values less or near these results! Of course the service grounded conductor (neutral) does need to be bonded to the case at the service disconnect to allow this path to source ? serving transformer.
According to the National Electrical Code premises wiring of 600 volts or less cannot use the earth for a ground fault path (250-4(A)(5) & (B)(4)). This type of circuitry must use equipment ground conductors & effective ground fault paths, which are known not assumed, from source to destination to enable OCPD protection (250-4(A)(3)-(5), 250 V, 250 VI, & 250 VII). Also equipment-grounding paths should follow the circuit route the same as the phases or neutral. All this to ensure a low impedance path from source to destination that ENABLES the operation of OCPD?s which in reverse a high impedance usually DISABLES the operation of the OCPD?s.
In summary we really have 3 worlds colliding with electricians and their use of grounding:
1 High voltage = return path for the unbalanced load/drain to open circuit/effective ground fault path/lightning & transformer failure control
2 Data/communication/signal = drain to clean circuit/lightning & transformer failure control
3 Premises wiring of 600 volts and less = lightning & transformer failure control ONLY!
My hope is to untangle the broad use for reasons to ground while untangling the broad use of the label ?electrician?. It will be good if this provokes discussion because these discussions will help equip us to explain reasons for grounding to others, possible even those in our trade but certainly those curious/related.
1 High voltage (lineman, transmission & utility service)
2 Data/communication/signal (Communication & System Installer/Technician)
3 Premises wiring of 600 volts and less (journeyman inside wireman).
Even the label ?electrician? is too broad and not descriptive enough causing confusion regarding installations especially grounding and bonding. These different electrical trades DO ground commonly to control lightning and transformer failures but that?s it, they do NOT share common reasons for ground fault control (equipment ground conductors & effective ground fault path) or even unbalance load return path, the grounded conductor (neutral).
It is most important to have a low impedance path that enables the highest amperes to instantaneously open a ground fault; ohms law (I=E/R) can help us understand this through some examples below.
1 High voltage: a ground fault to a reasonably low impedance ground will enable high current that will blow fuses or activate relays that open circuitry. High voltage will also install mid-point electrodes to lower impedance intentionally creating a parallel unbalanced load (neutral) return path.
A- 800A=22KV/25ohms*(electrode system ohms are environmentally controlled, unknown moment by moment, therefore so is the current)
B- 680A=17KV/25*
As you can see these circuits will open even with 650A protection all the more insured to open with lower ampere protection!
2 Premises wiring of 600 volts and less: Unlike high voltage 600 volts or less grounding to earth is not effective to open a circuit that has ground fault, in fact it usually allows circuitry to remain activated.
A- 4.4A=110V/25*
B- 11A=277/25*
C- 19A=480/25*
As you can see these circuits will NOT open even with 15 & 20A protection, respectively!
3 But an effective ground fault path ? EGC as qualified in 250-118 ? IS EXTREMLY EFFECTIVE to open a circuit in ground fault usually instantaneously!
A- 55A=110V/2ohms **(2 ohms is conservatively fixed with correct installation and not environmentally controlled)
B- 139A=277/2**
C- 240A=480/2**
As you can see these circuits WILL open instantaneously with protection values less or near these results! Of course the service grounded conductor (neutral) does need to be bonded to the case at the service disconnect to allow this path to source ? serving transformer.
According to the National Electrical Code premises wiring of 600 volts or less cannot use the earth for a ground fault path (250-4(A)(5) & (B)(4)). This type of circuitry must use equipment ground conductors & effective ground fault paths, which are known not assumed, from source to destination to enable OCPD protection (250-4(A)(3)-(5), 250 V, 250 VI, & 250 VII). Also equipment-grounding paths should follow the circuit route the same as the phases or neutral. All this to ensure a low impedance path from source to destination that ENABLES the operation of OCPD?s which in reverse a high impedance usually DISABLES the operation of the OCPD?s.
In summary we really have 3 worlds colliding with electricians and their use of grounding:
1 High voltage = return path for the unbalanced load/drain to open circuit/effective ground fault path/lightning & transformer failure control
2 Data/communication/signal = drain to clean circuit/lightning & transformer failure control
3 Premises wiring of 600 volts and less = lightning & transformer failure control ONLY!
My hope is to untangle the broad use for reasons to ground while untangling the broad use of the label ?electrician?. It will be good if this provokes discussion because these discussions will help equip us to explain reasons for grounding to others, possible even those in our trade but certainly those curious/related.
