redtail_MH
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Why doesn't the NEC require these systems to be grounded?
125Vdc Systems
- Thread starter redtail_MH
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Hillbilly Steve, thank you for pointing that out. I shot from the hip, and I apologize if I mislead anybody. The real answer lies in 250.20. From there you can conclude no system is required to be grounded if the conditions are met... Now by grounded I mean one of the load current circuit conductors has to be grounded. I am not implying the framework or exposed conductive surfaces need not be grounded for safety which is what I think you are referring to in 250.1, 250.2, 250.3, and 250.4
As to 125 VDC system does not meet the criteria of 250.20 simply because it is not AC. Which means it can either be grounded or not. It is a design choice on how to protect the current carrying conductors.
One method of protecting the conductors is the traditional way we are all familiar with is to ground or reference one polarity to something, then install OCPD at the source on the un-grounded polarity. It is very cost effective and reliable protection but is prone to outages and noise.
The other method involves floating the system, and installing OCPD on all the polarities (two in this scenerio positive and negative). If one polarity becomes faulted say to the grounded frame, nothing happens, it now becomes a grounded system and an alarm should go off to indicate so. If a fault should happen on the other polarity, then the OCPD operates to clear the circuit. Just like a 3-wire Delta system.
As to 125 VDC system does not meet the criteria of 250.20 simply because it is not AC. Which means it can either be grounded or not. It is a design choice on how to protect the current carrying conductors.
One method of protecting the conductors is the traditional way we are all familiar with is to ground or reference one polarity to something, then install OCPD at the source on the un-grounded polarity. It is very cost effective and reliable protection but is prone to outages and noise.
The other method involves floating the system, and installing OCPD on all the polarities (two in this scenerio positive and negative). If one polarity becomes faulted say to the grounded frame, nothing happens, it now becomes a grounded system and an alarm should go off to indicate so. If a fault should happen on the other polarity, then the OCPD operates to clear the circuit. Just like a 3-wire Delta system.
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