Grounding

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Eros

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As you all know a #6 is used to ground/bond the racking and modules from the structure to the combiner or the inverter. My question is, if I bring my string conductors (and #6) back to a soladeck and combine them in parrallel, by code i am allowed to run MC wire from the soladeck to the inverter thru the house, attic or inclosed walls. The issue is the wire size of the MC ground is not usually a #6. What can i do to keep my ground consistant back to the inverter ?
Thx
 
Eros said:
As you all know a #6 is used to ground/bond the racking and modules from the structure to the combiner or the inverter. My question is, if I bring my string conductors (and #6) back to a soladeck and combine them in parrallel, by code i am allowed to run MC wire from the soladeck to the inverter thru the house, attic or inclosed walls. The issue is the wire size of the MC ground is not usually a #6. What can i do to keep my ground consistant back to the inverter ?
Thx
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The reason why you commonly see #6 in the array field, is that there is an NEC rule about wire sizes #6 and larger can be subject to "physical damage". Smaller sizes require protection from physical damage such as a raceway, and therefore would only need to be as large as 250.122 prescribes based on OCPD ampacity. If no OCPD is required or present, you use 1.25*total Isc and pick out a 250.122 sized ground wire from that size (NEC2014 response), for photovoltaic DC applications. Example is if you combine your strings and have one combiner carry a combined circuit to the inverter.

What is physical damage? The NEC doesn't give a clear definition. This is an issue where a team of experts could be polled and 50% would say yes, and 50% would say no, for a given situation like this. Usually, anything inside a raceway, cable cladding, or other wiring structure is considered protected from it. Other situations such as open in the array field are subject to interpretation.
 
If it's okay to be using MC cable, then using the ground in the MC cable is fine. This particular rule (250.120(C), referred to by 690.46), one applies to EGCs that are not run with the other circuit conductors, and not inside a raceway or cable armor.
 
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