salgant
Member
- Location
- North Carolina
- Occupation
- PV Wire Engineer
While reviewing a single line from a client, I see a typical single string 20A conductor on a #10AWG wire back to the combiner box. The installer is using a messenger wire system. I have always used 310.17 for this, however my coworker pointed out that I should be using 310.20, which would require all wire in messenger systems to be #8AWG minimum.
I questioned what ambient temp we should actually be basing the calculations on as the customer's engineer did not specify. In addition, they may be using CAB which can break wires out into groupings of three, but we have no indication that they are doing that.
The big difference in tables are:
1. 310.17 ambient temp of 30°C. 310.20 ambient temp of 40°C.
2. No more than three single-insulated conductors.
My actual question is, what table do I actually use?
I questioned what ambient temp we should actually be basing the calculations on as the customer's engineer did not specify. In addition, they may be using CAB which can break wires out into groupings of three, but we have no indication that they are doing that.
The big difference in tables are:
1. 310.17 ambient temp of 30°C. 310.20 ambient temp of 40°C.
2. No more than three single-insulated conductors.
My actual question is, what table do I actually use?