Double pair electrical service line

[CYA]

I did an inspection this afternoon that I have questions about.  The service line was a double #3 copper line.  This seems to be a big issue to me but have not found anything in writing to hang my hat on.  Thoughts are greatly appreciated.

[Marc]

As far as I know, it's fine if all lugs are used within their listing.  All conductors need to be in the same wireway so that the inductive forces cancel out, otherwise inductive heating could result.  Conductor pairs need to be the same length so that currents are equally divided between them. Two #3s would work for a 200 amp service, not that I would do it.  I never have and I'd try very hard not to ever do it that way. I would not write it just because the conductors are in pairs.

Edited March 12, 2020 by Marc

[Jim Katen]

3 hours ago, CYA said:

I did an inspection this afternoon that I have questions about.  The service line was a double #3 copper line.  This seems to be a big issue to me but have not found anything in writing to hang my hat on.  Thoughts are greatly appreciated.

Parallel conductors are not a problem by themselves. But they're rarely, if ever, installed properly in a single-family home. If there's a problem with the installation, it will be with the details. For instance, I've never seen a 200-amp load center that features lugs listed for two conductors. Do you have pictures? 

[CYA]

[Jim Katen]

<strike>Those lugs are not listed for two conductors. The installation is wrong.</strike> 

Edit: 

I should probably say that the likelihood of those lugs being listed for two conductors is remote in the extreme. Check the panel schematic to be sure. 

The wiring mess on the neutral terminal bar makes me suspect that the installer was not entirely competent. 

[mtwitty]

#3 size are not allowed to be used in parallel. 1/0 AWG in the minimum size allowed for parallel feeds, per 310.10(H). For that reason alone, it's wrong.