[VAL] Re: Romex

[David Josephson <david@xxxxxxxxxxxxx>]

Speaking as another electrical engineer, I think people on this list 
should pay more attention to Gerald, specifically about electrical 
things! I can add a few bits of data to the discussion.

There is no difference between solid and stranded for DC or AC, at least 
any frequency AC that we'll be dealing with. The finer points of skin 
effect aside (stranded wire doesn't have to be Litzendraht to have 
reduced inductance, because it has more exposed surface area even if 
some of the surface area contacts other strands) solid and stranded work 
the same. That said, I used *no* solid wire in my 1971 Tradewind 
restoration; I have seen two connections that failed due to vibration 
work-hardening the copper and leading to a fracture, one potentially 
quite hazardous. There is still some Romex in there and eventually it 
will all come out.

The aluminum sheathed MC cable is available with stranded THHN 
conductors. I think this is overkill for Airstreams though.

The nylon outer jacket of THHN is provided to make it easier to pull in 
conduit. It deteriorates badly in sunlight.

It's hard to accept this, but solder actually weakens the typical joint, 
especially to stranded wire (because it concentrates stresses at the 
points where the solder ends). My trailer goes boondocking quite a bit 
and gets seriously shaken up, so making the connections rugged is 
important. I have not had a failure using properly crimped stranded wire 
with good quality terminals. That last point is very important. Scrimp 
on the wire if you like, but not on the terminals. There are two grades 
typically available -- those with opaque PVC jackets, many of them 
imported (and stamped from plated soft brass), and those from T&B or 
Burndy with see-through jackets (and contacts that are typically hard 
tempered brass, sometimes with a steel or copper insert). The 
transparent jackets are a requirement for use in aircraft; you have to 
be able to inspect the crimp to see that the wire made it out the other 
side, which you can't see in the opaque ones. Use the right size ring 
lugs for the wire you're using and the studs of the terminals on 
switches etc. and you'll not have problems with stray strands. Don't 
attempt to wrap a stranded wire around a terminal screw and expect that 
it will stay put under vibration.

As far as knowing what wire is which, color coding is good  but you can 
also label the circuits with a 3M tape that has numbers on it. Assuming 
that you don't have an aircraft shop you can visit that prints the 
circuit name every foot on the wire ;)