SURVEY: Powering big iron in your home.

From: William Donzelli <aw288_at_osfn.org>
Date: Tue Jun 4 20:07:18 2002

> I noticed that when I have everything on, the 25 A breaker gets
> warm. Fairly warm. Not hot, but markedly warm. I made sure the
> wires are screwed very tight and the breaker is seated right, but
> still it gets warm. That worries me a bit.

This is normal if the breaker is close to the trip current. Don't worry
about it. You may want to think about going to 30 Amperes.
 
> Also, I think that my #10 wire is under-dimensioned after all.

#10 is fine for a 25 Ampere circuit. Putting in a larger wire, like #8 or
#6 will not gain you anything unless the load is quite a long distance
from the breaker (voltage drop, basically - another thing that you should
not worry about in your situation).

> Since all the consumers are essentially doing some (more or less)
> good job of load balancing, eventually the neutral wire gets
> quite a bit of load, possibly beyond 25 A. Theoretically up to
> 50 A. So, I should have used #8 or even #6 then.

If the two sides are load balancing perfectly, the neutral will not pass
any current. In an Edison feed (as this is correctly called), the neutral
carries only the difference of the currents. If one side of the 240 VAC
system draws 20 Amperes and the other side draws 22 Amperes, the neutral
will "provide" the missing 2 Amperes. At worst case, with one side full
at 25 and one side off, the neutral will pass the 25 Amperes.

> However, the practical problem is that you can't fit #6 wire into
> a breaker contact screw. And even #8 is going to be on the low
> end with 50 A. The best thing would be if neutral was twice as
> thick here.

This is actually non-code. Do not do it.

> I spliced a branch off with split bolts and lots of electric tape.
> for insulation. The branch terminates in a dedicated box with
> the original outlets. The initially #8 AWG is distributed through
> #10 wires to the various outlets. Even some #12 to the two
> standard 110V outlets in that box.

Do you have a subpanel with breakers rated for the individual branches?
This is important. In almost every instance, if you go down any size of
wire from a larger feed, you must put in a breaker. If you do not, you
could cram too much current thru a branch, but the breaker feeding it will
not trip.
 
> My concern there is, of course, that (a) the split bolt construction
> may develop resistance and increased heat dissipation.

This should not happen, as long as you stay away from aluminum wire or
split bolts.

> Also (b) the
> way I downsize and distribute the #6 feet to smaller wires in the
> outlet box may lead to overcurrent if the devices aren't connected
> where they should. I did my best to have the big suckers on thick
> AWG and shorter length than the moderate consumers.

This is an example of my above point - plug something in to the wrong
outlet, and you may have a wire pair start to glow red, yet the big breaker
ahead will not trip.

> The problem of course is that to do it properly would require
> upgrading the main feed, replacing the main breaker panel running
> thousands of new wires, and sub-panels, where each machine essentially
> has its own breaker, and of course the outlets and plugs need to be
> all proper. Easy to spend $2000 or more in material and labor for that
> upgrade. For equipment we run a few hours per week.

As the son of an electrician, I can say that it is *always* good to do it
properly. Houses burn down due to faulty wiring all the time. Many more
come *damn* close - I have seen obviously charred and melted wires in
many houses, saved only because the wire was not run right up against a beam.

I would think, if you do this yourself, you could have this project done
for a quarter of the cost. You could probably reuse quite a bit of what is
already installed, as it seems like you just need to put in some subpanel
breaker boxes at stategic points.
 
The NEC may seem picky (it is), but it is realy just a bunch of common
sense rules. If you have any questions, please feel free to email me.

William Donzelli
aw288_at_osfn.org
Received on Tue Jun 04 2002 - 20:07:18 BST