DIYbanter - View Single Post - Combining two 30-amp circuits

wrote:
If I want to run an appliance that needs 50 amps, is there any
problem
with combining two 30-amp circuits of approximately the same length,
as
long as the part that carries the full current is using
properly-sized
cable? It seems like the circuit would have a 60 amp capacity.

Thanks in advance.

Lots of problems, including that it's probably contrary to code.
At least, the inspectors I've run into would be highly unlikely
to approve it.

I'm assuming you're talking about taking two existing 30-amp
circuits and connecting the corresponding phases together
in a 50-amp receptacle.

1. Load balancing. Since the resistance of the wiring is
low, small (absolute) differences in resistance can cause
one or the other parallel wire to carry much more than the
other. While you probably won't have 50 amps in one and 0
in the other, you might get 35 and 15.

The NEC does have provisions for parallel conductors, but
there are a lot of rules about it. It's not for the home
handyman.

2. Circuit breakers in parallel.

I've seen descriptions of circuit breakers wired in parallel,
but I believe they have to come from the factory that way.
Again, two random 30-amp breakers in parallel probably won't
trip the same way a 60-amp break will.

Also note that you need 50-amp "overcurrent protection", not
60,
since you have a single 50-amp load. (I don't think the NEC
has provision for 50-amp multiple-load circuits in residences,
except for "split" stoves.)

It might be possible to do something like what you're planning
if you really know what you're doing, but I think those of us
who need to ask for advice on the net (and many of us who don't)
would be better off running a fresh 50-amp circuit with
its own breaker.

-- Alan McKenney