A question for the experts, I would like to add a wall space heater in my
master bathroom. The unit that I like requires a 240V 20 amp circuit. I
have a finished ceiling in my basement so running a new circuit for this
will be very difficult. Running through the crawl space under the bathroom
is a 240V 50 amp line for my air conditioning system. My question is can I
run a sub panel off of this 50 amp line and put a 240V 20 amp breaker in it
for the new heater? The heater will only be used during the winter when the
AC is not in use and it will have a programable thermostast with a seasonal
shut off to insure that it is not accidently used while the AC is operating.
Also, the heater is hardwired so there is no plug or cord involved. Thanks
for your input.
If there is a 50 amp breaker in the entrance panel feeding the a/c now
you can insert a main lug sub-panel that has two breakers, one 50 amps,
and one 20 amps, in that line. The 50 amp breaker will feed the a/c
through #8 70 C wire and the 20 amp breaker will feed your heater
through #12 wire.
Very creative solution. Does the 50a line have a neutral and a ground; my
AC line does not. You will need them for a subpanel even if your heater
doesn't need it.
There is also the issue of where to put the subpanel.
A panel that does not supply line to neutral loads is not required to
have the neutral conductor in the feeder. The feeder must, of course,
include a properly sized Equipment Grounding Conductor (EGC).
What is not forbidden is allowed. The code specifically requires
running the neutral conductor from a transformer that is configured to
supply one to the service disconnecting means even if it is not used.
This is most commonly encountered in fire pump service disconnecting
means that are supplied from the same transformer that supplies the
regular service to a building. The code has no such requirement for
feeder supplied panels. It might be wise to label the panel with a
warning that it may not be used to supply line to neutral loads but even
that is not required.
IMO, you'd be well advised to leave that AC circuit alone. Panelboards
should not be installed in crawl spaces. If you are lucky the floor joists
run so that fishing a cable won't be difficult, or use Wiremold. Otherwise,
you may be able to run the circuit in conduit on the outside of the house
low on the siding or buried, then enter into the crawl space.
This concept should work. I don't believe you must have a neutral wire in the
sub panel, but you
must have an equipment grounding bus. If you can find a small panel with feed
through lugs (or
install double lugs), then you won't have to spring for another 50A breaker for
the A/C (assuming
this A/C feeder is protected at the source with a 50A breaker). Minimum panel
would be two slots to
accomodate the 20A breaker.
You thermostat will add complexity to the circuit and is probably not required.
should allow an A/C and heater to be considered non-coincident loads. A line
voltage thermostat for
the wall heater is the most common type. But if you have the contactor to
control the heater, that
is fine too.
Only issue I can think of is what is the disconnecting means for the heater? If
its the 50A feeder
breaker, will your inspector accept that?
He *could* tap into the 50A circuit; install a junction box in the
crawlspace. I think the "10 foot tap rule" would let him use #12 wire for
the tap conductors. Install a 20A fusable 2-pole switch for the heater.
It has to have fuses or a breaker to protect the tap wires.
The only problem I see is having a panel installed in a bathroom. But
maybe the switch enclosure is not considered a panel? I've also seen
little boxes with room for one 2-pole SWD (switch) rated breaker.
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