Hi, I'm hoping someone can help me figure out the best way to install an
Emon kwh submeter to monitor electrical usage in my garage. I bought a house
with one attached garage and a second detached garage. I want to rent out
the house and use the detached garage. I intend to run a couple compressors
and use an arc welder, plus it has electric heat and A/C. Bottom line is
that I want to rebate the tenant for the electricity I use in the second
My main panel has a double 50-amp breaker that feeds the garage's sub-panel
(3 - 6ga in 3/4" rigid pipe). The sub-panel holds up to six breakers and 4
slots are filled with 1-30 amp dual and 2-20 amp breakers. I would like to
use the remaining 2 slots for the welder's breaker (50-amp dual).
The submeter is model 1000 for 2-line, 240v, 1-phase, 100 amp. The submeter
must have 2 power feeds + neutral and must be powered by the line(phase)
being monitored by the corresponding Current Transformers (CTs). The leads
for the CTs can be up to 2000 feet long.
I can think of several ways to install the meter :
1) I can pipe in the meter on the house side from the main panel, add 2
15-amp breakers, run 14ga power to the meter (with 1-amp inline fuses), run
the lines for the CTs to the main panel and install the CTs at the 50
breaker. Problem is, I want to be able to read the meter without going into
the house. I don't think the meter is rated for the outdoors. Also, I don't
want to tear up the family room to add the conduit or run it outside the
house (a lot of work depending on where I finally put the meter).
2) Install the meter in the garage. Take up the last 2 slots in the subpanel
with 2-15 amp breakers for the meter, install the Current Transformers in
the subpanel and run power and the CT leads to the meter (not good cause
then I loose the welder, but easiest). Or, I could upgrade the subpanel with
one that has room for more breakers (not good - more work).
I don't think it matters if I install the current transformers in the main
panel or the sub-panel. The current is the same in both places. Yes, the
voltage drops at the garage but I am billed for watts-used which is the
same(?). Probably not a big deal any way, even if it did affect the metering
accuracy (<2% ???).
3) Run another pipe from the main panel to the garage - or replace the
existing 3/4" pipe (both very bad - a lot of work) - and run the 3
conductors that power the meter (14 ga) plus the 4 wires for the Current
Transformers (22 ga?) to the garage. Breakers would be in the main panel
inside the house . Is this an allowed run from the house to the garage?
4) If this is possible - Install the meter in the garage and tap off the
6-ga feeders coming in to the subpanel with 12-ga (with inline fuses - but
no dedicated breakers) - then run the taps to the meter (<1 foot). Run the
lead wires for the CTs from the subpanel to the meter and install the CTs on
the feeder wires at the sub-panel. Is this possible/advisable? It's easiest,
it lets me read the meter from the garage, and I don't loose the welder or
need to replace the sub-panel.
Thanks for any help or information on which is the best route to go.