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Pretty beginner on electrical. I have a 100 amp service (metered not against or adjacent to main dwelling - somewhere central in our mobile home court) with a 125 amp main box. 1300 ish sq ft, 3 1250 W back up floor board heaters on separate breakers, 3000 W water tank. Wood heat is main heat source. It's inspected to code and I'd like it to remain that way IF POSSIBLE. Wife is a potter and we want to wire a big kiln in the shed (nothing connected from shed to main bldg) for her. It requires a 60 amp breaker, 48.5 peaks amps, 11 150 Watts. I could A. put a 60 amp breaker on the main panel and run a wire straight to the kiln or, more preferably, B. install a sub panel.

I have my eye on a 70 amp sub panel that is 1 phase, 3 wire with a main wire size of #14-4 Cu. This has confused the crap out of me - #14-4 Cu. I understand that a 70 amp load requires a #4 AWG wire. I don't know why the 14 is in there. What about the other two wires since it's a 3 wire sub panel? What should they be rated? Is it hot-neutral-ground or hot-hot-ground? Anyways, the specs on the main box says that you can install a "subfeed lug kit" - am I on right track here? Is that how you'd install a sub-panel? Can you install a 70 amp sub-panel on a 125 main panel with 100 amp. service? Or would you put a 70 amp breaker on the main panel?

I'm in BC Canada. 130/150 total breaker count ("hot water tank" breaker is 15 amp x 2, and same with "front porch heat"). Isn't the total amps 125 for each side if the panel is rated for 125 amps? I'm not sure because our dwelling has passed an electrical inspection. I'm also guessing that adding to the main panel a 60 amp breaker for a kiln or 70 amp breaker for a sub panel would violate code.

How do I turn off the main service without getting zapped? I'd like to look inside the main box, but I don't want to fry.

Lastly the run to the shed in only 4 feet outdoors. The rest of the run is underneath our structure. About a 55'-60' run.

Help VERY appreciated!

Main Panel Specs

Main Panel

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You can rearrange your way out of your space shortage

While the presence of the service barrier in your panel makes clear that those two bottom-left "spaces" are actually useless as they are on the wrong side of the barrier to be used for a branch circuit or feeder, all hope is not lost. With some rearranging of the existing breakers, and the replacement of one of them, we can make enough room in the panel to add a feeder breaker for a subpanel.

To do this, we start by moving the "This bedroom lights, plug, + fridge" circuit from its current home in space 5A two slots down to the existing spare in space 9A. Alongside this, we also move the "Master bedroom + back outside plug" circuit from its current home in space 4B down to the spare in space 12B, leaving us with spaces 5A/7B and 2A/4B as open pairs at this point.

From here, we can replace the existing dryer breaker with a DNPL220230; note that this is not a common-trip breaker, as CEC 14-302(b) (at least as of the 2015 CEC I was able to dig up) permits independent trip breakers in multi-wire branch circuits derived from 3-wire systems irrespective of the nature of the load. The two 30A (inner) poles in spaces 5B and 7A are used for the dryer (just as they were with the DNPL153015 that formerly occupied that spot), while the two 20A (outer) poles that now occupy spaces 5A and 7B get the "Back bedroom electric heater" circuit from 2B/4A moved to them. This allows the DNPL152015 that occupied spaces 2 and 4 to be removed, thus freeing room up for our feeder breaker, namely a BR2100.

You'll want to go big here, so you don't have to go back later

Now that we can run a feeder from here, we're going to take the liberty to install not one, but two panels as part of this. The first one will be a CBRPL130, installed near the existing panel in the house, and fed using insulated 1/0 Al wire, either in the form of individual wires in conduit (hot, hot, neutral, with metal conduit as the ground path) or in the form of an armored (TECK90) cable. This provides ample room for future expansion; if you wished to, you could even use a CBRPM140 for this new panel to allow the existing panel to be taken out of service at a future date.

Now that the space crisis has been averted for the long haul, we can then move onto feeding the shed. This is best done using #4 Al in PVC conduit with a separate grounding conductor in the conduit, with a 70A (BR270) feeder breaker protecting the wires to the shed. We then fit a CBRPM112 at the shed, with the main breaker serving as a structure disconnecting means, and a BR260 in it for the kiln circuit, as well as a BR115 each for lighting and general receptacles.

With both these new panels, the bonding strap or screw should be removed, as they are both subpanels, just like your existing panel. Furthermore, it is a good idea to use an inch-pound torque screwdriver or torque wrench to tighten all terminal screws to the manufacturer's specified torque; this prevents embarrassing connection failures down the road. The good news is that the shed does not need a grounding electrode of its own (it is grounded by the feeder equipment grounding conductor as per CEC 10-208(b)).

As to service capacity...

One of the other major substantive differences between the NEC and the CEC is in how they calculate service loads. Unlike the NEC, the CEC does not count kitchen and laundry small appliance branch circuits separately from the base lighting and appliance allowance, as set out in rule 8-200(1)(a)(i) and (ii). It also uses a 6kW baseline range load (vs the 8kW baseline used by the NEC) and applies an aggressive 25% demand factor to miscellaneous loads when a range is present, as per rule 8-200(1)(a)(vii).

It is this last factor that keeps the kiln from pushing your service calculations over the limit. When we run the numbers, we come up with 120m2 of floor area for your house, giving you an extra 1000W of base lighting load over the 5kW minimum, alongside 6kW for the range (assuming the range is not over 12kW), 3.75kW for the 3 baseboard heaters (with no demand factors applied), and a remaining unfactored load of 8kW (3kW water heater and 5kW dryer) that is demand factored down to 2kW. This totals out to 17.75kW, or 74A @ 240V; from here, we add the 11.52kW kiln at the same 25% miscellaneous-load demand factor as the dryer and water heater, putting us at 20.63kW, or 86A @ 240V, well within what your 100A service can handle.

  • Do what ThreePhaseEel says... Brilliant. – Harper - Reinstate Monica Oct 25 at 4:00
  • @ThreePhaseEel - thanks so much for the thorough review and evaluation. Time to get crackin'! – Danny Oct 27 at 21:18
  • Question - I'm having trouble with the assignment of numbers and letters to the breaker spaces. 5A would mean five spaces down on the left side of the panel, correct? Using this method some of your assignments of spaces seem to be contradictory. I don't quite understand the 5A/7B and 2A/4B pairings. Thanks! – Danny Oct 28 at 2:37
  • @Danny -- 1 is top left, 2 is top right, 3 is the next space down on the left, 4 is the next space down on the right... – ThreePhaseEel Oct 28 at 2:38
  • I should of stared at it harder! Thanks again.. – Danny Oct 28 at 4:34
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Not gonna happen in this panel.

This panel is far, far, far too small to support any kind of house. I sure hope whoever specced that panel really, really enjoyed that latté :) seriously they might've saved $10-20... If you don't mind power being out for a couple days, I would say fit a big panel here and up-cycle this one to be the garage subpanel. But I gather that is unrealistic.

Panels are oversubscribed to some degree, but I'm concerned an additional 60A load will be more than is allowed.

If this tiny panel indeed supports subfeed lugs, you can come off it with 100A wire (#3Cu/#1Al) and go out to a subpanel like one of these, preferably an Eaton BR so you can share breakers. Since the wire is the same ampacity as the main breaker, it's protected by that breaker and doesn't need any additional protection.

Note that I'm recommending a positively ginormous panel compared to what you were thinking of. A house should have a number of spaces in the 40's, and 30 will get you there. I'd locate it somewhere it isn't too hard to reroute existing circuits from this panel to the new sub.

Double-stuffing doesn't make up for spaces. AFCI and GFCI require full spaces.

As far as the garage subpanel, this is tricky business because it's an outbuilding (i.e. no breezeway between them). You are limited to one of each type of circuit (120V, 240V) for instance, so the existing circuit plus the kiln. If this requirement becomes burdensome (subpanel, ground rods etc.) consider adding a breezeway instead :)

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