Need new subpanel from main then new subpanel in detached barn

[Donttouchthat]

Hope I can get some input here. I have a 200A main service panel for my house and 39 of the 40 slots are filled. Researching the panel (GE Powermark Gold # TM40BC) I see that tandem type breakers can not be used. I am trying to do a couple of things that am in need for more space so a subpanel(s) I think are needed. Due to a kitchen reno I need 2 additional 220v circuits. One for a single electric wall oven (2500w, stated at 20A). And the other for an electric cooktop (60hz, 6400w, stated 35A) In addition to the 2 lines, I want to run between 40-60A line out to my detached barn which I am renovating to include about a 550sf finished space with the remaining 300sf being left for garden/small workshop.

The attached drawing shows what I am thinking for the barn feed. My thought are to get a 100/125A subpanel to be adjacent to my main to get the extra lines I need. The oven states less than 4800w can go with 20A breaker. So 12/3 or 10/3 wire with a double pole breaker. The cooktop is an Italian brand with three wire (Black, Red, Green, no neutral) The manual says a 4 wire connection from supply and just cap off the white neutral. Does that sound right? Then the main other thing is to provide a feed out to the barn which I am planning a 4' deep trench that will contain all (LV pvc conduit, 2"conduit to run 3/4 PVC water line, 2" conduit for power line). The power lines would come into another subpanel. Maybe these would be 4 single type wires, and this panel would have a main shutoff. Does the main subpanel in the basement require a main shutoff (100A) as well? It is not practical to continue trench conduit that is entering the basement all the way right to the main subpanel. That is why I show a junction box but not sure if its kosher. Lastly the barn has electricity from line run from a 20A GFCI outlet in my house that goes in the ground through a conduit (15lf) into the barn. I don't know if that needs to be disconnected when the new line goes in, but I was thinking to keep it for outside barn lights and 3 way switch from house capability. Thanks for any input and/or questions!

 

[wyliesdiesels]

Hope I can get some input here. I have a 200A main service panel for my house and 39 of the 40 slots are filled. Researching the panel (GE Powermark Gold # TM40BC) I see that tandem type breakers can not be used. I am trying to do a couple of things that am in need for more space so a subpanel(s) I think are needed.

Can you combine a few circuits that are lightly loaded to make space for the additional circuits? you need 5 addl spaces... find 10 circuits that are lightly loaded..

Due to a kitchen reno I need 2 additional 220v circuits. One for a single electric wall oven (2500w, stated at 20A). And the other for an electric cooktop (60hz, 6400w, stated 35A) In addition to the 2 lines, I want to run between 40-60A line out to my detached barn which I am renovating to include about a 550sf finished space with the remaining 300sf being left for garden/small workshop.

The attached drawing shows what I am thinking for the barn feed. My thought are to get a 100/125A subpanel to be adjacent to my main to get the extra lines I need. The oven states less than 4800w can go with 20A breaker. So 12/3 or 10/3 wire with a double pole breaker. The cooktop is an Italian brand with three wire (Black, Red, Green, no neutral) The manual says a 4 wire connection from supply and just cap off the white neutral. Does that sound right?

If the oven doesnt need a neutral, then dont bother running **/3 NM-b. Just use **/2... especially with wire prices these days. same for the cooktop. It doesnt need the neutral so dont bother running wire for it.

Now, if this was a 50a circuit, that could be used for a range in the future, then i would run 4 conductor.

Then the main other thing is to provide a feed out to the barn which I am planning a 4' deep trench that will contain all (LV pvc conduit, 2"conduit to run 3/4 PVC water line, 2" conduit for power line). The power lines would come into another subpanel. Maybe these would be 4 single type wires, and this panel would have a main shutoff. Does the main subpanel in the basement require a main shutoff (100A) as well? It is not practical to continue trench conduit that is entering the basement all the way right to the main subpanel. That is why I show a junction box but not sure if its kosher.

yes you will need to run 4 wires for the subpanel- 2 hots, 1 neutral, 1 ground. The neutral bars in the subpanel need to be isolated and you will also need 2 ground rods. If you go with 60a feed, you will need #6 THWN black for the 2 hots and #6 THWN white for the neutral. the ground can be #10 but will need to be green insulated.

It would be cheaper if you went with #2 AL MHF which is usually around $1.2 per foot. this is good for 90a but can be breakered lower. It will need to be in conduit indoors which may not work for you

the barn subpanel will need a main disconnect if the panel will have more than 6 breaker handles.

the basement subpanel (if you one in) will NOT need a main disconnect since its in the same building as your main service panel.

Lastly the barn has electricity from line run from a 20A GFCI outlet in my house that goes in the ground through a conduit (15lf) into the barn. I don't know if that needs to be disconnected when the new line goes in, but I was thinking to keep it for outside barn lights and 3 way switch from house capability. Thanks for any input and/or questions!

yes that line will need to be disconnected. you could refeed it off the new subpanel.

 

[Donttouchthat]

Can you combine a few circuits that are lightly loaded to make space for the additional circuits? you need 5 addl spaces... find 10 circuits that are lightly loaded..


If the oven doesnt need a neutral, then dont bother running **/3 NM-b. Just use **/2... especially with wire prices these days. same for the cooktop. It doesnt need the neutral so dont bother running wire for it.

Now, if this was a 50a circuit, that could be used for a range in the future, then i would run 4 conductor.



yes you will need to run 4 wires for the subpanel- 2 hots, 1 neutral, 1 ground. The neutral bars in the subpanel need to be isolated and you will also need 2 ground rods. If you go with 60a feed, you will need #6 THWN black for the 2 hots and #6 THWN white for the neutral. the ground can be #10 but will need to be green insulated.

It would be cheaper if you went with #2 AL MHF which is usually around $1.2 per foot. this is good for 90a but can be breakered lower. It will need to be in conduit indoors which may not work for you

the barn subpanel will need a main disconnect if the panel will have more than 6 breaker handles.

the basement subpanel (if you one in) will NOT need a main disconnect since its in the same building as your main service panel.



yes that line will need to be disconnected. you could refeed it off the new subpanel.

thanks wyliesdiesels. I will take a look at those lightly loaded circuits to see if I can free up needed space. In an effort to keep the cost down I was wondering if I could do the following. I presently have a double pole 40A circuit with and 8/3 wire going to an electric slide in range which is about 80LF. As described in my post, I am replacing the range with the new oven and cooktop. If you look at my drawing, could I redirect that circuit (and 8/3 wire) to that "junction box" which would then connect with the individual 4 wires that will be going through the underground conduit to the new barn subpanel? If so what would be the max Amps I could run on the 8/3 copper cable? If the existing 40A breaker is max then what size would the 4 wires need to be to maximize full amperage at the barn? The wires need to travel a little over 100lf. Also can you give a description or link to what the 2 ground rod installation might look like? Thanks and sorry for the late reply, our power was out!

 

[Donttouchthat]

One other thing. I am surprised that the wall oven only needs a 20A circuit? I would have assumed 30-40A. This sounds normal for a single wall oven? Thanks

 

[wyliesdiesels]

max OCPD for 8/3 NM-b is 40a. so you cant go any larger on it.

personally i would just run #2 AL MHF as it will be almost half the price of running a smaller gauge set of copper wires (8-8-8-10)

as to your wall oven, no clue. what does the manual say for circuit requirements?

 

[Donttouchthat]

Regarding freeing up space. I guess this is referred to double tapping. How do I determine if my breakers will support that? Thanks

 

[wyliesdiesels]

Sq D breakers do.

but no need to double tap the breaker. just splice 2 wires into 1 with a wire nut and connect the one wire to the breaker.

 

[Donttouchthat]

max OCPD for 8/3 NM-b is 40a. so you cant go any larger on it.

personally i would just run #2 AL MHF as it will be almost half the price of running a smaller gauge set of copper wires (8-8-8-10)

as to your wall oven, no clue. what does the manual say for circuit requirements?

manual says under 4800watts then 20A OK. Appliance spec is 2500w. Just sounds light for an oven...
Re: 8/3 cable method. OK to join 8/3 cable to 4 (8,8,8,10 copper wires) in the junction box? Will this be weird/abnormal to do?

 

[Donttouchthat]

Sq D breakers do.

but no need to double tap the breaker. just splice 2 wires into 1 with a wire nut and connect the one wire to the breaker.

OK, I see.