Yet another question about 240v to two 120v outlets

Hello to all! I have a thought of something I MIGHT want to do: convert an existing 240 wire to two 120v 15a outlets
Power source: It is a separate fuse box that can conatin two 30 amp cartridges fuses cartridges. The wire coming from this box goes straight to a outlet in the kitchen where the Window AC unit use to run at. This box also has its own kill switch.
The wire: A 10/3(rd, blk, wht) with bare ground.
to place a two space/four circuit sub-panel on the wall with two 15 amp breakers. And feed the SP by extending the existing wire.
I see other posts about this but I have other questions:
What would be the volt/amp fuses to use in the fuse box? Would I need some type of step-down convertor to make sure the voltages are at 120v at the outlet? What other issues will I face?
I do not want to change anything at the main service panel, fuse box(except the fuses), or the existing wire. As I want the ability to use 240/30 amp if a need arises in the future.
Thank you.
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JustSomeShmoe wrote:

It can be done, but do you want to keep the 240V outlet live where it is while adding 2-15A outlets?
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Good question. I would yes, I saw at "Lowes" a two space sub panel and a four space one. I also saw something called "tandem" breakers.
How about a 30 amp breaker in one space and a 15 amp tandem breaker, or just get a four space SP.
Would a tandem breaker is good as two separate breakers?
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So as long as you do not use the 240V outlet at the same time as the 110v circuits, you should be OK. Tandem breakers should only be used if absolutely necessary, if there are space constraints in the panel. So I would buy a 4 space sub-panel. But just curious, is it possible to home run the new 15A circuits right to the main panel if you have the space? This way you do not have to put in a new subpanel.
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Sorry, I should have said that the SP will be placed upstairs were the outlet is located. No space on the main panel. it is 50 year old "pushomatic" type (if that's the correct name for the breakers). The wire in question runs off a dual cartridge fuses box that gets it power directly from the main power line not the main service panel which it sits next to. And changing the main service is too expensive a solution.
Thanks for the tip about the tandem breakers.
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I forgot to add: that I won't be using the 15 amps and the 30 amp at the same time.
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If you want to use an existing 10/3 to feed a small panel, disconnect it from the existing outlet, run it into your panel, connect the red and black to the main lugs, connect the white to the neutral bar, install a ground bar and connect the bare wire to it, and don't use the bonding screw. You can now install whatever loads you want that don't exceed the limits of the main

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OK so afar so good but a question concering the fuses. Lets use the following example: If I wanted to run two electric portable heaters at 120v 15a of course what fuses do I use? They come in pairs of course. Do I use 30 amp types? The 15a breakers will deliver to correct amps to the outlets but the ones I see have the range of 120-240 written on them, will the breakers deliver the correct voltage automatically as well?
Thanks
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I'm a little confused now. You stated that you would replace the subpanel, so there would be no fuses, just breakers. In any event, if you want to run 2 -15A electric heaters, you are pushing that 10/3 wire to the limit, since it is rated for 30A. Not a good idea. An option would be to install a 240V electic baseboard type heaters, since 240V units use half the current. The ratings on the breakers are just saying in general they can be used for 120 or 240 applications. Breakers depend on current to operate, not voltage.
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Sorry, for the confusion I see I should have explained where I want to place the SP. The power source I want to use is a cartridge fuse box in the basement at is next to the main service panel. The fuse box gets it power directly from the main power line and it feed the 10/3 wire to the outlet upstairs. I want to feed the SP from the wire from this outlet.
Thnaks for the warning about the 10/3 limit
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That's fine then, leave the thirty amp fuses just where they are. They become the main for the sub panel and just be sure not to overload the panel. Mikepier's suggestion of a 240 volt heater is the way to go

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I'll look into the 240v heaters Thnak you for the helpful information
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Thanks for the helpful information. The 240v heaters are a better solution.
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