confused myself

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diytexas
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confused myself

Post by diytexas » Thu Aug 15, 2019 12:30 pm

I have a 220v 8/3 wire coming from the main service panel to an old central a/c thats no longer used. I'd like to put in a subpanel and have some 110v 20A outlets. 220V will NEVER be used from this subpanel. For now, ignore, the setup in the main service panel.

Not using 220V, ever, whats the maximum amperage that can be drawn? Is it still ONLY 40?

This is what confuses me and I know its related to electrical fundamentals, just cant figure out what. There's (2) 8AWG 40A hot wires (one red and one black) in this wire. Since i'll never need 220V, Is there not someway to get the 40A from each wire? So, ultimately, Id have 80A total I can draw before the panel trips. (4) 20A breakers using 12/2

What am I missing?

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Aaron
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Re: confused myself

Post by Aaron » Thu Aug 15, 2019 6:09 pm

What it sounds like you may be missing is a neutral conductor, which would be a white wire. Typically 240V appliances, such as an AC condenser, do not use neutral because the condenser motor operates on the two legs of alternating current (the red and black conductors).

But if you hope to have a subpanel that feeds 120V circuits, you absolutely need a neutral conductor.

Now you said you had 8/3 cable. The /3 means there's three wires, but the ground conductor is NOT included in that count. So the cable jacket is labeled "8/3 with ground". In the case of three conductors, you'd have the black, red, and white along with a bare ground conductor.

8 gauge wire is typically is rated for 40 amps of current. It is commonly run from panels to oven/range receptacles and cooktops. Electric ovens and ranges in the past didn't use a neutral, but today they require one for the 120V control electronics and oven lights.

If you were to have a sub-panel connected to the end of a /3 with ground wire, you'd wire the red and black ends to the backplane lugs of the panel, and the white neutral into its terminal strip. That terminal strip MUST be electrically isolated from the ground, so the sub-panel enclosure must NOT be bonded to that neutral terminal strip. Instead, you would need to purchase a separate ground strip, install it in the panel, and then connect the ground from the /3 into it. Then all your branch circuits would have the same neutral and ground segregation, unlike your main service panel.

diytexas
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Re: confused myself

Post by diytexas » Thu Aug 15, 2019 7:15 pm

No there's a neutral. As for why two hots can't be combined to increase amp draw im assuming is because of the single neutral return?

Otherwise couldn't you just add a neutral and have two sets of 8/2 and fees a panel on a single hot and neutral? Never heard of it being done.

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Aaron
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Re: confused myself

Post by Aaron » Fri Aug 16, 2019 7:12 am

If you're wiring a subpanel, you would do it as I described above. Either you have a neutral conductor or you don't. If you do, you have one and only one to supply a subpanel.

The neutral wire is always the same size as one or both of the hots that run with it.

You never combine hots from both legs together lest you want to trip your main breaker at best, or take out a pole transformer at worst.

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emtnut
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Re: confused myself

Post by emtnut » Fri Aug 16, 2019 10:10 am

diytexas wrote:
Thu Aug 15, 2019 12:30 pm

Not using 220V, ever, whats the maximum amperage that can be drawn? Is it still ONLY 40?

This is what confuses me and I know its related to electrical fundamentals, just cant figure out what.
What am I missing?
To answer the 'electrical fundamental' ...

A 40A circuit is 40Amps, whether it's 240 or 120 volts

Power is what changes.
Volts X Amps = Power , so

240 X 40 = 9600 Watts
120 X 40 = 4800 Watts


Amps are the limitation on wiring. It's why we have 'high voltage' wires distributing power.
13.2kV X 40 = 580,000 Watts !! On the same 40A wire 8-)
~~ Ford Ford Ford Ford Ford Ford :mrgreen: ~~

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Aaron
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Re: confused myself

Post by Aaron » Fri Aug 16, 2019 11:33 am

You'll often see the term "ampacity" used to describe the gauge of wire. That word is a portmanteau of "amp capacity".

diytexas
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Re: confused myself

Post by diytexas » Fri Aug 16, 2019 11:48 am

emtnut wrote:
Fri Aug 16, 2019 10:10 am
diytexas wrote:
Thu Aug 15, 2019 12:30 pm

Not using 220V, ever, whats the maximum amperage that can be drawn? Is it still ONLY 40?

This is what confuses me and I know its related to electrical fundamentals, just cant figure out what.
What am I missing?
To answer the 'electrical fundamental' ...

A 40A circuit is 40Amps, whether it's 240 or 120 volts

Power is what changes.
Volts X Amps = Power , so

240 X 40 = 9600 Watts
120 X 40 = 4800 Watts


Amps are the limitation on wiring. It's why we have 'high voltage' wires distributing power.
13.2kV X 40 = 580,000 Watts !! On the same 40A wire 8-)
I guess the part I was missing is it's still a circuit limited by a neutral that is still a single 8awg wire with 40A limits..

diytexas
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Re: confused myself

Post by diytexas » Fri Aug 16, 2019 11:50 am

It's the separation factor that confuses me for some damn reason. If you wrap two 8AWG wires, you have a bigger gauge wire and more ampacity. But as long as they're separate.....the ampacity isn't "added", ever. Just voltage

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emtnut
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Re: confused myself

Post by emtnut » Fri Aug 16, 2019 8:00 pm

diytexas wrote:
Fri Aug 16, 2019 11:50 am
It's the separation factor that confuses me for some damn reason. If you wrap two 8AWG wires, you have a bigger gauge wire and more ampacity. But as long as they're separate.....the ampacity isn't "added", ever. Just voltage
I'm not sure what you mean by separation factor ??
And also 'if you wrap 2 8guage wires' ??

This has nothing to do with the neutral wire, it's just if you have a 120V or 240V circuit.
The neutral only comes into play if you need 120V (in a 120 or 240V circuit)
~~ Ford Ford Ford Ford Ford Ford :mrgreen: ~~

diytexas
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Re: confused myself

Post by diytexas » Fri Aug 16, 2019 10:39 pm

lol I think I've now confused everyone else now too.

Let's start over.

I have an 8 AWG wire coming from the service panel. Unused. Two hots. One neutral.

Can this be converted (in anyway possible) to provide more than 40 amps if I just need 120V? I dont need 240.

My thinking is this. I have two 8 gauge hot wires here. Each by themselves supports 40A. This can't be converted to two 40A 120V subpanels? (In anyway?)

Disclaimer: this is all curiosity. if it's against code or a fire hazard, or just impossible and defies science, it won't be done

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Aaron
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Re: confused myself

Post by Aaron » Fri Aug 16, 2019 11:03 pm

No.

diytexas
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Re: confused myself

Post by diytexas » Sat Aug 17, 2019 12:15 am

:lol:

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emtnut
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Re: confused myself

Post by emtnut » Sat Aug 17, 2019 11:22 am

diytexas wrote:
Fri Aug 16, 2019 10:39 pm
lol I think I've now confused everyone else now too.

Let's start over.

I have an 8 AWG wire coming from the service panel. Unused. Two hots. One neutral.

Can this be converted (in anyway possible) to provide more than 40 amps if I just need 120V? I dont need 240.

My thinking is this. I have two 8 gauge hot wires here. Each by themselves supports 40A. This can't be converted to two 40A 120V subpanels? (In anyway?)

Disclaimer: this is all curiosity. if it's against code or a fire hazard, or just impossible and defies science, it won't be done
If you in fact have #8/3 (2 hots, a neutral, and a ground ... 4 wires altogether), then you can put in a 40A subpanel. 40A x 240V= 9600 watts of power.
just to keep it simple, you install 4 - 20A 120V circuits (2 on each phase)(assume all are fully loaded)
Then you have 80Amps .... magic !! :mrgreen:
but those are 120V circuits, so 80A x 120V = 9600 watts of power.

clearer ???
~~ Ford Ford Ford Ford Ford Ford :mrgreen: ~~

diytexas
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Re: confused myself

Post by diytexas » Sat Aug 17, 2019 12:22 pm

I get all that. I mean we could put (10) 20A circuits, but it will still only dispense 40A when the subpanel or service panel 2 pole breaker trips that feeds this wire.

I don't understand why 120V panels don't exist (well, they apparently do, but aren't popular, at all).

If I have a buried 8/3, but theoretically have 4 devices that all need 20A, all the time, there's no way to utilize the full 40A of each of those two hot wires?

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Aaron
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Re: confused myself

Post by Aaron » Sat Aug 17, 2019 2:51 pm

Amperage (current) is drawn, not dispensed. Think of a truck towing a load. The fuse or breaker is like the linkage between the truck and the load it's towing. The linkage is designed so that it will break apart if the load exceeds the truck engine's towing capacity, so it protects the engine from overheating and blowing up.

120V panels used to exist in the past when homes had 60A panels. There's no practical use for 120V panels anymore because modern homes have both 240V and 120V load requirements and the 240V panel satisfy both.

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emtnut
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Re: confused myself

Post by emtnut » Mon Aug 19, 2019 7:34 am

diytexas wrote:
Sat Aug 17, 2019 12:22 pm
I get all that. I mean we could put (10) 20A circuits, but it will still only dispense 40A when the subpanel or service panel 2 pole breaker trips that feeds this wire.
it will give 40A 'on each phase'
So for 120V circuits, that's a total of 40A on A phase, and 40A on B phase, so 80A


I don't understand why 120V panels don't exist (well, they apparently do, but aren't popular, at all).
Apart from a small RV, I see no need for a 120V panel ??!

If I have a buried 8/3, but theoretically have 4 devices that all need 20A, all the time, there's no way to utilize the full 40A of each of those two hot wires?
So yes, you will get 40A from each wire.
If everything is 120V loads, then a max of 80A at 120V
~~ Ford Ford Ford Ford Ford Ford :mrgreen: ~~

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