Edumucate Me on Electrical Sub-Panels

[legion]

I have two empty slots left in the main (and only) breaker box for my house. The box is a Siemens 300 amp unit. Just coincidentally, I want to run two additional circuits for outlets in the basement. The problem is, I also want to install some sort of HVAC system for the basement (currently leaning towards a ductless system, but want room to change my mind). This leads me to believe that I should install a subpanel that can support the outlets, HVAC for basement, and have room for potential unknown future expansion. It is my understanding that those two empty slots in the main box can be used to wire the subpanel.

I've installed switches, lighting, breakers, and outlets, but never a subpanel. I may well contract that out, but I want to get an idea of the materials involved. I've looked online and found lots of information on how to physically do the wiring, but not a lot of information how to select specific materials. The plan right now is to install the subpanel right next to the main panel.

Here's what I think I need:

1) A subpanel
2) A breaker to feed the subpanel
3) A line to run from that breaker to the subpanel

Questions:

-What amperage should I be looking at for the subpanel?
-What amperage should I be looking at for the breaker to feed the subpanel?
-What gauge wire should I be looking for to feed the subpanel?

[daepp]

Is it possible to remove any single "full-size" breakers and install two in their place and thus eliminate the need for the subpanel? (said the non-electrician...)

[imcarthur]

With all things electrical, if you are not entirely comfortable & knowledgeable in electrical wiring & your local electrical code requirements etc, you should hire a licensed electrician.

What is the actual rating of your mains breaker?

Are the 2 empty slots on different ‘legs’ of the panel? An electrical panel has 2 main 120V bus bars internally. The breaker required to feed a subpanel must straddle the 2 bus bars for 240V to balance the load. Usually two adjacent breakers will straddle the bus bars. Calculate the load to the subpanel. 40A? 60A? Will that breaker fit in the slots available?

Ian

[creaturecat]

The actual wiring job is simple.
You just have to do it correctly. To code.
No room for error.

[VincentVega]

Questions:

-What amperage should I be looking at for the subpanel?
-What amperage should I be looking at for the breaker to feed the subpanel?
-What gauge wire should I be looking for to feed the subpanel

They are all related, determine what size sub panel and the other pieces fall into place. I would add 60 amps then just size the wire based on distance from the main panel.

remove any single "full-size" breakers and install two in their place and thus eliminate the need for the subpanel?

That can work too, it can help clean things up for little work and minimal cost.

Are the 2 empty slots on different ‘legs’ of the panel?

100%

Move things around a bit using tandem breakers where it makes sense (keep the same amp) and you'll have room for AC, sub panel...

[biosurfer1]

Originally Posted by creaturecat

No room for error.

Sure there is, thats what makes it fun!

I was working on a light switch yesterday and got hit with 110... a bit surprising, but doesn't hurt. Got zapped with 277 once...will not be repeating that again!

[sammyg2]

I re-wired my whole house a while back, wasn't really that hard. PM me and I'll walk you through it.

Here are a few pics of my project:


About halfway there:



Got the panel closed:





Hooked up to the street:






Legion?


Legion?

Where'd he go?




.

[Cajundaddy]

I have seen that scheit before and no I will not touch it.

Depending on how long the run, I would probably use a 60A subpanel to the basement and have everything in one place. A mini-split AC won't typically draw much juice for that application.

Add up the max expected amperage draw and rule of thumb oversize the wire and panel by 20%. I recommend having a pro handle this for you.

[dad911]

Lots of guesses here without knowing the codes.

The panel is rated for how many circuits you are allowed. Look for the spec on the panel cover/door, then post a pic of panel and we'll see if you can put in some tandem or quad breakers.

[cabmandone]

Code is a big deal on this one. You might need to ground the sub feed panel separately rather than grounding to the main ground lug of the main panel. I'd check your main breaker size on the main panel. I'd also check your power company to verify you have either a 200 or 300 amp service. If you have a 300 amp service I'd drop a 100 amp sub feed in.

A question tho, is your home heated and cooled by a central system? If so why not just add a few ducts in the basement? If you insulate the basement properly the heating and cooling load are negligible. Many times manual dampers can be added to your existing system to balance the space currently being heated and then add a few ducts with a central return in the basement to take care of it.

[Rapewta]

Two empty slots. Good. 60 amp sub panel in basement fed from a double pole, single throw breaker. #6 copper, 4 wire. Two 120 volts circuits, neutral and ground.
New sub panel will have two 120 volt sources @ 20 amps each and if you need...
you can have a 220 single phase circuit for whatever.

But I agree. If you need HVAC in the basement.... just connect it to the existing system and
route it per code.

[legion]

Correction: main breaker is 200 amp. I typed the original post from work and I couldn't double-check.

The house has a separate HVAC system for each floor and none for the basement. The existing HVAC systems have no excess capacity for the basement. (This is a common gripe of the builder in my subdivision.) The basement is a walk-out and the HVAC system would only be used in the worst heat/cold situations as it's pretty liveable most of the time.

[Rapewta]

Well, a 200 amp nulls out my suggestion.
Unless you live in a 1500 sq ft house... forget what I told you.

[sammyg2]

Originally Posted by legion

Correction: main breaker is 200 amp. I typed the original post from work and I couldn't double-check.

The house has a separate HVAC system for each floor and none for the basement. The existing HVAC systems have no excess capacity for the basement. (This is a common gripe of the builder in my subdivision.) The basement is a walk-out and the HVAC system would only be used in the worst heat/cold situations as it's pretty liveable most of the time.

Oh sure, make it all clean and neat with the wires hidden and stuff labelled.
Where's the fun in that?

There's nothing better than flipping switches one at a time, going all the way down the list, yelling at the wife each time, "was it that one"?
Then you figure out she's on the phone and you get to start all over, what a hoot. Weekends don't get much better than that.

[dad911]

Newish panel, that's good. Read the label and see how many circuits it is rated for.

I don't suppose natural gas is available, convert range/dryer would pick up circuits also.

Have you spoken to a decent HVAC guy? They can probably add zone dampers for basement.

[john70t]

Start with the city line from the pole. Go from there.
(that's the only thing I can add)

[porsche4life]

Originally Posted by sammyg2

Oh sure, make it all clean and neat with the wires hidden and stuff labelled.
Where's the fun in that?

There's nothing better than flipping switches one at a time, going all the way down the list, yelling at the wife each time, "was it that one"?
Then you figure out she's on the phone and you get to start all over, what a hoot. Weekends don't get much better than that.

No kidding... The jackass who wired our house blocked off 10 breakers and labeled them "general lights and outlets" If I ever find him, I'm going to kick him in the nuts, and then remove the labels off every can in his kitchen!

[look 171]

Originally Posted by sammyg2

Oh sure, make it all clean and neat with the wires hidden and stuff labelled.
Where's the fun in that?

There's nothing better than flipping switches one at a time, going all the way down the list, yelling at the wife each time, "was it that one"?
Then you figure out she's on the phone and you get to start all over, what a hoot. Weekends don't get much better than that.

Not what they teach you in school, but we usually take a hot wire from an outlet and ground it so it trips the breaker. It creates a little firework, but work well and for sure you know which breaker is connected to that section of outlets or lights every time. No more screaming at your wife because we all know they don't pay attention. Over the years, we found so many mislabeled breakers that when we trouble shoot anything we did not installed, we almost always ignore that list. When we go in and do work, if something seem funky or Mickey Mouse, we have a chat with the owner and yank it out and redo it just so that we all can enjoy our sleep in the evening.

[look 171]

Legion,

Why do you think you need a sub panel? What are your plans for the future? More electrical needed for power tools or a theater down there? If the answer is no, then I would utilize what you have and run your mini split system off the main panel. I don't know what's hooked up to it, but you can't be using up 200 amps.

[Scuba Steve]

Originally Posted by porsche4life

No kidding... The jackass who wired our house blocked off 10 breakers and labeled them "general lights and outlets" If I ever find him, I'm going to kick him in the nuts, and then remove the labels off every can in his kitchen!

This. Our 150A replacement main panel was installed in 1969 and is completely full. Unfortunately when I started the big renovation last year it was labelled as it was set up 45 years ago, but the place was remodeled in 1979 + an addition built that has its own subpanel in 2003. It was scary how many original, ungrounded circuits were done with 14ga wire/20A breakers and repaired with brittle old duct tape after an animal chewed things up. And forget wire nuts... most electrical work was done by just twisting the wires together and putting some electrical tape on them. At least I have half a clue what breaker goes with what circuit now.