I'm a new member there and not a licensed electrician, so consider the source and, if any of the heavyweights around here weigh in with contrary advice, please defer.

Yep, sounds like a lunatic did the wiring to me.

Are the two 30amp breakers in the main panel tied together or are they independent? If they're not dual breakers, you've got a problem, IMO.

Any chance you could post a photo of the open subpanel? Given what you've described, it might be good to look at the whole picture because there could be numerous additional errors.

I agree that the 12/2 shouldn't be protected by 30-amp breakers in the situations you've described. I believe there are exceptions (pertaining most often to motor surges), but I wouldn't make that assumption here. Others may differ on that.

As far as using 15-amp receptacles on 20-amp circuits, I don't think that's a problem so long as (1) they are reasonably modern receptacles and (2) they are not "back stabbed". (I think you need a 20-amp if it is a dedicated single-receptacle circuit, but that doesn't sound like the case here.)

Some in the trade recommend that when 15-amp receptacles are used in a 12AWG 20-amp circuit that the receptacles should be pigtailed rather than looped to ensure maximum continuous current flow. I believe that is more of a "best practice" preference, though, rather than a code requirement. YMMV.

Should you write up a plan and then pull a homeowners permit?

Absolutely, by all means.

Cheers, and good luck.

Wish the big guys had taken a whack at this, but since that hasn't happened (yet), I'll take a second pass. (Keep in mind the above-mentioned caveats.)

Replace the Main Serice Panel 30 Amp breakers with 20 Amp SPST breakers.

Disagree. You need a DPST breaker.

Replace the sub panel's 30 Amp breakers with 20 Amp breakers. Reduce the load on the Existing 20 Amp breaker.

Frankly, the idea of reducing "the load on the existing 20 AMP breakers" doesn't mean much to me. The whole idea of breakers is to reduce (that is, deny) overload.

I'm going to use that breaker to feed the ceiling lights and outside safety light and ceiling fan.

OK, but that's not terribly significant at this point, as I see it. What's more important is the overall scenario.

R&R the rusted ceiling fixtures.

No prob. Good idea.

One 20 Amp breaker to service the left side of the room (computer system)One 20 amp breaker to service the Right side of the room.

If anything, it's overkill. But no prob.

The Spare slot will be used to service the left side of the room (includes the air conditioner.)

Uh huh, OK.

My questions:

Currently the ceiling rafters are exposed and used as a quasi raceway for various 12/2 cables. Do I need to drill the joists (2X4) and run the wires through the rafters or can they stay on top of the joists and loose?

Well, you shouldn't leave them just laying on the "joists", that's for sure. They must be secured and protected, one way or another--whether that's by running through joists, or via conduit, or stapled to a board raceway. You can't just leave 'em exposed, loose and flapping.

You've used the terms "rafters" and "joists" but, I suspect, altogether imprecisely. If they are indeed 2 x 4, they may be part of a truss. That's not insignificant because drilling a lot of holes in trusses can be problematic structurally. The sparkies on this site may not like this, but electricians are notorious for drilling through anything, without understanding much about structural integrity. (OK, sparkies, let me have it! Go for it.)

I can't say for sure what your best solution is, but the friggin' wires have to be secured without causing structural problems. Mo' fax would be helpful.

Do I need to change out the Ser Panel breaker 240 vac (two 20 Amp breakers) in favor of a higher amperage?

That's probably a good idea, but ONLY after considering the wiring and the specs of the subpanel. With 20AWG between main and subpanel? No way.

Most likely, your solution lies with a 40-amp subpanel (fed by #8 wire) or possibly a 30-amp subpanel (fed by #10 wire), depending on the length of the run. But the solution is certainly not a higher capacity fed by #12 wire. The wire size between main and subpanel is VERY important.

Since the original installer chose to use 12/2 to run his welder, when I replace the 30 Amp breakers with 20 Amp, do I have to R&R the existing 12/2 Romex?

Geez. What kind of crappy welder did the guy have?

It seems to me that the issue here is: What kind of outlet is served? If it's, like, a 30-, 40- or 50-amp outlet (check the outlet configuration), you need to replace it with a 20-amp receptacle or reconsider the circuit altogether.

Are you also planning to run a welder? If so, you probably need something like 50-amp service (maybe 40) to the outlet, and that queers the deal altogether.

All open splices have to be in junction boxes, correct?

Correct.

Hope this is helpful.

It sounds like the 'electrician' used 12/2 to cable a 240v common neutral run to the branch panel.
If so, it's probably using the bare ground wire for both the neutral and ground (MAJOR VIOLATION), if it's grounded at all,and using the white insulated wire for a 120v hot leg.
If you are going to have either more than 20 amps, total, or any 240v circuits at the subpanel, you need to run a new cable from the main panel to the sub. I'd use 10/3 cable and a 30 amp DPST breaker at the main panel.

Randy - Cobraguy - Daver- Texas Readhead

Let me back-step a minute. The cable running from breakers 29 and 30 on the main service panel is 12/3. Breakers 29 and 30 are a STDP 30 Amp breakers. I want to drop them out of Service Panel and replace with two STSP 20 Amp breakers. These two breakers will feed a sub panel in the storeroom.

Breakers 31 / 32 are STDP 30 Amp. This feeds a 240 vac baseboard heat using 12/2 and ground. White is marked with black tape to signify that it is a hot line. I want to DSC the heater and replace Main Service. Panel with 2 Additional 120 vac SPST breakers.

Breaker 1 will service the right side of room Computer and peripheral equipments.

Breaker 2 Will service left side of room. Window A/C and workbench quad receptacle and two down stream double receptacles.

Breaker 3 will be a dedicated circuit for a laser printer. The printer's Instant On is about 18 Amps. Also, every 4 seconds, there is a 18 Amp inrush to heat the fuser.

There are 5 overhead lights with 12/2 Romex laying on top of 2X4 joists. Breaker 4 will service these connections. There is no ceiling. Should I drill the joists and run the Romex through the holes in the 2X4 joists and then secure the Romex to the joist where they split off to service their respective lights?

I would also like to use STSP breakers so that each hot side of the sub panel will be able to trip individually. Is that acceptable by code?

FYI - This room is a prefabricated wooden sheds that one of the previous owners had attached to the house where the old walk-out door from the garage was. It was used as his workshop.

"The cable running from breakers 29 and 30 on the main service panel is 12/3. Breakers 29 and 30 are a STDP 30 Amp breakers. I want to drop them out of Service Panel and replace with two STSP 20 Amp breakers. These two breakers will feed a sub panel in the storeroom."

If the 2 breakers are feeding a subpanel they MUST be double pole breakers or two single pole breakers with a tie bar. 20A is correct for #12 wire.

"Breakers 31 / 32 are STDP 30 Amp. This feeds a 240 vac baseboard heat using 12/2 and ground. White is marked with black tape to signify that it is a hot line. I want to DSC the heater and replace Main Service. Panel with 2 Additional 120 vac SPST breakers."

Not sure what you mean by this: " I want to DSC the heater and replace Main Service. Panel with 2 Additional 120 vac SPST breakers."

If you want to run two distinct separate 20A cc'ts from the double pole breaker you can use the previous 240V 12/2 cc't as one 120V cc't using the previous white wire as your new neutral wire. For the second cc't you'l need new 12/2 cable. If the previous 240V cc't was 12/3, then you wouldn't have to rewire and you could have used this 12/3 as a multiwire shared neutral cc't.

You can staple the cable to the joists if the cable isn't in an exposed location susceptible to physical damage from below. The AHJ's don't like homeowners hanging stuff from exposed cable like a clothesline. If the cable is exposed along the bottom, fasten a running board to the bottom of the joists and staple the cable to this running board.

That's all I can offer right now. If I've missed something I'm sure other experts will chime in.

As you now describe it, you can currently run 3 20 amp 120 volt circuits to the office (there are options if you want a 240 volt circuit). The two circuits with the common neutral need to be on a double pole breaker.
Make sure all of the wiring on each circuit is #12 or larger or you will have to derate it accordingly. (i.e. A 15 amp breaker if the circuit has 14-2 cable in it.)

Don:
Are you still using the welder on the circuit? If so it could have been wired properly from the get go. If I'm not mistaken some welders, like electric heating, uses 12/2 on a 30A circuit. Anyone with welder experience out there to confirm this?

Also, don't waste money replacing those 15A receptacles. It is standard practice to install 15A receptacles on 20A circuits, as 15A receptacles are rated for 20A of current to pass through. The only instance that calls for a 20A receptacle would be if there is only one outlet on a 20A circuit, and it is not a duplex receptacle.
Cheers

You need to verify the size of the wire used from the main to the sub panel - sounds like you're not sure if it's #10 or #12. If it's #12 you can't have 30 AMP breakers on it if it feeds a panel - doesn't matter if a welder is involved or not.

The sub panel requires 2 hots, a neutral, and a ground if you intend to have 240 volts available in it. Given a lack of information on the expected loads it would be hard to recommend what size feeder you need to the panel. Given the air conditioner and fan account for about half the capacity of the panel if it in fact does have #12 you may want to think about about a larger feeder.

At 9 AMPs the air conditioner(and possibly the ceiling fan - no ratings to judge) should probably be on its own 15 AMP circuit. Lights should have a separate circuit. I like to run circuits in garages and shops so that adjacent receptacles are on different circuits.

Unless you have something with a 20 AMP plug on it the 15 AMP receptacles are just fine, as pointed out above.

You DO NOT drill 2X4s if they are part of a truss. Wires may be fastened (stapled)to the tops of them.

There are prohibitions about adding (attaching) this type of building to an existing structure many places. I'd make some inquirys before getting too gung ho.

Uncle Bill etAl,

I am sure about the AWG of the feeder cable to the sub-panel. It is 12/3. I popped the can on the sub-panel and I have a Hot to two lugs a neutral to the neutral bus and a ground to the ground bus.

Again it is fed by a STDP 30 amp breaker in the main service panel.

I will staple the Romex runs to the top of the 2X4 joists. I'm the only one who uses this room so no one will be hanging anything from the runs. Do I need any type of separation between each run

As to my planned loads, all be 110/120 loads. The highest drawing load will be a laser printer that only draws 18 Amp in start up and then inrush for heating a fuser on the printer.

The second STDP 30 amp breaker in the main can was installed to feed a baseboard heater. "DSC" means disconnect. I have a much smaller 120 vac, oscillating heating I'm planning on using.

I was going to feed the AC on a dedicated line from one of the slots on Service Main and the Printer from the slot on Service Main.

Also, I've modified my wiring design to use a STDP 20 amp 120 vac breakers. I sure don't want 30 Amp running over #12 wires.

I'm confused. On top of the joists is the floor above. You mean below the joists? Despite what you think you will never do, do it right. Go through the joists or use running boards.

Could we please use STANDARD terminology here. Your colloquialisms are making my head spin. The things with the breakers in them are panels. All breakers are single throw. Please just say double pole.

By slots are we talking about positions in the main panel where you intend to install appropriately sized breakers?

If this room is unfinished, your 120v 15/20A receptacles must be GFCI protected.

OK, Ronnatalie -

What I was calling joists are the ceiling joists. Because this is a prefabricated shed, the ceiling joists are 2X4s, not 2X6s.

Let me start again, please. The service main panel is a 200 Amp, Challenger box. Breakers 29 & 30 are double pole 30 Amp breakers. These two breakers feed a sub panel using 12/3 wire.

Black to a hot lug, red to a hot lug, white to neutral bus and ground to ground bus. My current plan call for an R&R of the 30 amp breaker in favor of a double pole 20 amp breaker.

The sub panel hold four breakers, At present two of the breakers are 30 amp breakers that I'm going to replace with 20 Amp breakers. The other is a double 20 amp breaker, it services all the 110/120 for this room.

I'm going to replace that breaker with two individual 20 amp breakers. There should be no 30 amp circuits needed.

Breaker #1 will be a dedicated double receptacle for my laser printer.

Breaker # 2 will service the right side of the shed receptacles.

Breaker # 4 Will service the left half of the shed receptacles.

Back at Service Main, Breakers 31 and 32 currently a double breaker 30 Amp. feeds a baseboard 220 heater. The run is made with 12/2 cable.

Black goes to Breaker 31 and white / with black tape goes to breaker 32.

I'm planning on removing the double breaker and replacing it with a single 20 breaker. Removing the black tape from both ends of the white wire. Next I'll install a double receptacle to function as a dedicated line for the window AC and the ceiling lights.

Sorry if I confused you.

don, that sounds better. i have to admit tha ti re-read your other posts a few times and never did follow what you were planning on doing!

if it is a shed, then i would lay them on top of the joist and if nothing else stick a peice of plywood up to satisfy the AHJ if necessary.

Ah, but there is no ceiling. These aren't joists at all, but the bottom chord of some roof truss or collar tie. I get it. You need to use the running boards. You have to protect the exposed NM by having it follow the building surface.

Other than that it sounds OK, but I'd still consider just replacing the wire to the subpanel with 10-3 rather than the breaker. I'd also not put the lights on the circuit with the AC unless you like watching them flicker.

OK, I believe we have arrivied at the final draft. Is pulling a permit recommended?

The service main panel is a 200 Amp, Challenger box. Breakers 29 & 30 are double pole 30 Amp breakers. These two breakers feed a sub panel using 12/3 wire. The current plan calls for the R&R of the 12/3 with 10/3.

The sub panel hold four breakers, At present two of the breakers are 30 amp breakers that I'm going to replace with 20 Amp breakers. The other is a double 20 amp breaker, it services all the 110/120 for this room.

I'm going to replace that breaker with two individual 20 amp breakers. There should be no 30 amp circuits needed.

Breaker #1 will be a dedicated double receptacle for my laser printer.

Breaker # 2 will service the right side of the shed receptacles and the ceiling fan.

Breaker # 4 Will service the left half of the shed receptacles and overhead lights.

Back at Service Main, Breakers 31 and 32 currently a double breaker 30 Amp. feeds a baseboard 220 heater. The run is made with 12/2 cable.

Black goes to Breaker 31 and white / with black tape goes to breaker 32.

I'm planning on removing the double breaker and replacing it with a single 20 amp breaker. Removing the black tape from both ends of the white wire. Next I'll install a double receptacle to function as a dedicated line for the window AC.

In most jurisdictions pulling a permit is required for what you want to do (as are the resulting inspections). What is recommended? I can't "recommend" other than complying with the local law.

I have a question about the subpanel. You state "The other is a double 20 amp breaker, it services all the 110/120 for this room." If it's a double pole breaker with 120V, then it's a shared neutral multiwire cc't. Do you realize what that is? Are you going to run new cable for cc't 4 or just use the black and white of the 12/3? What will breaker 3 service?

You're welcome.

Hey, read your problem and even thou everyone seems to want to give you resonable advice,my advice to you is to call a professional, seems like you have too much going on to resolve over the internet. I am a licensed contractor and would really refuse to give this type of wiring advice to a novice. Remember faulty wiring can cause fires.
the best advice i could give to you if you wish to tackle this yourself is to call your local inspector and ask for advice and remember he will be inspecting. In the mean time I would turn off power to the area as it does not seem to be safe. Hope this was of help

Hey Sparky,

I'm not actually a novice here. I have a history of DIY electrical work.

I have every intention of taking this to an electrical inspector for the city and pulling a permit.

While it seems like a lot of work, it really isn't. I will most likely work on each issue to completion and then move to the next one.

I figure if I take my time and plod along, all work will be done in about 3 days. Since I'm retired, it gives me something to do.