200 amp service, wanting to have 3 sub panels

[transferguy]

posted by: wstauffer

Overview:

Our home was built in 2007. We have underground service wire from the curbside utility box to our meter rated at 400amps (because the utility company said it would not cost us any more to have 200amp, 300 amp, or 400 amp service wire, so why not?). Our main service box, however, is 200 amp service. I am not sure what the wire size is from the meter to the main service box.

Due to baseboard electric heat provisions upstairs, and a number of other circuit needs, our main service box is a 40 circuit box, and immediately beside it, is a 24 circuit 100 amp sub panel (has a 100 amp circuit breaker located in the main 200 amp panel to feed this 100 amp sub panel).

Question: I am in the process of wiring upper and lower garage attached garages (one below the other), and would like to put separate sub panels in both these upper and lower garages. I will be running an auto lift, welder, plasma cutter, air compressor, lighting, lathe, mill, etc. in either garage, but not at the same time. Can I run 100 amp sub panels in both the upper and lower garages? This would mean that I would have a 200amp main service box, 100 amp sub panel box already beside it, and two additional 100 amp sub boxes= 3 total sub panels in addition to the main.

The distance from the main 200 amp service box, and the attached garages is about 60 feet....figure 80 to 100 feet to allow for routing the feeder cables to the locations within each garage. With little exception, I will not be operating equipment in both garages at the same time most likely, but may operate multiple equipment within any single garage at the same time, if you get my drift. I am looking at running separate heat pumps in both the upper/lower garages, however.

The next question would be, does it make more sense to run feeder from the main 200 amp service to, say, the lower garage sub-panel box...then run another sub-panel feeder from that lower sub-panel up to the upper garage (instead of running two separate feeder lines from the 200 amp main service box)?

My explaination isn't as clear as it could be, so I will clarify if need be.

Of course, if possible, I would need to know the size of wire to use in running the feeders to these sub panels.

To run two separate runs of 85+ feet of feeder wire to these two sub panels doesn't make sense if I could run a heavier feeder, then run that other sub panel off of the first.

Most likely, I will be using aluminum wiring due to $$$. If running two additional 100amp sub panels won't work, what about 50-75 amp sub panels? I know I have the potential of running a "legitimate" 400 amp service due to the wiring to the meter, but would need to check on what wire size is from meter to 200 amp service. I know I've heard it is cheaper to run, say, "2" 200 amp service boxes instead of "1" 400 amp service box, but I'm not certain how many sub panels I can run to a 200 amp rated main service box. Having remote sub panels just makes more sense anyway considering I would have to run multiple circuits at too far a distance if i had just 2 200 amp main service boxes in one location so far away from garages.

many thanks in advance,
Bill

[transferguy]

posted by: suemarkp

You can have as many sub panels as you want in any size up to 200A each. The rub is you need to not overload a given panel or your main panel. I thought you were probably fine until you mentioned more heat pumps. Those can really push your load, especially if the aux heat is electric and the heat pumps run the aux heat during defrost (most do and should). In a 200A panel, getting a feeder over 100A is problematic. So if you want 100A in each garage, you'll need 2 feeders. If the combined garage loads would never exceed 100A, you could run a 100A feeder to garage A and use feed through lugs of 100A to garage B (you'd need to install a panel with feed through lugs, or install a 100A subfeed kit (looks like a circuit breaker with no handle and it usually need to go in the bottom but slots of the panel).

Will these heat pumps be turned off when you're not working in the garage, or will the thermostat always be on but perhaps just set to a lower temp when you're not in the garages?

To do a load calc, we'd need the nameplate amps or watts of your largest tools that would run simultaneously, the heat pump compressor MCA, and the heat pump air handler electric resistance heat in Amps, MCA, or KW.

The power company may not upsize the wire for a 400A service, which is why your wire is "rated" at 400A. The key discriminator for a 400A service is 2 things -- the rating of the meter base (they are 100A, 200A and 320/400A) and each is physically larger than the other, and the rating of the wires from the meter to the 200A panel. I'll bet those wires are only rated for 200A. It is definitely cheaper to put two 200A panels in parallel than to instal a single 400A panel. Some things also have to change when upgrading to 400A -- the ground/bond wire to a metal water piping system will have to be increased. That can be easy or hard depending on where it is and whether it is covered with finish material on the way there. The wire to ground rods or a concrete foundation electrode would NOT have to be increased.

Based on the length, I'd use 1/0 aluminum wire or #2 copper wire for a 100A feeder. The neutral could most likely be one or two sizes smaller (#2). The ground wire (yes, you need to run 4 wires) could be #8 copper for a 100A feeder and must have green insulation or be bare. I'd avoid aluminum for the ground wire, but if you need to go that way, then #6 aluminum would be needed and again it must be bare or green insulated. Bare aluminum wire should never be run close to the earth or buried directly in it. The type of wire to use will depend on how you want to get it there -- via an attic space and stud spaces, surface mounted exposed, direct buried, or in conduit (above ground only, or a mix of above/under).

Some panels may not have bending space for 1/0 wire. What is the distance from a circuit breaker lug to the side wall of your panel?

Mark
Kent, WA

[transferguy]

posted by: wstauffer

Hi Mark,
You are correct...after further checking, it appears that I have 400amp wiring from the road to the meter box, and everything including the meter box to the inside is rated 200 amp. Based on my needs at this time, it does not appear I need to add a second 200 amp main service box (to equal 400 amp service) at this time....so that can be taken off the table, at least for now.

As for heat pumps, I do not run an electric backup on my current heat pump, and will not run an electric back-up on the other two heat pumps. This should not be an issue in my particular situation. Also, the heat pumps will only run while I'm in the garage areas, which will be insulated and each garage is 24x28, so the heat pumps will be small. I know this isn't taking an actual load calculation into account, but I know my main heat pump is 3.5 tons and has a 30 amp breaker...these will be smaller heat pumps. I could also wire one or both heat pumps into my main 200 amp service box, if need be, since I am not running baseboard electric that our home was pre-wired for. Regardless, we should be ok with the heat pump loads.

As for the the two 100 amp sub-panels I want to add in garages "A" and "B," if I understand correctly, I can run a feeder from my main 200 amp service panel to garage "A," then run a feeder off of the garage "A" sub-panel to a 100 amp sub-panel in garage "B," so long as the total max load in both garages combined, at any one time, is 100 amps or less, with respect to the load capacity on the main 200 amp service, correct? (total house/garage load <200 amps).

Also, if I understand correctly, I can run "two" feeders off of my main 200 amp service, with one feeder to garage "A," and the other to garage "B." The advantage of this would be I could have a max load of 100 amps in each garage (200 amp combined) at the same time, with of course respect to the total house max load. Do I understand this correctly, as well?

With either option I chose, the wiring size would be the same....whether I run

option 1: two separate feeders to garages A/B, or
option 2: choose to run one feeder to garage A, then a feeder from garage A to garage B. Am I following you correctly so far?

option 1: would be a run of approximately 75-100 ft to each garage
option 2: would be a run of approximately 75-100 ft to garage A, then approximately 20-40 feet feeder from garage A sub panel to garage B sub panel.

My wiring choices (Aluminum vs Copper) would be the following size recommendations....again, double checking (still pricing/haven't decided on copper/alum yet). Wiring will not run to the exterior...all feeder runs will be from my main service, across basement, and directly through wall into garages A/B.

Aluminum: 1/0, #2 Neutral, #6 ground (or #8 copper ground)

or

Copper: #2, #6 Neutral, #8 ground

Are the above wire sizes correct regardless of which option I choose for the feeders?

Now the new:

I am confused with grounding requirements. My main 200 amp service, of course, has an earth ground to a rod outside. Do each of my new sub panels require earth grounds, as well? What about bonded/not bonded requirements inside each sub-panel? I'm reading some information that says each sub-panel needs it's own earth grounding rods, while others say this is true only if the sub-panels are in detached buildings. Garages A and B are both attached, one garage over the other.

As for the feeder wiring itself, I understand that it would have to be inside conduit if it is individual wires, but if it is a service-type wire (all wires within same insulation covering) it would not have to be in conduit...is that correct? I actually prefer to use conduit, if possible, regardless. So, what size of conduit would be recommended? Does the recommendation depend on Aluminum vs Copper, and/or individual wires vs. "all in one" wire? Obviously it has to be big enough to fit in, but I understand there are "cooling" needs of the wire. I prefer to run PVC conduit over metal, but am not sure what code calls for indoors.

Much appreciation in advance...a little wordy, but I tried to add detail for the benefit of understanding my specific needs, as well as perhaps being easier for someone else to understand this post that might have a similar situation they are researching. Great website!! I have some basic wiring experience as a homeowner/past landlord, but this is new territory.

[transferguy]

posted by: suemarkp

Posted by wstauffer

As for the the two 100 amp sub-panels I want to add in garages "A" and "B," if I understand correctly, I can run a feeder from my main 200 amp service panel to garage "A," then run a feeder off of the garage "A" sub-panel to a 100 amp sub-panel in garage "B," so long as the total max load in both garages combined, at any one time, is 100 amps or less, with respect to the load capacity on the main 200 amp service, correct? (total house/garage load <200 amps).

Also, if I understand correctly, I can run "two" feeders off of my main 200 amp service, with one feeder to garage "A," and the other to garage "B." The advantage of this would be I could have a max load of 100 amps in each garage (200 amp combined) at the same time, with of course respect to the total house max load. Do I understand this correctly, as well?

Yes. You also have another variant on the first choice, and that is to use a circuit breaker in garage A's panel instead of a feed through lug. If you put in a 60A breaker, that will provide a 60A feeder to garage B (so smaller wire could be used in that run to garage B, but less power is available there).

Posted by wstauffer
With either option I chose, the wiring size would be the same....whether I run

option 1: two separate feeders to garages A/B, or
option 2: choose to run one feeder to garage A, then a feeder from garage A to garage B. Am I following you correctly so far?

option 1: would be a run of approximately 75-100 ft to each garage
option 2: would be a run of approximately 75-100 ft to garage A, then approximately 20-40 feet feeder from garage A sub panel to garage B sub panel.

Yes. You use much more cable with the separate 100A feeders. It is quite difficult for one person to need a 100A feeder. A heat pump may be 20A, a couple of 240V tools and a compressor may be another 15A each, so that's 50A (use nameplate amps, not breaker sizes to determine this). Maybe another 5A for lights.

Posted by wstauffer

My wiring choices (Aluminum vs Copper) would be the following size recommendations....again, double checking (still pricing/haven't decided on copper/alum yet). Wiring will not run to the exterior...all feeder runs will be from my main service, across basement, and directly through wall into garages A/B.

Aluminum: 1/0, #2 Neutral, #6 ground (or #8 copper ground)

or

Copper: #2, #6 Neutral, #8 ground

Are the above wire sizes correct regardless of which option I choose for the feeders?

I would use a #4 neutral in the copper variant, not #6. In order to reduce though, you MUST have 240V loads connected.

Posted by wstauffer

I am confused with grounding requirements. My main 200 amp service, of course, has an earth ground to a rod outside. Do each of my new sub panels require earth grounds, as well? What about bonded/not bonded requirements inside each sub-panel? I'm reading some information that says each sub-panel needs it's own earth grounding rods, while others say this is true only if the sub-panels are in detached buildings. Garages A and B are both attached, one garage over the other.

Since this is an attached garage, you do not need ground rods or any earth electrode (attached means attached to the main house, not just attached to each other). Basically, if they are all under one common continuous roof, they are one building. The ground electrode system back at the main panel covers these panels.

Posted by wstauffer

As for the feeder wiring itself, I understand that it would have to be inside conduit if it is individual wires, but if it is a service-type wire (all wires within same insulation covering) it would not have to be in conduit...is that correct? I actually prefer to use conduit, if possible, regardless. So, what size of conduit would be recommended? Does the recommendation depend on Aluminum vs Copper, and/or individual wires vs. "all in one" wire? Obviously it has to be big enough to fit in, but I understand there are "cooling" needs of the wire. I prefer to run PVC conduit over metal, but am not sure what code calls for indoors.

True, cables (NM, SER, MC) aren't used in conduit and can be run on the surface or concealed in walls/ceilings. However, they must be protected from damage, so you'll most likely need nail plates in places if concealed or some type of running board/guard boards or conduit sleeve if exposed. Technically, even sch40 PVC needs to be protected from damage, but in a basement I don't think an inspector would require anything extra. If they do, you'd need guard boards on each side of it, or use sch80 PVC which doesn't require any damage protection.

The size of the conduit depends on what type of individual wires you choose (different insulation types are thicker than others, and aluminum is larger than copper for a given amp rating). I think you're looking at 1.5" to 2" conduit -- 1.5" if copper, 2" if aluminum wires are used. You can calculate the exact size once the conductors are chosen, but it is better to be a bit large than to try and pull it through a barely legal raceway. What really matters for pulling is the number of bends. Pulling anything through the legal max of 360 degrees of bends is quite difficult. But larger conduits have larger bend radii so they are a bit easier to pull. You may need to use conduit bodies, such as LB's, to get to where you want to go and those are also easier to work with when they are a bit on the larger size than bare minimum. Also, you need to make sure you have an available knockout in the size you want on both the source and destination panels.


Mark
Kent, WA

[transferguy]

posted by: wstauffer

Mark,

Many, many thanks for taking the time to reply to my many questions...wiring is one of those things you want to get right the first time, because you might not get that second chance. I am late replying because I became involved in a wiring project at my mother's home ironically....(tangent) all I have to mention is Federal Pacific Stab-Loc...I'm sure you you know the rest. I replaced the main service with Square-D Homeline (I do prefer the QO series, but the house will most likely be sold in the next few years). Overloaded circuits with no tripping=over heating.....melted outlets, charred wiring where the insulation fell off, etc. I will post some before and after photos in the appropriate place in this forum in the near future.

Back to my situation. I agree the 100 amp might be a little overkill for the typical shop, but I am not certain what my specific needs will be regarding my getting back into welding and machining, and adding electric heat treating. I want to size my service for some of the largest single phase welders I can run, as well as a high amp plasma arc that needs the air compressor, etc. My logic was that if I did not add additional service panels, the cost of running the welder circuits alone from my main panel that distance comes close to the cost of running sub panel wiring for 100 amp service. I know welding circuits have "duty cycle" considerations, which allow lesser size wiring for a given amperage requirement, but it's possible to have 100% duty cycle welders running at 50-80 amps input in a worse-case amperage requirement scenario. . I might as well bite the bullet and run 100 amp sub panels in each garage to be certain, but need to check on a few additional load requirements to be sure this is enough for the heat-treating equipment.

Oh, and by the way, it looks like Aluminum will get the nod for the service wiring unless I can get a good ebay deal on copper (unlikely with the length of run I need). Copper gets the nod for all other wiring beyond the panels.

Lastly, if I understand correctly, both sub panels, regardless of option A or B, will be "non-bonded/non earth grounding," thus the reason for the 4 wire sub panel service wiring, correct?

Again, many thanks! I think I'm on the road to making a final selection.

Regards,
Bill

[transferguy]

posted by: suemarkp

Yes, your subpanels are non-bonded and why there is the 4 wire requirement.

Circuits aren't always sized for the worst case load. A common example is a kitchen range in which a 40A circuit is fine for ranges up to 16KW. That could be a 66A load, but it is unlikely that would occur, and when it does it won't go all that long. So wires are sized for the average use (duty cycle) of the intended load. If you pick welders with a plug larger than 50A, you're most likely going to want to hard wire them. Have you priced an 80A pin-and-sleeve plug and receptacle? If the welder has a 50A plug, it can be wired with 6-2 romex and its load calculated value would be less than 50A. You can run a lot of 6-2 for the price of a feeder and panel (but the incremental cost of upsizing a panel is not that much more unless you hit some major limits or thresholds (see below). It is also much easier to run multiple cables through a 2x4 wall than to deal with conduits larger an 3/4" because of the nail protection required and the radius required for bends.

For al -vs- cu, I asked about terminal space. Residential panels aren't that wide, and there are clearance requirements from the breaker lug to the panel wall. If your feeders on the 100A breaker(s) don't leave via a knockout directly near the breaker (e.g. they go up or down or out the opposite side of the panel), then you need this much space between the breaker terminal and the panel wall:
#2 AWG - 2.5"
#1 AWG - 3"
#1/0 or #2/0 AWG - 3.5"

If you try to go out the wall next to the breaker, you need even more space.

So if you use 1/0 AL for this, you need to be sure you have 3.5" from the breaker terminal to the side wall (or any other obstruction or barrier next to the breaker lugs). Many panels only have 2.5 to 3", so that may force you to copper. Or, see if a 200A panel has more clearance -- there's no reason you can't use a 200A panel on a 100A feeder.

Mark
Kent, WA