1

I've previously mentioned in other questions my plans to upgrade two old and insufficient subpanels which serve my garage and its upstairs apartment. Note that the garage is attached to the house; it was an addition (in the mid '60s) but it is not a separate structure. The two panels are fed by a common feeder which is 3 x #4 copper in 1" EMT; the apartment panel is downstream of the garage panel and fed via a breaker in it. There is not a separate ground wire in the feeder although the EMT provides some ground continuity. In addition, since my service entrance panel is more than maxed out (the previous homeowner double-wired some circuits as the neutral bar was filled up, I'm planning to install a smaller sub-panel at the back of the house in an office/bath area I'm renovating and offload some circuits from the main panel. (See photo attached). The feed I'm planning for this new subpanel is 3 x #4 plus a #6 ground in 1" PVC, but I haven't cut any holes or bought any materials except for the panels themselves so far so I'm able to modify my plans if desirable.

I'm asking for recommendations for wiring and upgrading the grounds at all four of these panels. Currently the service entrance panel has a single ground rod driven I-don't-have-any-clue how long ago, and it looks badly corroded. At the back of the house, about 12 feet from where I'm putting in the new subpanel, there's a 1/2" ground rod which I drove myself a few years back when I found that an outlet where I wanted to place a computer did not have a functioning ground. The corner of the garage where the two old subpanels are has no ground and has a concrete walkway all around, but that's not a showstopper as I have a hammer drill. The two subpanels are within three feet of each other, so they ought to be able to share a ground connection. I'm not planning to upgrade the feeder in 1" EMT at this time as my eventual plan is to have a new, larger service entrance installed behind the home.

As the old saying goes, "I'd rather do it right than do it over." I definitely want a new ground rod for the garage panels, and I'm thinking that this is an opportune time to drive one or two new ground rods for the existing service entrance panel to replace the one which is corroded. For the new panel at the back of the house I could either drive a new ground rod, run wire about 20 feet around the perimeter of the room to the 1/2" rod I drove a few years back, or simply ground it back to the existing service entrance with the ground wire in conduit.

Since some of you will be curious, here are the projected loads for the various panels:

Garage Panel: Lighting (fluorescent, 8 single-tube fixtures), convenience outlets for power tools. Planning to add a 50A circuit for a welding machine (infrequent use) and to offload the laundry equipment (gas dryer [with provisions for electric], washing machine) onto this panel once it's changed out. Once service entrance is upgraded may add some more heavy-duty power tools on this panel, possibly a feed to a future swimming pool.

Apartment Panel: Small appliance & lighting circuits (gas range); 220V window AC/heat pump (20A circuit, downrated from original 30A as new A/C was more efficient). Eventually want to upgrade appliances to modern standards (dishwasher, disposal, installed microwave, etc.) but this can wait until I upgrade the service entrance.

Office Panel: Will be rewiring the back corner of the house which is the last vestige of fabric-covered ungrounded Romex which I'm aware of. Two circuits for computers and lighting, two circuits for a network closet and central sound system, offload HVAC (gas furnace, outdoor compressor, with provisions for eventual installation of ground-source heat pump and electronic air cleaner). Bathroom circuit. AFCI/GFCI protection as appropriate. Current Service Entrance Panel

2
  • 1
    "install a smaller sub-panel": (at least) one of our resident electricians constantly recommends against this. You should strongly consider returning the "smaller" sub-panel and picking up a large one. You're living the pain of running out of breaker space, don't put yourself (or a future owner) in that same pain again if you can avoid it for only a few bucks (in comparison to to the cost of the rest of the project) more. Having 10 spots used in a 40-space panel may look funny in comparison to 10 used in a 20-spot panel, but 11 new, unimagined circuits from now, you'll feel like a genius!
    – FreeMan
    Jun 20 '20 at 14:18
  • 1
    I would connect your 2 perfectly good driven grounding electrodes with #6 wire this solves the grounding issue having the electrodes further apart actually makes a better ground. And agree with free man why put in a small sub the cost difference is small when you compare them and you are sure to never run out of space, I had 1 customer purchase 3 panels over a few years if he would gone with the bigger one he would not have had 2 sitting around his garage and would have saved him a ton of $ only having to upsize the feeder instead of rewriting each time and upsizing the feeder.
    – Ed Beal
    Jun 20 '20 at 15:15
3

TLDR:

  • No need to upgrade main panel. A big subpanel will support your future needs.
  • You MUST upgrade your service (and service entrance) to 200A since your main breaker is already 200A. WTH?
    • This will handle everything you plan, and an EVSE also.
  • LOVE your EMT and rely on it for grounding. Consider it for your next run!
  • For #4 copper wire running in EMT conduit, upsize the 70A breaker to 90A. (instant capacity!)
  • That other bar is a neutral bar. Grounds are OK there in a main panel.
  • Having reclaimed your other neutral bar, remove the double-taps in the main panel.
  • Never again use a grounding rod as a substitute for a ground wire!

On the main panel

I see the installer made several questionable choices even if they are not Code violations.

Oh wait, there are code violations at the double-tapping of some neutrals, as well as the shared neutral lug. The bare neutral to the right appears to be your service feeder neutral. The insulated seems to be your subpanel neutral, and it belongs on the neutral lug on the left! (but don't runt off any more length please).

Also, I see a 200A main breaker. Given your modest loads, since you already have 200A, I wonder why on earth you need a service upgrad--- Oh, wait. Those service wires look awfully small to be 3/0 Cu. It looks to me like you have a 100A or 125A service with a 200A main breaker. Yeah, I would go ahead and upgrade that service to 200A A frikin S A P before you set those service wires on fire. But the good news is, you don't need to change this panel! It's not as full as you think, and your "subpanel" strategy has a lot of legs - you'll be fine! To repeat:

The installer chose to clip off all excess length, in the goal of "neatness" (and nobody gives out awards for that). This creates a great inconvenience (wires are too short to freely move breakers around) and also creates a thermal problem with so many active conductors bundled together, see neutral wires bound together. Never do either one!! Every hot and neutral should (not a Code requirement) to reach any breaker space in the panel (neutral for AFCI or GFCI). Unbound and slightly loose wires creates the airspace between wires needed for cooling.

You have #4 Cu wire coming off a 70A breaker. Now, if you look in the ampacity tables, at 60C thermal, #4 is allowed 70A, clear enough. However, wires run in conduit are permitted 75C thermal. That gives your #4 feeder 85A, and you are allowed to "round up" to a 90A breaker. So we change that feeder breaker to 90A immediately, and just bought ourselves 20A of headroom. Easy peasy!

You can squeeze 4 more full spaces out of this panel by doing more double-stuffing. That'll give you room for full-size breakers for 2 more subpanels.

Remember if you're staying with #4 Cu, that breakers at 90A if run in conduit. You should also evaluate aluminum for long runs, there's nothing wrong with it for feeder.

Neutral and ground bars

GE has a funny way of doing double-stuff breakers. They sell 1/2" width breakers that clip onto a "cruciform" bus stab unique to GE. So this is a GE Q-line panel for sure, and given the positions, it's clear all the spaces have the cruciforms. This panel has 16 spaces and can accommodate 32 circuits via the 1/2" double-stuffs.

Since there's no such thing an accessory neutral bar, it would be a grave oversight for a panel manufacturer to short you. Indeed, the bar on the left is a neutral bar that the installer has chosen to populate exclusively with grounds. It is legal in a main panel to put grounds on the neutral bar, but this has led everyone into an error in thinking. Simply evict the grounds from your other neutral bar and you'll have plenty.

Here is the spotter's guide: The steel case is grounded. Neutral bars are designed to be possible to isolate from the steel case. Ground bars cannot be isolated; they are bolted direct to the steel case. That's what you do; bolt on accessory ground bars anywhere you please. Either

  • a) use #10-32 (or any -32 or finer thread pitch at least #8) self-tapping screws to mount them, or
  • b) run a fat wire from the ground bar to the neutral bar, ideally in a place you can get a clamp ammeter around it.

Ground rods and grounding

Your plan to update ground rods is a good one. Remember there is such a thing as an UFER ground - this is poured into the concrete and brought out as a chunk of reinforcing rod etc. This is the best ground available. Look for this on each concrete pour. Other than that, if you are not confident of your ground bars, by all means put modern ones in! They must feed into the main panel to count. You can keep the substandard grounds connected.

At the back of the house, about 12 feet from where I'm putting in the new subpanel, there's a 1/2" ground rod which I drove myself a few years back when I found that an outlet where I wanted to place a computer did not have a functioning ground

Never do that! Ground bars only handle lightning and ESD (which was what you were after in that application). They do nothing for ground-faults of human-generated electricity, because dirt is too poor a conductor of electricity to return 30A of current. So you created the illusion of ground-fault safety, but none existed: you could've corrected that by GFCI-protecting the outlet, gaining its ground-fault protection along with the rod's lightning/ESD suppression.

although the EMT provides very excellent ground continuity

Fixed that for ya :) Seriously, I once accidentally returned several hundred amps of current through 1/2" EMT which was 50 years old and deteriorating from water damage. EMT is a fantastic grounding path. And you want a fantastic ground, because the better the ground is, the more likely a bolted fault will magnetic-trip (insta-trip) the breaker in 5ms instead of waiting 500ms for a thermal trip.

I know you want to use PVC for your next run because it's the "new shiny", but that's because it's cheap (and not in the good way). In commercial installations EMT is mandatory and PVC is not allowed. Consider staying on-board with EMT. It is superior unless you are going underground. And yeah, it handles the ground for you. I manage 9 buildings with over 2 miles of EMT - not a ground wire in any building. Our 800A service is grounded through two 4" EMT pipes. This, plus stranded wire, makes life much easier!

On speccing subpanels

We cannot say it enough: Go Big. Go really big. Going with a smaller panel saves you -- maybe, a latté. Will you still be able to taste that latté several years later when you are confronting another "box full" situation?

Figure on this new subpanel (or a fourth additional subpanel) taking heat/circuits off this existing semi-full main panel. There's no problem with your 200A service supporting four 85A subpanels like that, since the chances are bascially nil that they'll all be maxed at the same time. 85A = #4Cu in conduit.

Given your situation with your panel (plennnnty of amps; precious little space) I would use subpanels as your primary expansion method. I like to see houses finish a subpanel add with about 50 spaces (remembering those Q-line double-stuff breakers take half a space). This panel has 16, your two other subpanels have ??? and ???.

Feel free to stay GE, it's a perfectly fine panel. But don't count on the Q-line "double-stuffing" method; most breakers these days need to be AFCI, GFCI or both. AFCI must happen in the panel not the first recep (unless the run to that recep is EMT conduit, haha, I love that stuff!!) NEC 2020 brings GFCI requirement for 240V circuit and that can only happen in the panel. Together these rules are basically the death-knell of double-stuff breakers.

1
  • Thanks for a good answer. However, I'm still planning to relocate the service entrance. The main reason is that the existing service drop runs in an "L" around two sides of the garage on two power poles which the utility expects me to maintain, and it runs so closely (about 18") to the eave of the house that there physically isn't room for me to get up there and maintain gutters, paint, etc. My plan is to put a new service entrance and distribution panel at the back corner of the garage, preferably with an underground conduit running back to the power pole instead of a "drop".
    – ehbowen
    Jun 20 '20 at 22:23
0

All your grounding electrodes are required to be connected at the service, including the bootleg you added for the office receptacle. Do that now. Any other Electrodes that are accessible need to be bonded back to the service, you may want to read through the NEC section 250.32, 250.50 and forward to maybe get an understanding of what qualifies as a grounding electrode. The book is rather expensive, but free clunky access all NFPA documents are available online.

The size of the wire feeding grounding electrodes is based on size of wire feeding the service. An exception allows #6 to be the largest conductor you need for ground rods, but to other electrodes (such as metal water piping) 200A service requires #4, and a 400A typically requires #1/0. (Wire sizes assume copper.)

The Equipment Ground Conductor that is run as part of the 4 wires from the service to all other panels is adequate and all that is required for grounding the subpanels.

Often times when running multiple subpanels you only need small 60A panels, but itt sounds like you are planning loads at each one that will draw at least half of that right off the bat, you better plan for 125A feeders. Also new AFCI and GFCI requirements have rendered peanut breakers almost useless, don't use any panels with less than 30 full size breakers. You can also view those requirements in NEC 210.12 for AFCI and 210.8 for GFCI which now includes many 240v circuits.

1
  • The maximum size in a residence is #6 for rod pipe or plate electrodes and # 4 for ufer (concrete encased) electrode systems. Most ground busses allow doubling and up to 3 of the grounding conductors but the grounded electrode must be the only one under the screw , additional busses are cheap and easy to add to correct this issue.
    – Ed Beal
    Jun 20 '20 at 15:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.