MLO sub as Service Entrance?

[Wilkoe]

Hello,

I have a small 1 car garage in which I have a small wood-shop. As I am expanding my inventory of larger tools (table saw, band saw, joiner, planer) I find that I need to run some serious dust collection. Problem is I can't run two large tools (table saw AND dust collector) at the same time because it trips the 20 amp breaker. All of the garage receptacles are wired to the same 20 amp breaker along with most of the lighting in the garage and downstairs unit.

Attached is a photo of the service entrance. It appears to me that this is a Main Lug Only sub panel installed as the service entrance. The meter socket does not have a switch, it's just the socket. The 100 amp breaker on the panel in the photo is it. I need more power yet I have no space left. All the breakers are already of the double type. I had an electrician look at it and offered to wire in a sub-panel via the main lugs on the current panel.

House is 2 bedroom with 1 bedroom in-law downstairs in San Francisco built circa 1940's (i think) and was remolded in the early to mid 90's. Major appliances are natural gas (stove, dryer, water-heater). Both units share the water heater.

Can the experts chime in with thoughts please.

Why was such a small panel installed?
Why not use a service entrance panel with an actual main breaker?
Can anyone identify the service entry wires? I was unable to make out any of the text on the wire sheath. They are copper.
Does wiring in a sub-panel sound like a decent fix or is it only circumventing the root problem (undersized service entrance)?


For the record: I am not an electrician. I am a mental health worker and woodworker. I am NOT at this point considering doing this work myself, though I am interested in becoming knowledgeable.

 

[George Stolz]

When the place was built, six circuits were likely seen as plenty. 70 years have a way of overfilling a panel.

The electrician might have gotten the impression that if he didn't come up with the cheapest solution, the work wouldn't happen. Replacing the panel would be a more expensive solution, and what you have isn't wildly unsafe. I would change out this panel to get a clean "reboot", but you'll likely have costs to disconnect and reconnect to the utility, permits, and an outage for a day. It will likely cost twice as much as his original option, but if you're willing, future residents and electricians will probably thank you.

 

[dkidd]

The 100 amp breaker on the panel in the photo is it.

From what you are describing, the 100 amp breaker is serving as a branch mounted back-feed main breaker. Have the electrician perform a load calculation to see if 100 amps is sufficient. If so, his solution to sub-feed a panel from the main lugs could work.

 

[mwm1752]

How is the breaker locked in place & is the equipment suitable for service equipment -- looks a bit dangerous -- you may need to pull the meter & just add a disconnect ahead of the panel- take out back feed breaker & connect feeders to lugs - separate neutrals & grounds - now you have 2 more spaces for branch circuits

 

[Fnewman]

If I were anticipating adding a lot of new woodworking equipment, I would upgrade the service to 200A and replace the panel. Probably eeds to be done anyway.

 

[Wilkoe]

Thank you for the replies.

Replacing Panel: We rent, I'm on great terms with the landlord but I don't think I could convince him to pay to have it swapped out, at least not right now.

Breaker locked in place: I cannot discern any particular mechanical bonding strap/screw/otherwise but I'm also not sure what to look for.

Branch mounted back-feed main breaker: Had to google that one, yes that's what it looks like.

Adding Disconnect: Service wires come in through the back of this panel, not sure how I'd route them back out and through a disconnect without major modification, though I like that Idea.

Load Calculation: I can probably do this on my own and will sit down with a pen and paper.

The electrician said he could add a small surface mount sub-panel and route conduit along the wall to add a few extra receptacles for my power tools. I'm a hobbyist woodworker and so far my biggest motor is 110v 1-3/4hp on the table saw. Electrician mentioned that the only challenge would be using hard pipe to attach the surface mount panel from the main, as opposed to flex conduit, due to earthquake regulation stuff.

Advantage of this as explained to me is cost and not needing permits, which is also a bonus for the landlord.

Thank you all for your input.

 

[jaggedben]

This is extremely common in San Francisco, for whatever reasons, and there's probably no violation to fix other than adding a hold-down to the main breaker.
The hold down part consists of a screw that is put through the small hole in the middle of the main breaker, and which screws into either a threaded hole in the back of the panel, or into a plastic bracket that comes with the kit and which is inserted into a groove back there.

I have literally seen hundreds of San Francisco service panels like this. Most MLO subpanels nowadays are listed to be used as service equipment with a correctly in installed main breaker. 100A is very standard in San Francisco since almost no houses have air conditioning and thus don't require more, and/or because upgrading in older buildings is often not cost effective.

None of this has anything to with the fact that you're trying to run too many tools off a single 20A circuit. Upgrading the garage circuit to 40A and powering a subpanel with one or two more outlet circuits would certainly be an acceptable solution, code wise. By the book, a load calculation is required but I highly doubt it will indicate that a service amperage upgrade is required. I rather doubt an inspector will even ask for it.

 

[jaggedben]

By the way, legally you don't get off the hook from needing a permit just because you install a subpanel. If anyone wants to do more work on the house later then the permit fees will likely just be a deferred cost, not an avoided one, especially if the work is not done to code.

 

[JFletcher]

Aside from the 100A backfed main, I count 22 breaker spaces. There is no way all of them are anywhere near capacity. I bet at least a few are dedicated to receptacles that arent even being used.

If I were working on it, knowing you rent, the cheapest solution would be to look at the panel schedule, find two combine-able circuits that have little/no load (such as two lighting circuits), verify current draw, then combine them, thus freeing up a breaker slot for your shop, then run a new 20A branch circuit to your shop. Sounds easy, however as you stated you are not an electrician so please have one do the work. There are also numerous MWBC in this panel which have additional rules/code sections they have to follow, and you dont want to be messing with those.

Also, the bottom half of the 2p 100A breaker appears to have a strand of wire loose from the lug. If that is the case, have the electrician correct that and give the panel an inspection for loose wires, corrosion, scorched lugs, etc.

eta: a small subpanel from the lugs would work as well for your wood work, tho the larger sized wire and subpanel would cost a bit more than adding a 20A circuit as above

 

[norcal]

It depends on when the panel was installed if the lack of a hold down on a plug in breaker is a violation or not, 384-16(f) first appeared in the 1990 NEC, 2014 edition 408.36(D), and then it would depend on when it was adopted. California was really slow at adopting new editions, the 2014 is being adopted in January.

 

[JFletcher]

Missed the edit time:

Lastly, to answer your question re: such a small panel: with having a gas stove/range, water heater, and dryer, the load on the panel is going to be quite low. 100A is plenty barring a huge AC, sump/grinder/well pumps, or Spa there not being mentioned. The panel in this house (a 125A) uses 15 breakers and we have an electric oven, dryer, and water heater. The HVAC is another 2p, there is no main, leaving 7 breakers for everything else. As mentioned by someone above, a 1940s-1950s era home would have gotten by then with so few circuits.

 

[mwm1752]

It depends on when the panel was installed if the lack of a hold down on a plug in breaker is a violation or not, 384-16(f) first appeared in the 1990 NEC, 2014 edition 408.36(D), and then it would depend on when it was adopted. California was really slow at adopting new editions, the 2014 is being adopted in January.

you do not consider a live breaker hanging by unfused wires that was accidently removed from the panel a safety hazard -- then "if" the installation was compliant there is no need to fix -- Personally I would fix.

 

[jaggedben]

It depends on when the panel was installed if the lack of a hold down on a plug in breaker is a violation or not, 384-16(f) first appeared in the 1990 NEC, 2014 edition 408.36(D), and then it would depend on when it was adopted. California was really slow at adopting new editions, the 2014 is being adopted in January.

We routinely get asked to add hold-downs to old panels whenever we do any work in them. I would bet this panel is older than 1990 though. Westinghouse breakers, if I'm not mistaken.

 

[norcal]

you do not consider a live breaker hanging by unfused wires that was accidently removed from the panel a safety hazard -- then "if" the installation was compliant there is no need to fix -- Personally I would fix.

If it was compliant at the time of installation, then why would it be required? but if there were enough changes then I could see it being required, but I do agree is should be upgraded to current standards, but if it was compliant then I do not think it has to.

The one problem with panels manufactured before the hold down requirement for backfed plug-in type circuit breakers is parts may not be available to add the retainer.