Thread: Confused By Main Disconnect In This Panel

I saw this panel at my inspection yesterday. The panel has an unused 200 amp main disconnect and lugs at the top. The service cable coming in is a 100amp cable and is connected to the 100 amp double pole breaker at the upper right-hand corner of the hot bus bar. I flipped the 100 amp breaker to the OFF position and it shut everything in the house off so it appears to be functioning as the main disconnect for the panel.

Considering it's location inside the panel and the location of the unused 200 amp disconnect and lugs, how is this 100 amp breaker functioning as the main disconnect for the entire panel? I already have other wiring issues noted for the panel so an electrician is needed regardless.

Am I missing something?

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Originally Posted by Nick Ostrowski

...how is this 100 amp breaker functioning as the main disconnect for the entire panel? ...

Nick - It's energizing both legs, just like, or sort of like, the 200 amp breaker would be if it was connected. It's a "back fed" main breaker.
Pretty bizarre, though. I'd call for an electrician even if nothing else was wrong, and I imagine you would, too.

The way the 100 AMP breaker functions as the main is simple - the service comes in the screw terminal side of the breaker. Since all the power comes in this way when you turn off the breaker, as you discovered, you remove power from the panel. This method of "back feeding" a breaker to use it as a main isn't uncommon. It does appear to lack a required mounting kit that allows you to install a screw or clip that prevents accidental removal of the breaker, a code required item for this type installation. A several types of panels limit the place the mounting kit will install to the upper left 2 spaces.

What is uncommon is the presence of the 200 AMP breaker. I'm guessing that someone might have been looking to upgrade the service in the future and spent the extra money for a panel with a main. The breaker simply needs to be marked as "unused" and the 100 AMP plainly marked as the service disconnect.

Looks like you have a "sampler" of different breaker types. The blue handled Bryant/Westinghouse are acceptable in a CH panel of this type.

The panel is filled w/ other makes of breakers including the main breaker, the Siemens main will not have provisions for a code required retainer /holddown, SQ D HOM are not UL classifed to be used in other makes of panels as SQ D is of the opinion that a panel must only have the same manufacturers breakers used, I am also not aware of Siemens breakers being classified for use in Cutler-Hammer BR loadcenters.

It's messed up IMHO.

Thanks guys. Makes sense now. They already needed an electrician based on other issues inside the panel so this will just be added to the list.

It would need to comply with 408.36(D). Looks like it might be a panel that would hold more than 20 circuit breakers so they opted for a 200 amp panel in lieu of a 100 amp which is typically limited to 20 circuits.

408.36 Overcurrent Protection.
(D) Back-Fed Devices. Plug-in-type overcurrent protection devices or plug-in type main lug assemblies that are backfed and used to terminate field-installed ungrounded supply conductors shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panel.

The possibilities of why a 200amp MCB panel was used for a 100 amp application are many. 200 amp MCB residential panels, ( 20/40 circuit ), are mass produced at a quantity that no other panel configuration can touch. When on sale they often include a normally used compliment of circuit breakers. It makes them cheaper that buying a 100 amp MLO panel and buying all the branch breakers individually. It also may just have been living in someone's garage as a spare. Like R.M. pointed out; when a panel is back-fed through a C/B, ( I call it a feed through C/B ), that breaker must be fastened to the can and this one does not appear to be.