Thread: Why bolt the main breaker?

I always call these out and found myself wondering why the main breakers need to be screwed/bolted to the panel?

The obvious reason would be to hold them in place but it seems if them falling off was a problem then all of the breakers would need to be screwed on. Also, with the panel cover on I can't see one falling off.

Next, I'm thinking for identification purposes?


And yes.... the panel is messed up. It looks like it was pulled out of the bottom of a lake. Maybe this is that subpanel JP is always talking about

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A breaker that is "backfeeding" a panel MUST be retained in place. This is typical of many 100A main breaker panels, such as BR series panels where the service entrance cables land on the breaker and the breaker in turn backfeeds the busses.

Understand?

The reason behind the requirement to have a backfed main breaker held in place is safety.

When a circuit breaker is "back fed" the power is running through the breaker in the reverse direction then normally. In other words the power is running through the breaker from the screw terminals to the busbar in the panel.
Normally the power is running from the bus bar through the breaker to the screw terminals.

When a breaker is pulled ( or falls) off the bus bar the electric is no longer in the breaker as the connection to the power is broken. You are now holding an unenergized breaker

When a back fed breaker is removed from the bus bar the power is still in the breaker and more importantly still on the little tabs on the breaker..You are now holding an energized circuit breaker that is no longer in the panel.

To expand a little on that. My understanding is that it is required because on a back fed breaker, the breaker and wire is still hot, whether or not attached in place, while the other breakers and wires are dead if detached.

EDIT: Looks like I was beat to the punch.

And the reason is that the back-fed breaker will have energized contacts when the breaker is removed and the breaker handle accidentally or intentionally gets bumped to the 'On' position.

That would not be healthy for anyone who happened to be holding that breaker at that time.

Thanks guys... that totally makes sense. I knew there had to be a good reason.

I was wondering that myself. How long has this been in effect? I rarely see a back fed breaker bolted into the panel.

Not all the retainer clips are visible from the front. Some need to be viewed from the side closest to the wiring gutter.

Matt,

Are you sure the conductor to the upper right breaker are the service entrance conductors? And that breaker is back-fed?

I ask because there are conductors coming off the main terminals with NO overcurrent protection, other than the main back-fed breaker, and they should be protected on the supply end (the end in that panel).

Also, is that a cut off neutral conductor to the left of the red conductor in that main lug terminal?

Also looks like some greenish copper over to the left - probably from the water intrusion into the panel.

Got some screwy things in there, any more photos?

Originally Posted by Jim Robinson

I was wondering that myself. How long has this been in effect? I rarely see a back fed breaker bolted into the panel.

I did not see it in the 1987 NEC and I see it in the 1990 NEC .
Article 384.16(F).
So I will say since 1990 (unless I missed it in the '87)

Originally Posted by ken horak

I did not see it in the 1987 NEC and I see it in the 1990 NEC .
Article 384.16(F).
So I will say since 1990 (unless I missed it in the '87)

Ken,

You are correct, it was new to the NEC in 1990.

One little tidbit of info, the rule requiring a retainer on a backfed breaker ONLY applies to plug-in breakers, it does not apply to bolt-on type breakers, but other then I-T-E Pushmatic, bolt-on breakers are rarely found in residential situations....

Originally Posted by Rollie Meyers

One little tidbit of info, the rule requiring a retainer on a backfed breaker ONLY applies to plug-in breakers, it does not apply to bolt-on type breakers, but other then I-T-E Pushmatic, bolt-on breakers are rarely found in residential situations....

That's because those bolt-on breakers are ... already bolted on.

The code is addressing breakers which plug-in and can be removed simply by pulling the breakers out.

JP.... it was a bit of a 'head scratcher' for a minute. It is a split-bus panel where the lugs that would normally be the main's attachment point hold cables that loop around and energize the lower half of the panel. The pictured breaker is definitely the service breaker.

I might have suspected a modification but it was in a condo where that would be unlikely. I'm pretty sure it sits now as it was installed in 1981 but that really didn't change my recommendation.

At first glance I thought it was aluminum wiring and surprised for 1981... then I realized it was just REALLY heavily corroded copper.

Here a couple more pictures-

Originally Posted by Matt Fellman

It is a split-bus panel where the lugs that would normally be the main's attachment point hold cables that loop around and energize the lower half of the panel. The pictured breaker is definitely the service breaker.

Which means you have *7* mains - which is not allowed.

That panel has had its interior replaced with another brand, thereby voiding the listing and labeling, thereby creating a code violation of NEC 110.3(B) Listing and Labeling.

See those NM cables behind that panelboard interior in that enclosure? See how the mounting plate for the panelboard bus bars and breakers is bent? Dead giveaway that it has been modified.

Is that condo on the ocean? If so, salt air will do that to a panel when the windows are left open a lot. Also, that rusted and corroded enclosure needs to be replaced, along with an interior listed and labeled for use with the new enclosure.

There may be many like that in that condo.

Originally Posted by Jerry Peck

Which means you have *7* mains - which is not allowed.

That panel has had its interior replaced with another brand, thereby voiding the listing and labeling, thereby creating a code violation of NEC 110.3(B) Listing and Labeling.

See those NM cables behind that panelboard interior in that enclosure? See how the mounting plate for the panelboard bus bars and breakers is bent? Dead giveaway that it has been modified.

Is that condo on the ocean? If so, salt air will do that to a panel when the windows are left open a lot. Also, that rusted and corroded enclosure needs to be replaced, along with an interior listed and labeled for use with the new enclosure.

There may be many like that in that condo.

I'm with you on everything but the 7 mains.... I just see one. Once that's off everything is off, isn't it?

Originally Posted by Matt Fellman

I'm with you on everything but the 7 mains.... I just see one. Once that's off everything is off, isn't it?

You are correct, I forgot about the back fed main and counted the top section as I would for a split bus panel - which is kinda sorta is ... maybe.

I'm suspecting that the original interior was a split bus panel, however, the new interior may not actually be split bus, and those conductor jumpers from the top lugs to the bottom lugs may not be necessary - but the only way to know would be to remove the breakers and look at the bus. Almost every (to my recollection it is every) split bus panel I've seen has a blank and non-usable space between the top section and the lower section, and that panel has all the breakers side-by-side-by-side, indicating that the bus may not actually be split ... with "may" "not" being key.