Panel rating vs. Service disconnect

[Larry Coha]

Can the rating on the distribution panel be less than the main service disconnect?

For example, condo inspection today with meter and main service disconnect outdoors at 150 amps.

The distribution panel is rated at 125 amps.

[Jerry Peck]

Larry,

"Can" it be less? Well ... you just gave an example of such ... but the main service disconnect is "not allowed" to have a higher overcurrent protection rating than what it protects (i.e., the feeders and the panel mains).

For your condo example, the 150 main could be replaced with a 125 amp rated main breaker, provided that the feeders are also 125 amp sized or larger.

What was the rating of the other condo mains? Were they all/mostly 125 amp?

If so, there could have been a reason to have installed that 150 amp breaker (not a justifiable reason as they didn't also replace the panel and feeders). Maybe they 'solved' a main breaker tripping issue ... but didn't realize that they created a larger issue.

[Larry Coha]

Thank you, Jerry!

The feeders will support 125 amps. I don't know about the other units.

The meters and main disconnects were on the same exterior wall. Didn't check the other disconnects but you can be sure I will next time.

Thanks, again!

[david shapiro]

This won't usually be the case, but I believe a literal answer to your question is yes, it can be done legally, IFF the feeder is rated for 150 A and the distribution (sub-)panel has a 125A or lower main breaker. Or is MLO but is legally backfed through etc. All without any tap rules being involved.

One reason to do things this way is to provide an outside service disconnect per the 2020 NEC Second Draft (we'll see tomorrow 5/17 whether there are any Certified Amending Motions on this again) and at the same time not risk tripping it, unless the feeder itself is compromised, plus you have a local disconnect for all the branch circuits located indoors.

[Jerry Peck]

... the distribution (sub-)panel has a 125A or lower main breaker.

That has been something I have been promoting for many years, 'panel mains' - not acting as main service disconnects, but serving as a main disconnect for a panel (logically not needed for small 4-8-12 circuit panels, but for panels with more circuits, a panel main is a good safety feature to have (not required by anyone that I am aware of, but a good safety feature to have).