Electrical panel mystery

A few years ago I had an electrician install an electrical panel in my garage so that I could hook up my welder/generator to the house for partial backup in emergencies. The chosen circuits from the panel in the basement were re-routed into the garage panel. Everything is working just fine.
Yesterday I decided to redo my basement panel circuit layouts on the computer to make them look neater and more legible. In so doing I also recheck each circuit and discovered the following.
A basement circuit BP-4+5 has 40 amp breaker and controls rooms A,B and C and the garage circuit GP-14 (15 amp) controls room B and circuit GP-18 (15 amp) controls room C.
How can rooms B and C be both turned of from two different circuits, each on different panels?

The 40A double pole breaker feeds the garage panel.

The 45 amp may be the main entrance for everything. The 15 amp is for the individual rooms.

The garage panel is a subpanel to the basement panel. The 40 amp breaker in the garage panel powers the entire garage panel. Pretty standard.

It is unfortunate that the wiring was installed as such .
If the main breaker panel can not be retrofitted with a slide interlock between the generator breaker and the main breaker .
The following MA-24 would have been the next best solution .
http://www.generlink.com/generlink.html

I might guess the lights and 240 are on different circuits from 2 different panels. Using a mechanical interlock system is really important. Jim

(quoted from post at 12:08:22 03/10/20) The 40A double pole breaker feeds the garage panel.

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Yes that does make sense now. As you can tell I'm still learning about electrical issues. The garage panel does have a slide interlock on it. Thanks for the replies.

Doug, I can tell you how IT SHOULD BE WIRED such that a Genset could backfeed certain selected circuits (using a BRANCH circuit breaker) and often even via a separate sub panel if so choosen, such that there's no possibility of backfeeding the standard utiity service. They make relatively cheap mechanical slider lockouts whereby the MAIN breaker in a panel MUST BE OFF BEFORE THE BACKFEED BRANCH BREAKER (connected to genset) CAN BE SWITCHED ON. When the utility is hot and the main breaker is ON the backfeed branch circuit breaker (from genset) MUST BE OFF. That way the utility cant fry the genset nor can the genset kill a lineman.

Often when wiring a garage or shop or simply other small loads served by their own separate panel, the small sub panel is fed by a BRANCH circuit breaker in the main panel. If so for 120/240 single phase three wire service THE SUB PANEL NEEDS SEPARATE INSULATED AND ISOLATED NEUTRAL AND GROUND BUSSES

NOTE: When transfer switching from utility to genset, the Genset needs to be configured with a FLOATING NEUTRAL in some cases, but A BONDED NEUTRAL IN OTHERS. It makes a difference in if your switching or bonding the Utility and Genset Neutrals..Ask your electrician about that !!!!

NOT being there I hesitate to venture a guess as to exactly how its wired now (my advice offered above is standard and generic in nature) but I will offer my same standard advice, where fire and life safety is concerned at least consider consulting current practicing (NOT me I'm long retired from power distribution design) professional engineers and electricians and DONT RISK YOUR LIFE ON LAY OPINIONS !!!!!!!!!!!!!

Best wishes, good luck and KEEP SAFE

John T

I?m surprised an electrician who should know better would do that.

Don?t be too surprised. I have seen a fair amount of work done by a licensed electrician that I was very skeptical of.

I have 47 years working on generators.I agree with John T.You need to contact someone that knows the systems. Not Billy Bob across the street that thinks he knows.If you have a generator.Be sure it is a proper install. Mistakes can cost you a life. Or a lawsuit.I have seen the results of bad work.

If the slide interlock is on the sub panel in the garage (as stated) I think there is no real disconnect assurance at all. Jim

I never trusted the interlock system.