Hey guys. So I try to read all the questions and answers as much as possible. I was just wondering, why would one use a sub panel instead of a main breaker panel? Is there a difference? Just trying to understand. :)

Thank you guys

Good question, easy for an electrician to understand, but not so easy to explain in a few words.

There are three major components of an electrical service entrance, the utility meter, the Main Breaker, and a panelboard. The issue is where the Main Breaker gets located.

It can be at the meter location, it can be alone, or it can be located in the panel.

Having the Main Breaker in the panel is probably the most popular. It ends up getting called the Main Panel.

The location of the Main Breaker is critical. If the MB is in the panel, the panel cannot be too far into the building, as those wires feeding the panel are not protected by a fuse. So typically the feeder cable from the meter outside enters the building and connects directly into the panel quickly, Code requires the Main to be at "the nearest point of entrance of the conductors".

So, there are panels with Main Breakers, AKA Main Panels, and panels without the Main Breaker, still the Main Panel, but the Main Breaker is elsewhere.

Then there are "subpanels", which is nothing more that a panel supplied by the Main Panel. There is no technical term "subpanel" used by any Code. It is a trade term that is understood by tradesmen, but often misunderstood by laypeople.

The confusion, or critical issue, is grounding and bonding of a service. The connection of grounding the grounded conductor, AKA Neutral, can only happen at and/or before the Main Breaker. After the Main Breaker, the Neutral and equipment ground cannot connect.

So, I can have a Main Breaker in the Main Panel inside, and the Neutral and equipment ground are connected together, and you will see white and green or bare wires all on one terminal strip, and the panel is fed with 3 wires, two hots and one neutral.

Once I move the Main Breaker outside, the feeder to the panel must be 4 wire, with an added equipment ground conductor.. You will now find two terminal strips in the panel, one for the white Neutrals, insulated and isolated from any equipment ground, and a separate equipment ground bar for green and bare equipment ground conductors.

So, I can have a Main Panel with or without the Service Main Breaker, I can have a "subpanel" with a Main Breaker for that panel, but it is not the service Main Breaker.

Clear as mud?

A main panel is just that. One that contains the main disconnect, or main breaker, and has the service neutral bonded to the panel enclosure.
A sub-panel is any other panel fed from that main, and does not have the neutral bonded to the panel enclosure.
A main shut off, such as a main breaker, is not required in sub-panels unless the panel is located in a detached structure.

This is a VERY basic explanation. There is also the subject of service entrance cables/conductors, feeder cables/conductors, grounding electrode systems, bonding, etc.

A bit of clarification between my and TK's post.

I am calling a main panel one that contains the main breaker for simplicity reasons. A "main" panel after a remote main disconnect is treated and wired the same as a sub-panel. In this case it is not service equipment, but is a "branch circuit main panel" for lack of a better term.

I have always heard it called "branch circuit distribution panel" when the main breaker is located elsewhere. Using main is confusing to some... If you had a home with 2-200 Amp panels and a main breaker located elsewhere which of the two panels would be considered the "branch circuit main panel"?
I think the limit is 6' inside the home before a separate main breaker is required outside.

Quote:

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Originally Posted by Home_Inspector

If you had a home with 2-200 Amp panels and a main breaker located elsewhere which of the two panels would be considered the "branch circuit main panel"?

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Both.

Quote:

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Originally Posted by Home_Inspector

I think the limit is 6' inside the home before a separate main breaker is required outside.

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There is no set number. Some places it is 3', some places ten, some places an outside switch is mandatory.

The NEC and most local codes just say "nearest the point of entry". Very much open to interpretation.

Thanks for the clarification. Here it is 6 feet or 2 meters but wasn't sure if that was based on NEC or local code.

Where may I ask is here?

Stan quoted the correct statement "nearest point of entry", from the NEC. A local inspector can insert the length of service entrance conductor as he sees fit. Many use 10 feet of conductor inside the building, sort of taken from the "10 Foot Tap Rule".

Many look at each situation, if SE cable they want it as short as possible, if conduit, the footage is a bit more relaxed.

For those readers that do not know what this means, the conductors that supply a Main Breaker that is inside , with the meter outside, these conductors have no short circuit protection until they get to the Main Breaker.

When only cable, such as SE cable, any nail or screw that enters the cable will not trip any breaker or blow a fuse. The nail or screw will just melt. This is a huge fire hazard.

Many locations will not allow this cable to enter a building without having the Main Breaker outside, typically at the meter. Now there is no reason to worry about a short circuit with no protection.

Here is in Kentucky. I used 4/0 SE cable w/no conduit. The inside run is approximately 4-5' and closest possible to the point of entry. Replaced the complete system which was a 2 wire 60 Amp service that was in really bad shape with a 200 Amp service and panel. Replaced the extension cord servicing the detached garage, the past owners used, with 10-2 THWN in conduit to a code violating panel instead of a single disconnect. LOL Rewired and grounded everything except a few switches that were inaccessible w/o ripping out plaster but the light boxes they serve are all grounded. Added a full dormer and full bath to the upstairs. Renovated the first floor bath with all new fixtures, floor cover and lighting. Replaced the horizontal galvanized drain lines with pvc and most of the galvanized supply lines with copper. Renovated the kitchen with new cabinets, countertops, floor covering and appliances. Built a small addition for a utility room, that was originally in the kitchen, and built a deck off the addition. Replaced the furnace's natural draft vent system that had 3 elbows and was eaten up over the years by acidic condensates. Replaced the copper gas lines that supplied the water heater and furnace with black pipe and added dirt legs that were absent. Did all of the work myself with the exception of the vinyl siding, wrap and guttering on the dormer and addition. It's for sale want to buy it? LOL

They have electricity in Kentucky?

Hey, that's what they ask me about Maine.

I will bid $100.00 for your money pit.

Yes, they have electricity in Kentucky. It is primarily used to keep the tobacco plants warm in winter and cool in summer.

Electricity is also now I use at Churchill Downs and the track in Lexington, Kentucky.

However, it has not as yet been released to the general public, it's just to new.

Yuk, yuk. We lived in Lancaster, Kentucky for 15 years (about 30 miles south of Lexington). Don't laugh, but when I retired the only McDonald's in Garrard County was being built in Lancaster.

I have a good friend in Lancaster. Would be great here with just about any mechanical questions as he is probably the best auto mechanic in the state! Yes we now have electricity in Kentucky and I hear we are about to get plumbing soon! I'm keeping my fingers crossed!