Load Center Types

Whenever you see an MSP in the same enclosure as the meter, this is called a Meter/Main Combo, or simply referred to as a Meter/Main.
Most often these panels will either be end fed main breaker or center fed main breaker.
- Occasionally, you will see a main lugs only Meter/Main, but they are uncommon outside of Texas.

There are a couple of considerations to keep in mind with Meter/Mains:

Supply side tap type connectors are not permitted on Meter/Main type panels.
- This is due to most meter/main combos having hard bussing, manufactured service entrance conductors or bars instead of typical service entrance conductors.
- Identify manufactured conductors by looking for uniform straight segements and coordinating neat bends in conductors.

Center Fed panels:
- Give extra special attention to the position of the PV breaker.
  - The PV breaker needs to be the furthest space away from the main breaker as possible
    - Center Fed panels always follow the 120% rule(NEC 705.12(B)(3)(2); they are not compatible with the 100% rule (NEC 705.12(B)(3)(1)) as is the case with end fed load centers.
Main lugs only type meter mains (no main breaker) will need to comply with the NEC code cycle being enforced by the AHJ. In most Jurisdictions where this will be seen:
- Follow the 6 handle rule.
When we dont have the panel sticker on center fed panels we can assume the bus is rated for 125a

Main lugs only type meter mains (no main breaker) will need to comply with the NEC code cycle being enforced by the AHJ. In most Jurisdictions where this will be seen:
- Follow the 6 handle rule.

In the example to the right, only three handled disconnects are on this bus, so it would be considered in code in areas that allow the 6 handle rule.

2 | END FED - MAIN BREAKER

- This is the term used when the MSP is either interior or exterior but not attached to the meter.
- Must have a main breaker to fit this criteria
  - Can be a proper bolt on main breaker or a side fed plug in main breaker with a hold down kit.
    - look closely for where service entrance conductors and feeders are coming from/going.

There are a couple of considerations to keep in mind with Top/Bottom Fed Panels:

Supply side taps are generally allowed on this type of panel, unlike its meter/main counterpart.
Feedthrough lugs:
- If you see lugs on the opposite end of the bus bar from the main disconnect with feeders going to a sub panel (as pictured on the right), this will often be a feed-through lugs set up with the sub panel.
- The easiest way to accommodate/protect these feeders is to simply complete a supply side tap so that the MSP main breaker is now protecting those feeders.
- If this is not an option due to jurisdictional restrictions or if a supply side tap would require splicing of wires such as when a separate tap box is needed for supply side taps:
  - These feeds need to be protected either by a main breaker in the sub panel or by relocating the feeders onto a breaker in the MSP

By not exceeding the ampacity rating of these feeders with the utility supply (main breaker rating) combined with the PV backfeed rating.

End fed main breaker panels can use the following two guidelines for load side interconnection:
- 120% rule(NEC 705.12(B)(3)(2) will be always be preferred.
- 100% rule (NEC 705.12(B)(3)(1)) this rule simply allows you to place the PV breaker anywhere on the bus bar, it does not have to be positioned at the furthest space from the main breaker.

- This is the term used when a load center has no main breaker.
  - - look closely for where service entrance conductors or feeders are coming from/going.
- It is much more common to see this type of panel being used as a sub panel though it is possible to see this configuration used for an MSP:
  - When this bus configuration is being used in an MSP enclosure, we need to comply with the NEC code cycle being enforced by the AHJ
    - For most Jurisdictions where this will be seen, this will mean complying with the 6 handle rule.

There are a couple of considerations to keep in mind with Main Lugs Only Panels:

MSP:
- If the AHJ is enforcing the single main disconnect enclosure rule of the 2020 NEC, we will need to install a main breaker.
  - If this is not an available option, our only alternative would be an ESC.
- For 2017 NEC and earlier, we need to ensure the 6 handle rule is being followed.

For sub panels:
- It is probable that if you see this configuration on a sub panel, you are also looking at a feed-through lugs configuration with the MSP.
  - You need to ensure that feeders and bus bars are appropriately protected.
- When this setup is coming from an MS, the main disconnect in the MSP enclosure becomes the main breaker for this panel. This is only a recommended avanue for exterior or back to back sub panels:
  - We will default to the 120% rule (NEC 705.12(B)(3)(2).

- This is the term used when an MSP has an upper Supply Side bus which is lug fed with a designated breaker acting as the main feeding a sub bus bellow.
  - Look for a breaker with feeders circling back to the center of the apparent bus bar.
    - Some times the lugs for the sub bus will be very apparent, other times, they will be hidden underneath the breaker handles.
    - It is sometimes easy to mistake this for a main lugs only panel, but it is important to differentiate.
  - Look at the labeling for a bus diagram showing what the configuration looks like as a schematic.

There are a couple of considerations to keep in mind with Split Bus Panels:

If the AHJ is enforcing the single main disconnect enclosure rule of the 2020 NEC, this will result in an ESC.
For 2017 NEC and earlier, we need to ensure the 6 handle rule is being followed.
- Supply side connections are preferred though a load side breaker can be used under some circumstances; grab a supervisor to walk you through it if you are considering a load side connection.

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