NEC 705.12

[wyboy]

On a load side connection of a power source output circuit (fed from a solar array) to an existing 200-amp service that has 4 breakers but no main. How do I apply the requirements of 705.12? Would I add the total of all breakers?

 

[markhorst]

That might not be allowable at all. 705.12 (2020) states "... shall be permitted to be connected to the load side of the service disconnecting means...". It sounds like you don't have a service disconnecting means. And the 6-disconnect rule was removed in 2020e as per 230.71. In which case you'll need to add a separate service disconnect or main breaker.

What code cycle is your AHJ on?

 

[Carultch]

On a load side connection of a power source output circuit (fed from a solar array) to an existing 200-amp service that has 4 breakers but no main. How do I apply the requirements of 705.12? Would I add the total of all breakers?

If there is an externalized OCPD upstream of this panelboard, that OCPD takes the place of the main breaker for purposes of the 120% rule calculation. An example would be a 200A meter/main combo device, which then feeds the MLO main panelboard.

Otherwise, what you describe, is not a load-side connection by strict definition, due to not being on the load side of a service disconnect. The principle of busbar protection is still important, but this would be a supply-side connectio. See 705.11 in 2020, and used to be in 705.12(A).

The "sum of breakers" rule would cover busbar protection. Regardless of the mix of loads and sources among the 5 branch breakers, at least one of the breakers would trip before the busbar gets overloaded. If the 5 breakers add up to 190A, there is no way that you could draw 200A without first tripping one of the branch breakers.

It becomes a problem when the breakers add up to the busbar rating already, which is a likely case. There is no equivalent of the 120% rule to cover busbar protection, that justifies how to add a source to a fully-loaded MLO service panelboard. Even if an otherwise-identical panelboard with a main breaker could comply with the 120% rule.

And the 6-disconnect rule was removed in 2020e as per 230.71. In which case you'll need to add a separate service disconnect or main breaker.

You can still have multiple service disconnects when 2020 applies. It is just that you'll need separate enclosures, or partitioned sections of an enclosure (such as switchboard sections).

If this is an existing service that once was compliant, but now NEC2020 applies, you'll need to confirm in writing whether the AHJ will allow it. MLO service panelboards no longer comply, so brand new service would not be permitted as described. Given an existing MLO panelboard of 4 service disconnects that once complied, it presents no new safety hazard to add a 5th breaker to this panelboard for a supply-side interconnection. But not being able to comply with the current standard means you'll need an exception to allow it.