main lug panels....what protects them ?

[Stevenfyeager]

Main lug panels, ie, no main breaker...What overcurrent protection is there ? Power from the meter comes to the lugs in the panel, then to individual breakers, so what is there to keep from overloading the service panel ? Or overheating it ? Many older homes have these. Thank you.

 

[charlie b]

There is a requirement that there be an overcurrent device that protects the MLO panel. The main breaker of a main breaker panel does that job for that panel. For an MLO, you need an overcurrent device upstream. It can be at the meter, or it can be an enclosed breaker, or it can be a fused disconnect. But if a service conductor attaches to a meter and from there directly to an MLO panel, you likely have a code violation. One possibility is that the MLO panel has no more than 6 breakers, and the total rating of all breakers adds up to a number less than or equal to the rating of the panel.

 

[Stevenfyeager]

I recently installed a temp pole for a new house. I have a 125 amp meter base, with 100 amp conductors feeding a 70 amp main lug panel. The panel has four spaces. I checked with the electrical inspector before I built it and he said that's fine, all the temporaries he sees are built that way. I also wonder about all the older houses with these main lug panels.

 

[infinity]

Main lug panels, ie, no main breaker...What overcurrent protection is there ? Power from the meter comes to the lugs in the panel, then to individual breakers, so what is there to keep from overloading the service panel ? Or overheating it ? Many older homes have these. Thank you.

You are allowed up to 6 service disconnect which can be 6 CB's in a MLO panel used for a service.

 

[GoldDigger]

You are allowed up to 6 service disconnect which can be 6 CB's in a MLO panel used for a service.

And since the up to six breakers together form the service disconnect then the buses of the panel, being upstream of the service disconnect, would be treated as service conductors. Service conductors are generally only effectively protected by downstream breaker(s) and yet are not considered tap conductors subject to the NEC tap rules.

 

[qcroanoke]

You are allowed up to 6 service disconnect which can be 6 CB's in a MLO panel used for a service.

Also known as a split buss panel.
You can't get those anymore.

 

[kwired]

Main lug panels, ie, no main breaker...What overcurrent protection is there ? Power from the meter comes to the lugs in the panel, then to individual breakers, so what is there to keep from overloading the service panel ? Or overheating it ? Many older homes have these. Thank you.

Many of those you likely seen in those older homes probably are the previously mentioned "split bus" panel. Section nearest the main lugs usually designed to accept up to six two pole breakers - those are your up to six service disconnecting means. One of them is the main feeder to the rest of the panel and is usually labeled "lighting section".

 

[ggunn]

There is a requirement that there be an overcurrent device that protects the MLO panel. The main breaker of a main breaker panel does that job for that panel. For an MLO, you need an overcurrent device upstream. It can be at the meter, or it can be an enclosed breaker, or it can be a fused disconnect. But if a service conductor attaches to a meter and from there directly to an MLO panel, you likely have a code violation. One possibility is that the MLO panel has no more than 6 breakers, and the total rating of all breakers adds up to a number less than or equal to the rating of the panel.

I see residential MLO MDP's (MLO panels connected directly to the meter with no OCPD between them) all the time.

 

[kwired]

I see residential MLO MDP's (MLO panels connected directly to the meter with no OCPD between them) all the time.

Somebody had been missing code requirements. Today if there is six or less breakers installed and panel instructions allow it it is ok, but not many dwellings will have 6 circuits or less. Back when they still had the "lighting and appliance panelboard" definition, if you had 10% or more circuits that operated line to neutral and were 15 or 20 amps you had to have a main, even if you were trying to use the six mains rule that lighting panelboard rule forced you to have a main as even one single pole in those six is more than 10%.