breaker size

[kwired]

My company installs a lot of residential PV in San Antonio, and the majority of residential services we encounter there are MLO panels.

Other then the old "split bus" panels, why is that?

Most other panels you would think would have required a main. Even if the home only had six circuits or less, the old "lighting and appliance" panelboard as defined in older NEC versions would have required a main in or ahead of any of them that had even just one 30 amp or less 120 volt branch circuit fed from them.

 

[ggunn]

Other then the old "split bus" panels, why is that?

Most other panels you would think would have required a main. Even if the home only had six circuits or less, the old "lighting and appliance" panelboard as defined in older NEC versions would have required a main in or ahead of any of them that had even just one 30 amp or less 120 volt branch circuit fed from them.

I designed only commercial PV for about 4 years and have only gotten back into resi systems recently. Most of what I have been doing since I got the new job has been resi systems in SATX, and 90+% of the services I encounter there are MLO panels with no OCPD ahead of them. It came as a surprise to me, and some of these are brand new construction. SATX is under the 2014 NEC.

Last week I ran into a very old resi service in SATX that's 240 high leg three phase. That was weird, too

 

[ActionDave]

....Last week I ran into a very old resi service in SATX that's 240 high leg three phase. That was weird, too

I have heard that these were kinda common in the south around the same time air conditioning was becoming available.

 

[electrofelon]

True, but some AHJ's will not allow you to mount a solar breaker in a MLO panel with no OCPD ahead of it.

What is the exact reason? Does this result from a different interpretation of a section or just something they state in the local rules?

 

[Little Bill]

I have heard that these were kinda common in the south around the same time air conditioning was becoming available.

Correct, with only the A/C connected to the high leg.
I think most used a delta breaker.

 

[jaggedben]

...

Most other panels you would think would have required a main. Even if the home only had six circuits or less, the old "lighting and appliance" panelboard as defined in older NEC versions would have required a main in or ahead of any of them that had even just one 30 amp or less 120 volt branch circuit fed from them.

I designed only commercial PV for about 4 years and have only gotten back into resi systems recently. Most of what I have been doing since I got the new job has been resi systems in SATX, and 90+% of the services I encounter there are MLO panels with no OCPD ahead of them. ...

I have heard that these were kinda common in the south around the same time air conditioning was becoming available.

Around here it's fairly common to find service panels with two breakers, one for the air conditioning (usually 50A) and one for the 100A subpanel feed that handles everything else in the house. Often the AC's spot has split stabs so you can quad it up with your solar, while the 100A spot is solid stabs. You can find whole developments like this. They typically have 125A rated service conductors and service panels. My impression is that they date from an era after AC became standard in new developments, but before 200A services did.

You can see where the savings could come from in volume. Cheaper to have the lighting and outlet panel in the middle of the house so the average wire runs are shorter, but not for the higher amp AC circuit which is always going to a destination on the outside of the house, probably not far from the service panel. It just happened to work out for us solar guys thirty years later.

In California we also now have 'solar ready' stuff going on in new developments, by state regulation and incentives and as a selling point. So I've run into a couple new developments where all the service panels are Homeline MLO with space for 6 2-pole breakers and an admonition on the label not to put more than 6 handles in the thing (because you could, with some single pole breakers). Another section of one of the same developments had 225A busbars and conduits pre installed from the garage to the roof.

 

[kwired]

Around here it's fairly common to find service panels with two breakers, one for the air conditioning (usually 50A) and one for the 100A subpanel feed that handles everything else in the house. Often the AC's spot has split stabs so you can quad it up with your solar, while the 100A spot is solid stabs. You can find whole developments like this. They typically have 125A rated service conductors and service panels. My impression is that they date from an era after AC became standard in new developments, but before 200A services did.

You can see where the savings could come from in volume. Cheaper to have the lighting and outlet panel in the middle of the house so the average wire runs are shorter, but not for the higher amp AC circuit which is always going to a destination on the outside of the house, probably not far from the service panel. It just happened to work out for us solar guys thirty years later.

In California we also now have 'solar ready' stuff going on in new developments, by state regulation and incentives and as a selling point. So I've run into a couple new developments where all the service panels are Homeline MLO with space for 6 2-pole breakers and an admonition on the label not to put more than 6 handles in the thing (because you could, with some single pole breakers). Another section of one of the same developments had 225A busbars and conduits pre installed from the garage to the roof.

Those panels were code compliant - until you landed a 120 volt circuit in them, then you violated the "lighting and appliance" panelboard rules, which disappeared more recently - 2011 I think.

Rules on sizing the service conductors do change when there are multiple mains vs a single main as well. With multiple mains you only need to size the service conductor based on art 220 load calculations even if the sum of the ratings of the breakers is more then the ampacity of the conductor. But a single breaker needs to have overcurrent rating that matches the conductor or at least next standard size up.

The panel also needs to be rated to be used for multiple service disconnects, most of the "miniature breaker" styles are not.

 

[electrofelon]

The panel also needs to be rated to be used for multiple service disconnects, most of the "miniature breaker" styles are not.

Are you sure? I have never seen/noticed such a qualification. I figured aa long as it was labeled SUSE you could do whatever you wanted.

 

[kwired]

Are you sure? I have never seen/noticed such a qualification. I figured aa long as it was labeled SUSE you could do whatever you wanted.

Read that SUSE statement carefully - it often has that additional "when provided with a main circuit breaker" or something similar following it.

I am most familiar with Square D, and most say this AFAIK. You will find some marked "or when not more than six main disconnecting means are provided and the panelboard is not used as a lighting and appliance branch circuit panelboard", but is more common to find on the I-Line series then on QO series panels.

 

[jaggedben]

I've seen a lot of different things on labels. What kwired has said is certainly true of many of them, but I'd avoid generalizations.

 

[electrofelon]

Read that SUSE statement carefully - it often has that additional "when provided with a main circuit breaker" or something similar following it.

I am most familiar with Square D, and most say this AFAIK. You will find some marked "or when not more than six main disconnecting means are provided and the panelboard is not used as a lighting and appliance branch circuit panelboard", but is more common to find on the I-Line series then on QO series panels.

I have definitely seen the version that says (something like) "SUSE when no more than 6 disconnects are installed" which I always thought was kinda silly - duh. I dont recall one stating a main breaker be installed, Ill keep my eyes open.

Ive always been a little uncertain as to what makes something SUSE other than the label. I have been using siemens gear lately, and the material bill basically says "SE Label", and I have heard the gear guy say something like. "we can throw a SE label on on", all kind of implying there isnt anything different other than the label. Why would a manufacturer have to restrict MLO panel to only SUSE when a main breaker is installed?

 

[kwired]

I have definitely seen the version that says (something like) "SUSE when no more than 6 disconnects are installed" which I always thought was kinda silly - duh. I dont recall one stating a main breaker be installed, Ill keep my eyes open.

Ive always been a little uncertain as to what makes something SUSE other than the label. I have been using siemens gear lately, and the material bill basically says "SE Label", and I have heard the gear guy say something like. "we can throw a SE label on on", all kind of implying there isnt anything different other than the label. Why would a manufacturer have to restrict MLO panel to only SUSE when a main breaker is installed?

copied from Square D on line catalog from one particular series of I-line panels "Suitable for use as service equipment when provided with a main circuit breaker"

Another particular series has a footnote on the page that says "Suitable for use as service equipment if equipped with an integral main circuit breaker or when not more than six main disconnecting means are provided and the panelboard is not used asa lighting and appliance branch circuit panelboard."

Not sure what any labels fixed on the equipment say at this time.

Most QO and Homeline panels that I am aware of however require a main circuit breaker (even if need to be back fed with a hold down kit) if used as service equipment.