Derating for split bus?

[MPdesign]

I am looking at some apartments that have old split bus panels.
They have 4 main breakers at the top. 2@40amp, 1@30 amp, and 1@50 amp serving the lower half of the panel. The lower half is branch ckts only.

I have not kept up with the NEC changes well in the past 10+ years, this is weird, and I need help!
Is it legal now to replace this with a similar panel without upgrading the incoming conductors?
The incoming conductors were either #4 or #6 Aluminum. I could not tell for the age, lack of markings, and they were still hot.

I do not think the incoming service wire size matters either way. I think this cannot be done now, but I have never come across this.
Thank you for your insight.

 

[LarryFine]

Is it legal now to replace this with a similar panel without upgrading the incoming conductors?

Neither legal nor possible, as they're no longer made.

Each feeder should be protected at its ampacity, and you can use either MB or ML panels.

 

[MPdesign]

Assuming that the feed is short and does not require a disconnect outside at the meter. It is SER Cable.
Would it be legal to put a main lug panel, terminate to the main. Add the 4 main disconnect breakers in the panel, and then add a subfeed panel for the branch breakers? This is essentially the same as adding a trough, adding 4 enclosed circuit breakers off the trough, and then feeding a properly size branch panel from one of those feeds.
Is derating not allowed if that is done?
I am sure that it is not, but what is the exact reason.

 

[letgomywago]

Assuming that the feed is short and does not require a disconnect outside at the meter. It is SER Cable.
Would it be legal to put a main lug panel, terminate to the main. Add the 4 main disconnect breakers in the panel, and then add a subfeed panel for the branch breakers? This is essentially the same as adding a trough, adding 4 enclosed circuit breakers off the trough, and then feeding a properly size branch panel from one of those feeds.
Is derating not allowed if that is done?
I am sure that it is not, but what is the exact reason.

Just do a main breaker

 

[MPdesign]

No-one is going to do it. I am just asking what is illegal about it. It blew my mind the 1st time I saw the old split bus panel - I was thinking, this isn't legal... Then I thought about it, and I can see where it could have been legal then and I cannot point and say how it doesn't meet code now.
That is my question - it is a code question. How would that not meet code? Is the feeder not large enough for today's code? Or other?

 

[infinity]

So you have a feeder to an old split bus panel that you want to replace? You can just install a new MLO panel with the same size branch circuit breakers that are in the old panel. Your question also mentions derating how is that applicable?

 

[MPdesign]

I really think the wiring feeding the panel may not be large enough for the current code.
It is a either a #4 or #6 Aluminum SER cable. I think it is #6. I was able to confirm that the feed from the 50A to the lower section is #4 copper.
Photo to feeder

 

[kwired]

So you have a feeder to an old split bus panel that you want to replace? You can just install a new MLO panel with the same size branch circuit breakers that are in the old panel. Your question also mentions derating how is that applicable?

He maybe thinking about demand factor?

6 aluminum sounds likely to be too small though. Unless it is tin plated copper and is mistaken for aluminum. Still possibly on the small side but more reasonable than 6 aluminum.

 

[MPdesign]

Yes! Demand factor - not derating. The mind forgets after many years.
It is a either a #4 or #6 Aluminum SER cable. I think it is #6. I was able to confirm that the feed from the 50A to the lower section is #4 copper.
You can see both in the photos
Photo to feeder

 

[kwired]

Assuming that the feed is short and does not require a disconnect outside at the meter. It is SER Cable.
Would it be legal to put a main lug panel, terminate to the main. Add the 4 main disconnect breakers in the panel, and then add a subfeed panel for the branch breakers? This is essentially the same as adding a trough, adding 4 enclosed circuit breakers off the trough, and then feeding a properly size branch panel from one of those feeds.
Is derating not allowed if that is done?
I am sure that it is not, but what is the exact reason.

If this is the service disconnect no.

Those split bus panels used to be legal but haven't been for a long time and because of that they are not made anymore.

The idea was you were allowed six service disconnecting means. They typically had twelve pole spaces in the mains area- you could have 5 two pole breakers plus the one feeding the lighting section of the panel for your six service disconnecting means.

Before 2020 NEC you could still have six mains in one panel, if the panel was listed for this. Most load centers however have wording in the instructions that they are only listed for use as service equipment if there is a main breaker. If it is a feeder supplied panel no main breaker is needed, unless it is a separate structure then you still limited to six disconnects to disconnect all power at that building.

2020 still allows up to six service disconnects but they can no longer be in same panelboard or same vertical section of a switchboard.

In your situation would be much simpler and less cost to just put in a main breaker panel, even before these changes in 2020 NEC. Emergency disconnect on exterior is something else that may apply though.

 

[infinity]

I really think the wiring feeding the panel may not be large enough for the current code.
It is a either a #4 or #6 Aluminum SER cable. I think it is #6. I was able to confirm that the feed from the 50A to the lower section is #4 copper.
Photo to feeder

Aren't you just replacing the panel? If the existing feeder is working fine why do you think that there may be an issue? Even if someone added more load then the OCPD ahead of the feeder would trip.

 

[MPdesign]

Yes, but a #6 Aluminum SER feeder appears to be used per the photos. Even if it was #4...
If a new panel with a main is installed, that main should be rated for the wire. If I am correct, that is a 50-60 Amp main.

I know that would be completely legal and safe, but wouldn't it trip constantly to the point of being unusable?

Is that 60A main going to hold the load of the old breakers without tripping which includes 2-pole: 2@40amp, 1@30 amp, and the equivalent interior branch breakers that were on a 50 amp?




Photo to feeder

 

[infinity]

Yes, but a #6 Aluminum SER feeder appears to be used per the photos. Even if it was #4...
If a new panel with a main is installed, that main should be rated for the wire.

The panel does not require a main but you can use one. The feeder is protected by the OCPD at the origin of the feeder so a larger main breaker can be used in the panel without an issue.

 

[MPdesign]

The service wire has no main at the meter.
These panels are wearing out. I am talking about when replacing the panel - not just what is there now.
There are many of these apartments where they just replaced with a 100 MB panel on the existing wire without adding a disconnect at the meter. I assume it was not inspected.

Yes, but a #6 Aluminum SER feeder appears to be used per the photos. Even if it was #4...
If a new panel with a main is installed, that main should be rated for the wire. If I am correct, that is a 50-60 Amp main.

I know that would be completely legal and safe, but wouldn't it trip constantly to the point of being unusable?

Is that 50 to 60A main going to hold the load of the old breakers without tripping which includes 2-pole: 2@40amp, 1@30 amp, and the equivalent interior branch breakers that were on a 50 amp?

 

[infinity]

The service wire has no main at the meter.

That's the problem. You've been calling this a feeder to the panel when it is not a feeder because it lacks an OCPD ahead of the panel. You need to determine the size of the service conductors and size the main in the new panel accordingly.

 

[MPdesign]

I used to read the NEC cover to cover. I used to teach classes on grounding and bonding, motors, etc.
It has been a long time since then. I am sorry if my memory and word recall is not serving me well.

 

[infinity]

I used to read the NEC cover to cover. I used to teach classes on grounding and bonding, motors, etc.
It has been a long time since then. I am sorry if my memory and word recall is not serving me well.

No problem it just that you can see from this thread that the answers to your questions can be vastly different based on the terminology. Sorry for the confusion on my part I thought that this panel had a feeder.