120% rule for busbar rating for a meter socket load center

[AreGee]

There is a great thread discussion on sizing of OCPD and panelboards, etc. here:
https://forums.mikeholt.com/threads/80-rule.2556309/post-2611803

The MilBank spec sheet for U224MTBPL (200A panel) stated "200 amps continuous" .
The Siemens spec sheet for MC2440B1200CE says 200 amps continuous duty

Does "continuous" mean that the busbar is, in fact, rated for 200 amps continuous ?
In other words, is it permitted for five continuous 40 amp branch circuits to pull 200 A?

Or is the calculated load not supposed to exceed 160 amps?

 

[Carultch]

There is a great thread discussion on sizing of OCPD and panelboards, etc. here:
https://forums.mikeholt.com/threads/80-rule.2556309/post-2611803

The MilBank spec sheet for U224MTBPL (200A panel) stated "200 amps continuous" .
The Siemens spec sheet for MC2440B1200CE says 200 amps continuous duty

Does "continuous" mean that the busbar is, in fact, rated for 200 amps continuous ?
In other words, is it permitted for five continuous 40 amp branch circuits to pull 200 A?

Or is the calculated load not supposed to exceed 160 amps?

The 120% rule in 705.12 and 125% continuous load factor are completely separate issues.

The 125% continuous load factor has to do with the default factor you apply to continuous loads when sizing standard OCPD's. To avoid the 125% factor, an entire product assembly (breakers, busbars, enclosure, etc) needs to be listed for continuous duty, with continuous duty breakers within it. This is uncommon, except in purpose-built equipment. Add one standard OCPD to it, and you lose your continuous duty rating

 

[AreGee]

To avoid the 125% factor, an entire product assembly (breakers, busbars, enclosure, etc) needs to be listed for continuous duty, with continuous duty breakers within it. This is uncommon, except in purpose-built equipment. Add one standard OCPD to it, and you lose your continuous duty rating

So the combo panels that I listed above are capable for continuously delivering 200 amps as long as the OCPDs that are installed in the panel are equally rated for continuous duty.

 

[Carultch]

So the combo panels that I listed above are capable for continuously delivering 200 amps as long as the OCPDs that are installed in the panel are equally rated for continuous duty.

I suspect this is misleading marketing. It sounds like it is a rating that could work in theory, but good luck making it work in practice.

The product may have a continuous load rating as it ships to you from Milbank, but the problem is that I don't see any specifics on the intended product family of branch breakers. This leads me to believe that you are on your own to source the breakers. The 210.20(A) exception that allows continuous ratings in the first place, requires that it is an entire assembly be listed for continuous duty, in order to take credit for the continuous duty rating.

If you source a 3rd party branch breaker that isn't listed in a combination with the panelboard for continuous duty, then you lose the continuous duty rating of the panelboard assembly.

 

[jaggedben]

The Milbank appears to in fact say its rated for 200A continuous. That may be because (somewhat bizarrely for this day and age) it has a pull out fuse block disconnect. I have never seen a 200A meter/main with a molded case main circuit breaker with such a marking.

The Siemens I'm not getting any google results for. Typo?

I don't think the rating of the branch circuit OCPDs affects anything here. Your 40A continuous loads would need to be on 50A breakers. But you could have five of them, in the Millbank, without any demand factor.

That's my take anyway.

 

[wwhitney]

The Milbank appears to in fact say its rated for 200A continuous. That may be because (somewhat bizarrely for this day and age) it has a pull out fuse block disconnect. I have never seen a 200A meter/main with a molded case main circuit breaker with such a marking.

I'm fairly sure that all the Milbank data sheets that say that are referring to the meter socket only. The data sheet for the similar U224MTB (main breaker, no distribution) says the same thing: "Amperage Rating 200 Continuous Ampere"

Anybody seen one of these things or similar to see what the labeling in the main breaker compartment actually says?

Cheers, Wayne

 

[jaggedben]

That makes sense. Usually the meter socket rating is labeled as continuous and the panelboard isn't.

 

[suemarkp]

I've always found this labeling confusing. On their 400A meter sockets, they tend to call them Class 320 with 320A continuous, 400A non-continuous. The load calcs take continuous into account, so if a load calc comes to 400A, then a 320/400A meter should be fine. So does this mean a Class 200 meter (200A continuous) could be used on a 225A main panel at 225 non-continuous amps?

 

[jaggedben]

...So does this mean a Class 200 meter (200A continuous) could be used on a 225A main panel at 225 non-continuous amps?

Pretty sure the answer is yes. But practially speaking that would apply only to a stand-alone meter socket.

For whatever reasons, these are the single-phase meter/main combos I see almost always in the field.

• 100A continuous socket - with 125A (non-continous) panelboard or bussing (or sometimes 100A)
• 200A continuous socket - 200A (non-continuous) bussing or panelboard*
• 320A continuous socket - 400A (non-continuous) bussing

So the 200A sockets are 'overrated' (pun intended) compared to the other typical combos.

*'Solar Ready' panels have a 225A labeled panelboard but usually have other labeling stating or implying the max main breaker allowed is 200A.

 

[electrofelon]

I've always found this labeling confusing. On their 400A meter sockets, they tend to call them Class 320 with 320A continuous, 400A non-continuous. The load calcs take continuous into account, so if a load calc comes to 400A, then a 320/400A meter should be fine. So does this mean a Class 200 meter (200A continuous) could be used on a 225A main panel at 225 non-continuous amps?

I think so. If you do some digging, it's really hard to find as hardly anybody states in the literature, but at least some (all?) "200A" meter sockets are rated 250A maximum.

 

[Carultch]

I think so. If you do some digging, it's really hard to find as hardly anybody states in the literature, but at least some (all?) "200A" meter sockets are rated 250A maximum.

They could also in concept, carry a maximum current rating, which can be less than 125% of its continuous rating, and at most, 125% of its continuous rating. If it isn't specified in the product documentation, a meter socket's maximum current rating is 125% of its continuous current rating. Provided that your utility recognizes that you can take credit for a rating like this, which not all of them do. Understandably so, because it is kind of confusing.

So this means a 200A meter socket could have a maximum rating of 240A. This would restrict you to 225A maximum of OCPD, unless you have a special case where you can get a 240A breaker. E.g. an adjustable trip setting.

Why meter base manufacturers don't just "speak the same language" as the manufacturers of everything else, I don't understand. It seems like it would be a lot more civilized if we had 250A meter sockets and 400A meter sockets, instead of this madness with continuous vs maximum current ratings.

 

[electrofelon]

If it isn't specified in the product documentation, a meter socket's maximum current rating is 125% of its continuous current rating.

What is your source for that?

 

[Carultch]

What is your source for that?

This page discusses it.

How can a "class 320" service legaly/safely supply two 200 amp panels?

I have a "class 320" service with a single 320A meter that feeds two 200A main panels in parallel. USA, Evergy (formerly KCPL), Built 2014 How can a 320A service safely supply 400A of downstream ...

diy.stackexchange.com

This is also what I got when asking the Milbank representative about it, who only publish continuous current ratings for their metering products.
I'm confident that 320A sockets are built for any situation that would use up to a 400A of OCPD, since that's the main breaker sizes that most manufacturers pair it with, in a meter/main combo device. For smaller sizes, it is common that the fine print may contain a smaller maximum rating than 125% its continuous rating

 

[wwhitney]

So this means a 200A meter socket could have a maximum rating of 240A.

125% of 200 is 250.

Cheers, Wayne

 

[electrofelon]

This page discusses it.

How can a "class 320" service legaly/safely supply two 200 amp panels?

I have a "class 320" service with a single 320A meter that feeds two 200A main panels in parallel. USA, Evergy (formerly KCPL), Built 2014 How can a 320A service safely supply 400A of downstream ...

diy.stackexchange.com

This is also what I got when asking the Milbank representative about it, who only publish continuous current ratings for their metering products.
I'm confident that 320A sockets are built for any situation that would use up to a 400A of OCPD, since that's the main breaker sizes that most manufacturers pair it with, in a meter/main combo device. For smaller sizes, it is common that the fine print may contain a smaller maximum rating than 125% its continuous rating

I'm not sure I trust that source. And milbank told you that if a maximum or noncontinuous rating is NOT given, than it is 125% of the continuous? Is that just for their products or is that in the product standard?

 

[Carultch]

I'm not sure I trust that source. And milbank told you that if a maximum or noncontinuous rating is NOT given, than it is 125% of the continuous? Is that just for their products or is that in the product standard?

It could likely be just their standard. I had trouble getting a straight answer to this question when I asked. UL414 is the standard that governs amp ratings on meter sockets.

Siemens has meter sockets that explicitly give a 250A maximum rating, for their 200A continuous sockets.

125% of 200 is 250.

Cheers, Wayne

I'm aware of that. I was giving an example where it could be less than the full 125%.

 

[wwhitney]

I'm aware of that. I was giving an example where it could be less than the full 125%.

Sorry, misread "could" as "would".

Cheers, Wayne

 

[ggunn]

This page discusses it.

How can a "class 320" service legaly/safely supply two 200 amp panels?

I have a "class 320" service with a single 320A meter that feeds two 200A main panels in parallel. USA, Evergy (formerly KCPL), Built 2014 How can a 320A service safely supply 400A of downstream ...

diy.stackexchange.com

This is also what I got when asking the Milbank representative about it, who only publish continuous current ratings for their metering products.
I'm confident that 320A sockets are built for any situation that would use up to a 400A of OCPD, since that's the main breaker sizes that most manufacturers pair it with, in a meter/main combo device. For smaller sizes, it is common that the fine print may contain a smaller maximum rating than 125% its continuous rating

I have seen a 320A meter socket supplying two 200A panels many times.

 

[electrofelon]

I have seen a 320A meter socket supplying two 200A panels many times.

and one could put a 200A meter socket ahead of a 600A OCPD. There does not seem to be any requirement that a meter socket have overload protection that does not exceed its rating.

 

[jaggedben]

and one could put a 200A meter socket ahead of a 600A OCPD. There does not seem to be any requirement that a meter socket have overload protection that does not exceed its rating.

If it's an inline meter it's just a service conductor. 230.90 Exception 3