Service size after reducing Main breaker size

[ggunn]

2 answers to questions you did not ask but might be options:
1. You do have the option of a 175A main breaker. In such a case, many electricians (oh no, not me....) don't even do load calcs, they figure 175A covers 99.99% of 200A service loads.

I have hear of some PV designers (oh no, not me, either ) don't do load calcs in some situations but promise the customer if the reduced OCPD ever starts tripping the company will come back out and reinstall the PV system on the supply side for free. As far as I know no customer has ever collected on that promise.

 

[Sierrasparky]

2 answers to questions you did not ask but might be options:
1. You do have the option of a 175A main breaker. In such a case, many electricians (oh no, not me....) don't even do load calcs, they figure 175A covers 99.99% of 200A service loads.
You would need to finnagle your 80A PV output down to 65A though. (65A PV + 175A main brkr = 240A)
Remember you are allowed to use individual inverter output amps when adding them..... instead of adding individual inverter breaker sizes. This helps if there is considerable rounding up.
Sometimes a smaller micro inverter does the trick, with surprisingly minimal to no peak shaving losses.
Details.....
2. Do you actually have a 225A bus? That opens up a whole new world. That means 70A PV ......w/o downsizing nuthin.
Or 95A PV with a 175A main breaker.
E.g. many EATONs are 225A today.

200a bus, I don't think I have seen a single row all-in -one with a 225. I am sure that 225 is what the solar company told the owner.

 

[ggunn]

200a bus, I don't think I have seen a single row all-in -one with a 225. I am sure that 225 is what the solar company told the owner.

FWIW, Eaton CH panels from 150A to 225A have the same 225A bus. The solar company I retired from has it in writing from Eaton.

 

[Sierrasparky]

FWIW, Eaton CH panels from 150A to 225A have the same 225A bus. The solar company I retired from has it in writing from Eaton.

The label says 200. This is a Murray as the picture earlier states.


In any respect I got the single line from the solar installer.
I have a new question?

The Solar is controlled by a Tesla system. So can the back-feed breaker be larger than the bus where the maximum power output from the tesla system towards the main panel is controlled electronically.
705.13 new as of the CA electric code 2022
Is this the code exception?

 

[jaggedben]

The label says 200. This is a Murray as the picture earlier states.


In any respect I got the single line from the solar installer.
I have a new question?

The Solar is controlled by a Tesla system. So can the back-feed breaker be larger than the bus where the maximum power output from the tesla system towards the main panel is controlled electronically.
705.13 new as of the CA electric code 2022
Is this the code exception?

Yes. Well...

I don't know why you'd have a backfed breaker that's larger than the bus. But the 120% rule can go away with a PCS that is listed to limit the total current on the busbar. I'm doing it all the time now.

AND, if the PCS can control and limit solar (and not just battery), then using PCS you could upsize that breaker back to 200A. But I'm a little skeptical that the Tesla can actually do that, isn't this an older solar system?

 

[Sierrasparky]

Yes. Well...

I don't know why you'd have a backfed breaker that's larger than the bus. But the 120% rule can go away with a PCS that is listed to limit the total current on the busbar. I'm doing it all the time now.

AND, if the PCS can control and limit solar (and not just battery), then using PCS you could upsize that breaker back to 200A. But I'm a little skeptical that the Tesla can actually do that, isn't this an older solar system?

This is a new system installed over the summer. I have heard these PCS fail from time to time.

 

[jaggedben]

This is a new system installed over the summer. I have heard these PCS fail from time to time.

I've not heard of PCS failing. I'm going to bet whoever told you that is misinformed. What would surprise me a lot less is PCS not configured properly by the installer in the first place.

So the main breaker was also downsized this summer, when the PV was installed? I feel like someone didn't know what they were doing. But we'd need a lot more detail about the PV. It's not irrelevant to your original question if upsizing the main breaker is actually an option with a properly configured PCS.

 

[Sierrasparky]

I've not heard of PCS failing. I'm going to bet whoever told you that is misinformed. What would surprise me a lot less is PCS not configured properly by the installer in the first place.

So the main breaker was also downsized this summer, when the PV was installed? I feel like someone didn't know what they were doing. But we'd need a lot more detail about the PV. It's not irrelevant to your original question if upsizing the main breaker is actually an option with a properly configured PCS.

Main breaker was never touched. The question was if?

 

[Eddie702]

AFAIK the service size is the size of the MB

 

[brycenesbitt]

My Customer is adding new high current loads and a ADU so I need to calculate the load for plans. I was just observing the current service. It is a 200a panel with a reduced main to 150. If I use the standard methods and tools I come up with over a 150 easily, very close to 200a. Without knowing the rule here I cannot advise the client to eliminate a load or not.

Thanks

This is a clear case where getting an Emporia or other recording amp meter can help.
Or, try using the reined 2026 NEC load calculation methods and try to convince the AJH to accept it.
That panel is likely fine -- only the calculation is bad. Do the 30 day measure, and back it up with some utility data from the HO.

 

[ggunn]

AFAIK the service size is the size of the MB

It depends. For example, if one is contemplating a supply side PV interconnection, IIRC the NEC defines the service size as the ampacity of the service conductors.

 

[brycenesbitt]

It depends. For example, if one is contemplating a supply side PV interconnection, IIRC the NEC defines the service size as the ampacity of the service conductors.

A curious issue here is the utility often puts much smaller service drops, than the NEC rules would allow.
I suppose it's the utility's problem, but it is unclear WHICH service conductors should be measured.

 

[ramsy]

it is unclear WHICH service conductors should be measured

In my area POCO is governed by the NESC, which ignores NEC load calcs.

When POCO service drops burn apart, POCO keeps replacing them for free.

Even when property owners use hacks to install tankless WH, or upgrade services without permits or meter spot, which is most of the time.

 

[curt swartz]

In my area POCO is governed by the NESC, which ignores NEC load calcs.

When POCO service drops burn apart, POCO keeps replacing them for free.

Even when property owners use hacks to install tankless WH, or upgrade services without permits or meter spot, which is most of the time.

Actually California is the only state that doesn't use the NESC Californian has their own utility code GO95.

The last few 200 amp residential overhead services I have done PG&E has installed 4/0 triplex. I questioned the line crews and they said its a new thing and its insane. Now I'm waiting for them to start requiring 3" rigid as the minimum mast size.

 

[Sierrasparky]

This is a clear case where getting an Emporia or other recording amp meter can help.
Or, try using the reined 2026 NEC load calculation methods and try to convince the AJH to accept it.
That panel is likely fine -- only the calculation is bad. Do the 30 day measure, and back it up with some utility data from the HO.

Key word here is "add" I am keeping my nose clean. I'll do what the Book says or someone can have a EE take written responsibility. I don't do "it'll work, "it's just fine. .....If you do it per code then those numbers will last until the next un-permitted change. A new owner may and will use the home differently. .Respectfully, I just do not need the headache.

 

[Sierrasparky]

Actually California is the only state that doesn't use the NESC Californian has their own utility code GO95.

The last few 200 amp residential overhead services I have done PG&E has installed 4/0 triplex. I questioned the line crews and they said its a new thing and its insane. Now I'm waiting for them to start requiring 3" rigid as the minimum mast size.

have they stated a higher fault current?

 

[ramsy]

Actually California is the only state that doesn't use the NESC Californian has their own utility code GO95.

Yes, I see.

National Electrical Safety Code - Wikipedia

en.wikipedia.org

Most U.S. states adopt the NESC in some form or fashion. The state of California is an exception and writes its own utility codes, titled General Order 95 (GO95) for overhead lines and General Order 128 (GO128) for underground lines.

 

[ramsy]

California is the only state that doesn't use the NESC

Forgot to mention the ESR (Green book) published by my utility (So.CA.Edison) includes the National Electrical Safety Code in the definitions.

Electrical Service Requirements (ESR)

Access SCE's Electrical Service Requirements manual for guidelines on safe and compliant electrical connections for contractors and engineers.

www.sce.com