120% rule from sub to service entrance w/ no breaker provisions

Status
Not open for further replies.
GoldDigger said:
Yes.
There is absolutely no need to "protect" the utility feed any more than it is, but downsizing the 200A main to 175 will remove any possible argument about the stretch of 200A SEU between main and next panel down.
And for some AHJs that is a valid concern.
Click to expand...

what about the conductor i labeled B would you up size that to a 140 amp value if applying the 120% calculation must be applied up stream.
 
david said:
what about the conductor i labeled B would you up size that to a 140 amp value if applying the 120% calculation must be applied up stream.
Click to expand...

The same disputed argument applies to conductor B. If there is considered to be any chance of attaching a load to conductor B, then it has to be rated for 140A/1.20 or more. 70A is too small under that argument.
Even attaching a placard to the panel saying not to attach loads would not be enough for B. Conductor B would have to be labelled for no loads allowed anywhere that it was accessible.
 
david said:
what about the conductor i labeled B would you up size that to a 140 amp value if applying the 120% calculation must be applied up stream.
Click to expand...
Not unless it is tapped with loads. I would say that instead of resizing/upgrading/downgrading things to account for anything that might be done in the future, I would design for the way things are and what I plan to change. It is incumbent on anyone who makes changes later (I'm not talking about adding loads to existing panels, but taps, etc.) to make sure the resultant system is compliant.
 
Last edited:
ggunn said:
Not unless it is tapped with loads. I would say that instead of resizing/upgrading/downgrading things to account for anything that might be done in the future, I would design for the way things are and what I plan to change. It is incumbent on anyone who makes changes later (I'm not talking about adding loads to existing panels, but taps, etc.) to make sure the resultant system is compliant.
Click to expand...

"and where this distribution equipment is capable of supplying multiple branch circuits or feeders or both,"

In relationship to panel labeled A..what do the authorities in your area use in defining what capable of supplying loads means. I would guess that might bare on conductor labeled B being calculated at 70 amps or 140 amps.

With that i thank you all for your answers and comments

David
 
david said:
so apply the 120% rule to all buss up stream but not enforceable to the feeders

i think that is what you guys are concluding
Click to expand...

In 2014 it is unambigous that the 120% rule applies only to panelboards, not feeders. In effect, it's a 200% rule if the sources are at each end of the feeder, and a 100% rule if the feeder is tapped. (The actual rules are not worded that way though.)

I have been following the 2014 rules in my designs for a year or so now, even though we are still on the 2011 version of the code. As I mentioned, only one AHJ out of more than two dozen I've worked with trips us up over the feeder question.
 
GoldDigger said:
But the O that counts is the AHJ's. :)
No ambiguity in [2014] though.
Click to expand...
That depends on whether you use 200A (SER) or 225A (panel bus) as the base rating for the 120%.

In this case, the 225A bus is being used. Assuming the main and panel are really close, wouldn't replacing the feeder with a not-less-than-225A cable be less costly than replacing the main breaker?
 
Smart $ said:
That depends on whether you use 200A (SER) or 225A (panel bus) as the base rating for the 120%.

In this case, the 225A bus is being used. Assuming the main and panel are really close, wouldn't replacing the feeder with a not-less-than-225A cable be less costly than replacing the main breaker?
Click to expand...

FWIW, I'd wager not. Usually these arrangements consist of a main breaker on the outside of the home and a subpanel in the middle of the home somewhere. If the house is finished then $200 for a breaker costs far less than doing drywall.
 
jaggedben said:
FWIW, I'd wager not. Usually these arrangements consist of a main breaker on the outside of the home and a subpanel in the middle of the home somewhere. If the house is finished then $200 for a breaker costs far less than doing drywall.
Click to expand...
IIRC, the OP said the outside main is on a [detached?] garage and 225A MLO panel is inside the garage. I don't recall a distance being mentioned, but I was thinking immediately inside.
 
I hate to ask this question on the service disconnect exterior of the garage. The op indicated a 200 amp Disconnect I know its not the same one as this but if the disconnect is rated 200 amps not 225 how do you apply the 120% rule to this small buss
Sorry tried to in large it won't I held control then scrolled it larger that help a bit
 

Attachments

  • 200 Amp Disconnect.jpg
    200 Amp Disconnect.jpg
    7.9 KB · Views: 0
david said:
I hate to ask this question on the service disconnect exterior of the garage. The op indicated a 200 amp Disconnect I know its not the same one as this but if the disconnect is rated 200 amps not 225 how do you apply the 120% rule to this small buss
Click to expand...

That was mentioned as one reason that the Service Disconnect breaker might have to be made smaller. Although the fact that there is no way that loads could be interposed between the service end of the bus and the feeder end of the bus may convince most AHJs that the 120% rule does not apply.
 
GoldDigger said:
That was mentioned as one reason that the Service Disconnect breaker might have to be made smaller. Although the fact that there is no way that loads could be interposed between the service end of the bus and the feeder end of the bus may convince most AHJs that the 120% rule does not apply.
Click to expand...

I recall the discussion being it did not apply because it was not a load side connection. But most of the electricians land the service entrance to the breaker not to the Buss. I guess if it wasn't existing and you where building this new you could hit the buss with the service conductors.

Thanks I was following the last few comments and there seems to be some discussion on the 225 amp rated MLO panels Buss. But if the service entrance buss was 200 amp rated won't that proceed the 225 amp MLO Buss
 
Last edited:
david said:
I recall the discussion being it did not apply because it was not a load side connection. But most of the electricians land the service entrance to the breaker not to the Buss. I guess if it wasn't existing and you where building this new you could hit the buss with the service conductors.

Thanks I was following the last few comments and there seems to be some discussion on the 225 amp rated MLO panels Buss. But if the service entrance buss was 200 amp rated won't that proceed the 225 amp MLO Buss
Click to expand...
I know utility bus was mentioned, but IMO there is none. The service entrance conductor terminates directly to the service disconnecting means (i.e. the 200A breaker). I'm open to being corrected.

The 225A MLO panel bus is considered a feeder bus... but it's rating cannot technically be used for the 120% rule because the wire portion of the feeder is only rated 200A.

If prevailing conditions do not meet the requirements for the desired installation, down-rate the main breaker, or up-rate the feeder as required to match conditions, if possible. If that don't work, replace everything with equipment that meets the requirement(s).
 
Smart $ said:
I know utility bus was mentioned, but IMO there is none. The service entrance conductor terminates directly to the service disconnecting means (i.e. the 200A breaker). I'm open to being corrected.
Click to expand...

I agree that since the service entrance conductors land on the breaker first. The service conductors end there. The conductors load side of that breaker are feeder conductors. But I am a small fish swimming in a new pool. Most of these guys on this forum have way more experience on solar than I do so I would hesitate not to take their advise or learn from their experience.
 
Smart $ said:
I know utility bus was mentioned, but IMO there is none. The service entrance conductor terminates directly to the service disconnecting means (i.e. the 200A breaker). I'm open to being corrected.
Click to expand...

What I see most often here in northern California, that meets the general description, is meter/main combo service equipment with either bussing or factory installed conductors between the meter and the breaker. A feeder is installed to the lugs of the breaker.

So there may be bussing on the utility side of the breaker, but it's also really moot.

I'm looking forward to next year when I can point to the new code and tell these one or two AHJs to stop fussing over the feeder rating.
 
Status
Not open for further replies.
Top