400 or 200 Amp Service

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Smart $ said:
I agree it is intended to... but Exception No. 3 is not worded explicit enough to say absolutely. After all it is an exception. If you look at service entrance conductor requirements for ampacity, it is based solely on calculated load, with no consideration for OCPD rating.
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SE conductor sizing based on calculated load is good practice, one used for most conductor sizing. Then 230.90(A) provides sufficient guidance for OCPD rating.

I understand your angle with the proposal. But I don't think its necessary. I see the wording in 230.90(A) as descriptive enough to disallow a single overcurrent device in a multiple switch service from being larger than the SE conductors feeding the assembly.
 
shortcircuit2 said:
SE conductor sizing based on calculated load is good practice, one used for most conductor sizing. Then 230.90(A) provides sufficient guidance for OCPD rating.

I understand your angle with the proposal. But I don't think its necessary. I see the wording in 230.90(A) as descriptive enough to disallow a single overcurrent device in a multiple switch service from being larger than the SE conductors feeding the assembly.
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Let's compare...

First sentence of 230.90(A):
Such protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor.​

Second sentence of Exception No. 3:
The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.
​


Where is it written that the highlighted exception text cannot supersede the highlighted general statement text? As I said, it is an exception. If it only excepts part of a general requirement, it has to be explicit enough to discern. Current exception wording is not concise enough to say it only pertains to the "sum of the ratings". It can just as easily be interpreted to except any detail mentioned, including ampacity of service conductors.

PS: FWIW, I'm inclined to believe the CMP will see it the same as you :)
 
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After talking to the utility company the engineer said that I most likely have 400a service and that the service entrance cable was unprotected except for the transformer having some fault recognition but that didn't necesarrily limit current to 400a.

So I guess my next question is, can I downsize to 200a service? This way I could use a 200a combo meter? This could trip to prevent over 200a to either sec going to either panel. Seems this woud have all wiring downstream of the meter protected by a breaker.

If this is not possible, is there a 400a combo meter box that has 2 200a breakers?

Thanks again
 
skinnydip said:
After talking to the utility company the engineer said that I most likely have 400a service and that the service entrance cable was unprotected except for the transformer having some fault recognition but that didn't necesarrily limit current to 400a.

So I guess my next question is, can I downsize to 200a service? This way I could use a 200a combo meter? This could trip to prevent over 200a to either sec going to either panel. Seems this woud have all wiring downstream of the meter protected by a breaker.

If this is not possible, is there a 400a combo meter box that has 2 200a breakers?

Thanks again
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What are the service entrance conductor details ahead of existing meter (e.g. 400kcmil SE CU cable, or 400kcmil THWN-2 CU in RMC conduit)... if you can determine?

Yes there are 400A meter load center combos with feed-through lugs and capability of adding a second main 200A (feed-through) breaker.
 
Smart $ said:
The requirement is sound as long as it is used within the intent, but literal interpretation allows SE conductors to be unprotected. What if you only had a 100A calculated load and 2-200A service disconnecting means (SDM). You could technically run a 100A "main" SE conductor and a 50A tap to each SDM, assuming balanced loading of SDM's. What protects these SE conductors?

Existing Exception No. 3
Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.​

Proposed Exception No. 3:
Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the ampacity of the service conductors is not less than the calculated load or any supplied overcurrent device rating, whichever is greater.​

The example given above under my proposed revision would require all SE conductors to have an ampacity not less than 200A.
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I don't have much issue with your proposal, but from memory only - I'm pretty certain in your example those "taps" would need to be at least 100 amp conductors. Kind of a rare situation there but not impossible to come by.

In general I believe the individual supply to a fuse or breaker in this situation needs sized for overcurrent protection according to the setting of the overcurrent device, but at same time does not need to be larger then the service conductor supplying it.
 
kwired said:
I don't have much issue with your proposal, but from memory only - I'm pretty certain in your example those "taps" would need to be at least 100 amp conductors. Kind of a rare situation there but not impossible to come by.

In general I believe the individual supply to a fuse or breaker in this situation needs sized for overcurrent protection according to the setting of the overcurrent device, but at same time does not need to be larger then the service conductor supplying it.
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I'd need section in order to comment on your post. So far we have three different interpretations of the same exception. All the more reason to nail it down... :p
 
kwired said:
I don't have much issue with your proposal, but from memory only - I'm pretty certain in your example those "taps" would need to be at least 100 amp conductors. Kind of a rare situation there but not impossible to come by.

...
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Perhaps you are thinking of 230.79 rating of Service Disconnecting Means, (C) One-Family Dwellings... service disconnecting means shall have a rating not less than 100A, 3-wire.

Where there are two to six SDM installed under exception, does that apply to each disconnecting means that supply the dwelling?

I realize this don't apply to the OP, but could a dwelling unit have say 2-60A SDM in lieu of 1-100A?
 
Smart $ said:
Perhaps you are thinking of 230.79 rating of Service Disconnecting Means, (C) One-Family Dwellings... service disconnecting means shall have a rating not less than 100A, 3-wire.

Where there are two to six SDM installed under exception, does that apply to each disconnecting means that supply the dwelling?

I realize this don't apply to the OP, but could a dwelling unit have say 2-60A SDM in lieu of 1-100A?
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Did not even have that situation on my mind, would need to do some looking before I can comment any further.
 
How about 230.90 plus part(A):

230.90 Where Required.
Each ungrounded service conductor shall have overload protection.
(A) Ungrounded Conductor.
Such protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor.
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The general rule is the conductor shall have overcurrent protection that aligns with the conductor ampacity.

exception three does allow the overcurrent protection to exceed the conductor ampacity but it is only for when there is more then one overcurrent device. A tap from a common supply conductor that only feeds one overcurrent device IMO still needs to meet the general rule as it is only supplying one device.
 
kwired said:
How about 230.90 plus part(A):



The general rule is the conductor shall have overcurrent protection that aligns with the conductor ampacity.

exception three does allow the overcurrent protection to exceed the conductor ampacity but it is only for when there is more then one overcurrent device. A tap from a common supply conductor that only feeds one overcurrent device IMO still needs to meet the general rule as it is only supplying one device.
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And that's the reason for my proposed revision. The exception isn't explicit on that matter... even more so regarding the "main" before taps.
 
Downsize

Downsize

So now that I have found that I actually have 400 amp service, is it legal to put in a 200 amp combination meter panel that feeds one 200 amp main breaker inside, and then branch off of it with a 60 or 100 amp panel? This would allow me to only need one service entrance cable and save a lot of money over actually using a 400 amp meter combination. $120 vs $600 is a big deal to me and I don't need more than 200 amp service can provide. I guess my main question is, even though I have 400 amp service, can it be throttled to 200 amps at the meter base? Thanks again for all the help so far.
 
skinnydip said:
So now that I have found that I actually have 400 amp service, is it legal to put in a 200 amp combination meter panel that feeds one 200 amp main breaker inside, and then branch off of it with a 60 or 100 amp panel? This would allow me to only need one service entrance cable and save a lot of money over actually using a 400 amp meter combination. $120 vs $600 is a big deal to me and I don't need more than 200 amp service can provide. I guess my main question is, even though I have 400 amp service, can it be throttled to 200 amps at the meter base? Thanks again for all the help so far.
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Yes, it can be downgraded to 200A.

Given you already have a 400A service with two 200A service panels, and you state $$$ is at issue, I am perplexed as to why you'd even want to...
 
kwired said:
How about 230.90 plus part(A):



The general rule is the conductor shall have overcurrent protection that aligns with the conductor ampacity.

exception three does allow the overcurrent protection to exceed the conductor ampacity but it is only for when there is more then one overcurrent device. A tap from a common supply conductor that only feeds one overcurrent device IMO still needs to meet the general rule as it is only supplying one device.
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Now we are down to 2 interpretations...:)
 
shortcircuit2 said:
Now we are down to 2 interpretations...:)
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I agree it is likely the most common interpretation. The main reason for proposing revision is to assure some level of protection for service conductors ahead of taps. Even requiring common service conductor ampacity is not less than the largest of several OCPD's isn't full assurance. Basically all services are derived from a transformer secondary. Seems contradictory that to comply with Article 450.3(B) where the secondary supplies multiple OCPD's, the sum of their ratings cannot exceed what is permitted for a single OCPD. Seems like there should be a cap on the sum of multiple service OCPD's with respect to service conductor ampacity ahead of taps, too.
 
Smart $ said:
Yes, it can be downgraded to 200A.

Given you already have a 400A service with two 200A service panels, and you state $$$ is at issue, I am perplexed as to why you'd even want to...
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Part of the reason is I want to replace the federal pacific main breaker panels. Also, I would like to be able to run circuits from my outside panel. Also, I would like to be able to do work on inside panels without having to get power company and county inspector involved. Also, I am installing a hot tub i got for free and a 50a fpe breaker costs close to $100 by itself. Any one of these things would not make me want to change anything but the combination of all of them warrant me spending some money. But why spend $1000 for 400a when $500 for 200a is all I need? Thanks.
 
skinnydip said:
Part of the reason is I want to replace the federal pacific main breaker panels. Also, I would like to be able to run circuits from my outside panel. Also, I would like to be able to do work on inside panels without having to get power company and county inspector involved. Also, I am installing a hot tub i got for free and a 50a fpe breaker costs close to $100 by itself. Any one of these things would not make me want to change anything but the combination of all of them warrant me spending some money. But why spend $1000 for 400a when $500 for 200a is all I need? Thanks.
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I see. Thanks for elaborating.
 
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