Hypothetical-Table 310.15(B)(6)

[elohr46]

Jet, the code allows a 200 amp main lug panel as the main disconnecting means as long as there are no more than 6 means of disconnect. Say I install 4 breakers which has a calculated load of 190 amps.

The next guy comes in and adds a sub panel for the addition and puts a 100 amp breaker in there. Now the calculated load of the service has jumped up over 200 amps. No main breaker to protect it--

Is this any different. Even if I install 6 disconnect (breakers) what is to stop someone from adding the seventh.

Hopefully, the Electrical Inspector.

 

[roger]

Hopefully, the Electrical Inspector.

It is doubtful or at least rare that an inspector would revisit a job after it has been signed off as complete.

It is simple, we have no control over what happens after we leave a code compliant installation.

Roger

 

[jetlag]

So now let's revisit the 150 amp fusible disconnect, you can't stop someone from over fusing it after you are gone no more than you can stop somebody from overload this sevice after you are gone can you?

Roger

There is a lot of difference in some one knowingly installing an oversized fuse and someone adding a load to a panel that is supposed to be protected by the existing breaker, I also went to a long explanation about how the screw in fuse boxes finally got changed by the code so the 30 amp would not go in the 15 and 20 amp sockets. I made that post to show that I dont believe a 150 fuse should fit in a 100 amp holder either but your only reply was " and the point is " . I give up on replying to your post . :roll:

 

[jetlag]

Hopefully, the Electrical Inspector.

Believe me I know NEC 230.90 ex 3 well. If you have a handbook see exhibit 230.27 . That is the code I am saying I disagree with . In your example the 2 to 6 breakers should not be allowed to exceed the ampacity of the service entrance . The amount it could be exceeded should only be the amount the 2 to 6 breakers were increased to go to the next available size breaker . It would also help if a plaque was installed showing the MAX allowed for the breaker combo . They install the label on a lot of equiptment for the max breaker allowed . They could have different plaques that you buy at the supply house. To sum it up a box and SE should be sized by the load served and if more than one main breaker is used the sum should not exceed that of a single main breaker as calculated . If it is allowed to put any size main breakers you want on a SE as long as it is two of more , Why not just go to a non fused disconnect ? If you install 6 200 amp main disconnects on a #2 aluminum SE are the breakers serving much purpose ?

 

[roger]

I made that post to show that I dont believe a 150 fuse should fit in a 100 amp holder either but your only reply was " and the point is " . I give up on replying to your post . :roll:

My posts have not said anything about a "100 amp holder", I have been asking about a 200 amp fuse being installed in place of a 150 amp fuse.

Let me explain something to you, fusible switches are not sized per each fuse size, if you need a 150 amp fuse for OCP it will have to be installed in a 200 amp switch, my question was how are you going to keep the end user from installing a 200 amp fuse in this switch if the equipment is blowing the 150 amp fuse.

Now, if it makes you happy let's use a circuit that calls for a 70 amp fuse, this will have to be installed in a 100 Amp switch, how are going to be sure that the end user doesn't install a 100 amp fuse (there's your 100 amp scenario) in this switch in the future?

Roger

 

[K8MHZ]

The SEC 's are protected by the 200amp breaker in panel (A).then you have a 200 amp feeder conected on the line side of the 200 amp breaker in panel (A)feeding a 200 amp breaker in panel (B).

Lets say panel (A) is drawing 180 amps and panel (B) is drawing 180 amps
. So now you have 360 amps flowing through the SEC's and 180 amps on the feeders between the two panels ,,but neather breaker would trip because the breaker in panel (A)can only see 180 amps

That's what I'm thinking. I guess I should have been a bit more clear in my post.

Sorry.

 

[Dennis Alwon]

The only problem with Leo's post is that the conductors from Panel "A" to Panel "B" are not feeders. They are still service conductors.

Jet, because you do not like a section in the code that does not make it non compliant. I can give a million scenarios that are "what if". The point is the code is not perfect and there is always room for error if the next person doesn't understand what they are doing.

Roger has pointed a number of scenarios and I gave one with the 6 disco rule. You don't like it then change it. Apparently it has not been a huge issue or the rules would be changed and maybe some day they will.

I am sure some of this is financial. Think of a commercial building with a 4000 amp service. The cost for one 4000 amp disconnect to feeder a distribution panel would add quite a bit to the cost of a job. Now make that service 12,000 amps, etc.

We will always have handy men and EC that are not qualified to do some of the work they do. I know I have made my share of mistakes- perhaps that is more the fault of the testing and req. to be an EC.

I think about how much I think I know then I get humbled knowing that I probably don't know more than I do know.

 

[jetlag]

The only problem with Leo's post is that the conductors from Panel "A" to Panel "B" are not feeders. They are still service conductors.

Jet, because you do not like a section in the code that does not make it non compliant. I can give a million scenarios that are "what if". The point is the code is not perfect and there is always room for error if the next person doesn't understand what they are doing.

Roger has pointed a number of scenarios and I gave one with the 6 disco rule. You don't like it then change it. Apparently it has not been a huge issue or the rules would be changed and maybe some day they will.

I am sure some of this is financial. Think of a commercial building with a 4000 amp service. The cost for one 4000 amp disconnect to feeder a distribution panel would add quite a bit to the cost of a job. Now make that service 12,000 amps, etc.

We will always have handy men and EC that are not qualified to do some of the work they do. I know I have made my share of mistakes- perhaps that is more the fault of the testing and req. to be an EC.

I think about how much I think I know then I get humbled knowing that I probably don't know more than I do know.

Will you at least admit that it is odd that the code requires us to calculated the value of a main disconnect , and yet you can completely ignore this by using more than one main disconnect ? Couldnt they at least put some kind of limit on the total of the main breakers ? We have all kind of restrictions on tap conductors , shouldnt they give more protection to the SE ?

 

[George Stolz]

Will you at least admit that it is odd that the code requires us to calculated the value of a main disconnect , and yet you can completely ignore this by using more than one main disconnect ? Couldnt they at least put some kind of limit on the total of the main breakers ?

Will you at least admit it would make no practical difference?

We have all kind of restrictions on tap conductors , shouldnt they give more protection to the SE ?

Why? Quite often, the conductors belong to the utility, and they are aware that the load is often less than the NEC would claim.

 

[Dennis Alwon]

Will you at least admit that it is odd that the code requires us to calculated the value of a main disconnect , and yet you can completely ignore this by using more than one main disconnect ? Couldnt they at least put some kind of limit on the total of the main breakers ? We have all kind of restrictions on tap conductors , shouldn't they give more protection to the SE ?

I don't think it is odd but I do see the cause for concern but limiting to 2 breakers may not solve the problem either. The issue I have with no main is if you want to add a breaker you must install it hot or call the poco to disconnect. Not a likely scenario.

 

[jetlag]

Will you at least admit it would make no practical difference?


Why? Quite often, the conductors belong to the utility, and they are aware that the load is often less than the NEC would claim.

It makes a difference because if others would notice that code we might get it revised one day . I do agree that the NEC is an overkill of most calculated loads and the POCO knows this , but they have a bad habit of running the same size that is allowed in free air into an encloser also . Are we going for 100 , 10 more to go