400 Amp Meter Main

[kwired]

I already have but when I was on the phone I couldnt rattle off all of the violations that would come into play other than you cant do that because of this, and this, and this.


The DIY'er said the power company told him they used this setup for 400 Amp services all the time.

You can see where he would think that installing a 400 Amp Panelboard would be just fine.

It was the first time I had ever heard of anyone even thinking about installing it that way.

POCO probably only looks at it as a 400 amp service, which it is and to them does not matter if it is 1 - 400 amp load, 2 200 amp loads, or 75 loads that total 400 amps, but it is not capable of supplying a single 400 amp circuit.

That would make no difference IMO. If one conductor from one of the breakers got cut or disconnected somehow the entire 400 amps would be on the 200 amp conductor and breaker. :happyno::jawdrop:

It does not matter for the fact there is a 400 amp feeder being supplied. If it were supplying two separate panels but on a separate building or structure is where 225.30 issues are a problem.

It only matters if the service is on the building if you were to correct the problem by replacing the single 400 amp panel with 2 200 amp panels because, as Kwire points out, it would violate 225.30. That is why I suggested my fix to change it to a single 400 amp breaker at the meter and it comes a legitimate parallel feeder. But since you are not being called on to fix the obviously wrong and dangerous original design, it's a moot point and case closed. The only thing I would do is issue a letter stating the concerns and hazard so there is a paper trail showing you did your best to make the owner aware and move on.

Not much you can do but notify them that it does not meet codes and standards. I certainly would not be willing to make any change to it without some funds up front or I will likely be stuck with some 400 amp gear.

 

[jap]

The power company are the ones who provided the combo Meter Main with the 2 200amp breakers.
They provide it for all customers to that point.

As soon as the customer said he needed a 400 Amp 1ph Service this is what they came out and installed this setup next to the dip box by the utility pole.

The customer needed a single 400 Amp service because yes, they are installing a 400 Amp Xfr Switch and a generator to back up the entire Transmission site in the future.

That's why he questioned the 2 200 Amp Feeder Breakers.

I dont know of any case where you can use (2) Seperate Feeder Breakers to serve (1) Common Panel.
Regardless of wether its on the structure or remote from the structure.

But I can see where someone who didnt know any better could install it that way turn it on and never know anything was wrong.

 

[kwired]

The power company are the ones who provided the combo Meter Main with the 2 200amp breakers.
They provide it for all customers to that point.

As soon as the customer said he needed a 400 Amp 1ph Service this is what they came out and installed this setup next to the dip box by the utility pole.

The customer needed a single 400 Amp service because yes, they are installing a 400 Amp Xfr Switch and a generator to back up the entire Transmission site in the future.

That's why he questioned the 2 200 Amp Feeder Breakers.

I dont know of any case where you can use (2) Seperate Feeder Breakers to serve (1) Common Panel.
Regardless of wether its on the structure or remote from the structure.

But I can see where someone who didnt know any better could install it that way turn it on and never know anything was wrong.

Can't POCO just provide a meter base with no disconnecting means and allow customer to supply their own disconnect?

Around here they usually provide meter/disconnect on rural services, and at less cost than most contractors could provide them. But if a configuration is needed that they don't stock or are willing to get they have no problem with customer/contractor provided equipment either. It is after all the customers equipment either way, just a matter of who sold it.

 

[fmtjfw]

Holy Batman and Robin ... it is Legal!

Holy Batman and Robin ... it is Legal!

The Power Company out in the county not under local inspection provides combo meter mains.
On the 400 Amp Combo.They come with (2) 200 Amp 1ph Feeder Breakers.(Not 1 400).

They are telling the customer that these can be used for 400 Amp Services and typically they are for
(2) Seperate 200 Amp MLO Panels)

But.

The Customers and electricians that dont know any better are thinking that they can install a Single 400 AMP Panel and take a feed from each 200a breaker in the Meter/Main to the single 400a Panel.

Hearing this floored me.
But off the top of my head I could see where someone could actually do this and never know it was wrong.

:jawdrop:I've been going through NEC 2014 essentially page by page looking at the voltage change problems. What do I come upon but (which is also in 2011 and 2009)::jawdrop:

408.36 Overcurrent Protection. In addition to the requirement of 408.30, a panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panelboard.

. . .

Exception No. 2: Individual protection shall not be required for a panelboard protected on its supply side by two
main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard. A panelboard constructed or wired under this exception shall not contain more than 42 overcurrent devices. For the purposes of determining the maximum of 42 overcurrent devices, a 2-pole or a 3-pole circuit breaker shall be considered as two or three overcurrent devices, respectively.

WOW

 

[jap]

Oh my gosh, I cant believe what I'm reading here.

I've got so many scenarios in my head where this unsafe.

The handles are not tied together.
One breaker could be turned off and and the load side lugs would still be hot since the other breaker is still on.
Only turn off one breaker and you still have power to the Inside Panel.
If theres a fault in one of the 200a Feeds would both 200's Trip? I dont know.
Wouldnt the Feeder breakers actally trip if the load was to get to 200 Amps instead of the 400Amp Rating of the Panelboard?
How can you get a 400 Amp Feeder from (2) 200 Amp Breakers?.

And on and on.

This makes the urgency on putting handle ties on a MWBC seem useless.

What am I missing here?

 

[jap]

Now I'm thinking about paralleling (2) fuses to a common load.

I've never seen or would ever do that.

What would be the difference in this and setting (2) Fused disconnects side by side and feeding a common A/C Unit?

Why would you ever to that?

 

[fmtjfw]

When you compare it with:

When you compare it with:

Now I'm thinking about paralleling (2) fuses to a common load.

I've never seen or would ever do that.

What would be the difference in this and setting (2) Fused disconnects side by side and feeding a common A/C Unit?

Why would you ever to that?

240.8 Fuses or Circuit Breakers in Parallel. Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel.

But an exception for a particular case overrides the general rule, hence 408.36 Exception 2 allows two parallel OCPDs.

 

[jap]

But isnt the 400 Amp Feed completely comprimised whenever you have (2) 200 Amp Breakers feeding a common panelboard.

If the Amperage of the panelboard on either phase ever got to 200 Amps, One or Both Breakers should react to this amperage and trip.

I dont see how (2) 200 amp breakers in parallel could ever allow a 400 Amp Capacity.

I just dont see it,Unless there's some Electrical Science that I'm not aware of.

 

[jap]

What do you gain by any Fuse or Circuit Breaker wired in Parallel for that matter?

 

[fmtjfw]

If electricity has two paths to follow (in this case from the service conductor black, through the busbar in the CB enclosure to the black wires on each CB load side to the dual lugs on the black busbar of the 400A panelboard, the current will divide according to the parallel resistor formula. Let's take an example:

Internal resistance of a CB pole: 0.0 Ohms (totally made up figure)
resistance of black wire (4/0 100ft) from left hand CB to panelboard: .0062 Ohms
resistance of black wire (4/0 110ft) from right hand CB to panelboard: .00682 Ohms
total resistance: 1/R(total) = 1/(1/R(1)+1/R(2)) = 1/(161.3+146.6) = .00325 Ohms

if we have a I(total) of 400Amps and a voltage drop of E(drop) which must be the same in each wire (since their ends are effectively connected together)
The E(drop) is R(total) X (I(total) = .00325 X 400 = 1.3v

Now the current in the left black wire will be I=E/R = 1.3 / .0062 = 209.5 Amps
and the current in the right black wire will be I=E/R = 1.3 / .00682 = 190.5 Amps

The left CB may hold on this 209.5 Amps forever, but lets pretend it trips.
The right CB will now have 400Amps on it and will trip pretty soon.

If the load is 350Amps total they should hold forever.

The deal is that the CBs each see about 1/2 of the current.

Note I made a rather big imbalance of these parallel conductors to cause this problem. With closer (and more likely) lengths it should work just fine.

The same analysis applies to the red wires

 

[jap]

Wow, that's Interesting.

I should have done more studying when I was younger and less installation.

I would have and probably still wont ever use (2) individual breakers to protect a single load although everything seems to indicate that you can.

I would have never thought it.

Thanks,

 

[jap]

Although the electrical theory of it makes sense now, the idea of having to shut off (2) seperate breakers to safely work on something still doesnt seem safe to me.

I could understand if the 2 were somehow tied together, but they're not in this case.

 

[fmtjfw]

Although the electrical theory of it makes sense now, the idea of having to shut off (2) seperate breakers to safely work on something still doesnt seem safe to me.

I could understand if the 2 were somehow tied together, but they're not in this case.

I don't think feeding from two OCPDs is a good idea either. I'm just wondering where this exception came from.

 

[texie]

I don't think feeding from two OCPDs is a good idea either. I'm just wondering where this exception came from.

Hold on here, stop the train... You and the OP are confusing to separate rules here. Art. 408.36 is referring to a slit bus panel where you have, say, a 400 amp main bus that has 2, 200 amp breakers feeding 2 different buses within the same panelboard. This is entirely different and separate from the Art. 240 rule prohibiting fuses and circuit breakers in a parallel.
The installation as describibed by the OP is a violation and a serious safety hazard. I and others have offered possible solutions, but this just keeps on going. There is no way to read/study long enough to make this magically compliant or safe.

 

[fmtjfw]

Show me the words split bus, all I can do is read what is there

Show me the words split bus, all I can do is read what is there

Hold on here, stop the train... You and the OP are confusing to separate rules here. Art. 408.36 is referring to a slit bus panel where you have, say, a 400 amp main bus that has 2, 200 amp breakers feeding 2 different buses within the same panelboard. This is entirely different and separate from the Art. 240 rule prohibiting fuses and circuit breakers in a parallel.
The installation as describibed by the OP is a violation and a serious safety hazard. I and others have offered possible solutions, but this just keeps on going. There is no way to read/study long enough to make this magically compliant or safe.

408.36 Overcurrent Protection. In addition to the requirement of 408.30, a panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard. This overcurrent rotective device shall be located within or at any point on the supply side of the panelboard.

No mention of split bus here or in 408.30 which it references.

Exception No. 1: Individual protection shall not be required for a panelboard used as service equipment with
multiple disconnecting means in accordance with 230.71. In panelboards protected by three or more main circuit
breakers or sets of fuses, the circuit breakers or sets of fuses shall not supply a second bus structure within the same panelboard assembly.

I take this to mean that if you have a split bus panel (like the old common MLO 6 2-pole bus A with one of the 2-poles feeding bus B), that you can have only 2 main sets, effective killing the old style off.

Exception No. 2: Individual protection shall not be required for a panelboard protected on its supply side by two
main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard. A
panelboard constructed or wired under this exception shall not contain more than 42 overcurrent devices. For the purposes of determining the maximum of 42 overcurrent devices, a 2-pole or a 3-pole circuit breaker shall be considered as two or three overcurrent devices, respectively.

No busses mentioned here? Is this exception #2 an exception to Exception #1?

Exception No. 3: For existing panelboards, individual protection shall not be required for a panelboard used as
service equipment for an individual residential occupancy.

I have no idea what this is about other than grandfathering some old system.


If all three exceptions are related to split buses, then why isn't that mentioned in the original rule?

When used as OCPDs the 2 200A breakers serve to limit the current in each 4/0 sets to 200A. With a single 400A breaker, the current is divided in each 4/0 sets according to resistance and if one set were disconnected the set left could be supplied at 400A without tripping. The only hazard that I see is if only 1 200A breaker is opened believing it to be the only source to the panel. A hazard I'll admit, but not worse than the one you propose with two separate feeds to a split bus panel.

 

[kwired]

Maybe that section allows for interconnected sources of power? If so it could be worded better or better yet be located in art 705, or have a reference to see art. 705.

I really doubt it was intended as a way of allowing parallel overcurrent devices that are not a listed assembly.

 

[texie]

408.36 Overcurrent Protection. In addition to the requirement of 408.30, a panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard. This overcurrent rotective device shall be located within or at any point on the supply side of the panelboard.

No mention of split bus here or in 408.30 which it references.

Exception No. 1: Individual protection shall not be required for a panelboard used as service equipment with
multiple disconnecting means in accordance with 230.71. In panelboards protected by three or more main circuit
breakers or sets of fuses, the circuit breakers or sets of fuses shall not supply a second bus structure within the same panelboard assembly.

I take this to mean that if you have a split bus panel (like the old common MLO 6 2-pole bus A with one of the 2-poles feeding bus B), that you can have only 2 main sets, effective killing the old style off.

Exception No. 2: Individual protection shall not be required for a panelboard protected on its supply side by two
main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard. A
panelboard constructed or wired under this exception shall not contain more than 42 overcurrent devices. For the purposes of determining the maximum of 42 overcurrent devices, a 2-pole or a 3-pole circuit breaker shall be considered as two or three overcurrent devices, respectively.

No busses mentioned here? Is this exception #2 an exception to Exception #1?

Exception No. 3: For existing panelboards, individual protection shall not be required for a panelboard used as
service equipment for an individual residential occupancy.

I have no idea what this is about other than grandfathering some old system.


If all three exceptions are related to split buses, then why isn't that mentioned in the original rule?

When used as OCPDs the 2 200A breakers serve to limit the current in each 4/0 sets to 200A. With a single 400A breaker, the current is divided in each 4/0 sets according to resistance and if one set were disconnected the set left could be supplied at 400A without tripping. The only hazard that I see is if only 1 200A breaker is opened believing it to be the only source to the panel. A hazard I'll admit, but not worse than the one you propose with two separate feeds to a split bus panel.

You guys got me to checking further into this 408.36 Exception 2 business. Curiously, the NEC Handbook is silent on this. I found this thread- http://forums.mikeholt.com/showthread.php?t=136874 take a look at this as it is the same subject and backs my position, particularly post #8. This whole issue has been muddied up over the years with the prohibition of the old 6 main split bus panels and then the removal of the distinction between lighting and power panelboards, and then the change of the 42 circuit rule.
One thing is for sure in my mind- they did not mean to imply that you could use 2 breakers with 2 feeders connected to a 1 bus.
I will say that the wording leaves a lot to be desired.