Three Related Questions: #1

[RUWired]

Would it, perhaps, be more accurate to say that overcurrent protection is required, and that it can consist of up to six breakers (i.e., you don't need a single main breaker)? The design I am reviewing has four breakers connected to the bus bars, and all of it (including the transformer) is enclosed within this outdoor substation.

Yes it would be more accurate to say that. I was thinking the "secondary conductors" would not be protected because 240.21 doesn't mention multiple devices even though the "transformer secondary" would be protected with the up to 6 breakers.

 

[Smart $]

Would it, perhaps, be more accurate to say that overcurrent protection is required, and that it can consist of up to six breakers (i.e., you don't need a single main breaker)? The design I am reviewing has four breakers connected to the bus bars, and all of it (including the transformer) is enclosed within this outdoor substation.

1) How long are the wire conductors?

2) Is the bussing part of an assembly which houses the breakers?

 

[david luchini]

Yes it would be more accurate to say that. I was thinking the "secondary conductors" would not be protected because 240.21 doesn't mention multiple devices even though the "transformer secondary" would be protected with the up to 6 breakers.

I agree with Rick that you would need to terminate on a single breaker in this application.

Looking at 240.21(C), only part (3) for Industrial Installation specifically mentions multiple secondary devices. Part (4) - Outside secondary conductors, and Parts (6) - Conductors not over 25 feet long, both specifically mention terminating on a single OCPD.

Part (2) seems to imply multiple OCPDs (together with T450.3(B) Note 2,) but an I think an individual set of secondary conductors would need to be run from the secondary to each OCPD.

Only Part (3) seems to allow a single set of conductors to multiple devices, but as you have stated that it is not an industrial installation, Part (3) wouldn't apply.

 

[Smart $]

...

Part (2) seems to imply multiple OCPDs (together with T450.3(B) Note 2,) but an I think an individual set of secondary conductors would need to be run from the secondary to each OCPD.

...

Given primary over 600V, have to use T450.3(A)... but note 2 thereafter is pretty much the same.

I too believe the installation has to qualify under 240.21(C)(2) as described... and thus my earlier questions.

 

[RUWired]

Smart$ and David, your both saying note 2 to table 450.3A and 3B can only apply to 240.21(C)3?

 

[david luchini]

Given primary over 600V, have to use T450.3(A)... but note 2 thereafter is pretty much the same.

Yes, you are correct. I forgot we were dealing with a primary over 600V. But as you point out, the note 2 is pretty much the same for both Table A and Table B.

 

[david luchini]

Smart$ and David, your both saying note 2 to table 450.3A and 3B can only apply to 240.21(C)3?

I'm saying Note 2 of the Tables could apply to either 240.21(C)(2) or (C)(3), but not to (C)(4) or (C)(6).

Both (4) and (6) say the secondary conductors shall terminate at a single OCPD.

(3) specifically mentions multiple OCPDs.

(2) doesn't specifically mention a single OCPD or multiple OCPDs, so I would interpret that as allowing the multiple OCDPs mentioned in Note 2 of the Tables 450.3.

 

[Smart $]

Smart$ and David, your both saying note 2 to table 450.3A and 3B can only apply to 240.21(C)3?

I'm not.

 

[RUWired]

I'm saying Note 2 of the Tables could apply to either 240.21(C)(2) or (C)(3), but not to (C)(4) or (C)(6).

Both (4) and (6) say the secondary conductors shall terminate at a single OCPD.

(3) specifically mentions multiple OCPDs.

(2) doesn't specifically mention a single OCPD or multiple OCPDs, so I would interpret that as allowing the multiple OCDPs mentioned in Note 2 of the Tables 450.3.

I would take the word "device" as singular. Thereby ruling out (2)

b. Not less than the rating of the device supplied by the secondary conductors or not less than the rating of the overcurrent-protective device at the termination of the secondary conductors

 

[Smart $]

I'm saying Note 2 of the Tables could apply to either 240.21(C)(2) or (C)(3), but not to (C)(4) or (C)(6).

Both (4) and (6) say the secondary conductors shall terminate at a single OCPD.

...

Can apply to (C)(4) and (C)(6) also... as long as one set of secondary conductors is run to each OCPD.

 

[RUWired]

I'm not.

I don't see where you can have multiple OCPD's on the secondary of the transformer and still follow the rules in 240.21(C) without only applying (C)3.


Ok i see if multiple conductors are run. But the OP doesn't have this .

 

[david luchini]

I would take the word "device" as singular. Thereby ruling out (2)

b. Not less than the rating of the device supplied by the secondary conductors or not less than the rating of the overcurrent-protective device at the termination of the secondary conductors

Yes, but read that together with 240.21(C), which says "a set of conductors feeding a single load, or each set of conductors feeding separate loads..."

Applying (C)(2), each set of conductors feeding separate loads shall have an ampacity not less than the rating of the OCPD at the termination.

Ok i see if multiple conductors are run. But the OP doesn't have this .

That's why I agree, the application in the OP requires termination at a single OCPD.

 

[Smart $]

I would take the word "device" as singular. Thereby ruling out (2)

b. Not less than the rating of the device supplied by the secondary conductors or not less than the rating of the overcurrent-protective device at the termination of the secondary conductors

Why does it say the "device supplied" then "or" followed by a clause referring to an OCPD. Is this not saying the "device" is not an OCPD?

Then look at (C)(2)(2)... it lists switchboard, panelboard, disconnecting means, and control devices. Of those four items, only the last could actually be a device while none of the former three are an OCPD.

 

[RUWired]

Yes, but read that together with 240.21(C), which says "a set of conductors feeding a single load, or each set of conductors feeding separate loads..."

Applying (C)(2), each set of conductors feeding separate loads shall have an ampacity not less than the rating of the OCPD at the termination.

Yes i see, Smart$ gave that one away and it would make sense.

 

[RUWired]

Why does it say the "device supplied" then "or" followed by a clause referring to an OCPD. Is this not saying the "device" is not an OCPD?

Then look at (C)(2)(2)... it lists switchboard, panelboard, disconnecting means, and control devices. Of those four items, only the last could actually be a device while none of the former three are an OCPD.

I thinking with my reply, the OP only has one set of conductors. With multiple conductors, it would make sense that multiple devices would be allowed.

 

[Smart $]

I don't see where you can have multiple OCPD's on the secondary of the transformer and still follow the rules in 240.21(C) without only applying (C)3.


Ok i see if multiple conductors are run. But the OP doesn't have this .

It says a single load. A panelboard with many branch circuits is still a single load... because the panelboard is the load. This is similar to a machine that has one set of supply conductors to its control panel. Yet the machine has several branch circuits out to the machine, but is still a single load from the perspective of the supply conductors.

 

[david luchini]

Why does it say the "device supplied" then "or" followed by a clause referring to an OCPD. Is this not saying the "device" is not an OCPD?

Then look at (C)(2)(2)... it lists switchboard, panelboard, disconnecting means, and control devices. Of those four items, only the last could actually be a device while none of the former three are an OCPD.

This is a great point. I seem to remember a discussion a while back about what "devices" the first part of 240.21(C)(2) was referring to. Why doesn't the code just leave out the part about "over-current protective device at the termination" as "device supplied by" would seem to cover it. I'm not sure what distinction the code is trying to make.

 

[RUWired]

It says a single load. A panelboard with many branch circuits is still a single load... because the panelboard is the load. .

If this is so, then a service panel without a main could have more than 6 OCPD's because the load is the bus bars in the enclosure.

 

[Smart $]

If this is so, then a service panel without a main could have more than 6 OCPD's because the load is the bus bars in the enclosure.

The bus bars are not the load, the entire panel assembly is the load.

Additional thought: 240.21(C) general statement says a set of conductors feeding a single load, or each set of conductors of conductors feeding separate loads. If a or each set feeds separate loads, you could not feed any multiple loads (the ones that actually utilize power) with any set of secondary conductors.

 

[RUWired]

The bus bars are not the load, the entire panel assembly is the load.
.

So in 240.21(C)2(1)(B) you would call the enclosure assembly "the device". (as a single load)