240.21(C)(2) & 450.3(B)

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charlie b

charlie b

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This is a existing installation, in proximity to the equipment I am working with, but not within my scope of work. A 480 to 120/208 transformer feeds an MLO panelboard less than 10 feet away. There are 5 breakers installed, but there is nothing to prevent installing more breakers. I was planning to notify the owner that this is a code violation. Now I am not so sure. I don't see anything in 240.21(C)(2) that requires a main breaker or that limits the protection of the secondary conductors to six breakers. I see the six breaker limit in 450.3(B) for protection of the secondary windings. So that would have to be the basis for a violation, if there is one. But I don't see a rule saying that the panel must not be capable of having more than 6 breakers installed, though I have heard of jurisdictions that enforce that interpretation.

Do I need to inform the owner of an issue, or can I let this sleeping dog lie?
 
Since you said panelboard what about 408.36?

408.36 Overcurrent Protection. In addition to the re-
quirement 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 de-
vice shall be located within or at any point on the supply
side of the panelboard.
Exception No. 1: Individual protection shall not be re-
quired 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.
Exception No. 2: Individual protection shall not be re-
quired for a panelboard protected on its supply side by two
main circuit breakers or two sets of fuses having a com-
bined 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 pur-
poses of determining the maximum of 42 overcurrent de-
vices, a 2-pole or a 3-pole circuit breaker shall be consid-
ered as two or three overcurrent devices, respectively.
Exception No. 3: For existing panelboards, individual
protection shall not be required for a panelboard used as
service equipment for an individual residential occupancy.
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Charlie this comes up alot and some inspectors shoot it down based on "What If" IMO, it is compliant and you can have a 42 circuit panel with 6 breakers and still be compliant. The person installing #7 would be responsible to add a main lug kit or change the panel out.
 
Dennis Alwon said:
Charlie this comes up alot and some inspectors shoot it down based on "What If" IMO, it is compliant and you can have a 42 circuit panel with 6 breakers and still be compliant. The person installing #7 would be responsible to add a main lug kit or change the panel out.
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Dennis, how does this circumvent 408.36?
 
infinity said:
Dennis, how does this circumvent 408.36?
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IMO, you do not have to have a main in the PB but you do have to have an OCPD protecting the PB bus somewhere. It can be the main of the PB, but is not required to be.

However, if you are not touching this in your scope of work, my inclination is to let sleeping dogs lie. There is no good reason to involve yourself in a pissing contest over someone else's work unless you are being paid to do so.
 
petersonra said:
IMO, you do not have to have a main in the PB but you do have to have an OCPD protecting the PB bus somewhere. It can be the main of the PB, but is not required to be.
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According to the OP this panelboard is fed from a transformer how can it not have a main or OCPD ahead of it on the secondary?
 
Dennis Alwon said:
I don't see it circumventing it. That article as I read it allows no main so I am confused by your question
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While 408.36 does not require a main, it requires that the panel be protected at or below its rating. There is no protection between the secondary terminals of the transformer and the main lugs of the panel.
 
don_resqcapt19 said:
While 408.36 does not require a main, it requires that the panel be protected at or below its rating. There is no protection between the secondary terminals of the transformer and the main lugs of the panel.
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That's what I was getting at, right from the first sentence of 408.36.
 
don_resqcapt19 said:
While 408.36 does not require a main, it requires that the panel be protected at or below its rating. There is no protection between the secondary terminals of the transformer and the main lugs of the panel.
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infinity said:
That's what I was getting at, right from the first sentence of 408.36.
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PB protection is not required to be on the secondary... but with a 208/120V secondary, the required secondary protection could double as PB protection because 240.21(C)(1).
 
Smart $ said:
Protection is not required to be on the secondary in some cases... but with a 208/120V secondary, it is because 240.21(C)(1).
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I'm referring to the OP where a panelboard is fed from the secondary of a transformer, that panelboard requires some form of OCP be it a main CB within the panelboard or some other upstream device.
 
infinity said:
I'm referring to the OP where a panelboard is fed from the secondary of a transformer, that panelboard requires some form of OCP be it a main CB within the panelboard or some other upstream device.
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Yes, I know... but 408.36(B) Exception permits the protection to be on the primary side... subject to 240.21(C)(1)... which is moot with a 208/120V wye secondary. The secondary protection is not required to serve as the PB protection... but the PB protection is required to be on the secondary side. :blink:
 
Smart $ said:
PB protection is not required to be on the secondary... but with a 208/120V secondary, the required secondary protection could double as PB protection because 240.21(C)(1).
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If fault currents on the secondary can distribute across multiple lines or phases of the primary and go undetected, secondary OCPD is required in addition to primary OCPD. Examples of this are any 3-phase 4 wire system, and any 3-phase WYE system on either or both sides. I think this even applies to single phase, 3-wire.

The case where the primary OCPD can protect the secondary circuit by proxy, in proportion to the voltage ratio, are where fault current is guaranteed to line up across winding pairs. In such a case, you don't need secondary OCPD, given primary OCPD. Examples are 3ph/3wire delta-delta, and 2-wire single phase.
 
Carultch said:
If fault currents on the secondary can distribute across multiple lines or phases of the primary and go undetected, secondary OCPD is required in addition to primary OCPD. Examples of this are any 3-phase 4 wire system, and any 3-phase WYE system on either or both sides. I think this even applies to single phase, 3-wire.

The case where the primary OCPD can protect the secondary circuit by proxy, in proportion to the voltage ratio, are where fault current is guaranteed to line up across winding pairs. In such a case, you don't need secondary OCPD, given primary OCPD. Examples are 3ph/3wire delta-delta, and 2-wire single phase.
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We thank you for elaborating. :D
 
Thanks for the comments. I was away yesterday attending a design review meeting on this very project. I brought the issue up, and the owner's representative did understand the concern. I will be writing an RFI to formally document the issue, and then I can back away. This will not need the services of an engineer to resolve.

As to the relationship to my scope of work, we are replacing the service switchgear and the feeders to all equipment directly fed from the existing service switchgear. So that means we will replace the primary feeders to five existing step down transformers, but the panels downstream of the transformers are outside my scope of work. They just happened to be in the same rooms as the transformers, and so I took photographs of the panels. It was during a review of the photos that I noticed the issue.

My take on the subject is that a panel with 6 or fewer breakers can satisfy the requirements, provided only that the sum of their trip ratings is at or below the ampere rating of the panel. I also believe that the ability for a future project to install additional breakers is not an issue at the present. But I have heard of jurisdictions that would require some method of preventing the future installation of a seventh breaker.
 
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