230.90(A) Exception 3 debate

Status
Not open for further replies.
A

abmorse1

Member
Location
Tulsa, OK
A co-worker and I (both PEs) are debating 230.90(A) E3.

His contention is that it strictly pertains to the service conductors, and not the panelboard or switchboard containing the breakers used as disconnecting means. In other words, a 600A MLO service rated panelboard with a calculated load of 460A can not have breakers totaling more than 600A, even if the service conductors are allowed to be sized as small as (2) runs of 4/0.

We've also referred to 408.36 Exception 1, but his interpretation is that the exception removes the requirement for individual protection, i.e. an MCB, but does not remove the requirement for overcurrent protection, and that having multiple overcurrent devices that total more than the panelboard rating is a violation.

I contend that he's wrong, but can't find documentation that explicitly states that. We do a lot of light commercial and restaurant design, where this is common practice.

Thoughts?

PS - I've just joined the forum, but I have been referring to it for years whenever a code interpretation issue comes up. Thank you all for the great resource you've created here.
 
In my opinion the bus bars in the MLO are service conductors.

From article 100

Service Conductors. The conductors from the service point
to the service disconnecting means.
Click to expand...


Welcome to the forum.
 
abmorse1 said:
A co-worker and I (both PEs) are debating 230.90(A) E3.

His contention is that it strictly pertains to the service conductors, and not the panelboard or switchboard containing the breakers used as disconnecting means. In other words, a 600A MLO service rated panelboard with a calculated load of 460A can not have breakers totaling more than 600A, even if the service conductors are allowed to be sized as small as (2) runs of 4/0.

We've also referred to 408.36 Exception 1, but his interpretation is that the exception removes the requirement for individual protection, i.e. an MCB, but does not remove the requirement for overcurrent protection, and that having multiple overcurrent devices that total more than the panelboard rating is a violation.

I contend that he's wrong, but can't find documentation that explicitly states that. We do a lot of light commercial and restaurant design, where this is common practice.

Thoughts?

PS - I've just joined the forum, but I have been referring to it for years whenever a code interpretation issue comes up. Thank you all for the great resource you've created here.
Click to expand...

You will have to forgive me as I am wrapping my head around what your debate is. The charge of 230.90 is to provide overload protection. The general rule is as follows:

"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."

In regards to the exception # 3, it is permitting the following:


"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."


So forgive me if I am kinda lost in your question. Assuming your install meets the requirements of section 230.70(A)(1), the language in itself in the exception says that the sum (total) of ratings of the circuit breakers (added together) is permitted to exceed the ampacity of the actual service conductors....as long as the actual calculated load does not exceed the actual ampacity of the service conductors.

I am not sure where the disconnect is.....pardon the pun.
 
Yes, the service conductor ampacities are allowed to be sized per the calculated load on the service, and the total of the ampacities of the breakers is allowed to exceed that. The question is whether the rating of the panelboard or switchboard in this particular case is allowed to be smaller than the total of the breakers.

In normal situations, the panel is protected by its breaker (either MCB or upstream), so the total of the breakers installed in the panel isn't an issue. But in the case of an MLO service panel, the breakers are the overcurrent protection for the panel (as well as the service conductors). He contends that even though the service conductors can have an ampacity smaller than the total of the breaker, the panel can't.

To go back to the example in the original post, consider a service a 600A MLO service panel with (3) 200A breakers and (2) 60A breakers. Even though the calculated load for the service is 460A, he contends that the 600A MLO panel either has to be upsized to an 800A MLO panel, or we have to specify a 600A MCB panel to ensure the panel itself is properly protected.

I hope that clears up my question. I'm posting from home, and don't have my notes or handbook.
Thanks!
 
abmorse1 said:
Yes, the service conductor ampacities are allowed to be sized per the calculated load on the service, and the total of the ampacities of the breakers is allowed to exceed that. The question is whether the rating of the panelboard or switchboard in this particular case is allowed to be smaller than the total of the breakers.

In normal situations, the panel is protected by its breaker (either MCB or upstream), so the total of the breakers installed in the panel isn't an issue. But in the case of an MLO service panel, the breakers are the overcurrent protection for the panel (as well as the service conductors). He contends that even though the service conductors can have an ampacity smaller than the total of the breaker, the panel can't.

To go back to the example in the original post, consider a service a 600A MLO service panel with (3) 200A breakers and (2) 60A breakers. Even though the calculated load for the service is 460A, he contends that the 600A MLO panel either has to be upsized to an 800A MLO panel, or we have to specify a 600A MCB panel to ensure the panel itself is properly protected.

I hope that clears up my question. I'm posting from home, and don't have my notes or handbook.
Thanks!
Click to expand...

Again, read the definition I posted, service conductors continue to the service disconnect.

In your case that is each of the breakers in the MLO panelboard so the bus bars in the MLO are service conductors and covered by 230.90.
 
Status
Not open for further replies.
Top