I mentioned this issue at a conference recently and was told it’s none of my business because the manufacturer of the building is certified through the state and everything has already been inspected at factory. I whole heartedly disagree.
Available fault current is determined by the transformer provided by the specific electrical utility serving the area where they want to erect these buildings so it varies pretty widely. They also have no way of controlling the size transformer they get because it’s ultimately up to the utility and dependent on what they have available. Since it’s a site specific variable and these modules may have already been manufactured and shipped, I think it’s the AHJ’s responsibility to verify compliance per 110.9, 110.10, 110.24, 408.6, etc. (2020 NEC).
Do you guys have any experience with this? Thoughts?
Here’s an interesting example: 4 story building, 1st floor is constructed normally, 2-4 are modular. Main panel on the first floor separately supplies MLO panels on the modular floors. Each of those upstairs panels supply an adjacent panel via feed through lugs.
EOR did the fault study and it turns out the AFC exceeds the Short Circuit Current Rating of the panels and the branch breaker AICs (10 kAIC) that were installed at factory.
The EOR put a note on the plans that the contractor is responsible for coming up with a series tested combination via the breakers in the main panel. That’s a no from me - the EOR is responsible for providing those design parameters during plan review before the permit issues. Series rating may not even be possible.
It is my understanding that, depending on the manufacturer (and in this case, depending also on the equipment and devices already installed upstairs), a series tested combination that protects breakers in a remote panel may not be available. If it is, I think it still needs to meet manufacturer distance limitations; pretty sure if the equipment meant to be series protected is too far or too close, the series combo won’t work anyway.
Thoughts? Lend me your brain matter.
Available fault current is determined by the transformer provided by the specific electrical utility serving the area where they want to erect these buildings so it varies pretty widely. They also have no way of controlling the size transformer they get because it’s ultimately up to the utility and dependent on what they have available. Since it’s a site specific variable and these modules may have already been manufactured and shipped, I think it’s the AHJ’s responsibility to verify compliance per 110.9, 110.10, 110.24, 408.6, etc. (2020 NEC).
Do you guys have any experience with this? Thoughts?
Here’s an interesting example: 4 story building, 1st floor is constructed normally, 2-4 are modular. Main panel on the first floor separately supplies MLO panels on the modular floors. Each of those upstairs panels supply an adjacent panel via feed through lugs.
EOR did the fault study and it turns out the AFC exceeds the Short Circuit Current Rating of the panels and the branch breaker AICs (10 kAIC) that were installed at factory.
The EOR put a note on the plans that the contractor is responsible for coming up with a series tested combination via the breakers in the main panel. That’s a no from me - the EOR is responsible for providing those design parameters during plan review before the permit issues. Series rating may not even be possible.
It is my understanding that, depending on the manufacturer (and in this case, depending also on the equipment and devices already installed upstairs), a series tested combination that protects breakers in a remote panel may not be available. If it is, I think it still needs to meet manufacturer distance limitations; pretty sure if the equipment meant to be series protected is too far or too close, the series combo won’t work anyway.
Thoughts? Lend me your brain matter.
Last edited:
