NEC 110.16B(3) Label

[Tainted]

Suppose I have a 2500A fuse (see TCC curve below). The 3-phase fault current is 125,000 amps.

The TCC curve cuts off at about 40,000 amp. What clearing time must I put to comply with NEC 110.16B(3) if I can't see beyond 40,000 amps on that chart?

 

[jim dungar]

You would typically use .01 sec, unless you can get specific information from the manufacturer.
You cannot extrapolate any performance beyond what is shown on the TCC.

 

[Tainted]

You would typically use .01 sec, unless you can get specific information from the manufacturer.
You cannot extrapolate any performance beyond what is shown on the TCC.

But isn't that not worst case scenario? Where does it say you're allowed to use .01 seconds if the chart just cuts off at that time?

 

[ron]

But isn't that not worst case scenario? Where does it say you're allowed to use .01 seconds if the chart just cuts off at that time?

It is the worst case scenario. But you don't know what you don't know. The TCC stops at 0.01 seconds, so it will clear at 0.01 or faster.

 

[Tainted]

It is the worst case scenario. But you don't know what you don't know. The TCC stops at 0.01 seconds, so it will clear at 0.01 or faster.

Got it, so in my example my label on the service disconnect will be:

Nominal system voltage: 208V 3-phase
Available fault current: 125,000 amps
Clearing time: 0.01 sec
Date: 3/14/2025

Is this correct?

 

[ron]

Got it, so in my example my label on the service disconnect will be:

Nominal system voltage: 208V 3-phase
Available fault current: 125,000 amps
Clearing time: 0.01 sec
Date: 3/14/2025

Is this correct?

Seems correct to me based on the 2020 NEC. The language is different in the 2023 NEC.
This is from the 2020 Handbook

 

[Tainted]

Seems correct to me based on the 2020 NEC. The language is different in the 2023 NEC

NYC came out with a 2025 electrical code based on 2020 version so I'm trying to get familiar with the 2020 version. NYC is now requiring arc flash studies since they jumped to the 2020 version of the code.

 

[Tainted]

Seems correct to me based on the 2020 NEC. The language is different in the 2023 NEC.
This is from the 2020 Handbook
View attachment 2576152

I have another question.

Let's say I have a 3 section switchboard:

Section 1: CT (with incoming service conductors)
Section 2: 1200A+ Service switch
Section 3: Distribution

Where do I place the label? Do I place it on sections 1 and 2 since it's the service side? Or do I just place it only on section 2?

 

[jim dungar]

Where do I place the label? Do I place it on sections 1 and 2 since it's the service side? Or do I just place it only on section 2?

I always placed my label near the customer's nameplate, if they had one, otherwise it went near the manufacturer's nameplate. It was not uncommon to have multiple copies of the same lable on one long piece of equipment.