I am wondering if most electrical inspectors check for rejection clips when inspecting commercial electrical (fused) mains.

Yesterday I inspected an electrical service at a mall. The service consisted of a trough which feeds several meter sockets, and beneath each respective meter socket is a main for that particular unit.

The mains are fused at 200 amps (if memory serves me correctly). If you were there to inspect the electrical service, would you require rejection clips if you saw class R fuses installed in the main disconnects? Why or why not?

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I would reject it only if current limiting fuses were required. I would not penalize the contractor for installing a current limiting fuse when one was not needed. What is the available fault current at the disconnect? What is the AIC rating of the disconnect with out class R fuses installed?

We in Lake County also look for rejection pins. The code section 240.60 (b)Noninterchangeable requires:
"Fuseholders for current-limiting fuses shall not permit insertion of fuses that are not current-limiting".

As Eric pointed out if the fault current is below 10,000 SCA you would not require a current-limiting fuse in the first place, so why worry about rejection pins.

In my case the AIC was 10000 without class R, but the plans did specify the fuses. What I am noticing is that some inspectors and contractors don't even know what fault current is, and don't even think it's part of the code.

And Eric raises another important issue here. We know that the power company can provide us with fault current info but whose responsibility is it to provide the info?

A) The architect or engineer who drew the plans?

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B) The plans examiner. He should check for it on plan review and make sure it is noted?

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C) The inspector. He should call the power company and get the information himself?

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D) The contractor should get the info and verbally tell the inspector. Take him at his word?

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E) All of the above?

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It would be helpful to have a code requiring labelling of the available fault current. Heck, we make them label for arc flash, why not fault current?

Yes Nick it is a tough call when to ask the designer of the electrical plans to give you the calculated fault current at the service. When I review commercial plans, one of my standard correction comments is “Provide the calculated available fault current at the service disconnect(s)” There are several good ELECTRICAL engineers that provide it on all their plans. But they are few and far between. If the designer wants to give me the Power Co’s stated fault current at their transformer I will accept that. FPL is very good about providing that information. I make the contractor, owner or designer get that information. On small services where the transformer is a good distance away I do not sweat the issue. There are a few free AIC calculators out there on the web. I usually use Bussman’s calculator for verifying calculations.

Eric you hit the nail on the head.

In my particular case, the transformer sat 10 or 12 feet away from the service equipment. That was why I pressed the issue of fault current in that particular series of inspections.

Let all electrical plans examiners familiarize themselves with this comment for their comment sheets: (Thanks Eric!)

Provide the calculated available fault current at the service disconnect(s)!

If the job is exempt from engineering than even the electrical contractor could be the design professional on the job by state statute. Than it is his responsibility to provide that information.

The information should be provided at plan review for permitting. Having this information is needed, as the job can't be designed without it. This information affects all aspects of the job, the withstand rating (AIC) of the meter socket, service equipment NEC 110.9, panelboards circuit breakers, conductor withstand ratings, motor starters, disconnect switches, etc...etc... and the list goes on NEC 110.10.

Just getting the SCA at the service is just the first step 110.9(Part A). But 110.10 requires that all parts of the electrical system comply as well ( Part B through Z ) If you get my drift.
So it may be necessary to require a point to point fault current calculation.

Example: How can you comply with 620.62 selective coordination of overcurrent protection for elevators supplied by a common feeder? First off you need a point to point fault current calculation for each point from the service to each panelboard / switchboard and equipment. Than you need the to have the time current trip curve charts provided by the manufacturer of the equipment supplied on that job. Than you can review the overlays to verify breaker or fuse coordination for load current trip times, instantaneous trip times, and unlatching trip times.

Again (depending on the job) just getting the fault current at the service equipment may not be enough by code.

I agree with you Mike.

However, I was told again today that I am the only inspector in Florida and perhaps the entire United States of America, that even brings up the issue of fault current. In addition I was told that fault current is not part of the NEC.

So since I am the only one that cares about this, I was just trying to raise everyone's awareness of this issue. That was really the reason I started the post.

By the way, I think that Kevin Arnold with Cooper-Bussman does an excellent job explaining about fault current and selective coordination. He has always called me back whenever I had a question.

Well your not the only one...we in Lake county look for fault current at the plan review/permitting stage and permits are not issued without that information.

Sometimes depending on the job they will have to provide a point-to-point calculation. We also require selective coordination studies where needed. etc..etc.. Our plan review for fault current is very extensive.

Fault current is part of the NEC as there are at least 95 NEC code sections that deal with fault current in one form or another. In addition to the fact that all equipment is either AIC rated, panelboards are braced, and other components like meter sockets, motor starters, and conductors have withstand ratings. It is just the same as a voltage, or current rating.
1. Would you install a 208 volt panel on a 480 volt system? NO!
2. Would you install a 200 amp panel on a system where the load is calculated at 375 amps! NO!
3. So why than would one install a panel with a 10,000 AIC rating on a system capable of 19,285 SCA?

I'm glad to see there are others that look at this problem, as it is a Life Safety Issue.

So next time someone tells you that nobody looks for fault current you can tell them...Not True...
Lake County Does!

Keep up the great work Nick!

Hello guys. I agree with your statements. First, we should not penalize anyone for improving the level of protection by using current-limiting fuses. For the safety switches w/out rejection clips and installing rejection type fuses (Class R fuses), what happens when the Class R fuse operates and clears the fault? The contractor or maintenance (qualified person) who replaces it and restores power uses a One-Time fuse (Class H, 10kA AIC) in place of it because the rejection kit wasn't installed, then a violation has occurred. In my professional opinion, One-Time fuses shall not be used on service entrance equipment because of fault currents exceeding 10kA and future upgrades beyond our control (Transformer change outs). Easiest method is to enforce the higher AIC ratings and minimize any concern by doing so with the current-limiting fuses such as Class L, Class J, Class Rk-1 & Rk-5 and Class T. These will all have AT LEAST a 200kA AIC rating. Keep up the good work.