IC rating of breaker lower than Available SC of service transformer.

[francis.key19]

Hello,

Just ran into this and want to get the forum opinion. We have a 2500KVA service transformer feeding 3 indivisual circuit breakers (ie. no main). The transformer secondary is 480VAC phase to phase and is wired directly to each of the 3 breakers via single conductors (lots of them). One of the breaker has an IC rating of 30KA while other two are 65KA. The 30KA rated breaker was made by a company call Federal Pioneer (this plant is quite old). I am not sure the SCA at the secondary is more than 30KA but more than likely. Has anyone heard of this company.

This is an issue and I am concern because of the IC rating. I was told the plant was "grandfather" due to its age and we don't need to worry about this. Something is amiss.

Please give your opinion.

Thanks.

FK19

 

[ron]

I was just meeting with Pioneer. They have changed their name and consolidated with other companies.

http://www.pioneerpowersolutions.com/index.php/pioneer-transformers

The interrupting rating listed on the breaker is what it is. The company will not tell you any different.

You need to get the available fault current from the utility and calculate the reduction in the feeder lengths from where the utility tells you the value to the installed location for the 30kAIC rated equipment.

 

[jim dungar]

I am not sure the SCA at the secondary is more than 30KA but more than likely.

This should be your first step.
I agree it is likely to be more than 30kA.

The next item is the breaker, it should be replaced. Grandfathering known violations is not defensible under OSHA and NFPA70E (article 210.5 requires devices be able to handle the fault current).

 

[ron]

This should be your first step.
I agree it is likely to be more than 30kA.

I was hoping the breaker was a relatively small ampacity compared to the overall transformer capacity and the small feeder conductors would impose a good amount of impedance.

 

[jim dungar]

I was hoping the breaker was a relatively small ampacity compared to the overall transformer capacity and the small feeder conductors would impose a good amount of impedance.

It would be nice if this was so.

Although, if it is a small breaker, replacing it due to age and probable lack of maintenance might not be a waste of money.

 

[zog]

Hello,

Just ran into this and want to get the forum opinion. We have a 2500KVA service transformer feeding 3 indivisual circuit breakers (ie. no main). The transformer secondary is 480VAC phase to phase and is wired directly to each of the 3 breakers via single conductors (lots of them). One of the breaker has an IC rating of 30KA while other two are 65KA. The 30KA rated breaker was made by a company call Federal Pioneer (this plant is quite old). I am not sure the SCA at the secondary is more than 30KA but more than likely. Has anyone heard of this company.

This is an issue and I am concern because of the IC rating. I was told the plant was "grandfather" due to its age and we don't need to worry about this. Something is amiss.

Please give your opinion.

Thanks.

FK19

I think I can help you, what is the info off the nameplate of the breakers? Something like 65-H3?

 

[kingpb]

What is the impedance of transformer, ampacity rating of the 30kA breaker, and what are the size and length of the conductors?

Assuming infinite bus you can check to see what the worst case at the breaker would be, then you know if you have to investigate further.

 

[francis.key19]

I think I can help you, what is the info off the nameplate of the breakers? Something like 65-H3?

Hi,

Breaker is a 1000A rated breaker , FPE is the manufacturer model NM631000.

Thank you.

FK

 

[francis.key19]

What is the impedance of transformer, ampacity rating of the 30kA breaker, and what are the size and length of the conductors?

Assuming infinite bus you can check to see what the worst case at the breaker would be, then you know if you have to investigate further.

Transformer impedance is 5.92%, 12470 Primary/480 Secondary, length of conductor is approximately 70', 2 conductors per phase, 500mcm.

Thank you.

FK

 

[JDBrown]

Using the numbers you gave, I calculate* about 50.8 kA AFC at the secondary of the transformer and about 37.9 kA AFC at the breaker. Conclusion: the breaker needs to be replaced with one that has a higher AIC rating.

I have a follow-up question, though: How do you get away with feeding a 1000A breaker with 2 sets of 500 MCM? Even if we assume copper conductors and 75 degree insulation, that only gives you an ampacity of 760A. Am I missing something here?

*My calculations assume a 6:1 X/R ratio for the transformer, copper conductors with RHH insulation in steel conduit, and 0.85 power factor.

 

[francis.key19]

Using the numbers you gave, I calculate* about 50.8 kA AFC at the secondary of the transformer and about 37.9 kA AFC at the breaker. Conclusion: the breaker needs to be replaced with one that has a higher AIC rating.

I have a follow-up question, though: How do you get away with feeding a 1000A breaker with 2 sets of 500 MCM? Even if we assume copper conductors and 75 degree insulation, that only gives you an ampacity of 760A. Am I missing something here?

*My calculations assume a 6:1 X/R ratio for the transformer, copper conductors with RHH insulation in steel conduit, and 0.85 power factor.

Hello,

I am not sure how this happened. I am new to this plant and just start to see some of these issues. Thank you for pointing that out for that is next on my list to check (cables, ocpd...grounding).
I found a breaker today where the load side is wired to the top of the breaker and line side to the bottom. Breaker is 600A. I am going to rewire this breaker instead of putting warning label on like some has suggested.

Regards,

FK

 

[jim dungar]

I found a breaker today where the load side is wired to the top of the breaker and line side to the bottom. Breaker is 600A. I am going to rewire this breaker instead of putting warning label on like some has suggested.

There is no code violation if a breaker is wired line side on the bottom, unless there are actual labels on the breaker saying Line and Load.

It is actually quite common to find installations with Line on the bottom.

Disconnect/Safety switches are the only devices that carries the general requirement for Line on top (actually it is line on the blades).

Read the marking on the device, if the terminals are not marked, do not make any assumptions about line and load.

 

[GoldDigger]

The only thing the code cares about explicitly for a breaker is that the off position of the handle must not be the up position.

Tapatalk!

 

[kingpb]

It looks like this is a 1000A frame and you use plugs for the ampacity you want. Probably has a 800A plug, I hope. If not, you have a cable issue.

Since the infinite bus method indicates about 38kA at the breaker, you will need to find out what the actual available short circuit current is on the HV side of the transformer. Then by calculation you can determine if the breaker is OK or not.

 

[zog]

Hi,

Breaker is a 1000A rated breaker , FPE is the manufacturer model NM631000.

Thank you.

FK

NM's only were made up to 800A. Sure it isn't NN631000?

Edit: That ^ was for Federal Pacific NM's. The Federal Pioneer version did go up to 1000A, which is weird (Maybe those are Canadian amps )

You can replace the Federal Pioneer with a Horizon CMH361000, which has a AIC rating of 65kA at 480VAC.