Breaker Types

[MBLES]

We have an exisiting 480v 3ph 400a panel with XFMR that feeds 2 120/208 subpanels A and B. The print is asking for a 100a for a new 100a 120/208 to be feed from B panel. When installing breaker and panel what are the requirements for new panel and breaker as far as AIC ratings of breaker and panel. The print doesnt detail any panel or breaker. The drawings only specifiy contractor is responsible verifying AIC ratings. The Siemens P1 panels for 480v is 42k and both 208 22k on print. We are going to stay with Same Siemens brand for Sub panel. Shoulf we keep same 22k aIC for sub panel and breaker? What required information is needed to determine new panel and breaker, We are planning to use same brand and breaker 22l aic. The 480v panel also has some AHU that require new breaker for equipment. Again whats required information needed to determine breaker.

AM i over thinking this and keep all equipment the same and match all AIC for all breakers present? I just want to make sure we are following all NEC
when it comes to OCD

 

[Smart $]

FWIW, I do not see verify and determine as one and the same responsibilities. Verify means another entity determines the proper rating and the EC doing the verification just confirms the equipment meets or exceeds that rating.

More specifically, the EC would only have to make a determination (or request such be made) if going to a lower aic rating than that of the equipment immediately ahead of the new.

 

[MBLES]

FWIW, I do not see verify and determine as one and the same responsibilities. Verify means another entity determines the proper rating and the EC doing the verification just confirms the equipment meets or exceeds that rating.

More specifically, the EC would only have to make a determination (or request such be made) if going to a lower aic rating than that of the equipment immediately ahead of the new.

I agree with you. but for sake of new equipment to panel . if possible to answer Lets say the equipment is 65k panel and a 480v 45kw 3phase piece of equipment was going to be feed.What would need to be looked for to make sure installion correct breaker AIC ? Thst the breaker isnt a 100k?
10,22,or ??. I just want to educate my self a little better. and thanks for replies

 

[augie47]

The "proper" way would likely involve engineering taking into account the utility SCA, motor contribution, etc...

On most of the installs I see, the new breakers are selected by matching the existing ones . I feel fortunate when I inspect a job where that effort has at least been taken.
Of course in doing so you are assuming the job was originally designed properly, no significant changes had taken place and, in the event series-rating were incorporated, the new breakers are of a size that also series rate.

On the 208 side you could probably get a good idea by getting the nameplate data (voltage, kva,impedance) transformer and looking up the available current.

 

[Smart $]

I agree with you. but for sake of new equipment to panel . if possible to answer Lets say the equipment is 65k panel and a 480v 45kw 3phase piece of equipment was going to be feed.What would need to be looked for to make sure installion correct breaker AIC ? Thst the breaker isnt a 100k?
10,22,or ??. I just want to educate my self a little better. and thanks for replies

Assuming line-side equipment has the appropriate AIC rating, where the load-side equipment AIC rating equals or exceeds that rating, no additional evaluation is required.

 

[electrofelon]

For starters, Why not just calculate the fault current from the transformer impedence assuming infinite primary and see what you get? The op didn't say the transformer size, but based on the information given and making some logical assumptions, I'll bet the fault current will be quite low, well under 10k.

 

[augie47]

For starters, Why not just calculate the fault current from the transformer impedence assuming infinite primary and see what you get? The op didn't say the transformer size, but based on the information given and making some logical assumptions, I'll bet the fault current will be quite low, well under 10k.

I was thinking that also but then I checked some of my transformer charts and taking into account he is feeding a 400 amp panel his 208 transformer may well have a SCA of 22k+

 

[Smart $]

I was thinking that also but then I checked some of my transformer charts and taking into account he is feeding a 400 amp panel his 208 transformer may well have a SCA of 22k+

This is an area which I didn't touch in my earlier posts, i.e. having to start over or otherwise compensate at SDS transformers.

 

[electrofelon]

I was thinking that also but then I checked some of my transformer charts and taking into account he is feeding a 400 amp panel his 208 transformer may well have a SCA of 22k+

Well the 400 amp is the existing 480 panel, but certainly we are just guessing at the transformer size. Hopefully the op will let us know the size and impedance.

Another idea is to series rate the two breakers, in which case the 208 breaker could likely have a low AIC. Although without calculations, one would be assuming the rating of the existing 480 breakers was evaluated properly.

 

[310 BLAZE IT]

We have an exisiting 480v 3ph 400a panel with XFMR that feeds 2 120/208 subpanels A and B. The print is asking for a 100a for a new 100a 120/208 to be feed from B panel. When installing breaker and panel what are the requirements for new panel and breaker as far as AIC ratings of breaker and panel. The print doesnt detail any panel or breaker. The drawings only specifiy contractor is responsible verifying AIC ratings. The Siemens P1 panels for 480v is 42k and both 208 22k on print. We are going to stay with Same Siemens brand for Sub panel. Shoulf we keep same 22k aIC for sub panel and breaker? What required information is needed to determine new panel and breaker, We are planning to use same brand and breaker 22l aic. The 480v panel also has some AHU that require new breaker for equipment. Again whats required information needed to determine breaker.

AM i over thinking this and keep all equipment the same and match all AIC for all breakers present? I just want to make sure we are following all NEC
when it comes to OCD

OP, Looks like you're just looking to calculate the AIC on the transformer secondary for yourself. Please provide the transformer kva and impedance and this can be done. HOWEVER if looking at the secondary AIC assuming infinite primary based on these values you will possibly get something higher than 22k. This does NOT mean the equipment is improperly rated, just that you do not have a way to verify without much more involved calculation (engineering study) and utility coordination. This can be good as a CYA calculation but as the drawings do say 'verify' you may want to go with 22kaic. The calculation can also be found on the Eaton bussman phone app which I reccomended.

Sent from my SM-N920V using Tapatalk

 

[augie47]

Well the 400 amp is the existing 480 panel, but certainly we are just guessing at the transformer size. Hopefully the op will let us know the size and impedance.

.

oppps ! Going by my old man memory,.. thanks