Panel and breaker compatibility

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mikoal

Member
During an on site inspection how do you know what and/or if arc flash breakers are compatible with the panel?

I have not been on site yet, but I would like to know what to look for and determine it on site. IE: Do I look for size? slots?........

I would think that once I have the serial number of the panel, I can verfiy on catalogues. But i am also concerned with whether the manufacturer still has information on older panels.

Finally same question but for breakers. What "type" of breakers are there?
How do you know which is for which panel? Or what breakers are used in what situation. I'm not asking about GFCI vs regular. More like
THERMAL MAGNETIC BREAKERS
MAGNETIC BREAKERS
CURRENT LIMITING AND SERIES RATED THERMAL MAGNETIC BREAKERS
SOLID STATE TRIP BREAKERS

I dont understand when you will use one over the other, and what are the major differences in them?

Thanks!
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
During an on site inspection how do you know what and/or if arc flash breakers are compatible with the panel?
No such thing as an arc flash breaker. Did you perhaps mean Arc Fault Circuit Interrupter? If so, as a general rule you cannot use the breakers of one mfr in the boxes of another, unless the mfr has paid a healthy sum to UL for them to be tested for that. In some cases with the older "interchangeable" residential products whis was done because of the volume. But with the advent of the AFCI requirements I don't know if they apply any longer. You would have to ask very specifically and ask for documentation proving it, don't go by what a salesman tells you.

I have not been on site yet, but I would like to know what to look for and determine it on site. IE: Do I look for size? slots?........

I would think that once I have the serial number of the panel, I can verfiy on catalogues. But i am also concerned with whether the manufacturer still has information on older panels.
Most do, and most have not changed their panel designs in a long time so new breakers will be allowed in old panels. That is of course assuming the mfr still exists, many no longer do and when they get bought out by larger competitors, often they do not grandfather in older boxes. Again, you need to ask once you have the info, no way to know in advance.

Finally same question but for breakers. What "type" of breakers are there?
How do you know which is for which panel? Or what breakers are used in what situation. I'm not asking about GFCI vs regular. More like
THERMAL MAGNETIC BREAKERS
This is what you might consider "standard" breakers. Thermal is for long term overload, magnetic is for instantaneous short circuits.
MAGNETIC BREAKERS
These are application specific, in general you cannot use them in the field other than for exact replacement. Generally they are used in combination motor starters but the rules for them state they can ONLY be used in factory assembled and LISTED assemblies.
CURRENT LIMITING AND SERIES RATED THERMAL MAGNETIC BREAKERS
SOLID STATE TRIP BREAKERS
Two separate issues:
Current Limiting are breakers designed for high interrupting capabilites AND their ability to limit the fault current that is seen by devices down stream of them. Very specific engineered systems will call for this, not the average thing you see, and in general never on residential installations. Series Ratied breakers just means breakers of a SPECIFIC manufacturer can be used in combinations where the down-stream breaker can have a lower AIC than the up-stream one, but again, very specifically engineered and almost never seen in residential applications.

I dont understand when you will use one over the other, and what are the major differences in them?
I think it's wise to not jump into this without knowing, so if you come across something unusual in a commercial or industrial situation, you should seek out someone more experienced until you learn it.
 

mikoal

Member
No such thing as an arc flash breaker. Did you perhaps mean Arc Fault Circuit Interrupter? If so, as a general rule you cannot use the breakers of one mfr in the boxes of another, unless the mfr has paid a healthy sum to UL for them to be tested for that. In some cases with the older "interchangeable" residential products whis was done because of the volume. But with the advent of the AFCI requirements I don't know if they apply any longer. You would have to ask very specifically and ask for documentation proving it, don't go by what a salesman tells you.


Thanks for the reply Jraef, yea i meant arc fault breaker. Aside from the interchangeable product, is that the main rule of thumb? Base it on the manufacturer of the panel and get the same manafacturer for the AFCI?

The panels are Square D panels, so would square D AFCI work? Is there a lot of model/variation of an AFCI?

Most do, and most have not changed their panel designs in a long time so new breakers will be allowed in old panels. That is of course assuming the mfr still exists, many no longer do and when they get bought out by larger competitors, often they do not grandfather in older boxes. Again, you need to ask once you have the info, no way to know in advance.

So then there is no real way in telling by observation unless i've memorzied or am familiar with the catalogue and what that company offers?
So what information should I gather when on site? Just the panel serial?

This is what you might consider "standard" breakers. Thermal is for long term overload, magnetic is for instantaneous short circuits.
These are application specific, in general you cannot use them in the field other than for exact replacement. Generally they are used in combination motor starters but the rules for them state they can ONLY be used in factory assembled and LISTED assemblies.
Two separate issues:
Current Limiting are breakers designed for high interrupting capabilites AND their ability to limit the fault current that is seen by devices down stream of them. Very specific engineered systems will call for this, not the average thing you see, and in general never on residential installations. Series Ratied breakers just means breakers of a SPECIFIC manufacturer can be used in combinations where the down-stream breaker can have a lower AIC than the up-stream one, but again, very specifically engineered and almost never seen in residential applications.

I think it's wise to not jump into this without knowing, so if you come across something unusual in a commercial or industrial situation, you should seek out someone more experienced until you learn it.

Thanks! This was great. Just one more thing. AIC's. I know there are methods in calculating AICs, but is there an easy way or a general rule of thumb for AICs for panel, bus? and breakers? IE: 100A = 22kA etc.
 

zog

Senior Member
Location
Charlotte, NC
Just one more thing. AIC's. I know there are methods in calculating AICs, but is there an easy way or a general rule of thumb for AICs for panel, bus? and breakers? IE: 100A = 22kA etc.

You don't calulate AIC, AIC is a rating of an OCPD that has to be greater than the calculated availabel fault current, which depends on the system it is being applied to. There is no general rule of thumb.
 

mikoal

Member
You don't calulate AIC, AIC is a rating of an OCPD that has to be greater than the calculated availabel fault current, which depends on the system it is being applied to. There is no general rule of thumb.

what is a simple way or what is the way to determine fault currents?
 

skeshesh

Senior Member
Location
Los Angeles, Ca
Google infinite bus method and take a look. This is a simple approach that I know electricians and contractors like to use. It's a bit crude for detailed studies but if you just want to know the worst case down from a supplying transformer it can give you a quick worst case answer. A word of caution though: short circuit and in general power system studies for large and complicated systems are not simple and should be done with a qualified person, meaning they have to have the proper education and practical knowledge through experience.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Series Ratied breakers just means breakers of a SPECIFIC manufacturer can be used in combinations where the down-stream breaker can have a lower AIC than the up-stream one, but again, very specifically engineered and almost never seen in residential applications.
Actually series are probably seen more often in residential applications than they are in commercial ones. A series rating of '22/10' (Panel rated for 22KA using 10KAIC branch breakers) has been the defacto standard for main breaker loadcenters for more than 20yrs.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Actually series are probably seen more often in residential applications than they are in commercial ones. A series rating of '22/10' (Panel rated for 22KA using 10KAIC branch breakers) has been the defacto standard for main breaker loadcenters for more than 20yrs.
Hmmm, yes I forgot about that.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
what is a simple way or what is the way to determine fault currents?
Simplest way? Call the utility, they will have that available. It gets trickier when you have one large incoming service and you need to calculate it for a down stream panel off of an internal transformer.
 

mikoal

Member
Simplest way? Call the utility, they will have that available. It gets trickier when you have one large incoming service and you need to calculate it for a down stream panel off of an internal transformer.

but like jim dungar was saying typically residential installations has 22/10 as standard.
What other standards are there?
How did they come to these numbers?.
 

skeshesh

Senior Member
Location
Los Angeles, Ca
but like jim dungar was saying typically residential installations has 22/10 as standard.
What other standards are there?
How did they come to these numbers?.

The 10 and 22 that you're referring too is the AIC rating of the equipment and you choose them rating when you have the available fault current so the fault current does not exceed the equipment rating. I'm not sure how the numbers were chosen but I bet it has something to do with what's economical to manufacture.
Available fault current or short circuit current is calculated based on the impedance of your system. When the system is question is the utility side, the Poco has records, measurements and software to determine the available fault current. The same thing is done at a smaller scale on the customer side by the engineer who uses the value of the fault of the service and the impedance of the load side of the system to calculate the available fault downstream at the location of interest. The reason why residentials typically have a lower AIC rating is not because of a standard but since they are at the furthest load end from the utility distribution they end up with lower available fault currents and therefore require equipment with lower ratings.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
The 10 and 22 that you're referring too is the AIC rating of the equipment and you choose them rating when you have the available fault current so the fault current does not exceed the equipment rating. I'm not sure how the numbers were chosen but I bet it has something to do with what's economical to manufacture.
Available fault current or short circuit current is calculated based on the impedance of your system. When the system is question is the utility side, the Poco has records, measurements and software to determine the available fault current. The same thing is done at a smaller scale on the customer side by the engineer who uses the value of the fault of the service and the impedance of the load side of the system to calculate the available fault downstream at the location of interest. The reason why residentials typically have a lower AIC rating is not because of a standard but since they are at the furthest load end from the utility distribution they end up with lower available fault currents and therefore require equipment with lower ratings.

And the transformers that feed residential drops are small, usually only 1 or maybe 2 SFR drops per transformer. Not much fault current left by the time it gets to the Main device in the residence. For the most part, utilities will select the service drop components so that the AFC is 10kA or below on services that are under 400A, which covers 99% of residential users. 400A and up, it's virtually impossible to get that low, which becomes an issue on multiple dwellings sometimes. But even then, 22kA is usually enough.

But commercial and industrial? Whole different ball game.
 

skeshesh

Senior Member
Location
Los Angeles, Ca
And the transformers that feed residential drops are small, usually only 1 or maybe 2 SFR drops per transformer. Not much fault current left by the time it gets to the Main device in the residence. For the most part, utilities will select the service drop components so that the AFC is 10kA or below on services that are under 400A, which covers 99% of residential users. 400A and up, it's virtually impossible to get that low, which becomes an issue on multiple dwellings sometimes. But even then, 22kA is usually enough.

But commercial and industrial? Whole different ball game.

Absolutely. To be honest I have very little experience on the residential side but figured the theory is sound. Also while we're on the subject I never could get a straight answer on the "ultimate short circuit current" that was brought up in some posts. The last reference is an older post but the OP is talking about an extremely high available current noted as "ultimate" by the Poco:

http://forums.mikeholt.com/showthre...at-primary-utility-xfmr?p=1315650#post1315650

http://forums.mikeholt.com/showthre...hort-circuit-ratings?highlight=ultimate+fault

http://forums.mikeholt.com/archive/index.php/t-93441.html
 
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