Overcurent devices allowed!
- Thread starter jim1982
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pierre
Senior Member
- Location
- Westchester County, New York
Re: Overcurent devices allowed!
Tony Montouri of NYC, who passed away a couple of years ago told me the story behind this requirement. Tony was and still is very respected in the NYC electrical community.
There was a fire in one of the big NYC hotels, and this fire started in a panel enclosure that had too many overcurrent devices in it, creating enough heat to start the fire. I believe as a result, this fire killed quite a few people. A proposal was put forth and now we have the Max 42 OCPD in an enclosure.
Tony Montouri of NYC, who passed away a couple of years ago told me the story behind this requirement. Tony was and still is very respected in the NYC electrical community.
There was a fire in one of the big NYC hotels, and this fire started in a panel enclosure that had too many overcurrent devices in it, creating enough heat to start the fire. I believe as a result, this fire killed quite a few people. A proposal was put forth and now we have the Max 42 OCPD in an enclosure.
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: Overcurent devices allowed!
They are built to only accept 42 breakers.If you manage to install more you have used unlisted breakers
They are built to only accept 42 breakers.If you manage to install more you have used unlisted breakers
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Overcurent devices allowed!
There are many panels built that will accept more than 42 breaker poles. These paneboards are intended to be installed as "power" panels not "lighting and appliance branch circuit" panels.
It is usually the installer's, and always the inspector's responsibilty to make sure equipment is installed within the requirements of all applicable codes.
There are many panels built that will accept more than 42 breaker poles. These paneboards are intended to be installed as "power" panels not "lighting and appliance branch circuit" panels.
It is usually the installer's, and always the inspector's responsibilty to make sure equipment is installed within the requirements of all applicable codes.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
Re: Overcurent devices allowed!
I suppose this is why load centers have a maximum number of poles listed in the instructions, as well as a maximum number of spaces, to accomodate the total amount of heat from all the poles.
Is this one of the reasons they made load centers so much larger a few years ago? for better heat dissipation? or was that a bending space issue?
What the heck is the difference between the two?
I suppose this is why load centers have a maximum number of poles listed in the instructions, as well as a maximum number of spaces, to accomodate the total amount of heat from all the poles.
Is this one of the reasons they made load centers so much larger a few years ago? for better heat dissipation? or was that a bending space issue?
B
bthielen
Guest
Re: Overcurent devices allowed!
It sounds to me more like a panel design issue than a misuse issue and therefore more like a bandaid for a problem, unless there is more to this decision by the NEC than I understand. Limiting the number of OCPD devices in the panel to a specified number fails to consider the ability of the panel to handle temperature rise. It would seem more prudent to calculate the rise based on the application.
As a designer we must constantly consider temperature rise when deciding on the size and type of enclosures to use. Just because space is available doesn't mean devices can be added. I just designed an enclosure for 5 servo drives. Unless I included an A/C unit, I would have had to use an enclosure large enough to fit about 20 drives in order to handle the dissipated heat.
My checkbook may have checks in it but that doesn't mean I have the money in the account to back them up. I wish I could get my wife to understand that!
Bob
It sounds to me more like a panel design issue than a misuse issue and therefore more like a bandaid for a problem, unless there is more to this decision by the NEC than I understand. Limiting the number of OCPD devices in the panel to a specified number fails to consider the ability of the panel to handle temperature rise. It would seem more prudent to calculate the rise based on the application.
As a designer we must constantly consider temperature rise when deciding on the size and type of enclosures to use. Just because space is available doesn't mean devices can be added. I just designed an enclosure for 5 servo drives. Unless I included an A/C unit, I would have had to use an enclosure large enough to fit about 20 drives in order to handle the dissipated heat.
My checkbook may have checks in it but that doesn't mean I have the money in the account to back them up. I wish I could get my wife to understand that!
Bob
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
Re: Overcurent devices allowed!
I had more in mind if I am looking at a panelboard how could I tell the difference. From 408.14 it appears there is no physical difference. the difference is how its used.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Overcurent devices allowed!
You are right: the same model of panel can be used for either application.
If there is no neutral bar (i.e., 3-phase loads only), then it is a ?Power Panelboard.? If there are no breakers with a rating of 30 amps or lower, then it is a ?Power Panelboard.? If a panel fails these two tests, then the odds are that it is a ?Lighting and Appliance Panelboard.? Specifically, if there are 5 breakers (really, 5 pole spaces, but the rule is 10% of the overcurrent devices) that use the neutral and that are 30 amps or under, then the panel is a ?Lighting and Appliance Panelboard.?
The limit of 42 overcurrent devices applies only to the ?Lighting and Appliance Panelboard.? When counting up to 42, a 2-pole breaker counts as 2 overcurrent devices, and a 3-pole breaker counts as 3 overcurrent devices.
You are right: the same model of panel can be used for either application.
If there is no neutral bar (i.e., 3-phase loads only), then it is a ?Power Panelboard.? If there are no breakers with a rating of 30 amps or lower, then it is a ?Power Panelboard.? If a panel fails these two tests, then the odds are that it is a ?Lighting and Appliance Panelboard.? Specifically, if there are 5 breakers (really, 5 pole spaces, but the rule is 10% of the overcurrent devices) that use the neutral and that are 30 amps or under, then the panel is a ?Lighting and Appliance Panelboard.?
The limit of 42 overcurrent devices applies only to the ?Lighting and Appliance Panelboard.? When counting up to 42, a 2-pole breaker counts as 2 overcurrent devices, and a 3-pole breaker counts as 3 overcurrent devices.
- Location
- Massachusetts
Re: Overcurent devices allowed!
Do you have any more info?
I believe Square D makes some larger panels for use in Canada as I do not think they have the '42 rule'.
Jim other than double or triple tub panels (essentially separate panels anyway) I have never seen a panel that would take more than 42 poles.
Do you have any more info?
I believe Square D makes some larger panels for use in Canada as I do not think they have the '42 rule'.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Overcurent devices allowed!
Bob,
The Square D NQOD54L225CU is a 54 circuit panel with neutral bar for sale in the US. It is helpful for applications which use QO breakers with accessories such as shunt trip and alarm contacts, both of which take an extra pole space.
They also offer an NF54L2 and of course their I-Line series has the HCN41832N which has room for 54 pole spaces.
Bob,
The Square D NQOD54L225CU is a 54 circuit panel with neutral bar for sale in the US. It is helpful for applications which use QO breakers with accessories such as shunt trip and alarm contacts, both of which take an extra pole space.
They also offer an NF54L2 and of course their I-Line series has the HCN41832N which has room for 54 pole spaces.
- Location
- Massachusetts
Re: Overcurent devices allowed!
The 54 circuit Sqaure D is the one I had heard of but I had been told that it did not have USA UL listing.
Live and Learn.
The 54 circuit Sqaure D is the one I had heard of but I had been told that it did not have USA UL listing.
Live and Learn.
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: Overcurent devices allowed!
I seem to remember a square D piggy back QO that could clip in place of a regular QO breaker ,but that doesnt make it legal just cause it fits
I seem to remember a square D piggy back QO that could clip in place of a regular QO breaker ,but that doesnt make it legal just cause it fits
Re: Overcurent devices allowed!
In Canada I believe we can get 60 circuit panels in any brand.SQuare D and Siemens for sure.I also dont think there is any requirement preventing us from twinning any or all of these breakers.I know I have more than 40 overcurrent devices in my own panel.Ill look into the 60/120 issue though.
Ross
In Canada I believe we can get 60 circuit panels in any brand.SQuare D and Siemens for sure.I also dont think there is any requirement preventing us from twinning any or all of these breakers.I know I have more than 40 overcurrent devices in my own panel.Ill look into the 60/120 issue though.
Ross
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: Overcurent devices allowed!
Grumpy Gus...
[ January 18, 2005, 08:18 PM: Message edited by: georgestolz ]
If Square D designs a piggyback QO breaker to go into QO panels, why would that be illegal if you observe the 42 handle rule? There have been several occasions where I encounter a 24 or 30 space panel and obtain a legal, brand-specific piggyback breaker for it.
Grumpy Gus...
[ January 18, 2005, 08:18 PM: Message edited by: georgestolz ]
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Overcurent devices allowed!
First and primary - you should never install more circuits than the panel was designed and listed to hold.
The Square D QOT1515 (and other sizes) is a Circuit Limiting tandem breaker (Class CTL) which is constructed only to fit into certain Square D load centers and not into any of their panelboards. The Square D QO1515 (and similar sizes) is a non-CTL breaker and is labeled "for replacement purposes only" for use in very very old load centers manufactured (early 60's)prior to the CTL requirement. The frequent incorrect use of the non-CTL breakers has given them a local nick-name of "cheater breaker".
First and primary - you should never install more circuits than the panel was designed and listed to hold.
The Square D QOT1515 (and other sizes) is a Circuit Limiting tandem breaker (Class CTL) which is constructed only to fit into certain Square D load centers and not into any of their panelboards. The Square D QO1515 (and similar sizes) is a non-CTL breaker and is labeled "for replacement purposes only" for use in very very old load centers manufactured (early 60's)prior to the CTL requirement. The frequent incorrect use of the non-CTL breakers has given them a local nick-name of "cheater breaker".
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: Overcurent devices allowed!
Re: Overcurent devices allowed!
Remember spaces vs circuits which is probably a redundant. 42 ckts doesn't always equal 42 spaces. You may have a 24 space panel listed with maybe 32 circuits that allows the installation of up to (6) double breakers in specific location most likely at the opposite end from the main breaker. But a 42 space panel that is listed with 42 circuits means no messing around with "cheater" or the double piggy back breakers no matter how you may be able to get them in. The nameplate of the panel as listed by UL must be complied with.
My breaker application notes indicate that an 'F' frame breaker, which are industrial breakers of up to 100a or 150a ratings, have a heating watt of 10w. I believe thats for a 3p breaker. But that's besides the point. If the heating wats were to be assumed to be even as small as 1w/pole at FL in a 42ckt panel that's 42w of heat. Throw in some AFCI and GFCI breakers and those get slightly warm to the touch by simply being installed.
A breaker with an 40degC rated should carry its rating without tripping at 40degC ambient.
Using this is a bench mark it is common for panels in out are to be located in a basement where the ambient temperature is often less that 70degF or 21degC. 40degC is 104degF so you have about 20degC of rise to work with before the breaker starts to derate based upon that 100% of the breaker rating. But then there's the loading 80% rule which doesn't allow a 100% continuous load.
Then rise that ambient temperature and also take in to consideration the heating watts of each breaker. From that point I have to appreciate what UL testing has to conduct with all of the variables taken into account when listing a panel.
Remember spaces vs circuits which is probably a redundant. 42 ckts doesn't always equal 42 spaces. You may have a 24 space panel listed with maybe 32 circuits that allows the installation of up to (6) double breakers in specific location most likely at the opposite end from the main breaker. But a 42 space panel that is listed with 42 circuits means no messing around with "cheater" or the double piggy back breakers no matter how you may be able to get them in. The nameplate of the panel as listed by UL must be complied with.
My breaker application notes indicate that an 'F' frame breaker, which are industrial breakers of up to 100a or 150a ratings, have a heating watt of 10w. I believe thats for a 3p breaker. But that's besides the point. If the heating wats were to be assumed to be even as small as 1w/pole at FL in a 42ckt panel that's 42w of heat. Throw in some AFCI and GFCI breakers and those get slightly warm to the touch by simply being installed.
A breaker with an 40degC rated should carry its rating without tripping at 40degC ambient.
Using this is a bench mark it is common for panels in out are to be located in a basement where the ambient temperature is often less that 70degF or 21degC. 40degC is 104degF so you have about 20degC of rise to work with before the breaker starts to derate based upon that 100% of the breaker rating. But then there's the loading 80% rule which doesn't allow a 100% continuous load.
Then rise that ambient temperature and also take in to consideration the heating watts of each breaker. From that point I have to appreciate what UL testing has to conduct with all of the variables taken into account when listing a panel.
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