408.35 NUMBER O.C.P.D. PANELBOARD
- Thread starter tregarsa
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- New Jersey
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- Journeyman Electrician
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
Check out this old post:
Check out this old post:
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
384-15 of my 1959 NEC has the same 42-ckt. limit for a L&ABCP.
It was earliest NEC I could access easily. Have a 1940 & I believe a 1947 & a 1953 hidden away somewhere.
Side note: It is very common to see a 3-phase 42-ckt. full of 20A bkrs. 225A has been a readily available bus bar rating for these.
There are (14) connections to each phase. The 20A bkrs. can carry up to 16A continuously.
14 X 16A = 224A. Just an observation.
384-15 of my 1959 NEC has the same 42-ckt. limit for a L&ABCP.
It was earliest NEC I could access easily. Have a 1940 & I believe a 1947 & a 1953 hidden away somewhere.
Side note: It is very common to see a 3-phase 42-ckt. full of 20A bkrs. 225A has been a readily available bus bar rating for these.
There are (14) connections to each phase. The 20A bkrs. can carry up to 16A continuously.
14 X 16A = 224A. Just an observation.
physis
Senior Member
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
I wouldn't have guessed it goes back to '59 or further.
That certainly predates the common use of circuit breakers. (At least I assume). Although they are in my 1951? dictionary.
So, appearantly, the limit has been there essentially from the beginning. Or at least close to it.
The reasoning behind it might turn out to be interesting.
I haven't looked at Infinity's link yet.
I wouldn't have guessed it goes back to '59 or further.
That certainly predates the common use of circuit breakers. (At least I assume). Although they are in my 1951? dictionary.
So, appearantly, the limit has been there essentially from the beginning. Or at least close to it.
The reasoning behind it might turn out to be interesting.
I haven't looked at Infinity's link yet.
mdshunk
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Re: 408.35 NUMBER O.C.P.D. PANELBOARD
I'm talking totally from memory here, but I seem to remember reading that the 42 ckt limit was established due to a fire in a hotel panel in the 1930's(?). It was determined at the time that the heat built from 42 circuits in the typical structure of the day was all that the conductor insulations of the day could handle. Funny you mention this, because I recently saw an I-Line panel full of the adapter plates to accept QO plug on breakers. There must have been 150 breakers in that panel. This was in a factory with "qualified" people doing the work.
ADDED FROM IAEI:
"Maximum circuit limitations. Are 42 circuits a defensible limitation with existing technology? The limitation originated in the 1933 NEC, and was apparently based on a desire to limit the amount of combustible wiring associated with any one panelboard. Based on the limited material unearthed by the task group to date, this rule was apparently motivated by a fire in a New York City hotel back when the only available conductor insulation was combustible rubber. Clearly this is no longer appropriate substantiation to maintain the rule, however, perhaps there are other concerns, such as mutual heating effects of large numbers of conductors in a confined space. The panel previously rejected an attempt to remove this limitation in the 1971 cycle, but only with the assertion that it felt that it is necessary for safety."
[ May 15, 2005, 09:46 PM: Message edited by: mdshunk ]
I'm talking totally from memory here, but I seem to remember reading that the 42 ckt limit was established due to a fire in a hotel panel in the 1930's(?). It was determined at the time that the heat built from 42 circuits in the typical structure of the day was all that the conductor insulations of the day could handle. Funny you mention this, because I recently saw an I-Line panel full of the adapter plates to accept QO plug on breakers. There must have been 150 breakers in that panel. This was in a factory with "qualified" people doing the work.
ADDED FROM IAEI:
"Maximum circuit limitations. Are 42 circuits a defensible limitation with existing technology? The limitation originated in the 1933 NEC, and was apparently based on a desire to limit the amount of combustible wiring associated with any one panelboard. Based on the limited material unearthed by the task group to date, this rule was apparently motivated by a fire in a New York City hotel back when the only available conductor insulation was combustible rubber. Clearly this is no longer appropriate substantiation to maintain the rule, however, perhaps there are other concerns, such as mutual heating effects of large numbers of conductors in a confined space. The panel previously rejected an attempt to remove this limitation in the 1971 cycle, but only with the assertion that it felt that it is necessary for safety."
[ May 15, 2005, 09:46 PM: Message edited by: mdshunk ]
physis
Senior Member
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
Well, I'll have to add too.
Your bringing up the idea of combustible materials.
In those days, I could see that as easily being a contributing factor. Wool and tar insulation, or whatever they were using.
That though, hasn't been an issue since, basically, NM cable.
Well, I'll have to add too.
Your bringing up the idea of combustible materials.
In those days, I could see that as easily being a contributing factor. Wool and tar insulation, or whatever they were using.
That though, hasn't been an issue since, basically, NM cable.
- Location
- New Jersey
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- Journeyman Electrician
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
[ May 15, 2005, 10:22 PM: Message edited by: infinity ]
This would be code complaint if it were a Power Panelboard as defined by the 2005 NEC.
[ May 15, 2005, 10:22 PM: Message edited by: infinity ]
mdshunk
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Re: 408.35 NUMBER O.C.P.D. PANELBOARD
I guess I expected that would come up. I should have added that it was not. In fact, it was the only panel in the whole (small) factory.
pierre
Senior Member
- Location
- Westchester County, New York
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
"There must have been 150 breakers in that panel"
Was this in 1 enclosure?
Remember there are enclosures, and panelboards that are installed in enclosures.
"There must have been 150 breakers in that panel"
Was this in 1 enclosure?
Remember there are enclosures, and panelboards that are installed in enclosures.
mdshunk
Senior Member
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Re: 408.35 NUMBER O.C.P.D. PANELBOARD
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
The original NM cables used rubber insulation and woven jute or hemp for the sheath.
PVC insulation does burn if there is enough heat put into the reaction by another source of heat. Also, the 42 circuit limitation is based partly on the 30 conductor limitation of a wireway that is not derated for 31 or more conductors.
There is also a limitation of about 400 amps for a series connected short circuit rating that uses class J fuses in the feeder. Under some circuistance the maximum class J fuse in the feeder is 200 amps.
Also, having more than 42 branch circuit devices in a panelboard creates a wire management nightmare. There are quite a few times where I have stuck telephone distribution posts inside of a panelboard. If you do not use Bell System wire management methods with stranded wire it is very easy to pinch a wire between the box and the cover.
The original NM cables used rubber insulation and woven jute or hemp for the sheath.
PVC insulation does burn if there is enough heat put into the reaction by another source of heat. Also, the 42 circuit limitation is based partly on the 30 conductor limitation of a wireway that is not derated for 31 or more conductors.
There is also a limitation of about 400 amps for a series connected short circuit rating that uses class J fuses in the feeder. Under some circuistance the maximum class J fuse in the feeder is 200 amps.
Also, having more than 42 branch circuit devices in a panelboard creates a wire management nightmare. There are quite a few times where I have stuck telephone distribution posts inside of a panelboard. If you do not use Bell System wire management methods with stranded wire it is very easy to pinch a wire between the box and the cover.
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
physis - I do not think that ckt. bkrs. were real common in residential in this part of the country until maybe late 50's or early 60's.
But, ckt. bkrs., instead of plug fuses or cartridge fuses have been used in commercial/industrial for a long, long time.
40's anyway.
physis - I do not think that ckt. bkrs. were real common in residential in this part of the country until maybe late 50's or early 60's.
But, ckt. bkrs., instead of plug fuses or cartridge fuses have been used in commercial/industrial for a long, long time.
40's anyway.
allenwayne
Senior Member
Re: 408.35 NUMBER O.C.P.D. PANELBOARD
Back in NYC i did a school built circa 1910,There were sub panels upon sub panels upon sub panels added over the years.In MDP were splices bug taps galore.the call was for lights throughout the building dimming.I worked for the board of education at the time.Got there and the service buss bars were glowing red some braniac had retro fitted a 1000 amp feed through breaker on a 250 amp system.The wire was the old type cloth whatever they used at the time and was smoldering at terminations.Good thing this was during the summer and school was out.I ordered the repacement service and by new school year all was good.
But to think all those years our kids could have been burnt up due to stupidity.This was a k-5 school.
Back in NYC i did a school built circa 1910,There were sub panels upon sub panels upon sub panels added over the years.In MDP were splices bug taps galore.the call was for lights throughout the building dimming.I worked for the board of education at the time.Got there and the service buss bars were glowing red some braniac had retro fitted a 1000 amp feed through breaker on a 250 amp system.The wire was the old type cloth whatever they used at the time and was smoldering at terminations.Good thing this was during the summer and school was out.I ordered the repacement service and by new school year all was good.
But to think all those years our kids could have been burnt up due to stupidity.This was a k-5 school.
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