Gentlemen. We have now stuffed the bridgeport into the back bedroom
and have closed in the giant gaping 8x8' hole in the wall with spiffy
double 36" "french" doors.

This is part of a comprehensive remodeling project. We are converting
the house, a modest 29'x29' 2 bedroom house to an as yet unspecified
commercial purpose.

Some time ago I upgraded the old 100 amp electric service to 200
amps. At that time I moved the service entrance from one end of the
house to the other. Upon removing the old sheet rock from around the
old service entrance I discovered black charring of the insulation
face paper by each one of the romex wires that terminated at the old
box. In other words, the house was just a kiss away from "up in
smoke".

At this point, all of the old wiring throughout the house is dead.
The new service entrance does not connect to any of it. Instead, I
have limited, isolated wiring to two rooms of the house, the front
bedroom and kitchen.

In each room, a cluster of outlets drops down from a 100 amp branch
panel that will hold four 220 amp circuits. These boxes do not have
mains. Rather, they are each fed from 100 amp branch breakers in the
main 200 amp panel.

I have a couple more of these 100 amp boxes. Yesterday I happened to
read the installation instructions in one of these as yet unused
boxes. To my surprise - and discomfiture - I read words to the effect
that "This box is to be used only for branch circuits fed by a box
with not more than 100 amp mains. If fed from a branch breaker this
should be limited to 70 amps."

This is of no immediate concern as these boxes are in temporary
service and are not even close to pulling 50 amps never mind 70 or
100.

Nevertheless, reading this leads me to the presumption that for code?
purposes, branch circuit breakers are not rated as high as main
breakers.

Does anybody know the reason or logic for this?

Gracias. Vernon

Vernon wrote:


Nevertheless, reading this leads me to the presumption that for code?
purposes, branch circuit breakers are not rated as high as main
breakers.

Does anybody know the reason or logic for this?
Yup, interrupting rating. If you examine the breakers closely (may
require a magnifying glass) it will probably have a lable saying
something like "interrupting rating 10,000 A" or maybe "branch circuit
must not exceed 10,000 A surge capacity". This relates to the current
surge during a severe short circuit event. The breaker MUST be able to
interrupt the worst-case surge without exploding. Downstream branches
are protected by the current limiting effect of upstream breakers.
The main panel breakers in our building are huge things, and carry a 100
KA rating, the rest of the breakers have a 10KA rating.

Jon

Vernon writes:


Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

In each room, a cluster of outlets drops down from a 100 amp branch
panel that will hold four 220 amp circuits. These boxes do not have

Is that four twenty-amp circuits, or four "220" [usually labeled "240"]
*volt* circuits...?

mains. Rather, they are each fed from 100 amp branch breakers in the
main 200 amp panel.

"This box is to be used only for branch circuits fed by a box with not
more than 100 amp mains. If fed from a branch breaker this should be
limited to 70 amps."

I'll have to punt by agreeing with the other reply.

Do note that {unless something has changed...} you Shall keep neutral
and ground seperate at all subpanels; they are bonded only at one
point; the main disconnect.



--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

On Jan 9, 5:50*pm, David Lesher wrote:
Vernon writes:
Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. *In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

In each room, a cluster of outlets drops down from a 100 amp branch
panel that will hold four 220 amp circuits. *These boxes do not have

Is that four twenty-amp circuits, or four "220" [usually labeled "240"]
*volt* circuits...?

mains. *Rather, they are each fed from 100 amp branch breakers in the
main 200 amp panel.
"This box is to be used only for branch circuits fed by a box with not
more than 100 amp mains. *If fed from a branch breaker this should be
limited to 70 amps."

I'll have to punt by agreeing with the other reply.

Do note that {unless something has changed...} you Shall keep neutral
and ground seperate at all subpanels; they are bonded only at one
point; the main disconnect.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Jon and Dave. Thank you for helping me understand that. Indeed, I
meant to say each box would hold four 220 (240) VOLT circuits. These
are 20 amps each. Once I'm done each 100 amp panel will be capable of
carrying 200 amps and each 200 amp panel will have conductors capable
of twice that.

As to the romex wires terminating at the old box I did not notice any
charring of the wires. Just charred paper backing on the insulation.
However, I haven't looked that carefully on the other hand. I aspire
to run all wiring through rigid metal conduit surface mounted on the
interior walls and the main branch service conductors in 2" conduit
across the attic floor. Finally, I will have a 200 amp pass through
conductor in double barreled 2" conduit that will go out of the house
and feed a Syncrowave welder. The objective is to devote the entire
200 amp service to the welder if once in a blue moon I require 400
amps of TIG or stick welding grunt.

Finally, thanks for the tip about keeping neutral busses isolated from
ground at all downstream boxes. I was able to wrap my feeble brain
around that concept as a result of reading "the NEC for dummies" or
something like that.

All the best. Down with the rest. V

On Jan 9, 5:50*pm, David Lesher wrote:
Vernon writes:
Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. *In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

In each room, a cluster of outlets drops down from a 100 amp branch
panel that will hold four 220 amp circuits. *These boxes do not have

Is that four twenty-amp circuits, or four "220" [usually labeled "240"]
*volt* circuits...?

mains. *Rather, they are each fed from 100 amp branch breakers in the
main 200 amp panel.
"This box is to be used only for branch circuits fed by a box with not
more than 100 amp mains. *If fed from a branch breaker this should be
limited to 70 amps."

I'll have to punt by agreeing with the other reply.

Do note that {unless something has changed...} you Shall keep neutral
and ground seperate at all subpanels; they are bonded only at one
point; the main disconnect.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Now that I think about it I have another question. My scheme calls
for two identical 200 amp feed through boxes mounted back to back on
opposite sides of an external wall. Each of these boxes will hold
four 240v breakers. The box on the outside is connected to the
service drop. The second box is not yet installed. But once I
install it, I will feed the 200 amps out the bottom, through the wall
through double barrel nipples into the bottom lugs of the second box.
The interior box will contain four 100 amp breakers. Each of these
four branch breakers will feed a 100 amp box (with mains. Not the
boxes I'm talking about above), one in each room of the house (soon to
be drive-thru greasy spoon hamburger joint. Thus, each room will be
wired to its own 100 amp mains box.

As stated above, the 200 amps will pass through the top of the second
200 amp box and out again through the very same wall where it will
connect to a Syncrowave 300 welder which has its own 200 amp breaker
box. I will use doubled 3/0 wire throughout the double pass throughs
between these boxes and the welder.

Does anything seem not kosher with this arrangement? Thanks yet
again. Vernon

On 2009-01-09, David Lesher wrote:
Vernon writes:


Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

Or was it very *old* Romex -- which had an outer jacket which
was a woven cloth soaked in tar. Inside that was rolled paper separating
the wires, and more woven cloth over black rubber inner insulation over
the individual wires.

The black could simply come from migrating tar over the years.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 10 Jan 2009 06:52:54 GMT, "DoN. Nichols"
wrote:

On 2009-01-09, David Lesher wrote:
Vernon writes:


Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

Or was it very *old* Romex -- which had an outer jacket which
was a woven cloth soaked in tar. Inside that was rolled paper separating
the wires, and more woven cloth over black rubber inner insulation over
the individual wires.

The black could simply come from migrating tar over the years.

Good Luck,
DoN.


Indeed. Ive seen a fair amount of that,ln old homes here in the desert,
the inner paper picked up the tar in the heat and it looked like it had
gotten hot. Yet the insulation was still pliable, which it wouldnt be
if it had gotten hot enough to char.

Gunner


"First Law of Leftist Debate
The more you present a leftist with factual evidence
that is counter to his preconceived world view and the
more difficult it becomes for him to refute it without
losing face the chance of him calling you a racist, bigot,
homophobe approaches infinity.

This is despite the thread you are in having not mentioned
race or sexual preference in any way that is relevant to
the subject." Grey Ghost

"Vernon" wrote in message
...
On Jan 9, 5:50 pm, David Lesher wrote:
Vernon writes:
Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

In each room, a cluster of outlets drops down from a 100 amp branch
panel that will hold four 220 amp circuits. These boxes do not have

Is that four twenty-amp circuits, or four "220" [usually labeled "240"]
*volt* circuits...?

mains. Rather, they are each fed from 100 amp branch breakers in the
main 200 amp panel.
"This box is to be used only for branch circuits fed by a box with not
more than 100 amp mains. If fed from a branch breaker this should be
limited to 70 amps."

I'll have to punt by agreeing with the other reply.

Do note that {unless something has changed...} you Shall keep neutral
and ground seperate at all subpanels; they are bonded only at one
point; the main disconnect.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Now that I think about it I have another question. My scheme calls
for two identical 200 amp feed through boxes mounted back to back on
opposite sides of an external wall. Each of these boxes will hold
four 240v breakers. The box on the outside is connected to the
service drop. The second box is not yet installed. But once I
install it, I will feed the 200 amps out the bottom, through the wall
through double barrel nipples into the bottom lugs of the second box.
The interior box will contain four 100 amp breakers. Each of these
four branch breakers will feed a 100 amp box (with mains. Not the
boxes I'm talking about above), one in each room of the house (soon to
be drive-thru greasy spoon hamburger joint. Thus, each room will be
wired to its own 100 amp mains box.

As stated above, the 200 amps will pass through the top of the second
200 amp box and out again through the very same wall where it will
connect to a Syncrowave 300 welder which has its own 200 amp breaker
box. I will use doubled 3/0 wire throughout the double pass throughs
between these boxes and the welder.

Does anything seem not kosher with this arrangement? Thanks yet
again. Vernon

I think you should do a load worksheet and consult with an electrician
and/or an electrical engineer. If you have natural gas available consider
using that for the appliances.

On Jan 10, 12:52*am, "DoN. Nichols" wrote:
On 2009-01-09, David Lesher wrote:

Vernon writes:

Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. *In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

* * * * Or was it very *old* Romex -- which had an outer jacket which
was a woven cloth soaked in tar. *Inside that was rolled paper separating
the wires, and more woven cloth over black rubber inner insulation over
the individual wires.

* * * * The black could simply come from migrating tar over the years.

* * * * Good Luck,
* * * * * * * * DoN.

--
*Email: * * | Voice (all times): (703) 938-4564
* * * * (too) near Washington D.C. |http://www.d-and-d.com/dnichols/DoN.html
* * * * * *--- Black Holes are where God is dividing by zero ---

Hey Don,

I would call it "modern" romex. The house was built in 1978
thereabouts. Soon after I bought it in the early 90s I had the house
rewired. So I'm not sure if it's the original wire (probably is) but
it's the plastic coated stuff. I'm pretty sure the black on the
insulation vapor barrier is charring. V

On Jan 10, 7:27*am, "ATP*" wrote:
"Vernon" wrote in message

...
On Jan 9, 5:50 pm, David Lesher wrote:



Vernon writes:
Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

In each room, a cluster of outlets drops down from a 100 amp branch
panel that will hold four 220 amp circuits. These boxes do not have

Is that four twenty-amp circuits, or four "220" [usually labeled "240"]
*volt* circuits...?

mains. Rather, they are each fed from 100 amp branch breakers in the
main 200 amp panel.
"This box is to be used only for branch circuits fed by a box with not
more than 100 amp mains. If fed from a branch breaker this should be
limited to 70 amps."

I'll have to punt by agreeing with the other reply.

Do note that {unless something has changed...} you Shall keep neutral
and ground seperate at all subpanels; they are bonded only at one
point; the main disconnect.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Now that I think about it I have another question. *My scheme calls
for two identical 200 amp feed through boxes mounted back to back on
opposite sides of an external wall. *Each of these boxes will hold
four 240v breakers. *The box on the outside is connected to the
service drop. *The second box is not yet installed. *But once I
install it, I will feed the 200 amps out the bottom, through the wall
through double barrel nipples into the bottom lugs of the second box.
The interior box will contain four 100 amp breakers. *Each of these
four branch breakers will feed a 100 amp box (with mains. *Not the
boxes I'm talking about above), one in each room of the house (soon to
be drive-thru greasy spoon hamburger joint. *Thus, each room will be
wired to its own 100 amp mains box.

As stated above, the 200 amps will pass through the top of the second
200 amp box and out again through the very same wall where it will
connect to a Syncrowave 300 welder which has its own 200 amp breaker
box. *I will use doubled 3/0 wire throughout the double pass throughs
between these boxes and the welder.

Does anything seem not kosher with this arrangement? *Thanks yet
again. *Vernon

I think you should do a load worksheet and consult with an electrician
and/or an electrical engineer. If you have natural gas available consider
using that for the appliances.

Unfortunately, I can't do a load worksheet since I don't know what the
loads will be. That's why I'm trying to build in 100% overkill. I
indeed do intend to convert to gas (LPG) equipment as soon as we
determine that the location makes enough money to justify the
expenditure. My only concern (which is not to say there are not
others of which I'm unaware) is whether there are any code or design
issues with feeding through two back to back 200 amp Square D QO pass-
through panels of which I may not be aware. Indeed, that is a subject
worthy of consulting an electrician. V

On 10 Jan 2009 06:52:54 GMT, "DoN. Nichols"
wrote:

On 2009-01-09, David Lesher wrote:
Vernon writes:


Upon removing the old sheet rock from around the old service entrance I
discovered black charring of the insulation face paper by each one of
the romex wires that terminated at the old box. In other words, the
house was just a kiss away from "up in smoke".

Was the Romex charred? Usually it shows heat damage first. Common
cause is poor connections in the box.

Or was it very *old* Romex -- which had an outer jacket which
was a woven cloth soaked in tar. Inside that was rolled paper separating
the wires, and more woven cloth over black rubber inner insulation over
the individual wires.

The black could simply come from migrating tar over the years.

Good Luck,
DoN.
Very common. My dad was an electrician and he often came home black
from end to end efter pulling that old Romex.