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Home > Archive > Electrical code Compliance > June 2005 > Must main breaker be larger than oven breaker?
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| Author |
Must main breaker be larger than oven breaker?
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| John B 2005-06-17, 11:28 pm |
| Considering installation of 40A @ 240 VAC range-oven in apartment owned by
relatives. Structure built in 1965. Would have to have new circuit-breaker
installed in the apartment's sub-panel, which is inside the apartment. This
is feasible. A new conduit could be installed in attic, to location of new
range-oven. New AWG 8 wire would be used for this power connection.
Old dilapidated range-oven is gas, and cabinet considerations preclude
replacement with a new gas unit. Let's not get into the idea of gas unit,
therefore.
Problem seems to be that the feed from the downstairs sub-main, serving this
apartment, itself is AWG 8. That sub-main breaker is 40A @ 240V.
Question:
Is is compliant with NEC to have a 40A @ 240 V branch circuit for this oven,
when the whole subpanel is protected by a 40A @ 240 V sub-main?
Common sense would say "no," but that might not be what code says. The
overall danger is nuisance shut-offs of the sub-main, rather than threat of
fire, etc. We could advise any tenant to not run the air-conditioner and
oven at the same time...which sort-of makes sense, anyway.
If anyone can site the section of the NEC (I have 1990 book) which addresses
this issue, I would appreciate it.
| |
| Adrienne Hendrickson 2005-06-17, 11:28 pm |
| The ultimate approval for this would come from your local authority having
jurisdiction (AHJ). Having said that, my judgement is that 'no, you can't do
this' as you have described it.
NEC 384-13 requires the panelboard rating to be not less than the minimum
feeder capacity required. You can't just tell someone not to use the ac with
the stove. The panel load would have to be figured based upon the proposed
oven/range and any other loads already served by this panel.
Assuming the proposed oven/range is a new load, NEC 220-3(c)(1) and 31 gives
the requirements for determing if an existing residential service has
capactiy for a new load. Does the existing upstream panel have the capacity
to add this load as well as the sub-panel?
NEC 230-79(c) requires a minimum of a 100A service disconnecting means for a
one-family dwelling. NEC 230-79(d) requires a service disconnecting means of
at least 60A for all other installations (not fitting a thru c).
I would recommend that you hire a professional to do design and
installation. I'm assuming that any such electrical work, in your area,
requires a building permit and will be inspected by the AHJ.
Hope this helps
Adrienne Hendrickson
"John B" <jb@nospam.com> wrote in message
news:<i5LUd.7612$%X1.6511@fe07.lga>...
quote:
> Considering installation of 40A @ 240 VAC range-oven in apartment
quote:
> owned by relatives. Structure built in 1965. Would have to have new
circuit-breaker
quote:
> installed in the apartment's sub-panel, which is inside the apartment.
This
quote:
> is feasible. A new conduit could be installed in attic, to location
quote:
> of
new
quote:
> range-oven. New AWG 8 wire would be used for this power connection.
quote:
>
quote:
> Old dilapidated range-oven is gas, and cabinet considerations preclude
quote:
> replacement with a new gas unit. Let's not get into the idea of gas
quote:
> unit, therefore.
quote:
>
quote:
> Problem seems to be that the feed from the downstairs sub-main,
quote:
> serving
this
quote:
> apartment, itself is AWG 8. That sub-main breaker is 40A @ 240V.
quote:
>
quote:
> Question:
quote:
> Is is compliant with NEC to have a 40A @ 240 V branch circuit for this
oven,
quote:
> when the whole subpanel is protected by a 40A @ 240 V sub-main?
quote:
>
quote:
> Common sense would say "no," but that might not be what code says.
quote:
> The overall danger is nuisance shut-offs of the sub-main, rather than
quote:
> threat
of
quote:
> fire, etc. We could advise any tenant to not run the air-conditioner
quote:
> and oven at the same time...which sort-of makes sense, anyway.
quote:
>
quote:
> If anyone can site the section of the NEC (I have 1990 book) which
addresses
quote:
> this issue, I would appreciate it.
quote:
>
quote:
>
"John B" <jb@nospam.com> wrote in message
news:i5LUd.7612$%X1.6511@fe07.lga...
quote:
> Considering installation of 40A @ 240 VAC range-oven in apartment owned by
> relatives. Structure built in 1965. Would have to have new
> circuit-breaker
> installed in the apartment's sub-panel, which is inside the apartment.
> This
> is feasible. A new conduit could be installed in attic, to location of
> new
> range-oven. New AWG 8 wire would be used for this power connection.
>
> Old dilapidated range-oven is gas, and cabinet considerations preclude
> replacement with a new gas unit. Let's not get into the idea of gas unit,
> therefore.
>
> Problem seems to be that the feed from the downstairs sub-main, serving
> this
> apartment, itself is AWG 8. That sub-main breaker is 40A @ 240V.
>
> Question:
> Is is compliant with NEC to have a 40A @ 240 V branch circuit for this
> oven,
> when the whole subpanel is protected by a 40A @ 240 V sub-main?
>
> Common sense would say "no," but that might not be what code says. The
> overall danger is nuisance shut-offs of the sub-main, rather than threat
> of
> fire, etc. We could advise any tenant to not run the air-conditioner and
> oven at the same time...which sort-of makes sense, anyway.
>
> If anyone can site the section of the NEC (I have 1990 book) which
> addresses
> this issue, I would appreciate it.
>
>
| |
| John B 2005-06-17, 11:28 pm |
| Thanks for your reply.
The term "feeder" has always struck me somewhat confusingly; I tend to think
of it as synonymous with "upstream." I think "branch" means "downstream."
Can you elaborate on these terms?
"Adrienne Hendrickson" <ah9u@virginia.edu> wrote
quote:
> NEC 384-13 requires the panelboard rating to be not less than the minimum
> feeder capacity required...
Point taken that the apartment's sub-panel amperage rating must meet or
exceed that of the upstream line ("feeder") that bring power to said
sub-panel. This makes perfect sense. A panel rated for, say, 20A @ 240V,
protected by a 40A @ 240V main breaker could itself *become* a fuse, and
possibly a 4th-of-July ornament.
quote:
> The panel load would have to be figured based upon the proposed
> oven/range and any other loads already served by this panel.
The existing panel already has a branch circuit amperage (140 A @ 120 VAC)
total that widely exceeds the 40A @ 240 VAC main.
I think every panel I've ever looked at has a collection of circuit-breakers
("branch circuits"?) whose wattage sum widely exceeds the wattage rating of
the main breaker ("feeder"?) that protects the panel. If too many gadgets
and lights are turned on at the same time, without popping branch-circuit
breakers, then the main should pop. It has never happened, in my 50+ years;
I have never seen a main pop or even heard of this happening.
quote:
> You can't just tell someone not to use the ac with the stove.
Sure I can, as long as it's disclosed clearly before the tenant agrees to
rent. Why not? This is a legal issue, not an engineering issue.
The oven won't draw 40A most of the time, anyway.
I spoke with an electrical inspector for the relevant municipality, and he
said that the puny main, relative to the various branches, would not prevent
issuance of a permit. I will press the point about permit *closure* a bit
harder, if this plan becomes more probable.
| |
| Roy Q.T. 2005-06-17, 11:28 pm |
| I am sure most a Breaker are the same
size.
all you need is know that you will be dealing with to much redundancy,
or closeness to overture of overcurrent to be actually comfortable.
what if everyone of your personal components got together and fired up
all the grills and oven at once. Humph !
* Be sure you have nough protection at the Main to Cover your Dwelling &
that Oven Circuit.
you're probably all over with this....I like clowning around at times
takes the stress off the mess.
=AEoy
| |
| phil-news-nospam@ipal.net 2005-06-17, 11:28 pm |
| On Wed, 2 Mar 2005 14:12:16 -0500 Adrienne Hendrickson <ah9u@virginia.edu> wrote:
| NEC 230-79(c) requires a minimum of a 100A service disconnecting means for a
| one-family dwelling. NEC 230-79(d) requires a service disconnecting means of
| at least 60A for all other installations (not fitting a thru c).
If you are actually wiring in the new service, yes, that is required.
But for an existing service, the NEC is mute about requiring going
back and changing the service.
| I would recommend that you hire a professional to do design and
| installation. I'm assuming that any such electrical work, in your area,
| requires a building permit and will be inspected by the AHJ.
For an apartment with tenants, this would be the case in every AHJ
I know of. But I know of none, except certain large cities, that
require going back and changing things that were not in the plan to
be changed.
I'd say if each ONE stove element combined with air conditioning and
reasonable lighting forms a load diversity that does not exceed the
main breaker capacity, it would not require going back to the service
wiring to change it. Stoves do tend to get a good bit of leeway as
hardly anyone ever turns on all the elements at once. But it would
be a good idea to run an up to date load calculation and see where you
stand with respect to the service feed.
I once lived in an apartment building where one day it happened that
enough tenants turned on enough stove elements at the same time to
burn out the utility overhead primary feeding the building the pole
transformer feeding the building. I was expecting the transformer
to go next, as it was 25 kVA feeding 20 apartments with 40 amp stoves
and central A/C. But those were parts the landlord did stay away from.
--
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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