I would like to upgrade a 1987-vintage 125A combination meter main service
entrance panel to 200A. The existing panel is a semi-flush mount set into
stucco, underground service, I'd like to replace it entirely with a semi-
flush or surface moount box.
While pawing through the 1999 NEC (the one the county inspects to) I found
that 373-5(c) no longer allows the arrangement in the current box, all of
the NM cables coming in through a single opening with a bushing in the back
of the box.
So two questions, please.
First, what is the preferred method for bringing NM loads into a box like
this? 20 or so individual cable clamps seems bad, and I don't get how the
exception for one or more 18" conduits into the top of the panel is
supposed to work.
Second, can the existing ground wires (embedded in the stucco) be
disconnected from the old panel and re-used, or will I need to replace them
with new grounds?
Thanks for any guidance,
The reason you can't bring all your nm cables into your box through one
large connector is potential heat at that point (thats the theroy).
A common safe practice is to use 3/4 connectors and to limit each connector
to 2 or 3 nm cables each.
An increase in your service size precludes a larger ground wire. Your
existing ground is probably adequate,but your inspector may or may not call
you on this.
My opinion, Murray makes the best panel.
<< Your existing ground is probably adequate,but your inspector may or may
not call you on this. >>
If you are required to upgrade tour ground, you may also be required to bond
old and new grounds together. It probably is a sensible thing to do.
<< My opinion, Murray makes the best panel. >>
Square D QO series are the favored choices in our area. Opinion here is that
they are easier to work with. YMMV.
I can't answer the questions posed but, I have a question for you on this.
Do you have 200 amp service from the pole to your house? The reason that I
ask is this. We had 200 amp service installed in our house (built in the
60's) and the wiring from the pole, the mast where the service is attached
to the house, the meter and the panel all had to be replaced regardless of
condition to handle the 200 amp service.
This was in Ontario, Canada so it may not apply to you.
We have underground service, and a combined meter and distribution service
panel, so it'll be replaced as a unit. I'll need to trench out to the
service pad (about 30 feet) to allow the installation of the new feed.
I'm working off the 2002 code as I don't have a 1999 code.
Your talking about Stovepiping, it's fairly easy to do . You mount your
surface mount panel then attach your raceways through knockouts on the top.
When doing this, most people run a large conduit such as 2" and run all the
through it. This is a easy way to run the cables when the box is mounted to
concrete wall. I prefer to build a wood backer and individually clamp each
You mentioned it was a semi-surface mount, you would have to run it through
inspector before trying this.
Chances are you have a 8 ga. copper ground. You will need to up this to 6
ga. for your
connections to your ground rod.
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Your local inspector may allow you to circumvent this requirement because
the cables are fished in the wall. The wiring method used for your existing
panel isn't uncommon for that situation (at least in my area). If, for some
reason he doesn't allow it, just ask him what he recommends as a solution.
Your ground wires are probably too small......they need to be at least a #4
for a 200 amp service. Plus a portion of it (6") needs to be exposed for
connecting telephone and cable TV grounds.
When building an electric service one should try to contact the electrical
inspector who will be doing the actual inspection to get any questions
answered. While you have him/her on the line, ask him if the Power Company
has any requirements over and above the 1999 NEC......as some will. Most
power companies have a manual that is called "Standard Electrical Service
Requirements" (or similar title). Contact the Power Co. Engineering Dept.
and tell them that you are trying to obtain a drawing/diagram for a "typical
residential underground 200 amp service". They may be able to fax it to
you. The drawing will show meter base mounting heights, what kind of meter
base to use, clearances, grounding, grounding wire sizes, etc. As an
example, my area (actually the whole State) is under the 1999 NEC, however,
the Power Co. requires lightning arrestors (these are not required by the
1999 NEC) plus a few other changes not required by the 1999 NEC. The Power
Co. has the final say and you _won't_ get hooked up until you meet their
requirements also. Fortunately, there is usually good coordination between
the Power Co. and the local electrical inspectors, so the inspector will be
well aware of these additional requirements (if any).
I do have the local power company service requirements manual, and they
don't have much in the way of additional requirements beyond NEC 99 and
I'll definitely get in touch with the inspector before starting.
Many thanks to everyone who took the time to reply.
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