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Posted By: Bomzin Service Entrance Wires in Knoxville TN. - 09/12/05 10:42 PM
I was having a discussion with someone on a differant board and it was brought up that Aluminum wire could not be used to feed from service to panel. It was a not an electrician. Is this true and what is the reasoning behind it. Here in the state of Utah it is all that is used and don't see any problems with it when used correctly.

He also stated that for any home that is going to have central AC they had a 200 amp minimun on service requirments. Regardless of your load calculations.

Whats the scoop on this.
Thanks Bomzin
Posted By: Tiger Re: Service Entrance Wires in Knoxville TN. - 09/12/05 10:57 PM
In my experience the issues of aluminum wiring and 200-amp minimum services are both local ammendments to the NEC by the AHJ, not Code issues.

Dave
Posted By: BigB Re: Service Entrance Wires in Knoxville TN. - 09/13/05 01:52 AM
I have been told various things by mis informed people as well. The last one was that #14 wire is no longer allowed in new construction. This same person was "helping" a friend with a 200 amp upgrade, they were at Home Depot buying a piece of 2" EMT for the overhead riser. (Our POCO requires IMC). I just smiled at them and said good morning.
My granddad was a wise man. One of the few times that he spoke he told me that it is sometimes better to keep thy mouth shut and thought a fool than to open it and let it be known.

This is a good example to a good time to keep his mouth shut.
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Posted By: Bomzin Re: Service Entrance Wires in Knoxville TN. - 09/13/05 04:06 PM
Ok so it looks like Tiger thinks this is true with local codes writing it in and possibly 2 that think this is mis information.

I see it as possible, Tiger do you know this to be true or just taking a guess? Who is AHJ?

ty
Neil
Posted By: Bomzin Re: Service Entrance Wires in Knoxville TN. - 09/13/05 04:22 PM
Doh, Authority having juristiction , I knew that. Just put in an e-mail to the city inspector. Will post when I get info from the source.

Neil
I've seen homes with what was no doubt a greater current load in window A/C's than a central system would have provided.

Unless one is going all-electric, replacing several window units with a central system doesn't always need a service upgrade.
Larry You might be right in a practical sense because the window shaker load is hiding in the 3va per foot general lighting. Once you make it an HVAC load it has to be taken at nameplate value.
Posted By: markp Re: Service Entrance Wires in Knoxville TN. - 09/14/05 06:03 PM
Really??? Aren't window shakers considered fastened-in-place equipment and therefore have to be tallied on a service calculation (that is assuming they were planned for when the electrician installed the service).
Posted By: Bomzin Re: Service Entrance Wires in Knoxville TN. - 09/15/05 12:11 AM
Yes of course if the window unit were planned on you would have to consider it. Even after the fact it should be considerd.

The question still lies. If you do the math on a home in Knoxville and come up with only needing a 100 amp service or even a 125 but becuase you have electric range dryer and an AC unit you will be required to install a 200 amp service.

Also is aluminum wire ,SER, allowed or not from service to panel and if not what is the reasoning behind any of it .

Anyone from the city of Knoxville I mailed has yet to respond.

Just curious
Neil
Posted By: Tiger Re: Service Entrance Wires in Knoxville TN. - 09/15/05 12:39 AM
Sorry I missed your earlier challenge, Neil. I don't bump into the aluminum issue because I personally never use it.

On the 200-amp issue...Algonquin, IL, Village of Lakewood, IL, and in distant memory I believe Palatine, IL. In this area I won't quote a 100-amp service without calling the local building department.

Dave
My point was, nobody got a permit to plug in the window shaker. You generally have to get a permit for a central system.
Brownsville, Texas, I just looked at a service a few days ago at a house to which my g/f moved into with her family. 100A Cutler Hammer main with a 100A circuit breaker (feeding a subpanel), a 40A circuit breaker (this one feeding a 50A SQ D subpanel for a range, added later), and a 60A circuit breaker. Needless to say, there's 4 big bedrooms, a big living room, big dining room, LOTS of receptacles, LOTS of lighting, lots of electrical consumption. And oh yeah, central A/C.
Posted By: Tiger Re: Service Entrance Wires in Knoxville TN. - 09/15/05 11:52 AM
I've measured slowly increasing loads on 20-amp circuits which didn't trip the breaker until 24-25 amps. I've always wondered how much current is really required to trip a main on a slowly increasing load, & if the wire would handle it.

Dave
Posted By: iwire Re: Service Entrance Wires in Knoxville TN. - 09/15/05 01:27 PM
Dave if you take a look at the trip curves for breakers it can be surprising.

A 20 amp breaker (or fuse) may carry 24-25 amps forever and still meet all UL requirements.

Thermal trips are just not that accurate and the ambient temp has an influence on the breaker.

Don't worry about the wire, it can take it, 12 AWG is rated 25 to 30 amps anyway and the tables do not run on the edge of safety.

Bob
I believe that is the reason for 240.4(D) anyway. Larger circuits are usually designed for a specific load but circuits with receptacles on them get loaded by the end user until the breaker trips and then they unplug the clock.
Posted By: Tiger Re: Service Entrance Wires in Knoxville TN. - 09/15/05 06:08 PM
I understand how this works on 20-amp circuits, Bob. What I'm wondering about is how much current will a 100-amp or 200-amp main allow to pass without tripping. This type of loading (or overloading) seems likely with the addition of several sub-panels as additional loads are added to the main distribution panel.

Dave
Posted By: iwire Re: Service Entrance Wires in Knoxville TN. - 09/15/05 06:39 PM
Dave I looked up the trip curve for a basic Sqaure D 250 amp 240 volt 2 pole breaker.

It looks like it may carry 1.25 it's rated current from about 8 minutes to forever. (About 312 amps) It will carry 500 amps from 1 to 5 minutes.

I just do not see this as a worry, UL and the NEC are well aware of all these issues.

I doubt highly that properly terminated 250 amp condutors are going to burst into flames at 312 amps forever or 500 amps in 5 minutes.

Don't get me wrong if I see readings approaching 80% of a feeder or branch circuit rating I will be trying to get the customer to upgrade.

Bob
Posted By: Tiger Re: Service Entrance Wires in Knoxville TN. - 09/15/05 11:10 PM
I appreciate you looking that up Bob. I think the key words are "properly terminated".

It's All About The Connections.

(Lately I'm seeing loose neutrals and duplex receptacles with areas missing).

Dave
Posted By: Bomzin Re: Service Entrance Wires in Knoxville TN. - 09/15/05 11:46 PM
Speaking of connections. I had a remodell today and got into the panel. Always give them a good looking over. The main lugs had never been tightend. House was build in the 70's . One lug I put atleast 6 turns on . The other lug looked fine but the threads had seized. This is approx a 1500 square foot house with AC. By alrights it should have gone out by now. But visually looks ok. No signs of burn . To top it off before they installed breakers the mudder was kind enough to texture the inside of the panel.

Back on topic take this house for example. Someone correct me on this if I'm wrong going from memory. Lets do some math.

1500 sq foot home @ 3 VA =4500VA
first 3000va @ 100% 1500@35% = 525 VA

Total VA for house 3525VA
Range 8000VA
Dryer 5000VA
AC 5000VA
----------------------------
total VA 21,525
21,525 VA/240V = 89 Amps

So whats wrong with a 125Amp or 150Amp service. 125Amp service is a typical installation around here for me. We'll put on a 200Amp if there is a possibility of a hot tub or something in the future.

My question may still come out false.

Neil
Posted By: tdhorne Re: Service Entrance Wires in Knoxville TN. - 09/18/05 03:03 PM
I hope it is not to great a detour to say that I more often run short of breaker slots than I do of actual ampacity in the service conductors. My view of best practice is to provide separate receptacle circuits for each bathroom, refrigeration unit, appliance fastened in place such as disposal or dish washer, and so forth. The forty slots that come in a two hundred ampere panel makes that a lot easier.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
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