Determining amp service?

Originally Posted By: Ed Griffin
This post was automatically imported from our archived forum.



Other than looking at a main breaker, how can you calculate the amp service to a house?


Originally Posted By: gbeaumont
This post was automatically imported from our archived forum.



Hi Ed,


the total amperage that is available in a home, is a combination of many issues, the size of the service entrance conductors, the capacity of the electric meter, the amperage rating of the main disconnect, the stated total capacity of the main panel etc.

So the size of the service amperage is dictated, by the lowest rated component, for example if you have a 200 amp panel, a 150 and main disconnect, service entrance conductors rated for 100 amps, but the meter only rated for 60 amps, then you would have to report that the capacity of the system was only 60 amps.

I hope this helps, it may be worth you looking for a basic home inspection book, there are many to be found in either the regular bookstores, all within the book section at your local Home Depot.

Regards

Gerry


--
Gerry Beaumont
NACHI Education Committee
e-mail : education@nachi.org
NACHI phone 484-429-5466

Inspection Depot Education
gbeaumont@inspectiondepot.com

"Education is a journey, not a destination"

Originally Posted By: Ed Griffin
This post was automatically imported from our archived forum.



Gerry,


Thank you for the response. That is pretty much the answer I was looking for.


One more quick question on that. How can you tell what the service conductors are rated at?


Originally Posted By: gbeaumont
This post was automatically imported from our archived forum.



Hi Ed,


you just have to learn what size of wire, or type of wire is rated at in terms of amperage, for example #2/0 copper is rated for 200 amps.

Gerry


--
Gerry Beaumont
NACHI Education Committee
e-mail : education@nachi.org
NACHI phone 484-429-5466

Inspection Depot Education
gbeaumont@inspectiondepot.com

"Education is a journey, not a destination"

Originally Posted By: rpalac
This post was automatically imported from our archived forum.



Wire size rating Is as Jerry has stated.


Be careful:

Typically most houses have a Aluminum Service Entrance wire(a.k.a. SE Cable). This is okay by code. Aluminum wire is allowed in use for certain applications under specific restrictions. It must be terminated in the proper rated fitting (rating for Al or Al/Cu), you should uses a anti-oxidation past such as Nolux, Penatrox, ..etc..)
part of this is Article 310.14, Article 240.2(D),and several other sections (another thread)


Regarding using Aluminum as a service entrance wire:
The difference is that Aluminum wire and copper wire have to different conductive characteristics. #2/0 Copper is rated for 200Amps,where as it would be the same to use #4/0 Aluminum for 200Amp.
(#2/0 Aluminum is only rated at 150 Amps)

This is found in a table in the NEC (Article 310.15(B)(6)

Bob P.


Originally Posted By: roconnor
This post was automatically imported from our archived forum.



Also, the IRC has a very condensed residential electrical section with fairly easy to understand wire ampacity tables. Those are included with CodeCheck (has both CU & AL) which I highly recommend you have … icon_wink.gif … The following link is a sample wire sizing/capacity chart from one of the CodeCheck guides.


http://www.codecheck.com//images/CCWet01big.jpg

There are also a few topics on determining the service feeder cable size on older installs where ya can't read the cable markings ... ![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)


--
Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee

I am absolutely amazed sometimes by how much thought goes into doing things wrong

Originally Posted By: roconnor
This post was automatically imported from our archived forum.



. So you should be looking at the meter base. Generally, an older 60A service will have a small circular meter base, a 100A service will have a small square meter base, a 200A service will have a larger rectangular meter base, and 400A and up gets huge.


It?s important to get a handle on the utility service capacity because if ya see something like a 100A or 150A panel/feeder with a 60A meter base that?s a major red flag. Not only could the utility wires be overloaded, but that would indicate there was a panel upgrade done without a permit or inspections ? maybe even a Harry Homeowner special that has a lot of problems/hazards ? ![icon_eek.gif](upload://yuxgmvDDEGIQPAyP9sRnK0D0CCY.gif)

Maybe some input from one of our sparkies here on establishing a residential meter/service capacity, possibly with some pics, would be really helpful for some ... ![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)


--
Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee

I am absolutely amazed sometimes by how much thought goes into doing things wrong

Originally Posted By: Bob Badger
This post was automatically imported from our archived forum.



Interesting points by all. icon_biggrin.gif


My first reaction to the question was the service disconnect (main breaker or fuse) determines the service size.

That is only true when the service is properly wired.

As Gerry said you must go by the lowest rated component and as Robert says if any of the equipment is rated less than the main overcurrent device it is highly likely that the service has been improperly modified.

FYI if you can see the power company's conductors do not be alarmed if they are approximately rated 50% of the customers owned wiring.

There are a few reasons for this but all that really matters is the POCOs rating system works fine for them.

One real advantage of the smaller POCOs wire is that in the case of a short circuit on the houses service conductors the POCOs wire should melt out at the connection to the house before the service conductors burn.

Another thing, as far as the NEC is concerned aluminum is still a viable material for feeders and branch circuits, the alloy has been changed and the problems of the past are said to be gone.

In reality I have not seen aluminum smaller than 8 AWG sold since I have been in the trade.

Anti-oxidation pastes such as Nolux, Penatrox are not really required by the NEC, only if the instructions with the terminals say to use the pastes then you could say 110.3(B) requires it.


--
Bob (AKA iwire)
ECN Discussion Forums
Mike Holt Code Forum

Originally Posted By: roconnor
This post was automatically imported from our archived forum.



I agree with Bob about the AL wire. The newer AA-8000 series AL wire is much better and doesn’t have the same problems as older type AL wire. But for a given circuit, aluminum wire still has to be larger than if it was copper. The newer AL wire usually doesn’t require the oxide inhibitor compound as long as the connector is listed for AL, CU/AL, or CO/ALR (no marking means CU only).


The real problem is older AL wire AWG #10 or smaller (which should be solid, as #8 and larger must be stranded) in homes build in the 1960's to early 1970's with what is called "old technology" aluminum wire ... that's a red flag. Even AL wire up to a few code cycles ago had some issues, including AA-13000 series AL wire.

Good point about the utility service drop/lateral wires usually being significantly smaller than the panel feeder wires after the meter. Should help protect those load side panel feeder wires. Plus, I understand that the drop/lateral wires may be fused at the transformer which may blow/trip before the panel feeder wires fry ... although it's probably fused for higher loads than the IRC/NEC would require. Assuming the power company (POCO) didn't oversize their wires by mistake ...

Would be good to have some more input from the power company side of a residential service if anyone knows.


--
Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee

I am absolutely amazed sometimes by how much thought goes into doing things wrong

Originally Posted By: Bob Badger
This post was automatically imported from our archived forum.



roconnor wrote:
Would be good to have some more input from the power company side of a residential service if anyone knows.


Take a cruise to Mike Holt's and look for "Charlie the Utility Guy"

He is a Utility company engineer and has taught me a lot about POCO methods.

All POCOs are different but for this area you will not find over current protection on the secondary side of the POCO transformer other than the customer supplied one at the house.

As they feed many houses from one transformer it is very unlikely a service conductor short at a house will take out the primary OCP.

The only time I have seen that happen is when a cement cutting contractor cut through one of eight 4" conduits each containing 4 - 600 kcmil copper conductors.

These eight conduits fed a 3000 amp 480 volt service, when the one conduit was cut it took out a high voltage distribution cut out down the street knocking out a neighborhood.

The saw operator was shaken but fine. ![icon_razz.gif](upload://rytL63tLPMQHkufGmMVcuHnsuWJ.gif)


--
Bob (AKA iwire)
ECN Discussion Forums
Mike Holt Code Forum

Originally Posted By: roconnor
This post was automatically imported from our archived forum.



Bob … Good point about the possibility of multiple service wires/taps on a POCO transformer even if it’s fused. I guess the POCO thinks … “oh well, the service wire fried … at least the house wiring or transformer didn’t fry, so lets find out why it fried and then just drop another one” … icon_cool.gif


Thanks for the tip ... ![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)


--
Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee

I am absolutely amazed sometimes by how much thought goes into doing things wrong

Originally Posted By: Bob Badger
This post was automatically imported from our archived forum.



A person that worked on both sides, POCOs and EC explained to me this way.


The EC follows the NEC

The POCO follows the NESC (National Electric Safety Code)

The NEC is concerned with shutting the power off.

The NESC is concerned with keeping the power on.

Simplistic but I think it is pretty accurate, remembering that the POCOs use automatic re closers on large distribution circuits.

Tree branch on the line?

A couple of shots from the re closer and the branch goes away. ![icon_cool.gif](upload://oPnLkqdJc33Dyf2uA3TQwRkfhwd.gif)


--
Bob (AKA iwire)
ECN Discussion Forums
Mike Holt Code Forum

Originally Posted By: roconnor
This post was automatically imported from our archived forum.



Bob Badger wrote:
The NEC is concerned with shutting the power off.

The NESC is concerned with keeping the power on.

I think that's a good way to look at it ... ![icon_cool.gif](upload://oPnLkqdJc33Dyf2uA3TQwRkfhwd.gif)

In any case, I think it's just important to note that the size of the utility service drop/lateral is not really a concern ... just the meter base capacity and the utility drop/lateral condition, particularly at the weatherhead. That is as long as you don't have only 2 wires ... sometimes done for older 60A 120V small "shack" services. That would have trouble feeding my kids playhouse ...

Great point that Gerry made originally to check the meter base to see if the size at least matches the house feeders and equipment.


--
Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee

I am absolutely amazed sometimes by how much thought goes into doing things wrong