1/0 awg with 200 amp main breaker

[Scott Schultz]

I've noticed that when i inspected houses in the 10 year old range and older, I'm seeing the 200 amp main breaker protecting a 1/0 awg SEC. NEC currently states 2/0 awg for this size breaker and I guess that it used to be 1/0 at some point? anyway, I have been recommending that an electrician take a look and make a recommendation, whether it's ok or it should be upgraded. Is this the right call to make? My head tells me it's improper according to today's guidelines. What's your call?

Thanks

[Larry D. Kage]

Originally Posted by Scott Schultz

I've noticed that when i inspected houses in the 10 year old range and older, I'm seeing the 200 amp main breaker protecting a 1/0 awg SEC. NEC currently states 2/0 awg for this size breaker and I guess that it used to be 1/0 at some point? anyway, I have been recommending that an electrician take a look and make a recommendation, whether it's ok or it should be upgraded. Is this the right call to make? My head tells me it's improper according to today's guidelines. What's your call?

Thanks

It is wrong whether it is AL (#4/0 needed) or CU (#2/0 needed).

[Jim Port]

What was probably done was the panel was changed out to a larger size but the wires feeding it were not. If there is a properly sized OCP ahead of these you would be fine. The interior main breaker would just be a redundant means to shut down the panel. If there is no OCP ahead of the panel, defer for correction.

[Mark Nahrgang]

Not saying that 1 awg coming into the panel is correct, but isn't the 200AMP breaker AFTER the SEC? It's a shutoff that is protecting everything downstream from it. The SEC is bringing power to the breaker, not from it. If the SEC is protected at all, I would think that would be at the pole. Please correct me if I'm wrong.

[Frank P. Newman]

Bear in mind that the size of the SEC (from the 'pole' to the house) is determined by the PoCo, not the NEC.

[Jim Port]

Marc,

The overcurrent protection is preventing too much current from flowing through the service entrance conductors.

Imagine feeding this panel with #6. Would the breaker properly protect the wire before it burned up? The breaker would not protect anything as it would not trip until over 200 amps were flowing through it. By that time the wires would have have overheated and potentially caused a fire.

[Jeffrey R. Wicklander]

Originally Posted by mnahrgang

Not saying that 1 awg coming into the panel is correct, but isn't the 200AMP breaker AFTER the SEC? It's a shutoff that is protecting everything downstream from it. The SEC is bringing power to the breaker, not from it. If the SEC is protected at all, I would think that would be at the pole. Please correct me if I'm wrong.

I think that he just used the wrong term. By his descrip, he's talking about the load side of the meter. But, yes the SEC's are protected at the transformer.

Jeff

[Jim Port]

Originally Posted by jwicklander

I think that he just used the wrong term. By his descrip, he's talking about the load side of the meter. But, yes the SEC's are protected at the transformer.

Jeff

Sorry Jeff,

The cables before a main breaker or disconnecting means are unfused for all practical purposes. The fusing levels for a transformer are sized for the entire load served, not the individual load of a house served by that transformer.

This is the reason that the NEC requires the cables to be "as short as practical" inside a house without being fused.

[Jeffrey R. Wicklander]

Yes, the entire transformer itself is protected for all the loads coming off of it. Actually, I knew this but I had a temporary brainfart.

Jeff

[Jeffrey R. Pope]

This type of set up should be reported as a 100 amp service capacity, regardless of the breaker rating. The SEC has effectively reduced the maximum capacity of the residence.

If this were my inspection, I would certainly suggest replacing the SEC or reducing the service disconnect to 100 amps.

[Paul W. Abernathy]

Originally Posted by jpope

This type of set up should be reported as a 100 amp service capacity, regardless of the breaker rating. The SEC has effectively reduced the maximum capacity of the residence.

If this were my inspection, I would certainly suggest replacing the SEC or reducing the service disconnect to 100 amps.

BINGO......give this man a PRIZE.

The conductors on the load side of the meter and for that much the conductors on the load side of the service point at the drip loop is under the guidelines of the NEC. So if you have a conductor going to a breaker in the main panel and the breaker i sized larger then the SEC feeding it....most certainly a problem that needs to be reported and let your client choose to what level of acceptance they choose to live with...you have done your job.

[Mark Nahrgang]

Originally Posted by pabernathy

BINGO......give this man a PRIZE.

The conductors on the load side of the meter and for that much the conductors on the load side of the service point at the drip loop is under the guidelines of the NEC. So if you have a conductor going to a breaker in the main panel and the breaker i sized larger then the SEC feeding it....most certainly a problem that needs to be reported and let your client choose to what level of acceptance they choose to live with...you have done your job.

Paul,
What is the concern in this situation? I had a similar situation yesterday with a 100 Amp service that had a 125 Amp main breaker. I simply told the client that it was a 100 Amp service, and not 125.

[Paul W. Abernathy]

Well...what size were the conductors? Are they rated to handle 125A of potential current safely based on 310.15(B)(6) or are they sized per 310.16 from your visual observation?. Do you know the actual load....probably not so we have to take it at its face value.

[Mark Nahrgang]

Originally Posted by pabernathy

Well...what size were the conductors? Are they rated to handle 125A of potential current safely based on 310.15(B)(6) or are they sized per 310.16 from your visual observation?. Do you know the actual load....probably not so we have to take it at its face value.

From the meter to the panel it was #2 Alum. That was the smalled component, so that is why I defined it as a 100 Amp service. The main breaker in the panel was 125 amps.

[Paul W. Abernathy]

The reality is the 2 AWG is only good for 100A as you have stated. You put on the report the capacity but their is another issue...you provided the weakest link but the new issue is the se conductors are not rated for 125A...that would need a 1/0 minimum based on 310.15(B)(6). so this should also go on the report.