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).
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.
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.
Bear in mind that the size of the SEC (from the ‘pole’ to the house) is determined by the PoCo, not the NEC.
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.
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.
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
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.
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.
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.
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.
So if the meter is rectangular (200 Amps), and the main breaker is 125 Amps: The sec (between the two) which is rated at 100 Amps is too small? And that is an issue correct? What is the potential harm in such a layout? (The house was 60 years old.)
The potential harm is that you could over-load the SEC without tripping the service breaker.
The house could be drawing nearly 125 amps (throughout its circuits or in a short-circuit condition) and not trip the breaker. The SEC (rated at 100 amps) is your “weak link,” and could burn up.
Guys I’ve run across something similar on new construction this afternoon. Maybe I’m just and idiot, and that’s probably the case, but the panel is rated 200, the main disconnect is 200 and the underground service entry is 1/0 Aluminum. Meter is not on but similar construction in the neighborhood is using a meter rated for 200 amps. Here’s the pic?? What am I missing besides some brain matter?
Are you are asking about the conductors coming from the underground to feed the meter? If so these are sized by the power company, which operates under a different set of rules than the NEC.
mouse
