Well Mark we can’t see the bus rating from here, but if it were ME I would go with the weakest link and call it a 100 amp service due to the #2 drop.
Did you catch the 6 dissconnect violation?
…and you’d have no basis on which to make that claim.
Could you please explain? And how should he call it?
He shouldn’t. There’s nothing wrong.
I didn’t mean to imply there was anything wrong, except for the six disco rule,
I meant what size should he/would you call the service?
If the aerial drop is the only thing you think makes this a 100 amp (it doesn’t), then this is a 200 amp service. Only consider items from the point of attachment inward. Seriously, how far back are you going to go? Check the transformer on the pole? Gauge of the primary loop feed? Substation capacity? Certainly not.
Even in the extreme example below, this is still probably a 1600 amp service:
The breaker that was labeled “main” and had the wires running down to the bottom breakers was 60 amp.
How far can it go? Can it go from 60a to 300amp?
They probably would never do that, but the NESC rules are so complex that you could probably get away with that easily. They take into account the span, ice and wind loading, average design temperature, demand load, insulation type, etc. They don’t really have a table like the NEC has to look things up in. It’s a pretty complex calculation. The power companies do have rules of thumb the linemen work by, but in not every case do they change the aerial drop, nor are they specially obligated to by any rule or law.
How come the wires don’t burn up?
Mark,
As it has been said elsewhere in this post the wires are able to dissapate heat into the air and have different insulations. Typical circuits could be run with smaller conductors based strictly on their ampacities. This is not allowed under the NEC though.
If you were to amprobe a typical service it is probably drawing less than half its capacity.
On a somewhat related note, a POCO employee and I were talking about pole transformer sizing to see if the upgrade I was doing would impact the tranny. He said they run their transformers up to 140% capacity before they get replaced with a larger one.
So it is really none of our concern of the conductor size as HI’s have know way of knowing, correct? We should just look to see the insulators condition or if the feeds are low or in trees, anything else?
Just for kicks, open up the back of an electric stove and compare the wire sizes on the line side (#6-#8 awg)of the terminal block to the load size (usually #12). Different rules apply in different situations.
Thanks thats good to know.
Electrician for over 10 years in 3 states in the '70s and '80s. Mark Timpani, simply put: You are seeing a visually smaller conductor dropping down from the service pole and connecting to a visually larger conductor at the masthead and (usually) dropping down to the meter, then going to the main electrical service panel. A few salient facts:
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The conductors entering the masthead and descending to the meter->main panel cannot be smaller (of a lesser rating as per type of conductor) than allowed by code for the amp rating of the main panel in order to be approved by the inspector. It can be larger (oversized/overrated) but not smaller.
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If the service drop (masthead to meter) is inadequate for the potential load (too small, etc) the inspector will not pass it and the utility will not connect it. These conductors are typically an aluminum alloy, but may be copper (which would be smaller for the same amp rating), and are sized by amperage rating and environment, here in an enclosed conduit mast.
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Electrical utility service conductors (pole to house) are always aluminum (cheaper, lighter weight for long ariel spans) and for through-air applications can be smaller as they stay cooler.
From just the two points above, you can see that it’s quite normal for the utility service cables to be smaller than the cables they connect to at the masthead for the same expected load. Additional points to consider may include:
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Different cable types possibly used by the utility and the electrician working for the homeowner.
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The electrician got a killer deal on a huge roll of service cable and decided to use it even though it’s overrated for that service.
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The homeowner simply having overrated (larger) cables installed for whatever personal reasons.
Finally, the main reasons you needn’t worry about this issue so much are that:
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All service equipment – wire, boxes, etceteras – on the meter side of the main panel cannot be installed without breaking the local authority’s inspection seal on the meter.
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That seal guarantees that the installation – from panel to meter to masthead – has met code. Rest easy.
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A broken seal will be called in by the person who reads the meter, bringing an inspector to the house poking around and asking questions. If violations are found the service will be red flagged and locked OFF, shutting off electrical service to the house. Fines will be levied, tears will be shed.
Ahhh! The system works. Now don’t we all feel better?
They could do a 350% overload. Assuming enough reduced loading in between peaks (to allow oil to cool in between cycles) pole pigs can run 200 to 310% overloads with no loss of life. The reasoning behind this is thermal inertia insulating oil gives. Resi pole pigs are a perfect since load is incredibly cyclic. While people are sleeping or at work a pole pig may only see 1/15th of its rating; all that’s running may be a kitchen fridge and a dozen watts for standby loads like computers in sleep mode. However, as people come home and turn on lights, pre-heat ovens for dinner ect or wake up in the morning to a cold house turning on heat, toasters ect load rises significantly. This overload could drive the pole pig to a 200% overload for an hour or two with 310% overloading for 10 minutes, but since the oil has cooled sufficiently from the last cycle it will absorb the extra heat generated from the coil preventing it from overheating to thermal damage. When load drops down, the oil can give begin to cool giving off heat to air since no extra heat is being added now.
If the peak loading takes place in cold weather such as with electric resistance heating the overload can be even longer because of the extra heat dissipation to the surrounding air. If POCO decides to sacrifice pole pig life (cost factor to 30 or 40 years anticipated in service reliability) overloading can be again longer or even greater beyond the above.
With commercial application overloading cant be done to such a great extent since load tends to be more constant (flat line) rather than cyclic (saw tooth) causing oil to have less ability to cool so overloading isn’t done to the same radical degree. 125% for 3 hours is generally the max.
One a fun side note. In large power transformers, if one chooses to circulate the oil through the fins and have fans on them, a 30MVA transformer can easily become a 50MVA unit. A 20,000,000 watt increase just be being able to increase the amount of heat given off to the surrounding air. :mrgreen: