200 amp service. Am I to understand that the utilities service conductor is allowed to be smaller than the SEC to the home. Any limitations to this ? Looks like I have a 2/0 spliced into a #1.
It is up to the POCO…open air helps.
As Larry says, its about heat. An electrician explained it to me, because the wire is not enclosed and out in the open air the power company is able to use smaller wire than what the code books requires for enclosed wires in conduit or behind building materials.
What others said…
PoCo has its own rules.
Here’s something from my electrical field experience…
Not something for an HI report:
Smaller gauge on service drop is OK from the code standpoint (NESC, not NEC), but there are other issues.
The design issue (not safety or a code one) with the smaller conductor, is that when a large motor load kicks in (e.g. an a/c compressor), you get a brief dip in voltage – the lights dim, battery backups start beeping and clicking (sometimes), etc. etc.
Even though you may think you have a “beefier” service (200, 400A), the smaller service drop sometimes can’t handle the sudden increase in demand.
The "inrush" voltage dip is something that the PoCo’s usually don’t care as much about, or are very reluctant to address, because obviously it’s their expense if they agree to do it.
In cases like this, the customer can, of course make some “noise”, but how responsive the company might depend on the time of the year and on the area.
I’ve seen it a lot – someone gets a service upgrade, only to see the PoCo reconnect the same old wimpy service drop to now a thicker service entrance.
Its ok since wire in open air has a much higher ampacity because heat can be better dissipated as apposed to insulated walls like indoor wire.
Also, if the poco knows the home has all gas appliances or is very small they may further down size since the dwelling may never pull more than 100 amps on a 200 amp service.
In your case 2/0 AL spliced to #1 is typical for a service. I would however call the poco and let them know an insulator is missing on one of the joints. During a powerful windy storm I think on can guess what might happen:shock:
The NEC rules do allow (see Table 310.15(B)(20)) higher ampacities on open wire in addition to the NESC. NEC allows bare wire on insulators to be even higher.
I do agree with a smaller gauge causing issues. In most cases the run tends to be short and not to small, however sometimes cases can pull off very long runs or have an undersized transformer that can cause significant voltage drops. Large motor loads will be noticed upon start up. Always I good idea for an HI to be in say the kitchen or hall with lights on when an A/C starts, just to make sure no excessive dimming or blinking. Lots of dimming and blinking could indicate a loose connection or undersized drop as you mentioned. Well worth knowing before buying.
In some cases an undersized drop is actually essential. Poco will deliberately use an undersized drop to limit fault currents when the supply transformer or network can provide more than 10,000 ampers of fault current. Higher fault currents will force the use of higher current rated mains such as a 22KAIC or 65KAIC instead of a standard 10KAIC breaker and panel board. The smaller drop if run long enough can bring down short circuit currents considerably, thus a lower rated AIC equipment can be used saving on installation costs. In commercial and Industrial the concept helps with arc flash as well. (Think shorting a home electrical panel with a screw driver by accident. The limited fault current will cause a much smaller arc and thus less personal injury)
In case anyone interested the typical apmacities allowed by code on overhead service drops:
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet34
Hello All,
In less words…the POCO can do what they deem fit based on statistical data of the loads being drawn and well…if you are indeed talking about a “Service Drop” in the purest sense, the Utility owns it they can install what they want.
But traditionally it is based on data…or a lazy utility worker…either way they own it anyway.
Very, very informative. Thanks.
I’ve never dealt with anything but residential, so this puts in perspective the importance of the max fault current ratings for the breakers and the whole arc flash consideration.
The table in that leaflet gave me a pause. 4 AWG AL wire with XLP insulation rated for 115A? Wow… Yep, that’s open air to you…
Thank you gentleman. Learned a lot as I am sure others have too.
Hères one for you.
Where are thé black protective covers for those splices?
I do hope you did not pull them off yourself, if you did i would advise against doing this in the futur unless you are at least a certified electrician. Second if they were already missing and are at thé houses main service entrance mast you need to write it up and recommend it be immediatley repaired by licenced electrical contractor, fire hazard , shock hazard, short circuit hazard,
The above members are correct that the utility can do whatever they deem is ok. Also the code section referred to sounds correct regarding ampacity and open air current ratings. If you are really concerned you would need to check the service under load and see how much voltage drop you are getting phase to neutral on both the A phase and the B phase. The further you are from the transformer the worse it will be as the amperage increases so you can turn on the oven, AC etc to power the house to the max and then see. If you have a large load on say the A phase the B phase voltage jumps you have a bad neutral connection either at the transformer, the house weatherhead or the meter panel etc.
We can usually request a size increase with the excuse of additional power demands and lights dimming to get the drop upsized. Sometimes neighbors “forget” to pull permits when they upgrade services and loads and the transformer can be undersized etc.