Utility Service Conductors

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FaradayFF

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California
Hi All,
This question may not be appropriate in this forum, just wanted to ask how are the utility service conductors are protected. Say a set of overhead service conductors feed a customer. I suppose the overload protection can be provided at the mains breaker of the panel/meter supplied by these conductors.
How about protecting against the short circuit anywhere along the length of the service conductors before they enter the customers disconnect device. I haven't seen protective devices installed immediately downstream of the OH transformer, is the typical assumption by utility here is that we're dealing with a short run to the customer's disconnecting means, and in case of a fault, the fuses on the primary side of the utility OH transformer would clear the fault?

Thanks,
EE
 
There is actually a breaker inside a CSP transformer.
For a conventional transformer the fuse on the primary does the protecting

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Service conductors are often called "unfused conductors" by electricians. They are protected from overload (we do a load calculation) but not from short circuit or ground fault (unless a CSP transformer, I don't know if our POCO uses that). There are special rules in the NEC regarding service entrance conductors. Typically they are protected by the fuse on the primary side of xfmr.
* How far they can extend in the building, not specified in the NEC, but often in state/local rules, Here in WA we can go 15 ft of raceway into the building, other locations its 2,3, 5 etc feet.
* Special rules for bonding
*Type of raceway is restricted, in WA we can't use EMT for service conductors

Someone told me once the POCO service crews only carry #2 and #6 for service drops....
 
As the son of retired lineman i always questioned this as well. His response to me was the OH or UG service conductors are the sacrificial portion of their feed. There is no protection for them. The fuse above the xfmr protects only their mainline going back to the substation. The main on our side protects our stuff. The part in between is not protected and replaceable. This is FPL’s view and approach.
 
Flanative said:
As the son of retired lineman i always questioned this as well. His response to me was the OH or UG service conductors are the sacrificial portion of their feed. There is no protection for them. The fuse above the xfmr protects only their mainline going back to the substation. The main on our side protects our stuff. The part in between is not protected and replaceable. This is FPL’s view and approach.
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Is that why the conductors provided from the POCO from the pole to the house always seem way undersized compared to what we must run to meet their lines?
 
They have a completely diff standards for their wire sizing especially in free air conditions. Ive built two 400 amp resi services in the last two weeks and had to request both be fed with parallel runs. Otherwise they would have fed both with one single 4/0 drop.
 
Flanative said:
As the son of retired lineman i always questioned this as well. His response to me was the OH or UG service conductors are the sacrificial portion of their feed. There is no protection for them. The fuse above the xfmr protects only their mainline going back to the substation. The main on our side protects our stuff. The part in between is not protected and replaceable. This is FPL’s view and approach.
Click to expand...
The protection for the wire is generally on the fuse (conventional) or breaker (csp) on the transformer
with that stated, I’ve witnessed service drops with about all the insulation melted off from the wrong fuse on the transformer, or a streetlight wire connected to a 100kVa transformer.
 
Fred B said:
Is that why the conductors provided from the POCO from the pole to the house always seem way undersized compared to what we must run to meet their lines?
Click to expand...
POCO conductors are generally sized according to 95 degree rating in open air, with diversity factor, and experience.

We don’t always get it right...
 
Flanative said:
They have a completely diff standards for their wire sizing especially in free air conditions. Ive built two 400 amp resi services in the last two weeks and had to request both be fed with parallel runs. Otherwise they would have fed both with one single 4/0 drop.
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We would have also. If you had made that request to us it would have been an extra charge back to you.
400 amp residential service won’t pull 400 amps enough(if ever) to warrant that much wire.
 
electrofelon said:
What about without CSP, primary side say 12.47/7.2kv?
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We would use a 5D fuse.

csp breakers are sized from the manuf. they can be spaced different for motor loads npand other stuff, but I don’t know anyone that orders different.
10KvA=45, 15=65, 25=110, 37.5=160, 50=210
 
electrofelon said:
5 amps, so small! Fischer Price my first fuse. 🤣
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You would be surprised at amp draw on a substation. I have seen an entire circuit of residential as low as 25 amps on the entire circuit feeding several HUNDRED people.
In the summer that same circuit can be up around 200-250 amps, MAYBE a little higher on really hot days
 
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