POCO running 3/0 Al for a 400 amp service?

[JMBSD]

Working on a residential service upgrade in San Diego. POCO allowed us to run the upgrade to the nearest hand hole which is accessible vs running to the nearest transformer which is much more complicated. They ran the calcs and gave us the greenlight.

Got trench approval and opened up the hand hole today to find 3 phase 3/0 AL. Am I correct in assuming they're tapping a phase of 3/0 to run our upgrade? Is that standard practice? Seems way underrated for a 400 amp service... especially given that this is a multi family dwelling upgrade with will be using a substantial % of available power with electric conversions and EV charging.

At this point there's no turning back for us, but I'm trying to prepare for possible issues when they come back out to pull and terminate.

 

[Eddie702]

Who is providing and pulling the wire you or POCO? They all do it different on underground services. If they provide and pull then it's all on them.

Maybe you should call them. Their drawing could be wrong on what they think is available.

 

[augie47]

Common here
(sometimes smaller than 3/0)

 

[electrofelon]

I expressed concern once to a utility guy about their equipment. He said sternly and like he was annoyed, "let US worry about our equipment.".

 

[JMBSD]

@Eddie702 The POCO provides cable and pull. Our only requirement is to trench and install conduit w/pull string.

@augie47 Wow, smaller than 3/0? That's interesting.

 

[don_resqcapt19]

@Eddie702 The POCO provides cable and pull. Our only requirement is to trench and install conduit w/pull string.

@augie47 Wow, smaller than 3/0? That's interesting.

You are looking at the vastly inflated loads that you get when using Article 220. The utility is looking at decades of real world loads.

 

[ptonsparky]

Headed to danged near Oklahoma in a few days. The #6 to my daughters 200 amp panel seems to have worked well for the last twenty years or so. (New to her house)

 

[garbo]

While installing a 100 & a 200 amp service in a four floor old hundred foot long center city home I questioned PECO if they were going to replace the #6 copper rubber covered fraying wires in the end box. They said being underground the earth cooled it off. So I asked them that a wire rated for 60 amps is large enough for a load that could be close to 200 amps and they said yes.

 

[hillbilly1]

I was doing a service upgrade on a store that was doing an expansion. Existing service was 400 amp single phase, load was right at 400 amps per leg at noon with all the a/c’s running. We were moving the service. And dug up the underground so they could pour the slab. The poco used 3/0 AL. Wire was too hot to hold more than a couple of seconds.

 

[junkhound]

utility is looking at decades of real world loads.

HfH 4 plex I worked on, co-worker questioned poco on dist xfmr size, gas WH and furnace, all electric kitchens. 4 ea 200 A services. Poco installed a single 20 kW 1 phase xfmr - this was 22 years ago, AfaIk, still is the same 20 kW xfmr. In addition, poco said they typical operate single phase xfmrs at 40% over rating.

 

[ptonsparky]

In the case of my daughters house, I would guess someone replaced the old Main/Range fuse box with the 200. House has been flipped by amateurs but other than central HEAT/AIR, The demand is still low.

 

[James L]

A couple of years ago I wired a house with a 400 amp service, and the POCO (Evergy) planner insisted that I use a 750 compact in my mast.

I told him, you know that lineman is going to drag a 1/0 from that transformer and tie it to that 750

Sure enough, that's exactly what happened

 

[hillbilly1]

A couple of years ago I wired a house with a 400 amp service, and the POCO (Evergy) planner insisted that I use a 750 compact in my mast.

I told him, you know that lineman is going to drag a 1/0 from that transformer and tie it to that 750

Sure enough, that's exactly what happened

Just did a 800 amp single phase overhead service, I meet with the poco engineer to discuss upgrading the #2 triplex that was running to the existing 600 amp service ( about a 200’+ run to the transformer) he said he would upgrade to 4/0, and put in a bigger transformer, since it also ran the restaurant at the top of the hill!

 

[farmantenna]

I'm more concerned about voltage drop. The 300 amp 3ph 120/208 service to a small cabinet manufacturer building had a 135'+- long 1/0 aerial cable and their 230v 3ph machines were having low voltage ssues. We upgraded to 600 amps due to the load ,and because a new building was put next door with 400 amp service ,the utility upgraded the transformers and aerial to 4/0 but the customer is still complaining about low voltage.

 

[JMBSD]

Thanks for all your input guys. I enjoyed the stories more than the answer to my question! Guess the moral of the story is POCOs run exactly what they need and not a bit more.

Interesting side note is that the NEC must run such huge margins on amp rating since there are so many variables in all the ways wire is run vs the POCOs controlled environment where they know exactly what the wire will be subject to.

Anyhow, interesting stuff.

 

[zbang]

Remember that the NEC is a fire-prevention code, not design guidelines; and the PoCo has not as much a controlled environment as having a lot of data about how things they do work.

 

[Birken Vogt]

Also per the NEC we could get away with more "under engineering supervision". The poco has engineers of their own who are directly making these decisions.