Incoming utility cable capacity - A cautionary tale

[pete8314]

For those with Oncor as their PoCo, this appears to be the link to ask them a question.

 

[adelman]

Sorry adelman, I misunderstood. If you're not upgrading your main 200 amp service then no, you should not be on the hook for any infrastructure costs. Utilities like PG&E should be able to fund any infrastructure upgrades (for whatever reason) based on the increased revenues they'll get from additional electricity sales.

They fund their infrastructure repairs by requiring the customer to pay a second time, whenever they can get away with it. If you sue them, (1) you can never win your legal fees in the CPUC court and (2) they don't have to pay their own legal fees (the ratepayers pay, not the shareholders). This is a stacked deck in which they have no reason NOT to fight you.

 

[ModelS1079]

Can not thank you all enough for the feedback. A few quick comments:

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PS: I'm working on a charging/electrical infrastructure FAQ for the charging subforum, and this topic (ensuring your PoCo knows you're going to add 40A or 80A continuous load) is one of the items I have penciled in.

Great. Could have used this...about five days ago

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No. You weren't using current greater than your main breakers, but the power company's service cable was undersized due to oversubscription rules.

It is likely that if the fire progressed any more, it would have short-circuited the service entrance cable and the transformer would have blown its fuse (or blown up). That would have stopped the electricity, but by then the dripping insulation from the cables may have ignited your home anyway.

...Bottom line, as mknox said, you really need to tell your power company when you add significant continuous loads...

In non-smart-meter areas, the Power Company (PoCo) knows what size service you have (because they generally have an inventory of the meter base at a particular service location), but doesn't really know how much of that you are using on an instantaneous base. They have your average load over the month, and models they use based on time-of-day and temperature for an average home, but the details aren't available.

I'm glad to hear that everyone is safe. My Tesla *would* be back in my garage tonight, but today it received a special flatbed ride to Chicago where some of the queued up items are going to be addressed.

As a side note, this is why I am concerned about those who want to use 14-30 or 10-30 to 14-50 FrankenCables. You have a circuit breaker which is intended to be secondary protection, but if it doesn't blow (like the transformer's primary fuse) -- this is what tends to happen (except inside your walls instead of outside your home).

The town installed new cables to the house when =I installed ETS Heat the year before, including - so they thought - allowance for an EV to be added - we actually added the internal wiring for the EV charging then. hey simply undersized it then and - again when they added the actual EV meter and inspected just weeks ago - they missed that those wires had been inadequate. Wow. To be clear, they are overall a great company - that night last week was my very first power outage in ten years. hard to beat that. And they got everything up and working again before 4am. hard to beat that as well. As my own electrician said, "The left hand was not talking to the right". The took accountability, and fixed it - the cables up there now can handle more than twice the current load.

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It's not really my field...(EDIT: long, detailed, complicated explanation using terms I dropped in College physics)....If it did happen, a breaker should blow before we staged a repeat of your experience.

If this is not your field, you are ace-ing whatever your field is and it is time to move into EV Charging. Thanks for the input!

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It's not really my field...(EDIT: long, detailed, complicated explanation using terms I dropped in College physics)....If it did happen, a breaker should blow before we staged a repeat of your experience.

If this is not your field, you are acing whatever your field is and it is time to move into EV Charging. Thanks for the input!

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This is scary stuff indeed; thanks, Jim, for living to tell the tale in your own unique and humorous way! Glad that there was no damage too.
...Since I'm not getting an HPWC and am planning on juicing up only after 10 pm or so (and trickle-charging at work as well to reduce the charging time at home), I may not have issues, I hope.

I was trickle charging as well, to minimize peak charging cost and assure a warm battery on departure, until the night it flamed - when I charged at 40A. Would have bought hot dogs and got sticks if I'd just known how that would end up.

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Wow, what a story! I'm glad to hear that everybody is fine, there was no fault in the Model S or its accessories, and I also am fascinated to learn of this type of heating system!...My Model S has a single charger so I won't be pulling more than 10kW, but I am putting in a HPWC so conceivably a visitor with dual chargers might draw more... I will check with my electrician.

ETS - Electrothermal Storage, look at Steffes Heating, North Dakota.
Your last comment raises my concern about upgrading to HPWC or two EVs, two NEMA 14-50's - we are supposed to be rated for that now, but then again we were supposed to be rated for that before as well.

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Good to hear that everyone is Ok and thanks for the clarification.

Mod note: title updated to reflect the story; also search tags added. We'll move the thread to a better location in a couple of days, leaving it here for now will allow any worried members to easily find it.

Respectfully noted, the new title is very practical, but inciting much fewer PMs and general slander

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As a stockholder I became anxious when I read the discussion about moderators reviewing a post about a fire. Some people (i.e. desperate shorters, Jalopnik and others who don`t care about the truth) would love to get their hands on a "Tesla fire" story and totally misinterpret it. And when the story is first retold with false info, it doesn`t matter if the fire wasn`t caused by the car.

Glad noone was hurt! And as a stockholder I am glad Tesla is not to blame for the fire. But I do have one question; how could this happen? Don`t you americans have a main circuit breaker directly after your electrical intake? Here in Norway everyone has a main circuit breaker sized properly according to the dimensions of the cables entering the house. I am much more worried about people trying to install their own outlets in garages etc....

It is, in the end, a forum, not a Tesla Motor Corp site, and the stock? Yawn. Yes, I too am a stockholder, and if a single post on this forum can levy a change in the stock, maybe that is a buying opportunity...or, maybe we are in the wrong stock. CC: John Peterson

Issues re: main breakers in USA aptly addressed by more apt others above. Appreciate the sentiments re: family, who were certainly less concerned about the stock!

MKKnox great info thanks. Pm me if ever in Beantown and come see this electric rigging.
Robert your comments are always right on - thanks.

Finally, I have here for your review a picture of me with the electrician who set up the wires for charging my Tesla Model S. I can not imagine why I had a problem:

Nigel, okay with me whenever you want to move this thread to wherever threads go when they are duly threaded.
Just occurred to me that my avatar is...you?

 

[MikeK]

Nigel, okay with me whenever you want to move this thread to wherever threads go when they are duly threaded.
Just occurred to me that my avatar is...you?

That'd be NigelT, I believe. ;-)

 

[EdA]

Jim,

Glad everything/everyone is okay!

I think I know which daughter provided the best quote of the night...

/Ed


(Jim called me the day after it happened, which I think was the night or the night after I got delivery on my car).
Getting delivery on a car will set you back on reading the forums!

 

[NigelM]

Nigel, okay with me whenever you want to move this thread to wherever threads go when they are duly threaded.
Just occurred to me that my avatar is...you?

A thread going off topic is a sure sign it's run its course. Thread moved to NA Charging Standards.

 

[FalconNinetyD]

Looks like Henrik Fisker!

 

[neroden]

Indeed. Older 200A services are supplied by 2/0 AL cable, as mine were, rated for only 130-150 amps.

Huh. What's "older", and how would I tell? My house was built in 2004, so I'm expecting I'll be fine with my 200 amp service, but what do I know... and the cable's buried under the concrete slab under my house (for some insane reason), so if it caught fire it would be fairly spectacular and would require replacement in a *different location*. I think it could only happen if I had everything on at once, though.

I just assumed that the feed to the house was sufficient for conservative use of the 200 amp main breaker (200 amps intermittent 160 amps continuous, by the 80% rule). The entire point of a breaker is to cut off the service before it melts the wires, and the entire point of the main breaker is to cut off the service before it melts the wires to the house. Now I learn that in some houses the utility company has put in an undersized feed, without telling the customer to get a smaller breaker?

I guess in ModelS1079's case it was just a screwup, but from what others are saying this is actually allowed in many places. What the hell? Seriously, who lets utility companies get away with undersizing the wire behind the main breaker?

 

[FlasherZ]

Huh. What's "older", and how would I tell? My house was built in 2004, so I'm expecting I'll be fine with my 200 amp service, but what do I know... and the cable's buried under the concrete slab under my house (for some insane reason), so if it caught fire it would be fairly spectacular and would require replacement in a *different location*. I think it could only happen if I had everything on at once, though.

My home was built in the early 1990's.

You could remove the cover of your main panel and look for the wire gauge markings on the service-entrance cable coming to your main breaker. This will typically be the same size as the cable that feeds the meter. It doesn't guarantee it, however, and the only way you'd be able to tell is to break the seal on your meter base and open the cover to look at the cable.

I just assumed that the feed to the house was sufficient for conservative use of the 200 amp main breaker (200 amps intermittent 160 amps continuous, by the 80% rule). The entire point of a breaker is to cut off the service before it melts the wires, and the entire point of the main breaker is to cut off the service before it melts the wires to the house. Now I learn that in some houses the utility company has put in an undersized feed, without telling the customer to get a smaller breaker?

When you reach the larger service sizes, it's more about fault current protection (as mentioned earlier). Oversubscription is permitted because it's unlikely that you'll draw the full current.

I guess in ModelS1079's case it was just a screwup, but from what others are saying this is actually allowed in many places. What the hell? Seriously, who lets utility companies get away with undersizing the wire behind the main breaker?

To be fair, it's unlikely that it was the wire size itself. It takes a significant amount greater than the rated wire current to begin melting insulation. It was likely a splice that burned at the top of the weatherhead, from the service entrance cable to the aerial supply cable.

 

[mknox]

I guess in ModelS1079's case it was just a screwup, but from what others are saying this is actually allowed in many places. What the hell? Seriously, who lets utility companies get away with undersizing the wire behind the main breaker?

It might shock you to know that the whole electrical distribution system is "undersized" from the perspective of the capacity of all connected loads. I am actually fairly confident that ModelS1079's issue was a bad connection failing. A 200 amp residential service can draw no more than 160 amps on a continuous basis, but reality is that most homes don't draw anywhere near that by virtue of the fact that rarely do we have everything in the home on all at once. Even electric heat, water heaters, ovens etc. cycle on and off to maintain temperature. They don't pull their full nameplate load continuously. Distribution lines and transformers are sized to this diversified load, and can accommodate a certain duty cycle where the load goes slightly above the equipment rating with a cool down period following.

There is an interesting phenomenon known as “cold load pickup” that utilities sometimes have to deal with. This is a scenario that occurs when power is restored after a long(ish) outage and is usually related to areas with high concentrations of electric heat (but a/c equipped homes on a hot day would have the same effect). What happens is that when the power is restored, everyone’s heat (or a/c) all want to come on at full load all at once. This would overload the utility’s distribution lines and transformers (but not necessarily the service lines that come into the home) since the distribution system is designed to handle the average typical load. Utility workers will go around unplugging meters (and therefore cutting power) to every other house until the houses that are connected have “settled down” and are cycling their loads on and off again.

Continuous loads like thermal storage systems and EV chargers are something that utilities are going to have to factor in to distribution design standards going forward, because they have a similar effect as “cold load pickup” in that a number of high, continuous loads will be present all at the same time.

 

[neroden]

To be fair, it's unlikely that it was the wire size itself. It takes a significant amount greater than the rated wire current to begin melting insulation. It was likely a splice that burned at the top of the weatherhead, from the service entrance cable to the aerial supply cable.

Well, I don't have any splices; one run direct from the breaker to the meter, one run direct from the meter to the transformer at the pole. (Yes, my feed is underground, from a pole. I don't know why. I suppose I could look at the wire running up the pole, but I don't think it has any visible labelling on the cable.)

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It might shock you to know that the whole electrical distribution system is "undersized" from the perspective of the capacity of all connected loads.

Well, yeah, but that's just like the fact that I have 20 "20 amp" circuits on my 200 amp panel; they're not expected to all be on at once. It's the relationship to the house breakers which I find odd. Back in the bad old days when there weren't any full-house breakers, the problem wouldn't have surprised me. But I would have expected the house breaker to match the wire feed.

I am actually fairly confident that ModelS1079's issue was a bad connection failing.

Whew.

A 200 amp residential service can draw no more than 160 amps on a continuous basis, but reality is that most homes don't draw anywhere near that by virtue of the fact that rarely do we have everything in the home on all at once. Even electric heat, water heaters, ovens etc. cycle on and off to maintain temperature. They don't pull their full nameplate load continuously. Distribution lines and transformers are sized to this diversified load, and can accommodate a certain duty cycle where the load goes slightly above the equipment rating with a cool down period following.

Does the utility have utility-scale breakers/fuses for the distribution system? Always better to blow a fuse than to melt a wire or transformer.

There is an interesting phenomenon known as “cold load pickup” that utilities sometimes have to deal with. This is a scenario that occurs when power is restored after a long(ish) outage and is usually related to areas with high concentrations of electric heat (but a/c equipped homes on a hot day would have the same effect). What happens is that when the power is restored, everyone’s heat (or a/c) all want to come on at full load all at once. This would overload the utility’s distribution lines and transformers (but not necessarily the service lines that come into the home) since the distribution system is designed to handle the average typical load. Utility workers will go around unplugging meters (and therefore cutting power) to every other house until the houses that are connected have “settled down” and are cycling their loads on and off again.

Most interesting, thank you.

Continuous loads like thermal storage systems and EV chargers are something that utilities are going to have to factor in to distribution design standards going forward, because they have a similar effect as “cold load pickup” in that a number of high, continuous loads will be present all at the same time.

Yeah. Oy.

 

[mknox]

Well, I don't have any splices; one run direct from the breaker to the meter, one run direct from the meter to the transformer at the pole. (Yes, my feed is underground, from a pole. I don't know why. I suppose I could look at the wire running up the pole, but I don't think it has any visible labelling on the cable.)

Another common point of failure are the connections in the meter socket. This is especially true after a recent meter change if the new meter is not seated properly or if a lug breaks when the meter is installed.

Does the utility have utility-scale breakers/fuses for the distribution system? :smile: Always better to blow a fuse than to melt a wire or transformer.

Yes, but on the primary (high voltage) side of the transformer. If the current on the low voltage side (120/240v in a residential scenario) gets too high, the corresponding high voltage current will also rise and if the fuse is sized properly, it will blow. It's a tricky business. There is additional fusing upstream at the primary run-off, and further up at the distribution transformer station. You need to coordinate fusing so that a minor problem "down at the end" of a run doesn't trip a station breaker and take out half the town. It's not always perfect and enough current can still potentially flow on the secondary side to cause damage.

On a final note, most utilities will size the supply conductors (overhear or underground) between your home and the street to match the capacity of the service breaker in the home. No worries there. I suppose it is not out of the realm of possibility that a utility may allow a 100 amp to 200 amp upgrade (or maybe someone does this without contacting the utility) and the service wires are not changed out for one reason or another, but I think that would be rare.

 

[FlasherZ]

On a final note, most utilities will size the supply conductors (overhear or underground) between your home and the street to match the capacity of the service breaker in the home. No worries there. I suppose it is not out of the realm of possibility that a utility may allow a 100 amp to 200 amp upgrade (or maybe someone does this without contacting the utility) and the service wires are not changed out for one reason or another, but I think that would be rare.

Talking to my PoCo engineers, I was informed it was normal to provide 200A service on 2/0 AL at the time my home was built. Then again, there was only a 15 kVA transformer to serve the home, so I'm guessing they figure the primary transformer fuse would blow before the service conductors were overwhelmed.

 

[MikeK]

Does the utility have utility-scale breakers/fuses for the distribution system? Always better to blow a fuse than to melt a wire or transformer.

Yes. Yes, they do.

 

[neroden]

Yes. Yes, they do.

What an interesting switch. I would have expected a pure fuse, but I guess you have to use something mechanical at that scale...

Ah, fuses. If nobody minds a digression...
I grew up in a house with beautiful old-fashioned wiring from the 1920s. Fusebox of polished brass, with single-pole double-throw knife switches with polished wood handles on each circuit, and bar fuses which snapped into copper brackets. I was replacing fuses using wooden pliers at the age of 8... I remember my mother saying that most parents would be afraid to have a kid in a house with that much exposed current, but I was cautious. The wires were insulated in rubber and silk with the polarity indicated by black and white wiring. It was a top-quality install, for 1928. The electrical system was rewired in the mid-90s. The electricians walked off with the old fuseboxes, even though we asked them not to. I suspect they have them mounted on the wall of someone's home or office, since they admired them so much; it would be sad if they'd been thrown out.

 

[eledille]

What an interesting switch. I would have expected a pure fuse, but I guess you have to use something mechanical at that scale...

That's not a fuse, it's a device that disconnects the power line after it's been de-energized. It's not supposed to quite as interesting as that - one of the phases was still energized. Interesting info on youtube.

 

[ElSupreme]

Talking to my PoCo engineers, I was informed it was normal to provide 200A service on 2/0 AL at the time my home was built. Then again, there was only a 15 kVA transformer to serve the home, so I'm guessing they figure the primary transformer fuse would blow before the service conductors were overwhelmed.

Does this mean I could swap my 150A main breaker for a 200A main breaker? I have a 2/0 AL feed from the transformer. I am not going to do this, 150A is fine for me at the moment. But I am just curious. I remember thinking the 2/0 AL feed was questionable (only the highest temperature casing rating worked) for 150A when I looked it up.

 

[rolosrevenge]

So that video is a switch opening, which is done so the line crews can visually see that the line isn't connected. The breakers were supposed to have opened previously to denergize the line. One of the breakers failed and so you get that beautiful arc.

 

[FlasherZ]

Does this mean I could swap my 150A main breaker for a 200A main breaker? I have a 2/0 AL feed from the transformer. I am not going to do this, 150A is fine for me at the moment. But I am just curious. I remember thinking the 2/0 AL feed was questionable (only the highest temperature casing rating worked) for 150A when I looked it up.

That depends on a lot of variables, and my answer to you would be "no" without specific other information that would change it to "maybe". I'd never give you an unqualified "yes".

First, 2/0 AL is rated for 150A for 90 deg C applications. If, for some reason, you need to increase your main size from 150A to 200A, I'd be asking why. If it's because you're drawing more than 150A normally and tripping the main, that would be knowingly overloading the cable (not in a fault situation). If it's because your electrician went crazy and installed 25 lighting circuits in your home and you need a 40+ space panel, it might be different.

What this really comes down to, though, is that main breakers are generally sized for the panel's rating. Your panel is likely rated for 150A and is listed only for use with a 150A main. To put a 200A breaker in, you're likely going to have to replace the entire panel to get a 200A rated one. If it's your service equipment (attached directly to the meter), you're going to have to cut power (pull the meter) to replace it anyway, and in that case, you should size your entrance conductors for the service you're installing.

 

[ElSupreme]

That depends on a lot of variables, and my answer to you would be "no" without specific other information that would change it to "maybe". I'd never give you an unqualified "yes".

First, 2/0 AL is rated for 150A for 90 deg C applications. If, for some reason, you need to increase your main size from 150A to 200A, I'd be asking why. If it's because you're drawing more than 150A normally and tripping the main, that would be knowingly overloading the cable (not in a fault situation). If it's because your electrician went crazy and installed 25 lighting circuits in your home and you need a 40+ space panel, it might be different.

What this really comes down to, though, is that main breakers are generally sized for the panel's rating. Your panel is likely rated for 150A and is listed only for use with a 150A main. To put a 200A breaker in, you're likely going to have to replace the entire panel to get a 200A rated one. If it's your service equipment (attached directly to the meter), you're going to have to cut power (pull the meter) to replace it anyway, and in that case, you should size your entrance conductors for the service you're installing.

Thanks. This makes sense. I forgot about the panel rating when I asked the question. Like I said no plans to change out the breaker/panel any time soon.

And if I pop the main breaker in my house more than once I am unplugging some large load items (I don't need a range or dryer that bad) and calling Georgia Power for a bigger feed.