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Author Topic: line clearence  (Read 947 times)

Stephen Swaffer

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Re: line clearence
« Reply #10 on: October 31, 2019, 07:16:58 pm »

On resi, it is common to use a reduced size neutral-but most of the heavy loads in resi-oven/ac/water heater etc. are 220 which means they don't load the neutral ever.

A big reason for the limits on wiring over a roof is clearance for first responders/fire personnel.

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Steve Swaffer

Frank Koenig

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Re: line clearence
« Reply #11 on: November 01, 2019, 01:00:46 pm »

On resi, it is common to use a reduced size neutral-but most of the heavy loads in resi-oven/ac/water heater etc. are 220 which means they don't load the neutral ever.

That's interesting. I haven't seen that around here. All my neutrals, including the service drops/laterals put in by the POCO, are full-size. (These days I doubt PG&E is going to take any chances with anything given the extremely deep do do they're in.)

With respect to under sizing things, what strikes me is how much smaller the distribution transformer ratings are than the potential maximum load based on (downstream) overcurrent protection. My barn in the Foothills has 200 A service which, at 80% load, could draw 38.4 kVA. The pole pig is rated at 15 kVA. I guess the transformers have pretty long thermal time constants and the POCO doesn't expect homeowners to be refining aluminum full time.

--Frank
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Tim McCulloch

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Re: line clearence
« Reply #12 on: November 01, 2019, 01:15:01 pm »

That's interesting. I haven't seen that around here. All my neutrals, including the service drops/laterals put in by the POCO, are full-size. (These days I doubt PG&E is going to take any chances with anything given the extremely deep do do they're in.)

With respect to under sizing things, what strikes me is how much smaller the distribution transformer ratings are than the potential maximum load based on (downstream) overcurrent protection. My barn in the Foothills has 200 A service which, at 80% load, could draw 38.4 kVA. The pole pig is rated at 15 kVA. I guess the transformers have pretty long thermal time constants and the POCO doesn't expect homeowners to be refining aluminum full time.

--Frank

I spent 4 years trying to convince my PoCo they had a bad neutral connection in the drops (note the plural) from a transformer cluster.  They figured it out when the lawyer NastyGrams arrived.  They fixed the neutral and while the crew was there I pointed out that one of the phase leg transformers had started to puke its guts out.  Three months later they were back replacing the transformer that exploded and showered a neighboring business owner's car with PCB-laden cooling oil.

I have a pretty low regard for PoCo managers.  They simple assume that customers don't know shit about electricity distribution (and sure, most don't) but when you can speak their language and describe happenings in terms of volts and amperes you'd think the tendency to instantly reject a customer's observations would lower somewhat.  Nope, it takes losing power to a commercial block, swinging voltages and destroyed appliances and equipment (with the ensuing threats of lawsuits) to get them to believe you.
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John Roberts {JR}

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Re: line clearence
« Reply #13 on: November 01, 2019, 01:47:57 pm »

I spent 4 years trying to convince my PoCo they had a bad neutral connection in the drops (note the plural) from a transformer cluster.  They figured it out when the lawyer NastyGrams arrived.  They fixed the neutral and while the crew was there I pointed out that one of the phase leg transformers had started to puke its guts out.  Three months later they were back replacing the transformer that exploded and showered a neighboring business owner's car with PCB-laden cooling oil.

I have a pretty low regard for PoCo managers.  They simple assume that customers don't know shit about electricity distribution (and sure, most don't) but when you can speak their language and describe happenings in terms of volts and amperes you'd think the tendency to instantly reject a customer's observations would lower somewhat.  Nope, it takes losing power to a commercial block, swinging voltages and destroyed appliances and equipment (with the ensuing threats of lawsuits) to get them to believe you.
+1

I recall years ago calling my power company when my mains voltage was high and climbing higher one night.  :o

The service guy was convinced that I was mistaken but it was a slow night so he drove out to my house with his big a__ poco truck, to prove me wrong..... BUT I wasn't wrong.  8)

Then he said wait a minute while he drove up the road to the substation a mile away, where the bump auto-former was stuck on boost. As more of my neighbors shut down for the night who knows how high the mains could have climbed as more load dropped off? He probably used some percussive maintenance (hammer) to free the stuck auto-former actuator.

He didn't even say thank you, but I probably saved them from some burned up residential appliance claims.

JR

 
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Stephen Swaffer

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Re: line clearence
« Reply #14 on: November 01, 2019, 06:44:44 pm »

That's interesting. I haven't seen that around here. All my neutrals, including the service drops/laterals put in by the POCO, are full-size. (These days I doubt PG&E is going to take any chances with anything given the extremely deep do do they're in.)

With respect to under sizing things, what strikes me is how much smaller the distribution transformer ratings are than the potential maximum load based on (downstream) overcurrent protection. My barn in the Foothills has 200 A service which, at 80% load, could draw 38.4 kVA. The pole pig is rated at 15 kVA. I guess the transformers have pretty long thermal time constants and the POCO doesn't expect homeowners to be refining aluminum full time.

--Frank

The building my office is in has a 3000 amp/3 phase/480 volt service that I installed about 9 years ago.  The NEC requires 8 parallel runs of 500 mcm copper to meet that ampacity.  Base on their interpretation of the expected load, they ran 4 parallel runs of 500 mcm aluminum.  Since then, our load has increased-regularly drawing 1500 amps plus for long perios\ds of times-but the poco hasn't seen fit to use the other 4 runs of 5 inch pvc conduit they required me to install.

I suspect their attitude towards transformers is that if its overloaded they could replace it-but they would likely scrap the old one-so why not run the old one until it lets the smoke out?
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Steve Swaffer

Frank Koenig

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Re: line clearence
« Reply #15 on: November 02, 2019, 12:00:30 pm »

+1

I recall years ago calling my power company when my mains voltage was high and climbing higher one night.  :o

The service guy was convinced that I was mistaken but it was a slow night so he drove out to my house with his big a__ poco truck, to prove me wrong..... BUT I wasn't wrong.  8)

Then he said wait a minute while he drove up the road to the substation a mile away, where the bump auto-former was stuck on boost. As more of my neighbors shut down for the night who knows how high the mains could have climbed as more load dropped off? He probably used some percussive maintenance (hammer) to free the stuck auto-former actuator.

He didn't even say thank you, but I probably saved them from some burned up residential appliance claims.

JR

I had something very similar happen within the last year. At the Sierra Foothills place we have a little home-brew (Raspberry Pi based) telemetry system that monitors line voltage, among many other things. We have a text message alarm set at 130 V. One day I'm down in Palo Alto and my phone dings and sure enough the voltage is up around 138 or something. I knew it was real as we have a second monitor at another building that agreed. I call PG&E's main trouble number and try to explain the situation. The dispatcher had no idea what I was talking about (people frequently have no idea what I'm talking about, but we're not here to talk about that) but we came to an agreement to treat it as an outage and they sent out a truck.

About 2 hours later I get a call from the fellow on the truck (PG&E had, to their credit, successfully relayed my number to him) who acknowledged that the voltage was high (and rising :o ) and thanked me profusely.  I never found out what the cause was but in this case, apparently, a customer's monitoring had saved PG&E from a big problem. None of our stuff smoked, thankfully.

--Frank
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John Roberts {JR}

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Re: line clearence
« Reply #16 on: November 02, 2019, 12:31:35 pm »

I had something very similar happen within the last year. At the Sierra Foothills place we have a little home-brew (Raspberry Pi based) telemetry system that monitors line voltage, among many other things. We have a text message alarm set at 130 V. One day I'm down in Palo Alto and my phone dings and sure enough the voltage is up around 138 or something. I knew it was real as we have a second monitor at another building that agreed. I call PG&E's main trouble number and try to explain the situation. The dispatcher had no idea what I was talking about (people frequently have no idea what I'm talking about, but we're not here to talk about that) but we came to an agreement to treat it as an outage and they sent out a truck.

About 2 hours later I get a call from the fellow on the truck (PG&E had, to their credit, successfully relayed my number to him) who acknowledged that the voltage was high (and rising :o ) and thanked me profusely.  I never found out what the cause was but in this case, apparently, a customer's monitoring had saved PG&E from a big problem. None of our stuff smoked, thankfully.

--Frank
Probably same technology... a stuck auto former used to bump line voltage up/down to manage changing load locally. 

At least you got a thank you... 8)  Customers are unlikely to even recognize too much voltage. I noticed that my incandescent lights were brighter than I remembered. I suspect long term memory for brightness is as challenged as long term memory for loudness. So these were pretty bright.

JR

PS: FWIW that same substation looks like it now has monitoring instrumentation on high voltage lines leaving the sub-station in three directions, so they might be able to catch future events themselves.
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Jonathan Johnson

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Re: line clearence
« Reply #17 on: November 25, 2019, 01:25:29 am »

Since we've kind of wandered off-topic anyway, I might as well post this here.

When you have a power outage, never assume someone else will call it in.

For one thing, the more people who call in an outage, the easier it is for the PoCo to locate the point of failure.

For another thing, you might be the only one out of power.

Many years ago, I was at my grandma's when the power went out. I advised Grandma that she should call it in, she insisted that it wasn't necessary because someone else would surely have called it in.

With nothing to do (since the power tools I was using didn't work; I was there doing some fixit stuff), I wandered around outside and happened to look up at the transformer on the pole. I noticed the cutout hanging open -- that meant that only my Grandma and her neighbor were out of power, and her neighbor wasn't home. I went back in and told Grandma to call the power company, so she did.

A guy from the power company came and tried replacing the fuse in the cutout, but as soon as he closed it, the fuse blew with a loud report. (Those things can be L-O-U-D when they pop!) Ended up waiting a while longer for a crew to bring out a new transformer and hang it on the pole.

But, if she hadn't called it in (and I hadn't noticed the cutout being open), she could have been without power for several more hours.
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Frank Koenig

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Re: line clearence
« Reply #18 on: November 25, 2019, 12:17:19 pm »

When you have a power outage, never assume someone else will call it in.

Good advice, and not just with respect to power outages. Fires, accidents, medical emergencies, or even just "suspicious behavior": do the right thing and call it in. Worst case you irritate some dispatcher.

--Frank
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Daniel Levi

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Re: line clearence
« Reply #19 on: November 25, 2019, 04:39:12 pm »

In the UK we have a 3 digit emergency phone number for power cuts and the like, very handy.
If a fault is already known about/has been reported then it just gives you a recorded message so as not to waste operators time.
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Re: line clearence
« Reply #19 on: November 25, 2019, 04:39:12 pm »


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