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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: David Allred on October 31, 2019, 10:13:10 am

Title: line clearence
Post by: David Allred on October 31, 2019, 10:13:10 am
This maybe should be in the basement, but also potentially useful within the intent of this forum.

I want to attach a "lean-to" to the side of my porch to cover my firewood stack.  My pole to weather-head house entrance power feed passes over part of a roughly 8ft x 8ft concrete pad.  I can run the roof slope in 3 of the 4 directions.  The preferred direction (function and appearance) offers the least clearance to the line.
I know that there must be regulations of some sort for this type of thing.  I have seen driveway vertical, horizontal to structure, etc, on-line, but then the power line, as it nears the house, gets within inches of the house.  What's the difference?
I said "lean-to" but it may or may not be attached to the frame of the house, if that matters.  Does it?
Firewood should have clued you in, but being rural, no permit or inspection required. 
Thanks for any input.
Title: Re: line clearence
Post by: John Roberts {JR} on October 31, 2019, 11:00:48 am
You probably shouldn't touch the wires where rubbing against some structure could wear through wire insulation. Those drops are generally only 240V so not going to arc over like lightning across any modest distance.

I once had a lawyer try to hire me as an expert witness in court suing the utility when his client got shocked by bumping his aluminum ladder into a power drop... After I explained that his dumbass client had to literally touch the wire with the ladder to get a shock, my expert testimony was no longer required.  :o

JR

PS: of course free advice is worth exactly what you paid for it...
Title: Re: line clearence
Post by: Art Welter on October 31, 2019, 12:26:46 pm
I know that there must be regulations of some sort for this type of thing.  I have seen driveway vertical, horizontal to structure, etc, on-line, but then the power line, as it nears the house, gets within inches of the house.  What's the difference?
I said "lean-to" but it may or may not be attached to the frame of the house, if that matters.  Does it?
David,

Seems Mike Holt has already answered the legal questions here:
https://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/Article230-Services~20020219.htm

"230.24 Clearances

Service-drop conductors must be located so that they are not readily accessible, and they must comply with the following clearance requirements:
(A) Above Roofs. Overhead service conductors must maintain a minimum clearance of 8 ft above the surface of a roof for a minimum distance of 3 ft in all directions from the edge of the roof.

Exception No. 2: Where the voltage does not exceed 300V between conductors, overhead conductor clearances from the roof can be reduced from 8 ft to 3 ft, if the slope of the roof exceeds 4 in. in 12 in.

Exception No. 3: If the voltage between conductors does not exceed 300V, the conductor clearance over the roof overhang can be reduced from 8 ft to 1.5 ft, if no more than 6 ft of overhead conductors pass over no more than 4 ft of roof overhang, and the conductors terminate at a through-the-roof raceway or approved support. Figure 230-10 230-24Ax3.cdr

Exception No. 4: The 3 ft vertical clearance that extends from the roof does not apply when the point of attachment is on the side of the building below the roof. "


Although I personally wouldn't worry about the proximity of the overhead conductors any more than an extension cord, best to comply with the NEC, otherwise a sale of your property likely will require another renovation.

That said, in my experience, removing a woodshed is pretty easy compared to replacing a "dry well" with a septic system...

Cheers,
Art
Title: Re: line clearence
Post by: Erik Jerde on October 31, 2019, 03:13:55 pm
This maybe should be in the basement, but also potentially useful within the intent of this forum.

I want to attach a "lean-to" to the side of my porch to cover my firewood stack.  My pole to weather-head house entrance power feed passes over part of a roughly 8ft x 8ft concrete pad.  I can run the roof slope in 3 of the 4 directions.  The preferred direction (function and appearance) offers the least clearance to the line.
I know that there must be regulations of some sort for this type of thing.  I have seen driveway vertical, horizontal to structure, etc, on-line, but then the power line, as it nears the house, gets within inches of the house.  What's the difference?
I said "lean-to" but it may or may not be attached to the frame of the house, if that matters.  Does it?
Firewood should have clued you in, but being rural, no permit or inspection required. 
Thanks for any input.

It's my understanding (which could be wrong) that the wire from the PoCo isn't covered by the NEC.  Those wires connect to your service drop wires.  It's at the point of the splice where NEC compliance begins and where the PoCo responsibility ends.  The PoCo is usually responsible for the splice BTW.  Call your PoCo and see what they have to say.  The PoCo power legs are insulated (or they should be, if not get the PoCo to replace them - they do that for free in my neighborhood).  The neutral line is the only one that isn't insulated but that shouldn't be carrying much (if any) current anyways if you have a proper ground at your service entrance.
Title: Re: line clearence
Post by: Frank Koenig on October 31, 2019, 04:25:14 pm
It's my understanding (which could be wrong) that the wire from the PoCo isn't covered by the NEC.  Those wires connect to your service drop wires.  It's at the point of the splice where NEC compliance begins and where the PoCo responsibility ends.  The PoCo is usually responsible for the splice BTW.  Call your PoCo and see what they have to say.  The PoCo power legs are insulated (or they should be, if not get the PoCo to replace them - they do that for free in my neighborhood).

It probably varies by jurisdiction but this agrees with my experience in both the City of Palo Alto and Tuolumne County, CA. Check with the POCO.

Quote
The neutral line is the only one that isn't insulated but that shouldn't be carrying much (if any) current anyways if you have a proper ground at your service entrance.

This is false. The neutral and the parallel earth path between the earth grounds at the service entrance and the distribution transformer center tap together carry the difference current between the two hot legs, which can be as great as the full service current if all the load is 120 V and on one leg. As the ground path resistance is usually higher than the resistance of the neutral conductor of the service drop, most of this unbalance current flows in the neutral conductor. If everything is working correctly, however, the neutral should remain close to earth POTENTIAL as it's connected to earth ground at both ends.

--Frank

Title: Re: line clearence
Post by: David Allred on October 31, 2019, 04:46:22 pm
For reference:
Title: Re: line clearence
Post by: John Roberts {JR} on October 31, 2019, 05:36:17 pm
For reference:
Also be careful about stacking firewood, aka termite bait, near a wooden structure...

JR
Title: Re: line clearence
Post by: Tim McCulloch on October 31, 2019, 05:37:14 pm
The PoCo drop is regulated by Code on the client end but not on the pole side.  In some jurisdictions the PoCo supplies the drop cabling and in others the homeowner must supply the drop.

Like Ivan says, "It depends..."
Title: Re: line clearence
Post by: Dennis Wiggins on October 31, 2019, 06:00:14 pm
The neutral and the parallel earth path between the earth grounds at the service entrance and the distribution transformer center tap together carry the difference current between the two hot legs, which can be as great as the full service current if all the load is 120 V and on one leg. .

Just thinking aloud:  As household circuits are typically connected at random and the loads themselves intermittent, has anyone ever had a problem with too much current on the neutral?

Is it worth measuring under "full load?"

For the Homeowner?   Etekcity Multimeter MSR-C600
Title: Re: line clearence
Post by: Erik Jerde on October 31, 2019, 06:14:33 pm
Just thinking aloud:  As household circuits are typically connected at random and the loads themselves intermittent, has anyone ever had a problem with too much current on the neutral?

Is it worth measuring under "full load?"

For the Homeowner?   Etekcity Multimeter MSR-C600

N conductor is the same size as H.  If one leg is fully loaded and the other is at 0 then youíll see full load on the N.  Add any load to the second H and the N load will go down because of phase cancelation.

Itís the same as shared neutral branch circuits.  You only need to oversize the N if youíre sharing N between ckts on the same H leg.
Title: Re: line clearence
Post by: Stephen Swaffer 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.

Title: Re: line clearence
Post by: Frank Koenig 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
Title: Re: line clearence
Post by: Tim McCulloch 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.
Title: Re: line clearence
Post by: John Roberts {JR} 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

 
Title: Re: line clearence
Post by: Stephen Swaffer 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?
Title: Re: line clearence
Post by: Frank Koenig 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
Title: Re: line clearence
Post by: John Roberts {JR} 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.
Title: Re: line clearence
Post by: Jonathan Johnson 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.
Title: Re: line clearence
Post by: Frank Koenig 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
Title: Re: line clearence
Post by: Daniel Levi 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.