# A question for resi solar installers



## macmikeman (Jan 23, 2007)

Ohm's laws do not apply in residential PV work. What's on the installer's truck is the major determining factor in wiring. They have two more scheduled for the day.......


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## HackWork (Oct 2, 2009)

So this had nothing to do with tap rules (since this isn't actually a tap)?


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## Navyguy (Mar 15, 2010)

We have been asked in the past to use larger conductors by the utility because they do not have the equipment to connect the smaller sizes of wire. While not specifically for solar, we have also been asked in the past for illuminated bus shelters, billboard advertising, etc.

I remember reading somewhere that Ontario has a rule about minimum service size being 60 amp, but don't recall off the top of my head if that was just for residential or if it applied to signs, billboards, etc.

Cheers

John


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## active1 (Dec 29, 2009)

The utility here dictates the 1 line.
Here they do a net metering, with the energy credits less than what's billed.
That requires 2 meters for the 2 rates.

Here for resi they want it backfed off a breaker in the service panel which many times is outside to a separate disco then a net meter for the solar.
Not tapped off the service conductors.
Then the panel needs to be recalculated to see where they are at with the existing.

What the concern is a 100a panel could draw around 100a off the main and 21a in your case off the solar on a good day. Because you have 2 power sources the MCP is no longer completely protecting the buss, such as 121a in this case. I know there is more to it with inverse time CB.

Many time they say they would reduce the MCB size to adjust for this. Such as an existing 200a panel, what some call derated to 175a with a 175a MCB. Then a 25a solar backfeed.

But with the 100a service they can't go lower than the 100a main min requirement for resi. So the existing could be a 125a panel with a 100a main and a 25a backfeed.

Disclaimer is I do the commercial side.
That's where we tie in to the utility before the service disconnect.
Then go solar disco, CT, Main distro, sometimes panelboards, then inverters.

I would think the tap rules still apply.
Just like a multifamily with 1 service drop, split in a gutter to each meter, then tenant panels.

In this case the solar disco would need to be service rated.


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## chicken steve (Mar 22, 2011)

690.8 Circuit Sizing and Current. 

confuses me :blink:

what is meant by>>>

The sum of parallel-connected PV module–*rated short-
circuit currents* multiplied by 125 percent


~CS~


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## eddy current (Feb 28, 2009)

Navyguy said:


> We have been asked in the past to use larger conductors by the utility because they do not have the equipment to connect the smaller sizes of wire. While not specifically for solar, we have also been asked in the past for illuminated bus shelters, billboard advertising, etc.
> 
> I remember reading somewhere that Ontario has a rule about minimum service size being 60 amp, but don't recall off the top of my head if that was just for residential or if it applied to signs, billboards, etc.
> 
> ...


In the 90’s I installed the power for payphones. Sometimes the utility called for larger wire, but many times I ran a 10 awg, single phase 120 volt service for these phones. The utility tied them in without a meter as well.


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## Navyguy (Mar 15, 2010)

eddy current said:


> In the 90’s I installed the power for payphones. Sometimes the utility called for larger wire, but many times I ran a 10 awg, single phase 120 volt service for these phones. The utility tied them in without a meter as well.


If we were tying them into say the street lighting or something we used #10 also, but we generally did the connections. Some installs I remember not having to install a meter socket either; that was usually with bus shelters that the city ran so they were simply pay for their electricity.

I don't recall doing any "flat rate" billboards (but literally did 100's of them) so I may have) or other situations; never did a phone booth though. On a fairly recent solar install we had to use #6 for a 30 amp service because the utility asked for the larger wire.

Cheers

John


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## eddy current (Feb 28, 2009)

Yes the payphones were tied into the street lighting and I assume the city payed a flat rate to hydro.

Each one was a separate service though, ground rod etc. was good experience.


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## Majewski (Jan 8, 2016)

Where the hell did bs go?


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## HackWork (Oct 2, 2009)

Majewski said:


> Where the hell did bs go?


bs??


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## Majewski (Jan 8, 2016)

HackWork said:


> bs??


Backstay.


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## paulengr (Oct 8, 2017)

chicken steve said:


> 690.8 Circuit Sizing and Current.
> 
> confuses me :blink:
> 
> ...


Just what it says. The resistance through the panel is pretty high and the output current and voltage is kind of variable depending on the amount of sunlight, angle it is pointed at, how many panels are in series and parallel, and so forth, so ampacity gets rated according to the short circuit current which doesn't change no matter how much light hits the panel. Losses (I2R) kill efficiency with the square of current so oversizing wiring is not only common but beneficial to efficiency particularly when installing paralleled modules, running cable potentially hundreds to thousands of feet.

As to the 125% factor...this never made much sense to me. PV is almost a purely resistive load and there is no chance of an inductive surge. The 125% factor is essentially there because it "just works" to oversize things just enough to account for motor starting conditions but with PV that condition doesn't exist so the 125% rule as far as Code is concerned might just be a knee jerk reaction to something new and might eventually go away when someone nit picks it.


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## LeboElectric (Apr 9, 2018)

I need to learn solar panel installation.


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## jarhead0531 (Jun 1, 2010)

I installed solar as the foreman/electrician for Vivint Solar. We used to size the conductors to the actually amperage system was designed for. Eventually townships starting giving us a hard time about conductor sizing because the definition of service, and whether or not it applied to solar.

It eventually went to the DCA and it was decided it is NOT a service. Then they started failing us saying it was a tap and had to sized correctly. 

As we all know nothing cost more than a return trip, so to get around it we just started installing #6 as the smallest conductor back to main panel. Actually saved money as now we were only carrying #6, one less inventory item to manage and to have a loss due to waste.

Doesn't sound like it make much of difference but we would regularly go through 1500' feet of #6, and probably 5-10k of #10 a month PER crew.

BTW, solar work sucks, for those guys anyway.


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## farmantenna (Nov 22, 2012)

HackWork said:


> So this had nothing to do with tap rules (since this isn't actually a tap)?


it is a tap but not really. they're tapping the service conductors which are fused by the utility. It was also a fused disconnect with a bonded neutral. I've connected a few solar systems and all the engineered stamped plans dictated a #6 and I think it was ART 230.42 which states the ungrounded conductors can't be smaller than the disconnect which can't be a 30 so the next size is 60 and that's a #6 CU. It could also be their interpretation of what is minimum size of a service Also 230.79 says smallest service disconnect is 60 amps.

Again, every engineered plan with a line tap had #6 CU. I don't think it's a tap not longer than 10' because you could use a smaller wire if fused appropriately. If my understanding is wrong then I don't know but more than one engineering firm got into their head about their understanding of the NEC


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## active1 (Dec 29, 2009)

Too Late

HackWork is gone


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## trentonmakes (Mar 21, 2017)

active1 said:


> Too Late
> 
> HackWork is gone


Is he coming back?

He was a wealth of knowledge and pretty active and a bit of an azz. Lol

I kind of miss him

Texting and Driving


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## active1 (Dec 29, 2009)

I really don't know what's up with Hack.
He'll be missed.


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## Signal1 (Feb 10, 2016)

He's here.

He's just not posting. Wish he'd come back tho..................


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## Signal1 (Feb 10, 2016)

This is right now

*edit:* the first image didn't seem to upload, but it did.


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## macmikeman (Jan 23, 2007)

This certainly disproves Shunk's theory of pulling your hand out of the pail of water now don't it.................


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## MTW (Aug 28, 2013)

macmikeman said:


> This certainly disproves Shunk's theory of pulling your hand out of the pail of water now don't it.................


No, not at all.


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## active1 (Dec 29, 2009)

Hack's faking his own death


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## macmikeman (Jan 23, 2007)

MTW said:


> No, not at all.


I say it does, now don't go arguing with me or I'm making a portrait of you to post in my art gallery .........


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